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

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I'm slowly gathering parts to start building this very interesting project. Thanks to all who made that possible. This is my most complex build so far and I'm learning alot of new stuff along the way as well, which is nice.

I have a question. Does anyone who have finished this build posted any sound samples of it we can listen to? I know every build is unique, but it would be nice to listen to some sound samples while learning about the G9 power transformer trick etc  ;D



 
Edward said:
I'm slowly gathering parts to start building this very interesting project. Thanks to all who made that possible. This is my most complex build so far and I'm learning alot of new stuff along the way as well, which is nice.

I have a question. Does anyone who have finished this build posted any sound samples of it we can listen to? I know every build is unique, but it would be nice to listen to some sound samples while learning about the G9 power transformer trick etc  ;D

I'd also be interested in hearing peoples units with other options... I'll run some through when I get a chance.

I'm finishing a build for a friend and once its done I'm going to run some sound samples through it. It has edcors in it now but am going to put cinemags in it. Figured it will be interesting to compare the different transformers in the same exact build.


I used a PRR-176 with DRV/INA input and Edcor interstage on the most recent band to track vox and guitar through, and got to say it did its job very nice...when I listen to the beatles, It reminds me of the PRR-176 a little bit, same type of sound (probably cause the early beatles albums were slathered in Vari-mu!)

I could upload those but there would be nothing to compare them to.
 
abechap024 said:
astroschnautzer said:
abechap024 said:
astroschnautzer said:
Could someone suggest an output transformer, I am looking to be using this for mastering purposes + tracking, it can be a expensive one (lundahl)...

for output? just a 1:1 will work, there are literally thousands of possible options. Try a Jensen output transformer if you are in the states, or if lundahls are easier to get, I've heard very good things about them too. With 1:1s the difference of transformers can get harder to hear, (if they are decent quality to begin with) But if you are going for clean, try the jensen or lundahls. Sorry I don't have model numbers, as that takes the fun out of it for you.  ;) :D :D
Thanks, I got right there already, I'm just totally new to all this transformer stuff and am struggling with all kinds of info, like is 2:1+1 same as 1:1 and is balanced and unbalanced drive just the same as do I want to use a balanced or unbalanced output? And are you telling me that there probably won't be a audible difference if output transformers are used? How about the interstage transformers, how crusial are those transformers for the sound, saw some builds with lundahl input and some others (edcor?) in the interstage so was wondering that is the input that is the inportant bit?... Sorry for so many questions, totally new to all this stuff...

Hello,
Yes I totally understand, transformers are seemingly very confusing, with so many different options and the indepth math behind it all. I feel fairly comfortable with my view of transformers now, it could definitely be improved up, but I feel like its enough of a working knowledge...

Basically there are a couple things to worry about when selecting a transformer:

What level is it designed for?
You want to consider this because transformers have an optimum range of were they sound the best, hit them too soft and they don't sound as clean, hit them too hard and they start to saturate and distort. Usually the transformer designer worrys about this stuff, you don't have to worry about it. Unless you start using Mic transformers as line, etc etc etc switching them backwards etc etc etc.

What impedance are they designed for?
Thinking about transformers more of MIRRORS is an easier way that I find my brain can digest better. It reflects impedances to the circuit that has the output (sending the signal) and to the circuit input (receiving the signal) You want to match impedances for optimum transfer and frequency response. That is were the "600ohm" and "10kohm" transformers come from. Like speakers, the lower the ohm the more difficult it is for the output circuitry to drive the transformer. Yes transformers are a load, and you need adequate power to drive them. Also ratios are a part of this. Say you want to use a 1:2 output transformer for the output, cause you want a little more color...well your going to have to consider that whatever load you put on the output is going to look harder to drive (lower impedance) to the output because the transformer is 1:2. But also you will have an increase of gain on the output. On the other hand if you wanted to use a 2:1 output transformer for the output for more color, you would lose gain (not a problem here because the 176 has a bunch) but whatever load you drive will be easier for the output circuitry because it "looks" like a higher impedance to the circuitry thanks to that reflection of the transformer. Remember Higher impedances are easier to drive.

a 1+1:2 transformer is that same as a 1:1 they are just telling you that there are 2 completely independent windings on the primary. They could either be wired in series (in phase) to make it just like a 1:1 or in parallel to give it better bass response (more inductance) and a 1:2 ratio.

There are not free lunches in transformers, no free gain, as you can see you need the proper circuitry to be able to drive the various loads...

To answer your question a lundahl 1+1:2 would work fine just make sure you wire it correctly. If your going for transparency just wire the 2 primary windings in series to make it 1:1 (or 2:2, which is the same thing)
Thks for the detailed answer, so that means if I bough a 1+1:1+1 I could choose if I wire it 1:2, 1:1 or 2:1? Also still wondering about the interstage, how important that stage is for the sound?... And should I get a "balanced drive" version if I want a balanced XLR output?
 
astroschnautzer said:
Thks for the detailed answer, so that means if I bough a 1+1:1+1 I could choose if I wire it 1:2, 1:1 or 2:1?
Yes.

Also still wondering about the interstage, how important that stage is for the sound?...
Fairly important. I would get good ones.

And should I get a "balanced drive" version if I want a balanced XLR output?

I don't know what that means. Is it a type of transformer? If so any transformer is "balanced drive" and will drive a balanced XLR
 
abechap024 said:
astroschnautzer said:
And should I get a "balanced drive" version if I want a balanced XLR output?

I don't know what that means. Is it a type of transformer? If so any transformer is "balanced drive" and will drive a balanced XLR
Lundahl has this labelled as"drive type" on their website, many different types : http://www.lundahl.se/sidor/line_out.html    EDIT: Think I got some info : http://www.lundahl.se/pdf/ovrigt/feedbck.pdf ...This indicates (looking at the scematics) that I would need a unbalanced drive if input to transformer is taken from the "optional tranformer out" output which ha two pins... Am I correct?
 
Lundahl LL1540 for input and interstage is what I used. These stages (both stage require high impedance input) are most crucial if you want to invest in quality. PRR176 is surprisingly well fit for mastering if you don't skimp on the transformers and match the tubes.

Output transformer is far less picky. Any line level 600:600ohm transformer will do and they will all be very high spec and sound great. For example classic api EA 2503, Edcor wsm 600:600, Lundahl LL5402.  Lundahl might actually be a waste of money in this stage. Don't shy away from Edcor wsm 600:600 just because it's cheap. In my opinion it's their greatest product and easily the best price/performance ratio of any modern line level transformer.

While many opamps will sound great in this unit, check out PPA APP992 in the white market.
 
Kingston said:
Lundahl LL1540 for input and interstage is what I used. These stages (both stage require high impedance input) are most crucial if you want to invest in quality. PRR176 is surprisingly well fit for mastering if you don't skimp on the transformers and match the tubes.

Output transformer is far less picky. Any line level 600:600ohm transformer will do and they will all be very high spec and sound great. For example classic api EA 2503, Edcor wsm 600:600, Lundahl LL5402.  Lundahl might actually be a waste of money in this stage. Don't shy away from Edcor wsm 600:600 just because it's cheap. In my opinion it's their greatest product and easily the best price/performance ratio of any modern line level transformer.

While many opamps will sound great in this unit, check out PPA APP992 in the white market.
Thanks, this helps alot, and saves some money. Thanks for the opamp suggestion too, I had also planned to buy these because I read your opamp shootout here at the forum ( If these where them)...
 
astroschnautzer said:
]Thanks, this helps alot, and saves some money. Thanks for the opamp suggestion too, I had also planned to buy these because I read your opamp shootout here at the forum ( If these where them)...

These are the same ones. But since that shoot out I actually did a major project where I found out that in optimal environments (very difficult to create) there should not be significant audible differences between opamps (there are very little measurable differences, how could you then hear anything). In that shoot out tested APP992 in places where PSU and decoupling was sub-optimal, and this is where it sounded incredibly good. Kind of a safe choice. Perhaps it has better PSRR than many others, the test was shamefully unscientific. Don't draw too many conclusions from it.
 
Question:

I have one dual primary 115/230V toroidal transformer 50va 0-25v 0-25v and one mini open toroid 7.0va 12v+12v both from Rapid Electronics. I connected the primaries on the first transformer in series and feed it ~230VAC and the secondary side is also connected in series to get a center tap and 25VAC on each end. My first problem is that i measure ~29VAC between CT and each end and ~59VAC across both ends. Is my transformer not working correctly or is there something i'm missing?

However i went ahead an connected the second transformer to the first one, secondary side first and in series as well. On the primary side of the second transformer i get 115VAC, which i guess is ok?

Can some one confirm if this is ok?
 
Hi guys!
I am very happy with this compressor!!!
I would like to make a  mastering version,
but
can anyone help me to calculate the steps for switch version?
In-out - attack - release.
thanks
 
Edward said:
Question:

I have one dual primary 115/230V toroidal transformer 50va 0-25v 0-25v and one mini open toroid 7.0va 12v+12v both from Rapid Electronics. I connected the primaries on the first transformer in series and feed it ~230VAC and the secondary side is also connected in series to get a center tap and 25VAC on each end. My first problem is that i measure ~29VAC between CT and each end and ~59VAC across both ends. Is my transformer not working correctly or is there something i'm missing?

However i went ahead an connected the second transformer to the first one, secondary side first and in series as well. On the primary side of the second transformer i get 115VAC, which i guess is ok?

Can some one confirm if this is ok?

Thats fine, they are going to give you a little extra which is what you usually want.
 
abechap024 said:
Edward said:
Question:

I have one dual primary 115/230V toroidal transformer 50va 0-25v 0-25v and one mini open toroid 7.0va 12v+12v both from Rapid Electronics. I connected the primaries on the first transformer in series and feed it ~230VAC and the secondary side is also connected in series to get a center tap and 25VAC on each end. My first problem is that i measure ~29VAC between CT and each end and ~59VAC across both ends. Is my transformer not working correctly or is there something i'm missing?

However i went ahead an connected the second transformer to the first one, secondary side first and in series as well. On the primary side of the second transformer i get 115VAC, which i guess is ok?

Can some one confirm if this is ok?

Thats fine, they are going to give you a little extra which is what you usually want.

Thanks!

I have now learned that unloaded a transformer will give more voltage than when its drawing its rated current.

Do you think the smaller transformer will be fine with the higher load? Maby i should have gotten a 0v-18v, 0v-18v instead of the 0v-25v, 0v-25v...

...could a resistor be added to lower the voltage to <24VAC to the second transformer?
 
Edward said:
abechap024 said:
Edward said:
Question:

I have one dual primary 115/230V toroidal transformer 50va 0-25v 0-25v and one mini open toroid 7.0va 12v+12v both from Rapid Electronics. I connected the primaries on the first transformer in series and feed it ~230VAC and the secondary side is also connected in series to get a center tap and 25VAC on each end. My first problem is that i measure ~29VAC between CT and each end and ~59VAC across both ends. Is my transformer not working correctly or is there something i'm missing?

However i went ahead an connected the second transformer to the first one, secondary side first and in series as well. On the primary side of the second transformer i get 115VAC, which i guess is ok?

Can some one confirm if this is ok?

Thats fine, they are going to give you a little extra which is what you usually want.

Thanks!

I have now learned that unloaded a transformer will give more voltage than when its drawing its rated current.

Do you think the smaller transformer will be fine with the higher load? Maby i should have gotten a 0v-18v, 0v-18v instead of the 0v-25v, 0v-25v...

...could a resistor be added to lower the voltage to <24VAC to the second transformer?

No, you should be fine. A resistor is only going to add more heat. You might want to heatsink the heater regulator to the chassis though (using proper insulation of course!) But you will probably be fine.
 
Would Mouser part: 532-4880M work as an insulator here? Sorry for all my questions, but i just want to make sure the PSU part is at least a little safe before i proceed :)

Thanks for your help so far Abe!
 
astroschnautzer said:
Caold anybody give a hint on good quality meters that fits the 1u case from collectivecases..? hopefully from europe or ebay...


http://www.ebay.com/itm/Panel-VU-Meter-TN-73-0dB-1-288V-76x59mm-LED-lamp-NISSEI-/130384936913?pt=LH_DefaultDomain_0&hash=item1e5b8c3fd1


you have to take off the front cover and cut the bottom off of it for it to fit. Not that hard, just don't huff the fumes!
 

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