PRR-176 REV 4 Build Thread ***Manual up!***1/16/14 - (chk 1st post)

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berkleystudios

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Jan 4, 2012
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build butler link is down for me but i seemed to have found another working link so Im posting it again. http://buildbutler.org/

Working on the case now, and waiting on some parts to finish the DOAs. hoping to pass signal in the next week or two...
 

groselicain

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Feb 9, 2009
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Tennessee
Just a quick resurrection—did boneindian ever get his unit up and running? I just finished mine tonight and encountered the exact same issue he initially had with his regulators. Mine aren't fried, but they do shut off after fifty or so seconds, ceasing voltage to the heaters. I will admit that it was perhaps a little foolhardy for me to immediately build with all discrete op-amps, but I'm hoping someone finally worked out all the kinks so that I can get along with mine. First things first, though, it looks like I've got to grab some heat sinks.

Also, I thought I'd share a little irreverent case candy. This is what I used to house my build, considering some might argue it's closer to a 175-B than a 176:

 

groselicain

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So since he's not been active on the board since late 2014, I've emailed Abe to no avail. I'm sort of out of my depth here. Any suggestions? I wish there was someone I could just hand this to so they could figure out what I'm doing so wrongly.
 

shot

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Guys, I'm in the process of debugging my unit after my first (unsuccessful) power up.
Got one observation and one question.

I pulled out all the ICs and tubes and connected power only to the left channel.
Powered it up - SMOKE!
10R resistors on right channel smoked. Those two resistors on the right bottom edge of the main board.
Checked with schematic - they are current limiting resistors and they should smoke first in order to preserve other stuff from burning. Ok... replaced them...

I found out that if you plug the power connector on one part of the board (below left or right channel), that you actually deliver voltage to both channels! Why did Abe put two power connectors?!?! Only grounds are separated.
So I've connected ground on both channels but only power to the left.
Powered the unit - no smoke.

Now for the question...

On my unit, heaters are connected in parallel (adjusted to 6.3v) and 10R/5W resistor on PSU gets very hot!
Is that normal?
Should I install additional 10R before every heater as an additional load?


:)

Luka

 

shot

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So I went on to debug my unit.
Btw, this is one of two units I'm building! I went to byte the bullet and build simultaneously two units. That's four channels! Hehe!

I've went to read a lot through this and similar threads. Too many success stories gives me confidence that this will work one day.

I've returned to serial connection of heater wires. At first when I had them in parallel my PSU had tendency to shut down since 10R/5W was getting real hot. Now when connected in a way Abe originally suggested, everything is ok.
But check this out - the boards I got for tube connectors don't have pins 4 and 5 routed! There is no connection from tube socket pin to the pin on the bottom of the board! These are the boards I got from Abe later, after he realized that original tube pcbs had error (they routed backwards) . I've traced other pins on this "new" pcb and rest of it is proper.
So I had to hardwire the heaters directly to socket pins 4&5 instead of connectors AB/BC!
Anyway - heaters are good. Tubes glow and work on appropriate heater voltage.

My first channel is dead. It doesn't pass audio.
Channel two is passing audio but it doesn't compress. And level is a bit low.

But for now, my main problem is oscillation. It's very hard to diagnose where the faults are since after turning on the unit it takes about minute or so before I get motorboating oscillations and I have to turn off the unit.

I'm trying to find out what's wrong. I'll keep working on it in next days.

Motorboating starts when needle on the meter reaches it's top value. Somewhere there.
Voltages seem okay - I'll have to measure them few more times.
HT sits on 103vdc and that's supposed to be okay.
Other rails are also good.

I'll keep you posted in my debugging work.

If someone has constructive ideas please do post them!

:)

Luka
 

shot

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Update!

Still working on my units. I have focused on successfully building first one, after it's done I'll deal with the second one.

Just a quick question:

Is it normal to have output level fully CCW and still hear signal on the output?

I'm using linear pots on output. When I rotate it, starting from CCW and rising, in first 60% level stays the same. And then it starts to rise. But it's so weird that I cant turn off the volume completely!
 

shot

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Finally fixed all the bugs on my first unit! It's working like charm now!
I did a few mods on this unit. I decided to up the pad resistors from 470R to 680R in order to get the better level in sidechain, used different transformers (OEP Z3003), put a lorlin switch to select five different HP frequencies in the sidechain and I've put a SPDT switch on the front panel to select different timing capacitor values
Since I'm too diy obsessive I did a custom front panel all by myself to accommodate extra controls.
Now I have to trim a bit those timing caps (2.2uF sounds too slow), replace linear pots to rev.log. and fix leds in meters and that'll be it!
:)

Luka
 

geotone

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May 7, 2013
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Thanks Luka for keeping us updated! It's actually a motivation to pick up my own 'almost-done' build again and finally finish it.

And show us some pictures please :)


/G
 

shot

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Here are some pictures!

Click on thumbnails to enlarge


Front panel detail



Main board
Notice the different transformers. I've etched adapter pcbs to fit those transformers and covered them with copper tape. Copper tape shields are grounded with extra red wire to chassis. Unfortunately, this wasn't enough to stop the hum so in the end I had to remove the power transformer outside to a separate box


At first I used 6BC8 tubes. But I got a couple of PCC85 tubes so I decided to test them and I love those so they are keeper! They have more gain so they react differently. Basically, compression kicks in with lower input level. I had to up the heater voltage to 18v (9v per tube) since these use this heater voltage. If kept with 12.6v (6.3v+6.3v) they had some self oscillation on 18khz. These tubes made unit's self noise drop by aprox 6-10db on the output! It has to do with the gain of the tubes.



PSU
So I moved my power transformer to this plastic box. In this box there's a 5V power supply (old mobile phone charger dissasembled). It sends aprox 8v (!!) through VGA wire to the unit onto the front panel power switch. When switch is ON, current goes back to this box into the 7805 regulator and into the relay that turns on the power transformer. I used the same VGA cable to send all the AC voltages into the PSU in the unit. There's also two LEDs for status and fuse. Wiring the vga cable took some trial-n-error since some pins on vga are connected by default. I didn't know that at first! Chassis/Earth and 18v 1.2A wires are doubled since vga cable has AWG26 thick wires inside!


this is where this cable enters the chassis


and this is the psu with all the regulators mounted on chassis for better heatsinking


After I moved the transformer to a different box, I decided to put a metal screen between the PSU and the main board. It helped to eliminate the hum on the right channel to -104dbFS measuring in my computer with in and out on the unit maxed.

Sidechain filter
Here on the left you can see my assembly of different capacitors that provide different freq. of high pass on sidechain. It's a bit messy but it's firm enough not to short anything. I think this is the best feature I did for this build and it provides so much flexibility when using this compressor. I didn't expect it to be that good!


There's also SPDT switch on front panel that chooses 1uF or 2.2uF tantalum cap for timing. It was impossible to take a photo of it since it is hidden under the meter and some wires.


:)

Luka
 

boneindian

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Mar 25, 2012
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Brooklyn
I'm back from the dead but my unit still has yet to draw breath...

Getting it back on the table this week though, I think I'm going to start by (after rereading this thread) ditching the discrete op-amps and throwing ICs everywhere for now and see if I can't get my power issues sorted out.

I'll report back

 

MaxD

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Apr 28, 2017
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Greetings, could anyone point me in the direction of place where I can buy a PCB for the PRR 176 (4th rev)?
AC store says out of stock and I have not received any info from then on the possible future availability..

Thank you in advance for any help
 

Slaps_Bassy

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Apr 28, 2013
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Since Abe seems to be AWOL, does anyone have the build docs they could post for download?  I've had the boards sitting around for a while, and I'm finally getting around to them only to find that I should have saved the files when I had the chance.

Thanks in advance.
 

Slaps_Bassy

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Apr 28, 2013
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Thanks for submitting those files Vito!  I'm assuming once the admins approve the files they will show in your post?
 

boneindian

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Mar 25, 2012
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vitopower said:
Just emailed rev 4 manual & BOM with docs (wiring guide, schematics, jumper info, layout) to admin, should be available soon.  8)

Any updates on these docs?  After a month or so of inspecting every inch of my PSU for errors and replacing the +/- 18V regs one last time I'm still getting the same crazy/weird readings as when I gave up two years ago.  Not passing anything on the positive rail even though the reg is getting hot.  Negative rail reg stays cool and sometimes passes -30V before shutting off. The trimpots don't seem to have any effect at all.  I'm also back to all ICs for now .

I also managed to splash some water on the wiring guide which immediately rendered the colored wires illegible  ....so yeah, I wish I'd saved the documents when I had the chance ::)
 

manulaf

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Mar 5, 2013
Messages
42
HI !

I use this prr176 since few year now and I'am really happy with it. I choose the input attenuator option with a Bourns 600 ohm T-pad attenutor. Sound's great !
But for mastering purpose I d'like to swap the T-pad attenuator for a stepped one. Is there somebody who can help me to find a cheap solution to that ?
Thanks very much.
Manu
 

man-bot

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Dec 20, 2008
Messages
87
Is there a spot where the build docs for this project are located?  Finally getting some time to work on this and I realized Abe's site is no longer up and I have a Rev 1 board and no docs.

If anyone can point me in the right direction that would be awesome!
 

scott2000

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Feb 21, 2015
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Sunny...Sometimes Florida- USA
Winetree said:
The P.S.B. shows NP next to some caps.
Does the NP mean NON POLARIZED caps.?

Looks that way .....
https://buildbutler.org/build/prr-176-rev4-main-board#_47uF-NP

I have an old Mackie mixer that labels the + and - for the non-polars as well..... kinda confusing but nice to know...


 

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