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Technical Assistance/Advice Thread

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You need to compare the results as a voltage divider so one end to wiper and then the other end to the wiper. 

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^Yep, thanks!

I hooked up a 9V battery to the input-gnd and plotted 11 points wiper-gnd (around 15 deg rotation/point) and moved from channel to channel without varying rotation. They actually plot out pretty close. There is one point at around the 9th point where the L is louder than the R, which was probably close to where I was listening at.

2CP2511 plot.jpg

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The point at 9 is 4.1815V (L) vs. 4.0713V (R). I believe this is about 0.25dB (0.23). It was definitely audible but was at the point where I initially was wondering if I was hearing things or not :)

This is in a known amp; the TKD 4CP601 I was using doesn't exhibit this behavior, nor does a 2CP2511 25K pot I also have. I don't know if partsconnexion will do anything about it (or TKD), but I guess I will ask them and supply the data.

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On 3/11/2018 at 5:40 PM, luvdunhill said:

You might calculate the difference in dB - usually a good ear can hear say 0.5dB difference - might be a good sanity check.

I ran some numbers yesterday at finer points and came up with this. I used a bench supply set for 1.007V (and had to adjust as I was running these to keep it there), feeding both deck inputs at once..

  • I used the same DMM on both sides (HP3468), moving the test clips at each pot position.
  • I took the voltage from wiper to ground for each deck (V1, V2) and used 20 log(V1/V2) to calculate the dB difference.
  • It was slightly above 0.5dB around the area that I was listening in (position 39).

If I didn't do this correctly, let me know :)

TKD graph2.jpg

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Partsconnexion replaced the pot with one they apparently hand selected. I supplied my data and graph above to them, and did let them know I had soldered it in. I returned it.

The replacement arrived today so ran numbers on it in the same manner as before. It looks much better:

 

TKD graph3.jpg

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On 8/20/2017 at 12:42 PM, Laowei said:

My amp is dead quiet. In my 2 case GG, I tie PS and Amp grounds to a single star ground on the Amp chassis. IEC ground is connected at the PS chassis and then carried separately to another point on the Amp chassis. My input is the same as yours, with XLR pin 1 grounded to the chassis, but I leave the pot's ground left floating (with each L and R  +/- signal ground connected for the attenuator to work). Being balanced, they will null.

With your pot ground connected to the amp boards and then daisy chained to the PS board, possible ground loop there. Try disconnecting and see if the hum is still there. 

https://www.tortugaaudio.com/articles/humming-along-to-the-pin-1-problem/

 

IMG_2599.PNG

I'm wiring up (or getting ready to) a 2 box Dynahi build and a new Buffalo III pro build.  If I read the Rane article, the Tortuga article, and this post correctly I should connect IEC inlet ground to the chassis, Pin 1 of each XLR to the chassis, and PSU ground to the chassis for each box, then float the pot grounds in the Dynahi amp box.  Is that correct?

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The “pot grounds” as you call them, should be connected to the PSU ground. The two Dynahi chassis should be connected together. Then a ground loop breaker between PSU ground and the chassis. XLR pin 1 should be connected to the chassis. IEC Earth to the chassis via proper hardware.

 

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On 2/9/2019 at 6:46 AM, Kerry said:

Just got this tapping guide.

SHARS Self Aligning Tap Holder

I'm really happy with it and thought I'd share :) 

Apparently a good tool, will get one. Wish it had No-mar teflon face like some countersink microstop limiters.

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Just wanted to share one of my most favorite acquisitions among hundreds of manual and electric tools.

Heinrich deep throat is capable to punch holes in the center of 400mm panel (hello large enclosures like Modushop Slimline).

No burrs, very clean holes, any hole is perfectly perpendicular to surface, and waaayy more accurately positioned than made by drill bit as you can never avoid drill bit wandering. Precision is close to CNC milling.

I also use smaller punch Roper Whitney XX with smaller throat.

IMG_20180826_183811_1.jpg

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8 hours ago, Helium said:

Apparently a good tool, will get one. Wish it had No-mar teflon face like some countersink microstop limiters.

Good idea.  I think I'll try to make the Teflon face and attach it.

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Recieved my Shars Tap Holder this afternoon. Put it to use on a CF electrostatic amp I have been putting off working on because I dreaded tapping threaded holes by hand. It really works slick and the results came out great. 

Thanks for posting this Kerry. Nothing beats the right tool for the job. 

1D5756C2-4EAA-44D5-A217-F9B1B5685B05.jpeg

Edited by Laowei
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Wow, I'm looking for something like that to make the CFA holes!

Edir: A small guide on how to use it?

Edited by jose

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10 hours ago, jose said:

Wow, I'm looking for something like that to make the CFA holes!

Edir: A small guide on how to use it?

This is one way to do it. 

Position the PCBs in the pattern/spacing you want on graph paper. Transfer draw holes to be drilled aligned on the graph grid. Add centerline of pattern to grid. Then cut down paper and use centerline and grid to position on heat sink and tape it down securely. Then locate PCBs on graph grid drawn holes and tape down. Use centerpunch in PCB holes to dimple heat sink to prevent drill wandering. I leave the grid paper and PCB there to act as a visual template when drilling. 5595261A-AA64-4A72-8743-BA2B82CB9368.jpeg

 

 

I use a cheap Harbor Freight desktop drill press to get the tap drill holes drilled perpendicular to the heat sink face. For M3x0.5 threads I use a 3/32 (.094) inch tap drill size. I preset the stops for a drill depth to around 6-7mm, as to not break out the other side of the heat sink. And then drill all the holes. Pull the PCBs and graph paper off and deburr the drilled holes so that the rough edges are flush with the heat sink surface. 

Then mount a M3x 0.5 bottoming tap in the Shars tap holder (the T handle shaped piece). Slip it into the Shars alignment stand (this holds the T handle piece perpendicular to the surface), and then using a little light lubricant, carefully hand tap each hole drilled. After each full turn of the tap, back turn 1/4 turn to cut off the internal chip. Repeat until you can remove the tap and easily screw in the length of the machine screw used for assembly.

FYI, I cleaned the cheap shipping lube off the sliding parts of the tap holder because it was squeaking badly when used. Replaced with a little Never Seize and now it spins without a peep.

 

9F054B92-821D-4927-BF46-34CB76403937.jpeg

205BA366-BA3D-4A13-8600-0AD7052A3502.jpeg

 

 

Edited by Laowei
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easiest to print out the file 1:1 from the gerbers. If your printer is exact, and virtually all laser printers are, this is the most accurate way.

then center punch, drill, then tap.

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Thanks to both.

I do a copy of the pcb to use it as a template too. I'm used to doing tap holes but I admit that I have never needed so much precision. For example for transitors I use a 2.5mm drill and then a 3M tap with a "manual tap" (I don´t know if it's like that in English, sorry) . I don´t usually have problems but I would like them to be perfect. 

My biggest question was how to use the tap holde tool correctly. Now that I have seen the photos, it has become clear to me. Today I bought that tool in the UK. I hope it arrives soon. 

Edited by jose

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My biggest concern hand tapping was snapping off in the hole due to angular misalignment. That should not happen with the Shars tool. 👍 

I think you will like it when you use it. It works very well for what it was intended for. Thx to Kerry for sharing.

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Yeah, Shar tools look nice. They’re only 10 miles from me and we go up to St. Charles fairly frequently.


Sent from my iPhone using Tapatalk

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Guys, yesterday I used my Shars Tap Holder with the CFA heatsink... incredible, in just 25 minutes I had finished screwing all the holes. All have been perfect !!!!

Normally for this work I would need hours and surely some thread would be skewed.

Great purchase and great discovery. Thank you!!!!!

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I want to convert a 580v DC bias to a 230v DC bias for so I can use both modern and older stax phones off my amp. Would a simple voltage divider do the trick or would I need to be careful about something else? The plan is to just tap of the pro bias outputs L/R and then use a voltage divider to get correct bias.

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I would rather tap off the B+ via a voltage divider. 

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