I'm having problems getting both of my CounterPoint boards working, and I'm a bit confused on how to connect RG1/RG2 to GND. By not connecting either side of RG1/RG2 to ground I get a 2.56Mhz oscillation on both borads.

One side of RG1/RG2 goes to the In- and In+ respectively. Connecting that to ground stops the oscillation, but of course that grounds the input signal. Connecting the other side of the resistor to ground seems wrong also.

I guess I should move the side of the resistor that goes to the input to ground and then jumper the input pins to the non-grounded side of the resistor. Ex. move pin 1 of RG1 to Gnd, and connect In- to pin 2 of RG1.

Yes, No?

RossG

Hi Ross. Sorry I missed this post.
RG1 and RG2 should be connected as follows. One leg goes in the pad which is connected to output. The other leg is connected to GND.

Originally I intended to do the symmetrical feedback (thus the dual pads for that leg) but found that the compensation required made it not sound great to me.

Cheers!
Russ

Sure any decent metal film should work fine. :)

Hope this helps. :)

The current draw from each side of each CP should be about 105ma or so.

You may need to adjust the 3W R down a bit in the CRC of the LCBPS.

Try shorting that R with a piece of wire. See if that helps you maintain 15V.

Yes measure offset from out+ to out-. It should not be more than 1-2mV.

CC5 and CC4. I would try 100pf anything up to 1nf should work ok.

The power supply rails. :) I would reduce to +/-11V until you get it stable, then move it up.

Also make sure that there is only one GND wire going from the VA power supply on the DAC to the LCBPS. Don't use the GNDs from the DAC output in this case.

Cheers!
Russ

So last night I rewired all the grounds on my chassis to be a tree structure. Each ground on the power supplies and each board have a separate wire connecting back at the same point which is the ground of the +6 supply on the LCDPS. There are no board to board ground connections as before. All input/output connectors on the chassis make no electrical contact with the chassis. I think I've eliminated any ground loop problems.

I reduced the rails of the CP to +/-12V, put in a 510Pf caps (the only caps in the suggested range that I had on hand) for CC4 & CC5. The CP board now oscillates at 3 MHz, more than before. When I disconnect the input connections from the Buffalo the oscillation stops. To be specific, with nothing connected to the input or output terminals of the CP it oscillates when power is applied but stops when the relay switches. When I add in the connections to the Buffalo, with no signal going into the Buffalo, the CP oscillates.

While the Buffalo was disconnected from the CP I measured the output terminals of the Buffalo at 1.7 volts each. All terminals are at the same voltage, so I assume the opamp in the CP will reject the common DC offset.

So with the Buffalo connected to the CP board, I've been able to stop the oscillation by placing my fingers across C7 & C8 (which stops the oscillations on the Out- side) and across C6 & C2 (which stops the oscillations on the Out+ side). I must have my fingers across all the caps at the same time and resting my wrist on the chassis to stop the oscillation. I guess I'm putting in a high impedance to ground on the capacitor cases. But somehow I don't find this to be a reasonable solution to stop the oscillation. Maybe I can train my wife to do that whenever I play the stereo.

Russ, would reducing the feedback on the CP help solve this problem without increasing the distortion very much?
Back in the mid 70's I was building a discrete component differential power amp (the Tiger 0.01) and it took some tweeking of the feedback resistors to stop it from oscillating also. So I know these circuits are a bit tempermental.

RossG

RossG

Ross

May not be much of a comfort, but my CP boards have been running in my system for a couple of weeks now. First I followed the silk screen for RG1/2. CPs worked from first start up. Sounded really good.

I am using the outputs balanced into Hypex amps with no pre amp. I had a little discernible hum.

Last night I finally got around to moving one end of RG1 & RG2 to the ground pad. Hum now almost inaudible even with ear pressed to speaker.

My earthing scheme is a bit messy (shall tidy that when I re-case the whole DAC soon) but I have to say that now the Buffalo/CP sounds truly fantastic.

I can only think there is something else at play with your set up to give you this oscillation issue.

Keep with it though, I think you'll get it sorted and the results will be worth it.

Mark

Nic

I rarely visit TNT-Audio and have never posted there. The more I see the responses one tends to get to "subjective reviews" on forums, the less inclined I become to go down that route. All I can say is that every step with the Buffalo has seen improvements, and I started off fairly happy with it (voltage out into TPA BALLSIE). I feed it from a CD-Pro2M transport or Squeezebox, and have separate supplies for SPDIF receiver (not the onboard Buffalo circuit), digital and analog circuits (the latter fed via a super-reg) and LCBPS for the CPs. I use a Volumite to control attenuation, and feed the balanced output directly into the Hypex amps - which you will most likely love).

The changes to the RG1/2 connections last night provided the icing on an already sweet listening experience for me. PRAT. dynamics, sweet tone, depth, low level detail "integrated" into the music like a fine turntable. More listening required of course, but I am truly pleased.

FYI - I have fed the output single ended into a "Starfish" pre amp I have, just for comparison. The CPs seemed to behave themselves.

Regards

Mark