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

[ilfungo]

I was thinking the same thing ....
but I can not do this....?

 

[Kingston]

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...?

even -30dB to 0dB is enough. In fact I did exactly that. You know, bebek and their cheap 24-step elmas...

 

[kilmister]

Thanks Kingston!

 

[jandoste]

Thanks Abe,

yes, it was a short on the right channel ??? : Now it works but I have some NOISE and don't know where it comes :-[ :-[ ?

any idea?

Thanks

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]

A sneak peak of my project...
Initial testing going on. Sound passes through no noticeable hums or buzzes.
Still have to do stepped attenuators, some DOAs and nice front panel instead this wooden one.



Sound good this far, thanks Abe!

-Paavo

 

[abechap024]

Thanks Abe,

yes, it was a short on the right channel ??? : Now it works but I have some NOISE and don't know where it comes :-[ :-[ ?

any idea?

Thank

Good! Me thinks you have a grounding issue somewhere, Your in Rev 2 right? With the off board power supply? Unless you did something wrong it is more than likely ground loop, or something.

Do you have an oscilloscope? Check the power supply. Also measure the Smoothed DC before the regulators make sure you have AT LEAST a couple of volts headroom if not more (example 21V DC before regulator being rectified down to 18V) If you don't have headroom than the regulators can't regulate properly = noise. Just trim the regulators down if you need more headroom in the power supply. (which inversely effects audio headroom, but usually not a problem)

I'm sure I mentioned this before, but just to make sure, Ground all your XLR jacks directly to chassis then connect chassis and audio ground only at one point. Some people uses a low ohm resistor (10r) in parallel with a low ESR capacitor (poly 0.1uf) to connect the two grounds. I haven't found that necessary, but to each their own.

Also, I forget if you have a scope available to you or not, but It might help you isolate the power rail that has hum. If that is the case, or if its coming from the transformer (probably not if your using a torriod, unless it is getting hot) or ground loop.

Remember it IS something, always. Sometimes I think its voodoo or majic or Wht the hck. But its always something. Sorry hard to troubleshoot over the net.

PS Builds looking really cool guys!

 

[detonator]

Perhaps a noobish question, but I don't care. I was wondering if it possible to create a switch between at output stage? This is ment to switch between the chip or the transformer.

 

[abechap024]

Perhaps a noobish question, but I don't care. I was wondering if it possible to create a switch between at output stage? This is ment to switch between the chip or the transformer.

Yes. One easy way would be to wire up both and then using a DPDT switch (or even better a relay) just switch between the 2 output (pin 2 and 3 in the xlr)

 

[detonator]

Thanks abe

 

[labak]

Hi All!

Sorry for this question but What are the real specs of the Power Xformers?
I wanna built an external Power supply for, and I would like to try to avoid 2 Xformers! Is there somebody who find the Power Xformer one piece?

Thanks for this project!

 

[kilmister]

Power transformer was discussed in Rev1 thread:
http://www.groupdiy.com/index.php?topic=44586.msg583319#msg583319

Be sure you read all posts - especially Kingston's

-Paavo

 

[mrcase]

Hey all!

Which powertransformers would you suggest for 230V Europe build?
how would I connect the two transformers?

cheers

 

[Hank Dussen]

If anyone is interested, I have a custom made 230V transformer from the group buy, for sale.
I didn't use it, because it doesn't fit in a 1U case.

Pieter

 

[Holger]

Hi, I'll take the transformer

 

[detonator]

I'm interested when it's leftovet

 

[herrmann]

I just noticed that my unit is actually out of phase. On both channels. I checked the 2623 output wiring, and it's good : input orange, Hi output black with green and brown connected. Has anyone this issue too ?

 

[astroschnautzer]

Could someone suggest an output transformer, I am looking to be using this for mastering purposes + tracking, it can be a expensive one (lundahl)...

 

[abechap024]

I just noticed that my unit is actually out of phase. On both channels. I checked the 2623 output wiring, and it's good : input orange, Hi output black with green and brown connected. Has anyone this issue too ?

I'll run some tests and confirm. Easy solution would be to switch pins 2/3. You can do this because using an output transformer and/or the drv134 or that chips are fully differential, it will work even into unbalanced equipment

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. 

 

[astroschnautzer]

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. 

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...

 

[abechap024]

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. 

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)