PRR-176 Vari-Mu REV 2 - *Group Buy 7/13!*
- Thread starter abechap024
- Start date
Help Support GroupDIY Audio Forum:
I know this has been discussed, so I apologise for bringing this up again. However...
I'm considering implementing the Gyraf "trick" of reverse connecting a transformer to obtain HV for the tubes, and have checked a couple of Gyraf's schematics showing this.
1 Since the centre tap of the first transformer is used in the derivation of + and - power rails, how then should the secondaries of the first transformer then be connected to the primary of the second transformer.?
2 What would be a suitable VA ratings for each transformer?
Thanks for any help. Cheers, Paul
I'm considering implementing the Gyraf "trick" of reverse connecting a transformer to obtain HV for the tubes, and have checked a couple of Gyraf's schematics showing this.
1 Since the centre tap of the first transformer is used in the derivation of + and - power rails, how then should the secondaries of the first transformer then be connected to the primary of the second transformer.?
2 What would be a suitable VA ratings for each transformer?
Thanks for any help. Cheers, Paul
Hey,
1) where are the notes on calibration?
2) And....where are the AB's?
Can we hear this comp in action? The youtube clip is useless as its recorded through a room mic??????????????? whats with that?????????????
thanks in advance
Michael
1) where are the notes on calibration?
2) And....where are the AB's?
Can we hear this comp in action? The youtube clip is useless as its recorded through a room mic??????????????? whats with that?????????????
thanks in advance
Michael
hey,
refering to this clip here right?
http://www.youtube.com/watch?v=X5KcJumut8Y
we are not talking about the same clip!!!!
where is your clip?
Have you got anything you have done recently with your prr on the mix bus?
regards
Michael
refering to this clip here right?
http://www.youtube.com/watch?v=X5KcJumut8Y
we are not talking about the same clip!!!!
where is your clip?
Have you got anything you have done recently with your prr on the mix bus?
regards
Michael
Sorry mate, confusion abounds!
http://www.youtube.com/watch?v=HjP2e-bq4Ao
this one has the PRR176 on the guitar, in stereo. The guitar is recorded through a pair of gefells with nickel capsules into a jensamp germanium and then squeezed by the PRR176.
I haven't used it on mix buss yet, but it's an interesting idea. We'll definitely try that!
Cheers,
B
http://www.youtube.com/watch?v=HjP2e-bq4Ao
this one has the PRR176 on the guitar, in stereo. The guitar is recorded through a pair of gefells with nickel capsules into a jensamp germanium and then squeezed by the PRR176.
I haven't used it on mix buss yet, but it's an interesting idea. We'll definitely try that!
Cheers,
B
muffy1975 said:
it was a long time ago...
but I think the first revision page does have some useful info on that, no?
http://groupdiy.com/index.php?topic=44586.0
have to catch my flight, so I'll check that later in the evening. But this is what I can find in that now:
Trimmers:
1k VR3, VR9 ....this balances the power between the 2 halves of the 6BC8 tube. Helps if you don't have a perfectly balanced tube.
100R VR1,VR4 adjust for minimum "thump"
1k VR5, VR2 Control Meters, Power on, let it warm up for a bit (10 minutes or so) turn until meters read "0" gr.
What I did was setup a 18kHz burst in the DAW that repeats every 1s or so, put it on loop mode and then adjusted VR3 / VR9 and VR1 / VR4 for minimum thump. You can "detect" thumps by lowpassing everything below 1kHz and take a look at the meter in the DAW from the compressor return after the lowpass. You want as small a signal as possible. That's it!
VR5 / VR2 is your classic zero adjust.
Hope that helps!
but I think the first revision page does have some useful info on that, no?
http://groupdiy.com/index.php?topic=44586.0
have to catch my flight, so I'll check that later in the evening. But this is what I can find in that now:
Trimmers:
1k VR3, VR9 ....this balances the power between the 2 halves of the 6BC8 tube. Helps if you don't have a perfectly balanced tube.
100R VR1,VR4 adjust for minimum "thump"
1k VR5, VR2 Control Meters, Power on, let it warm up for a bit (10 minutes or so) turn until meters read "0" gr.
What I did was setup a 18kHz burst in the DAW that repeats every 1s or so, put it on loop mode and then adjusted VR3 / VR9 and VR1 / VR4 for minimum thump. You can "detect" thumps by lowpassing everything below 1kHz and take a look at the meter in the DAW from the compressor return after the lowpass. You want as small a signal as possible. That's it!
VR5 / VR2 is your classic zero adjust.
Hope that helps!
ethervalve
Well-known member
Hi Muffy,
Baadc0de's advice is spot-on. I'd just add that, if you can, try to buy 6BC8s tested for balance. If that's not possible, I'd recommend trying to get a few extra tubes (they're relatively inexpensive). I had trouble calibrating my 2nd PRR-176 to the same level of performance of the first one I built until I swapped out the tubes.
Good luck, I'm sure you're going to love this compressor. It's definitely my fav.
Baadc0de's advice is spot-on. I'd just add that, if you can, try to buy 6BC8s tested for balance. If that's not possible, I'd recommend trying to get a few extra tubes (they're relatively inexpensive). I had trouble calibrating my 2nd PRR-176 to the same level of performance of the first one I built until I swapped out the tubes.
Good luck, I'm sure you're going to love this compressor. It's definitely my fav.
labak
Well-known member
Hello all!
Are PCC189 compatible with this compressor?
It's a real pain to have matched pair of 6BC8.
I've bought 10 pairs and still have from 1 to 5db difference of level compression.
My comp is a stereo with just one set of knobs for both channels, no link and outboard threshold pot. All built with Vishay/dale precision resistors.
Best regards.
Are PCC189 compatible with this compressor?
It's a real pain to have matched pair of 6BC8.
I've bought 10 pairs and still have from 1 to 5db difference of level compression.
My comp is a stereo with just one set of knobs for both channels, no link and outboard threshold pot. All built with Vishay/dale precision resistors.
Best regards.
ding
Well-known member
Ding, if you are going to use a fender lamp or similar recheck your labeling left and right beside the lamp hole. It looks very tight and the nut/flange of the lampholder could overlap the marks 8) would be a bummer, it's looking cool 
ding
Well-known member
Good looking out. Yeah it's still a work in progress. I got the too many knobs too little space syndrome. I am definitely going to print it out and try things before I send it to the printers. I am so excited about this project. This compressor is so customizable! Once I get a final design I might want to get more people in on it to try and save a few bucks at panel express. I definitely want some nice pultec style 1.5 knobs. I'm definitely a knob guy hence my too many knobs problem.
hence my too many knobs problem.ding
Well-known member
Trying to find a matched pair of these is proving to be a tough task. Does anyone know where to get a matched pair preferably in the US to avoid the long, bumpy trip?
ding
Well-known member
Final design! 1.5 inch knobs (pultec/fairchild style), chicken head or stockli on switch, vintage 1ma circular meters from evelBay. I got rid of the time constant mod because I had to make room for those knobs . No biggie. I am trying to source some cool SPDT and DPDT switches with the black plastic on them like electric guitar switches. Anyone have a good source? Also go with anodized natural aluminum with black letters or black anodized aluminum with white letters? Any suggestions?
Thanks all. ;D
. No biggie. I am trying to source some cool SPDT and DPDT switches with the black plastic on them like electric guitar switches. Anyone have a good source? Also go with anodized natural aluminum with black letters or black anodized aluminum with white letters? Any suggestions?Thanks all. ;D
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