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goldenreference low voltage power supply


kevin gilmore
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James, all:

Nice writeup BTW.

6 hours ago, jamesmking said:

3. if you have the dual output board (which has both positive and negative output rails) either you populate the middle diode bridge only and use a transformer which is centre tapped OR you populate the two outer diode bridges and use a transformer with two separate output windings. If use use synchronous rectifiers instead of diode bridges use must use the second option and use separate windings for positive and negative rails. Do not populate all three bridges. If you use a centre tapped transformer you must connect the centre tap to the middle screw terminal (which is connected to the GRLV ground plane) of the 5 terminal AC input block . Do not use a synchronous rectifier to the centre bridge it will not work correctly and can result in the driver mosfets of the synchronous rectifier burning. 

Correct me if I'm wrong, but I believe you can use a dual secondary transformer as a CT simply by tieing the two secondaries together?

http://engineering.electrical-equipment.org/wp-content/uploads/2013/07/Dual-Voltage-Transformers-1.jpg

All of the GRLVs that I have built use dual secondary transformers and dual bridges, and I don't foresee a reason to use the single bridge for one.

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Hi Pars, that is correct. However, if someone already has a CT transformer, i.e. only three leads coming out of the secondaries, then a single bridge is a must use and there is no way around it.

However, ordering a new transformer I would as well prefer ordering it with two secondaries. Then you have all the connection freedom. 

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9 hours ago, jamesmking said:

Golden Reference LV Build Guide

Schematic for the golden reference LV:

parts in green are new additions compared to the published schematic pdf in joamats post above. Parts in purple set the output voltage, parts in brown are the optional fine output adjust and parts in dark blue are the optional power led.

2087031191_goldenreference6dLV.thumb.JPG.a9e8ca560ebca1caa71d0c25c9df184b.JPG

Component Layout

 

481539799_goldenreferencelv.thumb.JPG.1e9480701ef04045862a731a6566717d.JPG

 

Optional parts and Options:

1. if you don't want to have a power led fed from the LV board omit the 2K resistors R13, R14 and the led D3

2. if you don't want very fine adjustment of the output voltage omit the 1M resistors R17, R18, R23, R24 and the trimmers RV2 and RV1. If you want more adjustment range reduce the value of the  resistors. With 1M ohm resistors the fine adjust can only change the output voltage by a few mV.  Replacing with 810K resistors provides a little more adjustment range ~ 20mV but at the expense of decreasing the temperature stability. A cheaper alternative for good output accuracy is to use 1/4W 0.1% low ppm e.g. 15ppm resistors for the voltage set resistors and omit the fine adjust completely - which is cheaper and improves the temperature stability.

3. if you have the dual output board (which has both positive and negative output rails) either you populate the middle diode bridge only and use a transformer which is centre tapped OR you populate the two outer diode bridges and use a transformer with two separate output windings. If use use synchronous rectifiers instead of diode bridges use must use the second option and use separate windings for positive and negative rails. Do not populate all three bridges. If you use a centre tapped transformer you must connect the centre tap to the middle screw terminal (which is connected to the GRLV ground plane) of the 5 terminal AC input block . Do not use a synchronous rectifier to the centre bridge it will not work correctly and can result in the driver mosfets of the synchronous rectifier burning. 

Note the GRLV cant output less than the voltage of the voltage reference, ideally for proper regulation the output needs to be more than about 2V higher than the LT voltage reference. So for about 12V or less output it is recommended you change the 10V reference for a 7V and the zener diodes for a 7V. For 12V output 10V reference or 7V reference can be used but the 7V reference version may have less noise. Maximum output is constrained by the voltage rating of the caps and is about 30V without modifications.

 

_MG_6214_DxO.thumb.jpg.8ea42af854ab0bdfefd40879a36f76c7.jpg

 

 

Setting the Output Voltage

For the positive output R8 and R7 control the output voltage along with the voltage reference,

the output voltage is ((R7+R8)/R7)*voltage reference output D5. Assuming you keep R7 at the stock value of 1.5K:

output voltage change R8 to
3k = 30V
1.5K = 20V
750 = 15V
300 = 12V

In general to calculate R8: ((Voltage required * R7)/voltage reference D5 output) - R7 = R8

 

For the negative output R10 and R9 control the output voltage along with the voltage reference,

the output voltage is ((R10+R9)/R9)*voltage reference output D7. Assuming you keep R10 at the stock value of 1.5K:

output voltage change R9 to
3k = 30V
1.5K = 20V
750 = 15V
300 = 12V

In general to calculate R9: ((Voltage required * R10)/voltage reference D7 output) - R10 = R9

 

Photos of finished boards for reference:

This version uses a single diode bridge so this is setup for a centre tapped transformer, also has the trimmers and resistors for the power led populated but no power led installed. The build uses 4700uF reservoir caps and silmic 220uf output caps and 1/4w resistors from vishay and dale. This is what you get using the BOM link in this post (see bellow) and is very close to the original BOM published near the beginning of this thread.

 

_MG_6115.thumb.jpg.a939bcdff885836dd38acf0f595e7e1b.jpg

 

This version is setup for dual separate transformer windings, and has no power led or trimmers implemented. It also uses synchronous rectifiers instead of diode bridges, nippon chemicon 10000uF reservoir caps, Panasonic FR series 220uF caps and 1/2W 50ppm 1% koa resistors. The resistors that set the output voltage are 1/4W TE 0.1% 15ppm for increased temperature stability and output accuracy. This is my current default build.

 

_MG_6212_DxO.thumb.jpg.d6dc5d0140108dc590995b8a148b4b11.jpg

 

BOM (based on 10V voltage reference and all options being populated)

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=edda1bdbf7

 

Component list with cap size information

Br1,Br2,Br3              = 2 x 4A 100V RS402L  use 2 for dual winding transformer use 1 for centre tapped transformer

 C,C                            = 2 x film 4.7uF 50V 5mm lead spacing 0.5mm lead diameter

C,C,C11,C12,C14,C15                   = 6 x film 0.01uF 100V  5mm lead spacing max size ~ 7.6mmx3mm 0.5mm lead diameter

C1,C2                        = 2 x 50V 4700uF 10mm lead spacing max diameter 25mm, 22mm more comfortable fit main reservoir cap I also use Nippon Chemicon 63V 10000uF which just fit.

C3,C16                     = 2 x Tantalum 35V 10uF ESR=2 Ohms 5mm lead spacing 0.5mm lead diameter

C4,C5                        = 2 x Multilayer Ceramic 50V 47pF 5mm lead spacing 0.5mm lead diameter

C6,C10                     = 2 x 220uF 35V silmic or Panasonic FR series 5mm lead spacing 12.5mm max diameter

C7,C8,C9,C13         = 4 x tantalium 35V 47uF ESR=0.8ohms 5mm lead spacing 0.5mm lead diameter

 

D,D,D,D                    = 4 x 1N914

D1,D2,D3,D8,D9     = 5 x 1.7V red led        4 are required one is for optional power led leally all 4 main leds should be from the same batch and have similar characteristics.                            

D10,D11                   = 2 x IN4007G 1A 1000V

D4,D6                        = 2 x IN4739A 9.1V 1W    use 7V zener for <=12V output

D6,D7                        = 2 x lt1021-10        10V voltage reference  use 7V for <=12V output

 

Q4                              = 1 x MJW21194G

Q5                              = 1 x MJF15031G

Q7                              = 1 x MJW21193G

Q9                              = 1 x MJF15030G

Q1,Q3,Q6,Q13         = 4 x KSP92TA

Q2,Q10,Q11,Q14    = 4 x KSP42TA

Q8,Q12                     = 2 x DN2540N3-G

 

R1,R4                        = 2 x 150 1/2W

R13,R14                   = 2 x 2K

R15,R16                   = 2 x 10K

R17,R18,R23,R24                            = 4 x 1M, 810K = +-20mv adj range optional for fine adjustment

R2,R5,R11,R12       = 4 x 1K

R20,R21                   = 2 x 500

R3,R6,R19,R22       = 4 x 10

R7,R10                     = 2 x 1.5K

R8,R9                        = 2 x 750  for 15V output change as necessary for your output

 

RV1,RV2                  = 2 x 100K optional for fine adjustment

 

U1,U2                        = 2 x OPA134PA

 

Building

Once you have decided the build options and output voltage, construction is straightforward given there are no high voltages. Depending upon the current draw the large power transistors on the side of the board may require heatsinking. The metal tab is live so they will need to be insulated from the heatsink/chassis.

Socketing the reference and opamps is optional but it does make replacement and reuse easier.

Make sure the caps are installed with the correct polarity. The line on the tantalums denotes the positive Terminal whereas the line on electrolytic caps denotes the negative terminal.... the film caps can be installed either way around as can the small ceramic caps.

For the leds the longer leg is the + leg and this goes to the + mark on the pcb

be careful to install the opamps and voltage reference chips the correct way around they will get very hot very quickly if installed the wrong way.

make sure you don't place as ksp42 where a ksp92 should go of visa versa. Its easy to do since they look identical and its not easy to see all the markings once populating the board is finished.

 

Testing

If you have a means to control the input voltage to the board e.g. a variac, then with no load connected to the grlv the outer leds (closest to the LT voltage reference) should just start to glow at about 2.4 to 2.5VAC rms input voltage to the board and the output of the GRLV should be around 1V DC. If you cant get the outer leds to light with about 3VAC rms input, stop and disconnect, something is definitely wrong. By 3VAC rms the outer leds should be bright. 

Increasing the variac output further should see proportional rises in the GRLV DC output voltage until the output reaches the expected output. At this point the inner leds closest to the zener diode may not have lit and although basic regulation has been achieved, the input voltage is too low for full low noise regulation. Increase the input voltage a little more and the inner leds should light. This should happen with after about an additional 1 volt AC rms is added to the input. The output voltage should not increase. 

As a very rough rule of thumb, without load, the grlv needs about 2V less input AC rms than its DC output. So for example for 12v output expect regulation to just happen at about 10VAC rms input but the inner led not to light until about 11VAC rms. Note this figures depend on tolerances, the diode bridge voltage drop, led characteristics etc and are a rough guide only. Adding a load to the GRLV will mean it needs a higher input voltage in order to regulate since some of the sources of voltage drops are dependant on current draw e.g. the diode bridges. So if you adjust the variac to just get the inner led lit with no load don't be surprised if it goes out when you draw a few hundred milliamps.

Another way to test is to connect the AC in of one rail to a current limited DC power supply. Set the current limit to say 0.005A (12mA) and slowly increase the voltage. Bellow about 3.3VDC input to the GRLV there should be low current draw <10mA. At about 3.4VDC the outer led will start to light and current draw should still be <10mA. Around 8.5VDC input current draw should reach about 10mA. The inner led close to the main cap should begin to light at about 2.6VDC input above the expected output e.g. 14.6VDC input for 12V output. At this point current draw should be about 20mA and you may need to increase your DC power supply current limit. Increasing the DC power supply output past this point should not result in increasing current draw or increasing GRLV output. Note when you increase the DC power supply voltage you will get an initial current draw spike as the resouviour cap charges to the new voltage level but the current draw should quickly subside to the figures shown.

If the GRLv regulates and behaves as expected with no load and has no warm components or varying output then you can continue to load testing. The easiest way to do this is with an electronic DC load. I setup my load so that it will abort the test if the output voltage of the GRLV exceeds 0.2V above or bellow the no load output. A properly working GRLV with enough input voltage will vary very very little with current draw - much less than a traditional 78xx/79xx voltage regulator. I then load at 50mA and check for hot components, and then in 100mA steps up to 1A. Above about 400mA the large main transistors will get hot if they are not heatsinked... this is normal as the current draw increases there is more power dissipation in the transistor. Note transformers and diode bridges etc do drop more voltage as the current draw increases so if the inner led goes out at higher current draws check the input voltage to the GRLV has not decreased too much for the GRLV to regulate. Don't load test about above 300mA for long periods without heatsinking the main transistors.

 

Additional Checks

The voltage reference output voltage should be present between pins 4 and 6 of the LT reference and be stable and very close to the spec sheet voltage. Use fine tip probes and be careful not to short any pins together when probing:

 

_MG_6220_DxO.thumb.jpg.f6ceeb38dbca1b9fbf4bbacfb6833b64.jpg

The opamp compares the voltage reference with the output voltage from the voltage divider (the resistors which set the output voltage) and creates a correction signal. Pin 2 of the opamp is connected to the voltage reference and pin 3 is connected to the voltage divider. When working correctly, the voltages with respect to ground to pin 2 and from ground to pin 3 should be identical and be the same as the output of the voltage reference measured above.

 

_MG_6221_DxO.thumb.jpg.72e157a68968b7f4cb88e075dbd41441.jpg

 

 

 

Excellent post, James - thank you!!

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Hi all!

Been reading jamesmkings' build guide, trying to understand the project before me. Please forgive me in advance for a lot of stupid questions.

1.       Reference voltage is mentioned throughout, as opposed to desired output voltage or RMS voltage after the bridge or even voltage off the primaries. What in the heck is reference voltage? Where is it measured? My specific build is +/-20 volt rails for an SS Dynalo.

 

2.       The 100K output trimmer pots. Some of you seem to use them to closely match + and – rails. Some of you don’t, it seems for reasons of temp stability or drift? Is that really a big issue here? I can purchase 1% resistors, and like James’ reference design use higher end R7-10 resistors as he did. What I really don’t have any control over is how well the transistors are matched, nor the diodes (my handheld meter (4 digits) has a diode checker, and that’s the limit of the sophistication of my tools). It seems with these limits trimming would be a joke. What gains other than satisfying my OCD nature are had by buying a 7 or 8-digit multi-meter (hopefully with a transistor checker), and at what cost to go from good to very good?

 

3.       The 4.7uF film cap, parallel to the 220uF electrolytic. That’s a bypass cap, right? A way to get the benefits of a better sounding film cap while the 220uF does the grunt work. If I remember right, bypassing increases the range of frequencies of ripple/noise shunted to ground, but I may have that wrong. It’s approx. 2% of the 220uF. Being that those are what supplies the boards after the GRLV, is there any major disadvantage to bypassing the 4.7uF cap as well, other than fitting it on the board? ( https://www.partsconnexion.com/AURIXO-79184.html )

 

4.       James mentions after unloaded tests with a variac to use an electronic DC load. I’m already going to have to buy a variac, I’d like to save some money, plus I wouldn’t have to learn to use something else. Instead, can I get a pair of cement resistors, and if so, what approx. value?

 

5.       On the variac, you can purchase cheapies off ebay for $50, but you can also find used ones  that look better built. What’s a good bargain for a used variac, and what names should I look for?

 

Thanks again, and have a great day/night!

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  1. The reference voltage of 10V comes from the Linear Technology LT1021DCN8-10#PBF. You normally won't need to measure this unless you have problems with the output voltage.
  2. You don't need to worry about transistor or diode matching on these. If you like, use 0.1% low tempco resistors for the R7-R10. You will get acceptable +/- voltage tightness with 1% resistors, particularly if you match those.
  3. No. Just use the specified Wimas with the 220uf Panasonic electrolytics and you will be good. Do not buy that cap from Partsconnexion and ignore all the audiophool bullshit.
  4. I never test these loaded, and I don't think you need a variac, particularly if you pay attention when building (right part in right place, etc.). I've never used a variac with a GRLV even though I have one. Just make sure you have your desired +/- 20V before connecting an amp board, and you should be fine.
  5. DItto.
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4 hours ago, ShortBtwnHdset said:

Hi all!

Been reading jamesmkings' build guide, trying to understand the project before me. Please forgive me in advance for a lot of stupid questions.

1.       Reference voltage is mentioned throughout, as opposed to desired output voltage or RMS voltage after the bridge or even voltage off the primaries. What in the heck is reference voltage? Where is it measured? My specific build is +/-20 volt rails for an SS Dynalo.

reference voltage is the LT chip 10V normally or 7V version for <=12V output. As mentioned in my original post the opamp compares the reference voltage to a portion of the output voltage and corrects any difference. So for a 20V grlv you will use the standard 10V reference which is in the bill of materials.

4 hours ago, ShortBtwnHdset said:

 

2.       The 100K output trimmer pots. Some of you seem to use them to closely match + and – rails. Some of you don’t, it seems for reasons of temp stability or drift? Is that really a big issue here? I can purchase 1% resistors, and like James’ reference design use higher end R7-10 resistors as he did. What I really don’t have any control over is how well the transistors are matched, nor the diodes (my handheld meter (4 digits) has a diode checker, and that’s the limit of the sophistication of my tools). It seems with these limits trimming would be a joke. What gains other than satisfying my OCD nature are had by buying a 7 or 8-digit multi-meter (hopefully with a transistor checker), and at what cost to go from good to very good?

The grlv is so low noise it could be used in many situations e.g. as a voltage standard for calibrating other equipment. In that case a precise output is needed, hence the trimmers. The wider the range of adjustment the lower the temperature stability which if you are using it as a voltage standard is a potential issue. For a power supply in an amp having exactly 20.000V output rather than 20.1V is not an issue. This is why I don't populate the trimmer adjustment. Kevin even build a grlv using extremely expensive very low ppm resistors and measured the voltage drift over an entire day just to see how the the grlv was and the result was extremely stable but the resistors alone probably cost more than your amp build....

 

4 hours ago, ShortBtwnHdset said:

3.       The 4.7uF film cap, parallel to the 220uF electrolytic. That’s a bypass cap, right? A way to get the benefits of a better sounding film cap while the 220uF does the grunt work. If I remember right, bypassing increases the range of frequencies of ripple/noise shunted to ground, but I may have that wrong. It’s approx. 2% of the 220uF. Being that those are what supplies the boards after the GRLV, is there any major disadvantage to bypassing the 4.7uF cap as well, other than fitting it on the board? ( https://www.partsconnexion.com/AURIXO-79184.html )

In my experience power supply caps do not make a massive difference to the sound. I go for low effective series resistance and high reliability. Dont forget most of kevins designs have 0.1uF power supply byass caps on the amplifier boards themselves.  This cuts out some noise picked up in the wires between the psu and amp boards. So in effect the 4.7uF caps are bypassed anyway (I am not familar with your amp build but its worth checking the amp pcb to see if it has bypass on it - some of the published amp schematics don't show the bypass caps but they are on the pcb.). Where they matter more is when they are in the audio path e.g. as a dc blocking capacitor between two amplification stages. Most of kevins designs use dc servos to cancel the dc and avoid the use of coupling caps in the audio path. The only exception to this I have built is the Megatron and currently that just used wima caps.

for the cost of parts connect "audiophile" caps you could be well on the way to buy a cheap ebay variac....

I find the panasonic FR series caps for the 220uF output cap sound good and are quite cheap.

I use a wima for the 4.7uF.

Kevin measured the GRLV in a clean room when he was working at a university and the noise levels are incredibly low. bypassing the film cap with a medium value pF ceramic or similar might reduce the output impedance at very high frequencies but some ceramics e.g. multi layer can be microphonic...

4 hours ago, ShortBtwnHdset said:

4.       James mentions after unloaded tests with a variac to use an electronic DC load. I’m already going to have to buy a variac, I’d like to save some money, plus I wouldn’t have to learn to use something else. Instead, can I get a pair of cement resistors, and if so, what approx. value?

variac is useful especially if you plan to build high voltage power supplies and can also be used to slowly power up the entire amp when completed in case their are issues with the amplifier boards. But if you are on a tight budget a variac is not necessary. You could do the grlv tests powering it up with a current limited dc power supply if you have access to one. DC load is useful simply for its versatility. In reality if it powers up under no load with no issues its probably fine.

I use my variac a lot. The reason I like a variac is

1. I can bring up the board slowly and check for overheating components. before there is so much energy in the circuit things go pop.

2. I know if the outer leds don't light at a certain input voltage I have a problem and can stop the testing immediately. If I see the output increasing past the point where it should regulate I know I have a problem. Im paranoid and its all about finding issues at as low voltage and therefore low stored energy as possible to minimise damage. This technique has saved me money.

3. I might not have a transformer with the correct outputs for the power supply I am building and I can use the variac to reduce the output of a transformer to the level I need. e.g. lets say I need 23VAC for my 20V output grlv and I only have a 50VAC transformer. 50VAC might be too high for my chosen input cap and if its not I will get considerable heat in the transistors as they try to drop the large excess input voltage. Instead I turn the variac up until I get the output voltage I want from my transformer... That way I only need to keep one low voltage transformer around to test any grlv and one high voltage transformer to test any GR HV....

4. if you are planning to build high voltage power supplies the build cost and potential for nasty damaging failures are higher and a variac can reduce the collateral damage if something goes bang.

If you are only planning to build one thing and are on a tight budget and build carefully a variac is a luxury rather than a necessity.

There are designs for DIY DC loads on the internet I built it myself and wrote custom code for it. My philosophy is test everything especially power supplies well. Also sometimes forum members ask about particular loads or when loads are "safe" or heat output or voltage drop at certain loads. I also can also use it to test the true capacity of batteries, usb power banks etc. In other words its a useful experimental tool for me. If you are on a budget some high wattage resistors would be fine. If you decide to load test at all.

voltage drop = current *  resistance so if you are outputting say 20V and want to test at say 0.1A (100mA) then V/I = R 20V / 0.1A = 200ohm.

power = V * I

so 20V *0.1A = 2W so a 5W 200ohm resistor should be ok for this current draw.

power requirement will go up with current draw so for 0.5A at 20V you will need a 40ohm resistor and the power dissipation will be 10W so at a minimum you will need a 15W resistor. Many high wattage resistors specifications assume they are bolted at a suitable heatsink so by the time you have purchased a range of resistors and some heatsinks you can get into the price range of a diy dc load which could handle 100V multiple amps be programmable, run automated tests etc..

If you then build a power supply with a high output voltage say 30V all these resistors will have too low wattage ratings and the current draws will also be higher. A Dc load provides a current draw which is independent of the output voltage of the device its testing. load resistors cant do that. But again if you are only planning to do one build and or are on a budget load testing is optional.

 

4 hours ago, ShortBtwnHdset said:

5.       On the variac, you can purchase cheapies off ebay for $50, but you can also find used ones  that look better built. What’s a good bargain for a used variac, and what names should I look for?

Im using a cheap one of ebay. It works for me. 

4 hours ago, ShortBtwnHdset said:

Thanks again, and have a great day/night!

the grlv is an easy build (unlike the gr78/79xx smd boards), so as long as your soldering technique and attention to detail are good there is a very good chance your grlv will work first time. I wanted my build guide to be comprehensive, it was not my intention to scare you into buying test equipment you might not use much. Good luck with your build.

James

 

Edited by jamesmking
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The desirability of the Panasonic for filtering and power rail uncoupling is the higher ripple rating and lower ESR. At that size/voltage, the Panasonic FR is rated for 1.65A and 30 mohms, the Kemet 1.35A and 42 mohms. Not a big difference, but it's there.

Edited by Beefy
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Just to give my 2 cents because it had been my learning experience too while I was building various projects.

I would discourage using boutique expensive parts on first few builds while you're still learning the basics of building/following directions before learning the basics of how the circuit and builds work. This is for all intents and purposes your own personal experimentation stage. A lot of things will go wrong. You will install diodes backwards, make solder bridges, miss out on the insulation pads on heatsink/chassis mounted transistors, and plenty others. It will be slow and learning will be an iterative process. In the end your chassis will be full of holes on top of apprentice marks and the boards will probably have lifted traces from constant solder-desoldering or wrong solder temperature. The outputs might not work the first time or even the third or fourth time.

By then it will dawn on you that your boutique ultra low PPM resistors and silver plated wires and expensive tantalum caps had costed you more than buying a decent headphone amplifier. It will be discouraging things will start to look not worth it to proceed with the project.

To use standard components are entirely fine. Triple check orientation before soldering and double check after. If you're building a 20V power supply, it's entirely fine to get a reading of 19.80V because you're not just measuring the PSU output but you also have your meter's accuracy levels that could affect the reading.

Almost always, your second build will be better than your first build.

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Thanks, for all who posted!  Looking at specs on these electrolytics, its surprising how few hours their rated at!😲 I never realized they were that low. Obviously we have many electronic components that have lasted longer than 1000 hrs, so those ratings must be at some percentage of rated specs, but it does make me wonder!

The variac will be dual purposed, as I have several pieces of audio gear that have been in storage for years. I'm sure the electrolytics in my amp and CD player will need reforming. My preamp thankfully doesn't use them (If I remember right). Went from home to small apartment living, and just don't have room for my home system.  My speakers also haven't aged gracefully (Apogee Stages). I got into the audio bug again with headphones because it's a lot easier space wise to manage.

I'm thinking if I can do a test load using cement resistors at about .25 amp, that should be fine. 20V/.25 amp equals 80 ohms, 20v X .25A equals 5 watts, this should do https://www.mouser.com/ProductDetail/Vishay-Dale/RE65G80R0C02?qs=sGAEpiMZZMtlubZbdhIBIO9u8NSWRDaQ0Ik%2Fvj6PQ48%3D . 

Anyway, thanks again gents!

 

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41 minutes ago, ShortBtwnHdset said:

Thanks, for all who posted!  Looking at specs on these electrolytics, its surprising how few hours their rated at!😲

That is rated lifespan at the maximum temperature, ripple current and voltage. Pretty insane conditions for most audio gear. Lifespan increases dramatically as temperature and ripple current fall to more reasonable levels.

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6 hours ago, ShortBtwnHdset said:

I'm thinking if I can do a test load using cement resistors at about .25 amp, that should be fine. 20V/.25 amp equals 80 ohms, 20v X .25A equals 5 watts, this should do https://www.mouser.com/ProductDetail/Vishay-Dale/RE65G80R0C02?qs=sGAEpiMZZMtlubZbdhIBIO9u8NSWRDaQ0Ik%2Fvj6PQ48%3D

I would put a higher load if you want to load test it. Like at least 0.5A or even 1A.
Here you can build a simple and flexible load tester.

Edited by starcat
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  • 2 weeks later...

Just wanted to give a little update. Progress has been made, the board is partially populated with IC sockets, most resistors and diodes, and some tantalum and film caps. All those transistors included in my ebay purchase end up only for the SuSy Dynalo boards, so I made another order with Mouser last night. MJW21194G and MJW21993G have been out of stock for a while, may have to find another source (Digikey out as well).  KSP42TA's are out as well.

This is my first build, and my soldering skills were tinkerer level at best. I had no idea how rusty I was! As IC sockets were center of board, I started with those, and it took a redo of a pad or two to get the hang of it. Glad I bought flux cleaner! I definitely am not of production level skill, but all of the joints now look good under a magnifier.  Hardest part seems to be using just enough solder and not too much. Have bought liquid flux for the IC sockets, wasn't really a problem here but looks like it will be necessary for large IC sockets on SuSy boards.

I need to start looking at transformers, hopefully toroids. Problem is, I may actually need another secondary winding and associated DC board to power peripherals. I'm hoping at some point to add options such as input sensitivity, remote volume, or multi-source switching. Do you think a 12 volt rail, maybe half an amp, should cover those capabilities? 

I'm hoping to start looking in goodwill shops for a temp case, repurposed from some other audio component. Just basically need the sheet metal and the IEC outlet (hopefully w/fuse holder), maybe a mount for the volume control,  and even a possible input connectors or two. I'll permanently case when I've gotten everything working and have a  picture in my head of the finished product. I have to look thru a lot more of everyone's builds for inspiration. 

More to come!

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Regarding the MJW21194/21193s: I believe some people use 2SC5200/2SA1943 instead of these. A bit lower power, but would be fine for a Dynalo. I think the pinout is the same, but I would check it first.

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20 minutes ago, ShortBtwnHdset said:

 Hardest part seems to be using just enough solder and not too much.

I have found using smaller diameter of solder helps very much with this problem. I now use .025/.6mm ones almost exclusively now for this kind of work.

Edited by mwl168
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Hey all! Quick question, James' guide shows a mouser project list (BOM) link, and in that are trimmer pots, 500K. The schematic shows 100K pots. Which should I order if I want that capability?

Status update, I started populating what transistors I had and few other parts. Found I had put one of the tantalums in wrong orientation, and in removing it, ended up melting one of the tiny film caps, so will have to replace it as well. Was able to get the tantalum out without lifting the solder pad, hope I'm as lucky with the film cap. Friend advised me to sacrifice parts instead of reusing them, in service of saving the motherboard pads.

I'm still having some issues with using too much solder, have one transistor where a leg on the other side collected a small blob. Will try and solder wick that off. I'm using a fairly coarse (read big) soldering iron, so that may be a contributor. It's a larger iron with a temp range adjustment, about a 45 watt max, so the tips kinda large. May need to buy a smaller tipped soldering iron/station for this build.

I have ordered the MJW21194G and MJW21993G as a pair, as well as the KSP42TA's off of ebay. Coming from UK and Germany; this pandemic has really screwed up supply chains. Mouser notified me backorders would be as late as January, so I needed to do something. Hopefully, they're not China knock-offs, but we'll see. Will still be up to 3 weeks before all those are delivered. Once the transistors are in, I'll populate the large caps and connectors. Won't be getting the transformer until I'm closer to having board fully populated.

That's all I've got for now. Have a great day!!!

 

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You need to get a more suitable solder iron, and I would invest in a solder sucker as well, such as an Edsyn Soldapullt or something like that. I'm not sure where you got your board from, but on any of the HC boards, I've never even come close to lifting a pad. Same with 1oz boards from seeedstudio, etc. Also, if you are using lead-free solder, one word: DON'T

 

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On 8/16/2021 at 4:31 PM, ShortBtwnHdset said:

Hey all! Quick question, James' guide shows a mouser project list (BOM) link, and in that are trimmer pots, 500K. The schematic shows 100K pots. Which should I order if I want that capability?

 

 

Status update, I started populating what transistors I had and few other parts. Found I had put one of the tantalums in wrong orientation, and in removing it, ended up melting one of the tiny film caps, so will have to replace it as well. Was able to get the tantalum out without lifting the solder pad, hope I'm as lucky with the film cap. Friend advised me to sacrifice parts instead of reusing them, in service of saving the motherboard pads.

I'm still having some issues with using too much solder, have one transistor where a leg on the other side collected a small blob. Will try and solder wick that off. I'm using a fairly coarse (read big) soldering iron, so that may be a contributor. It's a larger iron with a temp range adjustment, about a 45 watt max, so the tips kinda large. May need to buy a smaller tipped soldering iron/station for this build.

I have ordered the MJW21194G and MJW21993G as a pair, as well as the KSP42TA's off of ebay. Coming from UK and Germany; this pandemic has really screwed up supply chains. Mouser notified me backorders would be as late as January, so I needed to do something. Hopefully, they're not China knock-offs, but we'll see. Will still be up to 3 weeks before all those are delivered. Once the transistors are in, I'll populate the large caps and connectors. Won't be getting the transformer until I'm closer to having board fully populated.

That's all I've got for now. Have a great day!!!

 

The 100K vs 500K trimmer does not effect the adjustment range that much, I have used both but not longer implement the trimmer adjustment in my builds because there are better and cheaper ways to get reasonably high output accuracy. The 1M ohm resistors have a larger effect on the adjustment range then the value of the trimmer. You will get very little adjustment range - just a few mV using 1M resistors. Reducing the 1M resistors to  810K still only gives a few 10s of mv adjustment. This is still typically not enough to correct the inaccuracy in output due to 1% resistors in the voltage set circuit anyway. So unless you go for 0.1% resistors in the voltage set, don't bother implementing the voltage trimming because it will not have enough range. Remember too the larger the adjustment range the lower the temperature stability of the output - almost all trimmers have temperature co efficient that are 10x worse than 0.1% resistors. So the to summarise options are

1. 1% resistors in voltage set + trimmer. disadvantage trimmer not enough adjustment range to connect for 1% resistors plus loss of temperature stability plus good quality trimmers are not cheap.

2. 1% resistors in voltage set + no trimmer, cheapest option with better temperature stability than option 1 and not much worse voltage accuracy

3. 0.1% resistors in voltage set and no trimmer. best temperature stability. Voltage accuracy much better than option 1 or 2 and only slightly more expensive than option 2

4. 0.1% resistors in voltage set and trimmer. better temperature stability than option 1 but highest cost of all the options. Only useful if you really must have an exact output voltage and you have a 5.5 digit volt meter or better to measure it with.

A good quality soldering iron is a must especially if you are going to solder high voltage boards or smd. I use the hakko fx888d - which has a terrible user interface but otherwise works well for the builds in these forums and has a wide range of tips available. There are irons with more wattage, faster heating tips etc but for me the 888d was a good compromise between quality and price.

I have used jlcpcb for all my pcbs and have never had a track lift when soldering and only had one through hole lift when desoldering and that was me being careless and forceful rather than pcb quality issues.  I use a duratool disordering station (because I hate desolder wick) but other members love solderwick. 

 

I entirely agree with  Pars unleaded solder is garbage, I tried lead free soldering and gave up and went back to lead. Lead free needs higher temperatures which means more joint oxidisation and trip wear which means more flux and more aggressive flux to stop the oxidations which means more tip wear - and the flux fumes are very bad for you all. The smoke during soldering is not vaporising lead its flux fumes and lead free makes this worse. The only time leaded solder is dangerous is if you eat it. The leaded free solder makes poorer joints which crack more easily because the joints are more brittle.  When the EU tried to get rid of leaded solder the military, aerospace and other industries requiring high reliability were either exempt or "opted out" because of high failure rates and reliability issues with lead free. Its only really consumer goods that went lead free...

There are some good guides to soldering technique and the need for flux on youtube:

 

good luck with the transistors

James

 

 

 

Edited by jamesmking
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Hey all! 

7 hours ago, jamesmking said:

"So the to summarise options are ...3). 0.1% resistors in voltage set and no trimmer..."

"...A good quality soldering iron is a must..."

" I use a duratool disordering station (because I hate desolder wick) but other members love solderwick."

I had gotten the .1% resistors per your suggestion, so will probably go this way.

 I used to have a great temp controlled digital display soldering station, bought surplus from an aircraft tool shop, but it degraded over time to being unusable, and the 45 watt was originally a 'get by' purchase for a project. I'll have to investigate the Hakko, what I'm using currently just isn't working well.

 I already have a de-soldering station bought for my last project, but I use solder wick as well. Neither seem to totally remove all solder enough to get the components back out in one shot, so maybe I am using some non-leaded type. Until you and Pars mentioned this, I didn't know it was a 'thing'.

 

Pars, as to where the boards are from, I really don't know, it was an Ebay purchase. Solder is regular electronics grade solder, thin stuff, but I have no idea of the composition. Seems to be slightly thicker than a mechanical pencil lead. I'll have to look online for leaded thin solder to be sure.

 

 

Edited by ShortBtwnHdset
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Hey all! 

Pars, you have a post early in the thread, around page 4 I think, where you used rectifier boards and Schottky's instead of large bridge chips. There is a .002uF cap and a 330 ohm resistor in the pic, might I get values (voltage/wattage) and/or PN's for those? Bought rectifier boards from Partsconnexion, and want to tack those on to each, so need similar compact parts. Thanks!

 

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Those were a snubber based on a post in 2010? by John Swenson on diyaudio. There has since been much more work done on these. See this thread: https://www.diyaudio.com/forums/power-supplies/243100-simple-math-transformer-snubber-using-quasimodo-test-jig.html

Sorry, it is long. For the combo recommended as a swag by Swenson, I had some MKP1837 22nf caps laying around, and just used crap Radioshack carbon 330R resistors.

Edited by Pars
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