Just finished my Pearl II. I have some oscillations +/- 30mV of DC offset before the cap and ~5mV on the output(maybe my DMM). I removed C7, with it oscillations were ~+/- 100mV. It is dead quiet with my F6, sounds quite lovely. However, it is not enough gain with my Denon DL-301, I have to turn B1 all the way up to reach normal level. Should I check something else to eliminate these oscillations?
An externally hosted image should be here but it was not working when we last tested it.
Ok, so it looks like I have problems similar to discussed above: drifting DC offset and terrible hi-freq hiss when I play music. So what was the solution? Dead 3310? Hm, that would be strange. It works and make sound with the dead transistor? Both channels? It's very annoying. This sound not just mental trust me!
30mv oscillation is normal. As for the gain, if you built it stock, you need to bump it up to work with a LOMC cartridge.
As for the noise, check out this post. The Pearl 2 needs a "zobel" network on the input with certain high-inductance cartridges.
http://www.diyaudio.com/forums/pass-labs/232327-strange-problem-pearl-2-sae-cartridge.html
Thanks!
Gain: I added another 1k on the top of the R14. That gives me 500R instead of 300 recommended for LOMC. What do you thing gainwise: normal listening level should be at 3 o'clock of volume knob, right. Just not to add more gain in Pearl ll than needed. What do you think about it?
Zobel: does it change sound overall or just compensate ringing? How important is the component quality in there?
Gain: I added another 1k on the top of the R14. That gives me 500R instead of 300 recommended for LOMC. What do you thing gainwise: normal listening level should be at 3 o'clock of volume knob, right. Just not to add more gain in Pearl ll than needed. What do you think about it?
Zobel: does it change sound overall or just compensate ringing? How important is the component quality in there?
Thanks! The only one thing I do not like: it gives such a big pulse into my speakers after you turn it on so the woofers are about to jump out. Does some one have the same thing? Being more specific offset jumps up to 7v when you turn it on and then falls to 70mV. And start drifting...
I have put two CL60 thermistors in series in my PSU. With these the pulse into my speakers is not that big. Still, to avoid it completely, I have made it my habit to switch on the Pearl first, and then my amp. Switching off the other way round.
Can I calculate Zobel using the formulas for speaker Zobel circuit? Any ideas where I can find inductance value for Denon DL-301mkII?
Remove the cartridge loading capacitor - C22, if memory serves me...
Also, you probably need some heatsinks on the regulators.
Also, you probably need some heatsinks on the regulators.