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

[ilfungo]

Hi Manulaf

"I saw that there was a plate balance trim in the latest revision of prr176. Why removed it ? Can it help me to fix my issue ?"

I'm just studying a little mod to add 1k trimmer for plate balance....
I  say you when I'm ready.

On my unit I've a strange problem.
The meter stay on 0, but on the left channel if I move the release pot, meter go up and down.
If then I switch in stereo mode, the meter are totally out , left -2 right + 2... :-\
Thanks

 

[shot]

I'm slowly going through BOM to create my shopping cart.

I noticed that on positions R11, R12, R65 & R66 there is 3K3 marked on the PCB
But on the schematic (included in BOM pdf document) it says 6K8
(check just after T3 transformer on schematic)

What is the correct value - 3K3 or 6K8?
What did you guys use?

 

[ilfungo]

Hi Shot

6k8 is the right value...

 

[johnnyscotch]

Hey guys,

C112 on the PSU pcb is marked 47uF 25v, but the BOM says 100uF 25v


Also C110 is marked 100uF 16v, but on the BOM it says 470uF 25V

Do you follow the silkscreen or BOM?

thanks!

 

[johnnyscotch]

according to Abe,

these values aren't that important, so you can use what's on the silkscreen, or what's on hand.

cheers

 

[berkleystudios]

Are y'all testing the psu with the main board not connected/ no load.  When testing my voltages were way off/ not really existent...

 

[shot]

Just curious... been looking at Retro176 front panel and I notice there's a "interstage" switch and "assymetry" switch.

Interstage switch bypasses interstage xfmr, right? Does that make any sense? What would be the benefit sound-wise? Can it be done in our PRR176 with relays if the interstage transformer is mounted off-board?

And what the hell is assymetry switch for??

 

[ilfungo]

Just curious... been looking at Retro176 front panel and I notice there's a "interstage" switch and "assymetry" switch.

Interstage switch bypasses interstage xfmr, right? Does that make any sense? What would be the benefit sound-wise? Can it be done in our PRR176 with relays if the interstage transformer is mounted off-board?

And what the hell is assymetry switch for??

Good questions.....
???

 

[manulaf]

Hi
I solved some issue:
- I find some new tubes well balanced so there is less thump and no more motorboating.
- I swap a fautly 5534 in the sidechain stage and now I have the same compression on the two channels
My unit sound great even more in stereo mode !

But
- I still have oscillation at extremes settings. (CW input knob)
- The output level is not really high in fact. With input at 9 O'clock (4 db gain reduction) I have to put the output knob fully CW to have decent output level.
I use a carnhill VTB output trafo.

Thanks for your help

 

[G-Sun]

Hi!

How is the behavior of the PRR 176 compared to let's say a LA2A or a 1176?
What's the ratio, attack and release like?
How is the stereo-tracking? Is it hard to calibrate right?
Are frontpanels available?

 

[ilfungo]

Hi
I solved some issue:
- I find some new tubes well balanced so there is less thump and no more motorboating.
- I swap a fautly 5534 in the sidechain stage and now I have the same compression on the two channels
My unit sound great even more in stereo mode !

But
- I still have oscillation at extremes settings. (CW input knob)
- The output level is not really high in fact. With input at 9 O'clock (4 db gain reduction) I have to put the output knob fully CW to have decent output level.
I use a carnhill VTB output trafo.

Thanks for your help

Hi manulaf!
My 176 strange... my 176 have much gain!!! I also used carnhill on the output.

Hi G-Sun
176 for me  it's more similar to a 1176 but with something special...
I prefer it vs 1176 on vocals and on some instruments ( trombone , bariton sax, ....stereo drum buss)
The stereo tracking for me is not perfect but it's good in some range. ( I've tried 5 pairs of 6bc8 buyed as a matched).
I've just added a trimpot for plate balance and all is better ( thumb, matching)!!!
I've also changed the fixed pad with trimpot and I'm experimented with less pad and all seems good.
It's not hard to calibrate just use the ABE procedure and all is done.
I can't help you about frontpanel.
Ciao!

 

[G-Sun]

Hi G-Sun
176 for me  it's more similar to a 1176 but with something special...
I prefer it vs 1176 on vocals and on some instruments ( trombone , bariton sax, ....stereo drum buss)
The stereo tracking for me is not perfect but it's good in some range. ( I've tried 5 pairs of 6bc8 buyed as a matched).
I've just added a trimpot for plate balance and all is better ( thumb, matching)!!!
I've also changed the fixed pad with trimpot and I'm experimented with less pad and all seems good.
It's not hard to calibrate just use the ABE procedure and all is done.
I can't help you about frontpanel.
Ciao!

Thanks!
I was thinking the PRR-176 lik a sort of levelling amplifier, but then I was mistaken I guess. Good to know.

Edit: I think I mixed the prr-176 with the D-AOC..

 

[manulaf]

Hi manulaf!
My 176 strange... my 176 have much gain!!! I also used carnhill on the output.

Hi Ilfungo
I use 20db pad ! But I will test the t-pad option.

How I can do the plate balance trim option ?

Thanks

 

[berkleystudios]

do i need a 100ohm  trim on the "thump" or can I use something like a 5k? dont want to do an order for 2 trimmers...

 

[johnnyscotch]

Is anyone using the Collective Cases case for this?

If so, how on earth do you fit everything into it?

The PCBS and torroid are REALLY tight, and the VU meters from Hairball are too low at the bottom of the faceplate, also, there was no hole on the front panel for the zero adjust screw, I had to drill one, that's no problem, but everything else doesn't seem like it's going to work.

 

[shot]

Just a quick question!

Is it critical to use polypropilene  Wima 0.1 uF caps in this build?
I went through schematic and they are all used as a bypass to ground, so if I use something cheaper here would that affect performance?
I can't get Wimas in local stores, I'd have to order them abroad, while I can get cheap Kemet PET caps locally.



Luka

 

[MichaelD]

Hi,
Just finished building this unit and am a bit confused.
Among other mods, after reducing r33 470r to 30r to get more room for threshold activity,
This unit seems very limited! It has a very short window of compression, a single sweet spot, nothing more. Attack and release work mild at best and are not smooth but quirky.

All voltages seem accurate. Been using CBC8 tubes. Also using 10/10 Edcors all aound; no hum after adjustments. Been switching between attenuator input and not. Not much difference. It seems very lack luster and boring. Is this normal?
Is something wrong? This can’t be right, right?

Any help would be appreciate!

Thanks
Michael

.

 

[redmojosteve]

Hi
I am just populating the boards for this project but I am a bit confused about the best potentiometer values to use. I have spotted a number of possible alternatives mentioned in the thread and I was wondering if there was a general consensus on the preferred values. Any hints would be appreciated.
Cheers
Steve

 

[ilfungo]

Hi,
Just finished building this unit and am a bit confused.
Among other mods, after reducing r33 470r to 30r to get more room for threshold activity,
This unit seems very limited! It has a very short window of compression, a single sweet spot, nothing more. Attack and release work mild at best and are not smooth but quirky.

All voltages seem accurate. Been using CBC8 tubes. Also using 10/10 Edcors all aound; no hum after adjustments. Been switching between attenuator input and not. Not much difference. It seems very lack luster and boring. Is this normal?
Is something wrong? This can’t be right, right?

Any help would be appreciate!

Thanks
Michael

.

Hi MichaelD
I've build 4 of this units and I've used Ic's input end not T-Pad (I've tried it but very limited possibility on compression level)
My experiences with Edcor transformer on different units are very bad....
Too much hum and very strange frequency responce
I'm not an expert but only my experiences.
In 176 with Edcor on input I've a very low possibility because the unit distort very early, but, with lundahl is another story for me.
Edcor on Interstage = HUM, I think it's very delicate spot .
perhaps, I agree with you on the timing of the attack and release, I'm experimenting a little bit of time on this, and also on  input and output pot tipe.
Another problem :
With Lundahl no hum or strange noise , only
too much hiss ( fo me)
But there is something I love on this unit and I want to experiment more!!!

 

[MichaelD]

Hey, thanks for a response ilfungo.
There was a little hum but after adding some shielding it’s gone.
I too am experimenting with things. I’ve changed the values of some of the resistors and have gained a wider area of compression and the attack and release work better….but not great yet.

I will also be trying a different type of pot for the input and output.
Please let me know if you have any success with this. I might add some DOA’s later, but at this point it doesn’t seem worth it. The sound just doesn’t seem interesting enough to merit more work.
Thanks again