Those LEDs you listed are 2.2 v forward voltage drop.... I think you need the 1.7 V variant if it's anything like the dynahi?

They drop 1.7 in use for me....and that is what is listed on the data sheet as typical.

Those LEDs you listed are 2.2 v forward voltage drop.... I think you need the 1.7 V variant if it's anything like the dynahi?

Edited September 3, 201411 yr by GrindingThud

Ahh ok, I only checked the Mouser spec page.

This is what we use for 1.7V led: 859-LTL-307ELC

 

the lead spacing on the board for the .1uf cap is 3.5mm but the .1inch caps do fit.

 

the 5pf caps are 5mm lead spacing

 

by the way, I have a new name for the thing...

 

PureBipolar    (tm&c)

 

would apply to the ss dynahi too.

 

Also the footprint for the resistors on this one is 0.5 and not 0.6 as on most of the other designs. 

Edited September 3, 201411 yr by spritzer

that is because (among other reasons) birgir wants things to be as tiny as possible.

It offsets my petite stature... 

any downside to running at 15V? I thought I spied 20 on the silkscreen

Mmm, parts incoming.

any downside to running at 15V? I thought I spied 20 on the silkscreen

 

Less voltage swing and power aside, there are none. 

any downside to running at 15V? I thought I spied 20 on the silkscreen

 

The OP07 datasheet specifies a maximum of +-18V supply voltage so I personally wouldn't go above if using that opamp. I am going to run mine at +-16V (mainly based on the 15VAC transformers I have on hand).

OPA445 for the higher rails. 

What is the preferred sequence for adjusting the pots on this unit? The 3rd one is messing with my mind.....

remove the opamps. make sure the 2 pots that adjust output voltages are in exact center

hook it up, and adjust the led bias pot for best output voltages around zero.

put the opamps in, and adjust the other pots for pin6 on the opamp close to zero.

Got it, thanks again!

I have a bunch of matched jfets I was planning to list, but life is too crazy now... I drug them out of a pile and moved them to yet another pile and am not sure where they are, or I would check. Hit me up week after next and I should be able to have time to locate them.

I can supply LSK170 in 1% matched quads (or higher). I don't really want to part with the p-ch part though. Anyone think there would be any demand for these?

Thanks anyway Marc. I have 2SK170s but don't have any p channels.

I did some board stuffing while I think of what to do about the j74s. I read that the Linear parts are different enough from the Toshibas that they are not direct drop-ins so I can't do complementary pairs from different manufacturers. Decided not to bother with offboarding the CCS offset adjustment so I'm going to just put in the 20k resistors. Need to put in another mouser order and populate the attenuator boards, so I can actually start programming the damn thing. Preliminary testing is good with the uC, it connected to my phone through the cloud just fine with the wifi antenna I bought. It's a small planar antenna with an adhesive backing so should be easy to mount to an enclosure.

 

Just want to make sure I have the ubal to bal boards traced correctly so I don't build it wrong (not sure if a schematic has been posted). It's a cascoded diff pair with source degeneration and a CCS tail into a wilson current mirror driving output BJTs? Are the LEDs across what I think is the mirror used for Vbe temp tracking or some other purpose?

 

the boards you have are the ss dynalo boards, here is the schematic

http://gilmore.chem.northwestern.edu/kgdynalobalssproduction.pdf

your boards are slightly different.  work fine with the that340 part

and a 10k pot. just amazing sound into all headphones I have tried.

 

the unbalanced to balanced thing is

http://gilmore.chem.northwestern.edu/ubaltobald.pdf

and really the that340 needs to be replaced with fets for high impedance

sources

Thanks! Yes, my boards are missing the CCS adjustment but they have the trimpot for offset on the servos. I saw the Dynalo SS schematic previously but didn't see the ubal to bal one.

 

I noticed the input diff pairs aren't cascoded in your schematic but seem to be on the board? Also, would you recommend putting in a CCS adjustment for the ubal to bal CCSes?

the pots on the opamps will actually do very little. and the front end is not cascaded

 

the 10uf servo caps need to be 1uf and the bias resistor should be 240 to 255 ohms.

 

change parts as necessary to make that board identical to the schematic.

Edited September 12, 201411 yr by kevin gilmore

the pots on the opamps will actually do very little. and the front end is not cascaded

 

the 10uf servo caps need to be 1uf and the bias resistor should be 240 to 255 ohms.

 

change parts as necessary to make that board identical to the schematic.

 

 

Yeah I'm sure it does very little as the OP07/OP27 max offset is already 1.5mV and the thermal stability of trimpots aren't very good. I should have followed the datasheet with a 20k pot but got 100k instead. For anyone that has these older version boards and want to put in the trimpot, you're going to also need to jumper the NC pin to the offset pin if using the OP07/OP27 since the pinout of the OP07/OP27 are slightly different from the OPA445.

 

The servo caps I put in are 2.2uF MLCC, will use 255 ohms bias resistors and will add in the LED bias adjustment after all since you said so. The bias resistor slots are actually marked 510 ohms on the silkscreen. I have followed the values in the schematic over the silkscreen for the other resistors as well.

 

So I should also follow the schematic and not the board for the ubal to bal as well?

 

 

The CCS resistor value is 100 versus 180, there's 50 ohms in series on the output, and again I believe the front end to be cascoded with the extra BJT and the voltage divider from the rails to gnd connected to the bases but could be wrong.

 

Going to make this as KG approved as possible eventually since it's the KGITSOCH, I will build scaled down Dynahi power supplies for this thing. It will have three transformers with pass FETs connected to offboarded heatsinks to give the feel of the DIY T2 supply. I will also put in the MM stage you posted somewhere that you designed in the '70s unless you have a newer design.

Edited September 13, 201411 yr by mypasswordis

The 1M servos are now 100k and the integration cap is 1uf.

and the input resistors to ground are 100k (does not matter if you use the jfets)

latest board pic

http://gilmore.chem.northwestern.edu/ubaltobald3.jpg

With any luck, the boards should be in Monday. Here's the case work so far:

Boards are in from https://www.pcbnet.com/Quotes/introductory-offers

Great company to work with, boards look nice, I hope to have it up and running this weekend :

Edited September 27, 201411 yr by GrindingThud

Got it up and running, this is a cool amp!