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The Counterpoint I/V analog stage

post #1 of 26
Thread Starter 
I've been away from building DAc's for a while but noticed this new analog stage at Twisted pair audio. I'm enthused to see a new discrete analog stage as there are so few available: Borbely (which needs to use old R2R DAC chips), Pass (same issue), and the zapfilter (compromised universal design.) My experience is that a discrete analog stage can have a very positive impact to sound quality.


The issue I see with this Counterpoint is the fact that you need a balanced to SE converter. Now unless I missed something, all the balanced to SE designs are opamp based which would negates the purpose of building a discrete analog stage. I remember Pass had a discrete line stage that could be used to convert balanced to SE but I'm not sure this has the SNR (hum) reduction you are supposed to get when you tie a balanced signal into SE. I hate the sound of audio transformers so thats out of the question (they are never transperent.)


So I am curious to know if Counterpoint builders are all using balanced amps or if there is a smart solution for those of us with SE amps?


.
post #2 of 26
The funny thing about this whole discrete vs opamp thing is that the people from Twisted Pear have said that the counterpoint doesn't sound any better than the IVY.

To not put words in the horse's mouth: http://www.diyaudio.com/forums/showthread.php?p=1760597
post #3 of 26
I know you hate them, but put a 600:600 output transformer on the output of the discrete differential design.
post #4 of 26
Thread Starter 
Quote:
Originally Posted by 00940 View Post
The funny thing about this whole discrete vs opamp thing is that the people from Twisted Pear have said that the counterpoint doesn't sound any better than the IVY.

To not put words in the horse's mouth: Twisted Pear Audio - Buffalo32S - diyAudio


That could be a testament to this particular design, not all discrete stages sound the same any more than different opamps sound the same.
post #5 of 26

It might be cheating...

Discrete Opamp?
post #6 of 26
Quote:
Originally Posted by regal View Post
all the balanced to SE designs are opamp based
it's pretty trivial to construct a discrete version, I have.
post #7 of 26
Here's one balanced to SE line receiver, a modification of the Dynalo based on a suggestion by JCX:



Here's another: DAC project completet - Page 20 - diyAudio
LL
post #8 of 26
Easy-to-build I/V stage - diyAudio

I've seen others around that are basically discrete op-amps.
post #9 of 26
Quote:
Originally Posted by regal View Post
Now unless I missed something, all the balanced to SE designs are opamp based which would negates the purpose of building a discrete analog stage.
There are several all-discrete preamplifier circuits over on diyAudio that can be used as balanced to SE converters... the Pumpkin preamp and UGS preamp are two that have multiple-hundreds-of-pages threads.
post #10 of 26
Quote:
Originally Posted by cobaltmute View Post
Easy-to-build I/V stage - diyAudio

I've seen others around that are basically discrete op-amps.
One key difference in these (Jocko's, many variants based on it or similar) is that they use no feedback. Try that with an opamp...
post #11 of 26
Quote:
Originally Posted by Pars View Post
One key difference in these (Jocko's, many variants based on it or similar) is that they use no feedback. Try that with an opamp...
To be fair you should mention (if) they are capacitor coupled designs.
post #12 of 26
Quote:
Originally Posted by luvdunhill View Post
To be fair you should mention (if) they are capacitor coupled designs.
To be fair, this is what Jocko gave away. Apparently he servo's it and there is no capacitors in the "real" designs.
post #13 of 26
Look at one such as rbroer's less-simple design for tda1541a or the tooleIV... no caps, with DC servo. Harder to get stable without the feedback, but doable. Sounds better (to me at least), and maintains very low input impedance throughout the audio band (important for I-out DACs).
post #14 of 26
I got my counterpoints put together a little over a week ago now. If you buy the kit there are a few things you should know ahead of time.

1) the rg-1 and 2 resistors go in the far hole and the ground point, not both holes the board shows for the resistors. I was dicking around with my boards for hours because I didn't know this.

2) One lbps will not suffice. First of all, you have to short the resistors so one lbps will reach 15 volts. My counterpoints won't work(lots of static) below about 14.5 volts. I have the cover off and a desktop fan blowing over it because it overheats powering both cp boards after 20-30 mins. You will need 2 lbps for them or a sigma22 or something.

3) Get output caps ahead of time. I have quite a bit of dc across the outputs. Luckily my firstwatt amp doesn't seem to be affected by it. I ordered all 0.1% resistors myself instead of using the 1%'s in the kit and still got a lot of dc offset.

I get noise on mine when I put the cover on the case. I don't know if its a grounding issue or from the power supplies being close. I'm deciding if I want to buy a second lbps supply, o22 or the placid to power them + I will be putting the power section in a different case when I do that.

I have slight static, can't hear with music going, in the left channel only but I think that is just from running both off one lbps + wires are longer to reach the left board now(and they run right past/next to the other supply for va/vd). Besides that the sound is excellent. Running buffalo-> cp's -> firstwatt f1 -> k1000 all balanced.
post #15 of 26
I was a beta builder for the counterpoint with a buffalo DAC (24 version). In my humble experience, it certainly sounds a hell of lot better than the IVY - but only where the rest of your system is up to showing it off. The major gains are there in terms of soundstage depth, realism and superb mastery of whatever is playing.

I used it SE only - I used + and GND out and put a 1.4uF blocking cap on the output. Actually I went back afterwards and built a second pair for a friend. He had buffalo into IVY as well and he was of exactly the same opinion.

Other thing to be aware of is that the countrpoint is mono - ie you need 2 counterpoint boards for stereo (both channels are on the one IVY board).

IVY can be improved using fancy power supplies, but the coutnerpoint with just TP plain LCBPS is easily better than IVY with fancy PS.


All of the above with usual disclaimer of in my system YMMV


Fran
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