PRR-176 Vari-Mu REV 2 - *Group Buy 7/13!*

[ilfungo]

hello Abe
thanks for the help!
I tried everything
with a capacitor of 100pF partially solve ....
just do not understand what could be the problem.
There is a procedure for calibration?
I want to be sure it is not a calibration problem
(all components used are perfectly matched )
Thanks

 

[ilfungo]

Thanks for this wonderful project!
I think I've solved all the problems ...
I have just one doubt:

I used as a Lundahl 1540 interstage
What is the value optional resistor for this transformer?
THANKS!!!

 

[abechap024]

I used as a Lundahl 1540 interstage
What is the value optional resistor for this transformer?
THANKS!!!

Pretty sure you want 100k on the interstage primary, and then on the secondary you can leave open if it sounds good or try 10k-1k

 

[ilfungo]

R36 100k?
R 168 open 1-10k ?
thanks

 

[abechap024]

R36 100k?
R 168 open 1-10k ?
thanks

Yes. Also you are working on a rev 1, right? in order to keep things as organized as possible you should direct any further questions to the rev 1 thread. Sorry for any confusion!
Best,
Abe

 

[ilfungo]

Thanks Abe
no i'm working on rev 2!!!
I've used all the rev 1 components and transformer for rev 2.....

Sorry for a stupid question but, because the resistor value (R36 and R168) are perfectly reversed compared to those used with Edcor?

 

[abechap024]

Thanks Abe
no i'm working on rev 2!!!
I've used all the rev 1 components and transformer for rev 2.....

Sorry for a stupid question but, because the resistor value (R36 and R168) are perfectly reversed compared to those used with Edcor?

oh! Okay, my mistake, I figured because on rev1 they are silked "opt" and on rev 2 they are silked "1k" and "100k" respectively.  And your right r36 should be 1K. So just stick to the silk, thats why its there!
Best,
Abe

 

[ilfungo]

hello
I need a little help:
I still have problems with the meter,
marks perfectly half of the true compression.
I read on a post that changing some resistor values ​​in the circuit you can use a VU meter.
Can you tell me what resistance?

HP filter I used 1uf + .1 uf

I would like to move more of the cut on the side-chain (180-200Hz)
What is the value of capacitor should I use?
Thanks

 

[herrmann]

Hey guys,
Just finished my unit !

I love Jeff's knobs 

"Kingston" input mod, edcor 4:1 interstage, and 2523 output. Well, all is working good, and sound very good, except a nasty 50Hz noise coming around the edcor. Ordered a pair of 1540, hope this will solve the problem.

 

[ilfungo]

Great Job herrmann!!!!
With lundhal 1540 I've solved all my noise problems....

 

[abechap024]

Looks Great! Congrats!

So how are you debalancing the inputs? is it going into the Discrete opamp and then into the input pot and the the TX?

 

[herrmann]

Exactly.
I don't know how to setup correctly the threshold trim, for what I understood, it's just a matter of personal taste ?
And I just discover that my tubes are microphonic (ebay sylvania 6bc8), should I be worried about that, or is this kind of tube prone to be microphonic ?
Thanks

 

[abechap024]

Exactly.
I don't know how to setup correctly the threshold trim, for what I understood, it's just a matter of personal taste ?
And I just discover that my tubes are microphonic (ebay sylvania 6bc8), should I be worried about that, or is this kind of tube prone to be microphonic ?
Thanks

Yes, I don't have an exact value to set the threshold at, but how the calibration procedure would go is (after you've done your THUMP removal) you would set for X dB of output from you signal generator, set the input both to MAX (that way you can take the input potentiometer  tolerance out of the equation) and attack all the way fast and release also all to the fast. Then you adjust your threshold down till you get 1dB gain reduction.

Yes some (most) of the tubes I've used seem to have a little bit of microphonics. Haven't noticed it adversely affecting performance too much, though haven't strictly tested for it.

 

[kilmister]

I have also question about threshold.
If I've undertund schematic right 1k trimmer is gain adjust for sidechain circuit? I thought if there's any advantage to put pot on the frontpanel to have user adjustable thershold? Opinions?

Cheers,
Paavo

 

[Kingston]

I have also question about threshold.
If I've undertund schematic right 1k trimmer is gain adjust for sidechain circuit? I thought if there's any advantage to put pot on the frontpanel to have user adjustable thershold? Opinions?

Cheers,
Paavo

It's a set and forget. What kind of levels you are pushing into the tube stage, and how much compression you expect out of that. It's not threshold at all, but headroom. Think about it like you would with a 1176. I personally set it quite loud, so that very low input level is "some compression" and very high input level is a "fist in you face aih!".

 

[herrmann]

Received and soldered my interstage lundahl. Noise almost away, I still have a residual AC noise, I suspect the Hammond transformer I use for 100V (http://www.hammondmfg.com/229.htm)
I will try to move it and see.
Also, when I made the thump adjustment, I discover that one of my tube gets funky/distort really bad. Time to buy another tubes, will try RCA.

 

[WNStudios]

Mine is on the way, should be mostly populated by the end of the week. Still a long way to go though.

 

[jandoste]

Hey Abe,
I almost finished and everything seem ok expect R116 and R115  smoke ... I checked all wire connexion and they look ok! Do you have any idea?
I use 990C and edcors....
Thanks

 

[abechap024]

Hey Abe,
I almost finished and everything seem ok expect R116 and R115  smoke ... I checked all wire connexion and they look ok! Do you have any idea?
I use 990C and edcors....
Thanks

Yes, you probably have a short on the right channel.

 

[kilmister]

It's a set and forget.

Roger that!

Another opinion plz.
What you guys think about stepped in and output attenuators with 2dB steps from -40dB to 0dB? I have a feeling the range would be fine...?

-Paavo