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

Ummm guys.... I fried the resistor that sits directly after the negative rail V Reg.... Refresh my memory please, if you will, why it would do that... Outside of the obvious, I did something wrong.  There was somewhere around 48-50 volts on the negative rail.... I'll take pictures of my board and post them too. Any suggestions would be greatly appreciated.... I think I have everything wired up properly.... Also my heater voltage is off for some reason as well... I think that's all that's stopping it from working properly. Tubes aren't even getting warm

I've got a couple of questions for some of you guys on this build. I have recently acquired some Rev 2 boards, is there a specific build thread for it, or can I work off this build thread? I can't seem to find the Rev 2 build thread by searching.

Another question is for the folks that chose to go with the Edcors. How do you like them? Do you find your unit noisy? Where you able to come up with some shielding and PSU placement tricks to help this? How is the sound of the Edcors? I know for myself I'm looking to beef up stereo stems or mono sources. I also have a budget and the Lundahls and Cinemags are just not in it. It seems that by using the Edcors the sound would be much more full and large. I'd love to get some thoughts from you guys on my assumptions. Also, is it possible to have both a discrete ouput and tranformer output with selectable outputs? I'd like to have the option for both if it's possible.

Lastly, what do you use your unit for? What do you feel it works best on?

Thanks! Hope to hear some responses!

Jerome Mason

Hi
I still haven't got my PRR-176 operating yet but I have been away for a while so I haven't had much chance to run any more checks yet. I've just noticed that on the inputs, in tiny writing, it states "jumper for normal operation". I've not seen any reference to jumpers at this location anywhere else. It's a Rev 4 board. Have I missed something here?

Cheers

Steve

Hi
I think I can answer my own question! Having re-read the earlier pages of this thread I clearly need to jumper the inputs. I will also recheck all of the other jumpers as I am not convinced I have got them quite correct. Aside from that, my voltages look much better now that I have changed the resistors in the PSU
Cheers
Steve

Hi
Well I've put the jumpers on the "spare" input pads and it seems to be working. At last! I'll put it through its paces over the next couple of weeks and I'll take a couple of pictures for this forum. I've managed to pack it all into a 1u case but with the transformer mounted in an external enclosure. It's the only way it fits in 1u and it keeps most of the noisy AC out of the box (the transformer magnetic field anyway).
Cheers
Steve

Got it all working. Here is a photo. I hope I've attached the correct one!
Cheers
Steve

Congratulations, Steve.  Really beutiful and full working.  Did you use 470R pads?  What's your opinion about sounding?

Hi Anvl
Thanks for the kind comment. I used the 700R resistor value for the pad input, following your suggestion. It seems to be working on the bench (to be more correct it's actually a table!). I'll put it through it's paces with some other studio equipment and report how it sounds. I'd built a couple of 1176 compressors some time ago and an EZ760 so I have something to compare it with.
Cheers
Steve

Beautiful build Steve! Congrats!!!

I'm wondering, are there any disadvantages when you mount power regulators on the back of the case compared to soldering them in their place on the pcb? I know your way is better in terms of cooling, but what about long wires that connect the pcb with regulators - can they create hum when crossing audio lines?

In two builds I've done exactly the same, mounted them onto the back of the case, but it was not crowded too much so I could separate their wires away from any wire carrying audio. But this is a bit different situation since it's very crowded in here!



Luka

In my opinion, it doesn't matter where to put voltage regulators in terms of hum because there is no AC power signal through them.  Steve was very clever to put power transformer out of the case.

Hi Luka, Thanks for the compliment.
I originally had the power regulators on the power PCB but they got very hot as has been mentioned earlier so mounting them on the case, and with a heatsink, keeps things cooler. I had a couple of problems when I was building it, firstly I'd got the jumpers wrong and then I had to modify the reversed PCBs for the tubes. The transformer wouldn't fit in a 1U case anyway but there isn't any room as it is quite busy as you say. Hence I put the transformer in a separate enclosure which keeps the noisier side of the AC away from any signals. I've done this before with some other builds and it does help keep the noise down.
Cheers
Steve

One PSU question...

I got 128V on high voltage rail.
WITHOUT LOAD!
Should I drop it to 100-110v?
Or I should consider that okay and expect it to drop to 100-ish when I build the main board and connect it?

What do you guys measure on this rail when your psu is unloaded?

Hi
128V is probably a bit high. I was getting around 116V without load originally but it didn't drop so much under load. I changed the values of the resistors in the PSU in line with suggestions in an earlier comment in this thread which brought it down to a more manageable value. In the end I got around the desired 100V under load with the resistor mods.
Good luck and watch those high voltages as it's easy to forget you are dealing with something which can be deadly.

Cheers
Steve

Well, I figured it can't be that high value so I went to install different value of resistors. With 3 x 3K9 it is now at 111V. I think that will be fine.

I'll stop here for now. From monday I'm finally going to holidays vacation, so I'll continue when I get back to town!

8)

Would you find the prr 176 good for tracking?
Acoustic guiar and bassguitar?

After some years of active use I came back to this project for fixes. My project has significantly diverged and been upgraded from any of the available revisions but thought I'd post the part that applies to everyone.

I always thought the recommended 1uF time constant cap sounded very nervous and like a stompbox. In other words the maximum attack and release time didn't really work all that well except for, well, guitar. Not what I wanted or needed. On the other hand the "stereo" sidechain switch results to parallel caps ie. 2uF in total. After all these years of use this has worked far better overall. But this kind of combined monosum sidechain doesn't work for a lot of stereo material. And I want the same sound for mono channels.

The fix is very easy. Use 2uF caps instead. Now I get a steady lub-dub fat vari-mu sound. Stereo still gets double ie. 4uF, but now the overall sound changes less. Ears detect less a difference between 1-2uF than 2-4uF it seems.

I have quite a bit of experience with this compressor and its use with sound shaping. I recommend these values for  you all.

Kingston, thanks for that information! Luckily I was just in the process of ardering the last bits and pieces, so I could just add that to the list. Perfect timing for those timing caps!


Best, G

Hi all,

I'm putting this together, finally.

I am almost there: today I started checking and setting voltages. I followed Anvil's advice on the 100V rail, and it seems to work: arrives at 101  8) . I also set the heaters to 6.3.

However, when I connect the third rail and the ground connection, the trafo (Don's) gets very hot immediately. Looking at the schematic, that doesn't seem too surprising, as one of the 18V connectors is basically sent straight back to ground! I am certainly not the most knowledgable electronics person, but that strikes me as slightly weird. Since no-one else has reported trouble with it, I guess I must be doing something else wrong. I checked all the components, set the trimmers to a middle position etc.


Any Advice? Thank you!

Bringing it back from the grave!! Long time since my last Groupdiy post, after starting working as a monitor engineer and shop manager I almost have no time, but it's slow season and back to the DIY!  I am working on the wiring and the opamps. Build butler is down and I am missing a resister on my 2520s... Need to dive a little  deeper to find out what it is.

Just powered it up for the first time and nothing blew so that was a relief, lots of fine tuning to do, and my case will be a mess but hopefully in the end it will pack with all kinds of discrete, transformer, tube, varimu goodness.


Thee PRR 176 will live!!!

I haven't finished mine yet so don't get too down on yourself. I'm very close thought but you know, some times life before DIY.