FWIW, I have about 2.2 - 2.25 Volts between the collector and emitter of the Vbe multiplier (2sd669) after warm-up and at quiescence. The heatsink is comfortably warm to the touch at this bias, which is not necessarily optimal - it's just a convenient level where the amp doesn't sound too edgy/scratchy (i.e. not deep into Class-B with audible crossover distortion) and the heatsink doesn't get too hot.
Of course, this bias will vary across different batches of the 2sd669 and depends on the ambient temperature, so it's just a first-order ballpark number. You can increase or decrease it based on audible sonics.
Thanks linuxguru, Iv'e measured and realised that when I adjusted the bias I was reading in the wrong place. I have now adjusted the bias properly and all is ok.
I've accidently ordered the wrong pre-amp because it was cheap. It is an unbalanced input to balanced output, but it uses two dual op-amps so I will have to re-work it to be similar to the yuanjing pre-amp. I'll post the URL next. Perhaps you can advise. I liked it because I have a 12-0-12 transformer I am using for the relay.
I've accidently ordered the wrong pre-amp because it was cheap. It is an unbalanced input to balanced output, but it uses two dual op-amps so I will have to re-work it to be similar to the yuanjing pre-amp. I'll post the URL next. Perhaps you can advise. I liked it because I have a 12-0-12 transformer I am using for the relay.
It should be ok - all you need to do is to ignore the additional differential output. At any rate, there's plenty of space on that preamp board for all kinds of mods.
The transformer does a slight hum for 1-2 seconds when switch on (fades out quickly and is barely audible). It does not really get warm.
I have now built a relay board that connects speakers 2 seconds after power on and disconnects them 250ms after power down. This effectively works around the loud pop. However i am still concerned about a bad cap...
I have measured voltages across each cap: The red WiMa's measure 0V from leg to leg is that correct? The electrolytics (10.000uF) measure around 27V. Thanks for all your help!
I had a hum, but it went altogether when I earthed the volume control. I'm waiting to fit a pre-amp, but it sounds so good I wonder if i'll bother. Like linuxguru, at first it didn't sound much better than the yuanjing amp but as it bedded in it improved a lot. It is certainly the best amp I have ever made. It is hooked up to a Audiolab cd8000, Roksan dac,and Linn speakers.
Barry - that looks really neat and nicely assembled in that EBay rack case. I've created a new thread at Solid State for all matters related to the Goldmund/Symasym kit, to avoid confusing the readers of this thread who may be looking for info related to the Yuanjing and related gainclones.
Here's the link to the thread pertaining to the Goldmund/Symasym at the Solid State forum:
http://www.diyaudio.com/forums/solid-state/165588-jims-audio-goldmund-symasym-clone.html
I'll link back from there so that the earlier discussions about the Goldmund on this thread will also be accessible easily to readers of that thread.
Edit: The two knobs are source selector, and volume control, right? That is just perfect - nice and simple.
Here's the link to the thread pertaining to the Goldmund/Symasym at the Solid State forum:
http://www.diyaudio.com/forums/solid-state/165588-jims-audio-goldmund-symasym-clone.html
I'll link back from there so that the earlier discussions about the Goldmund on this thread will also be accessible easily to readers of that thread.
Edit: The two knobs are source selector, and volume control, right? That is just perfect - nice and simple.
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hey,
barry.childs thanks for asking. I have not really solved the problem, but i have worked around it by installing a relay board that connects speakers only after some time after power on and disconnects them quickly after power down. This seems to work ok.
I have another question that i hope someone can answer: I want to include a tone control section (bass/treble) and have found a nice schematic which i have built you can see it here: http://www.elv-downloads.de/service/manuals/17806_Klangeinstellbaustein/Klangeinstellbaustein_KM.pdf
It needs a supply of 12-35V DC, 15mA. What is the best way to connect it? Probably get 12V from the pre-stage Supply for the NE5532? Or is this a bad idea? I would be very glad if someone could tell me the exact way to wire it up.
You guys are really great, very nice lookin amp barry! You seem to have the same case (19" rack) that i used 😀 (i bought from a german ebay seller).
barry.childs thanks for asking. I have not really solved the problem, but i have worked around it by installing a relay board that connects speakers only after some time after power on and disconnects them quickly after power down. This seems to work ok.
I have another question that i hope someone can answer: I want to include a tone control section (bass/treble) and have found a nice schematic which i have built you can see it here: http://www.elv-downloads.de/service/manuals/17806_Klangeinstellbaustein/Klangeinstellbaustein_KM.pdf
It needs a supply of 12-35V DC, 15mA. What is the best way to connect it? Probably get 12V from the pre-stage Supply for the NE5532? Or is this a bad idea? I would be very glad if someone could tell me the exact way to wire it up.
You guys are really great, very nice lookin amp barry! You seem to have the same case (19" rack) that i used 😀 (i bought from a german ebay seller).
You could connect it to the unregulated section of the preamp's supply, so as not to charge the preamp's regulator with the additional current. Or you could skip the tone controller's 7810 and connect the 12 V from the preamp's supply at the point, where it says +10V in the diagram.
The +/- 12V from the Yuanjing board is noisy, mainly because of bad grounding - the ground for the regulators is sitting in the midst of fairly heavy (upto several amps) return currents from the speakers. The only reason this even works is because the better opamps (e.g. LM4562) have high PSRR.
If you're using a separate tone-control board, it would help to regulate the rails with 3-terminal regulators on the tone-control board, or use a separate regulated PSU board fed directly from a different transformer winding.
Yes, that's the same case. Amazing value, but I will be adding additional screws to the front panel or will get a aluminium one from RS components. Your best bet with the 12v supply is to get a separate small 12v transformer. It will up the cost but eliminate any noise.
Hi again,
i have now connected the tone control board directly to the unregluated section for the ne5532 (before the 12V regulator). I can not hear any noise or hum.
I mainly wanted the tone regulation to increase bass a little bit and tune down treble but i have found out that my ALPS RK09L Potentiometer (10K log) which i used for volume control was the reason for the weak bass and sharp highs (!). I have now wired a cheap "Omeg" Pot and that has increased bass quite a bit and tuned down the treble to a much more natural sound. I found out about this on a german board where someone complained about this ALPS pot and poor bass... I could not believe it at first but it seems to be true.
I am now very happy with the amp and it's overall sound! Thank you all for your help.
PS: Barry, i can see on your pictures that your front-plate is also curving a bit. I got rid of this by putting small washers on the screws between frontplate and rest of the case. (I also use small screws+nuts instead of the handles)
i have now connected the tone control board directly to the unregluated section for the ne5532 (before the 12V regulator). I can not hear any noise or hum.
I mainly wanted the tone regulation to increase bass a little bit and tune down treble but i have found out that my ALPS RK09L Potentiometer (10K log) which i used for volume control was the reason for the weak bass and sharp highs (!). I have now wired a cheap "Omeg" Pot and that has increased bass quite a bit and tuned down the treble to a much more natural sound. I found out about this on a german board where someone complained about this ALPS pot and poor bass... I could not believe it at first but it seems to be true.
I am now very happy with the amp and it's overall sound! Thank you all for your help.
PS: Barry, i can see on your pictures that your front-plate is also curving a bit. I got rid of this by putting small washers on the screws between frontplate and rest of the case. (I also use small screws+nuts instead of the handles)
I suspect most of the blame should not be directed to the 10k pot.
What is the value of the DC blocking capacitor feeding the 10k pot?
The loss of treble could well be the increased source impedance from the big pot as seen by the amp input creating a lower F-3dB RF filter frequency that has moved down into the HF audio range.
Bad selection of component values leads to both of these problems, not the component types.
The pot is connected directly between the IN/OUT Pins of the Yuanjing board without additional capacitors. Do i need one here? I thought not because it is after the NE5532 stage...
That looks correct to me. That's precisely why the jumper has been added. You don't need another cap there. Thanks for the advise regarding the case.
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Hi all
Finally got my case finished so here are some photos.
Ebay spec MK1 amp featuring Yuanjing 3886 board.
Speaker protect and soft start boards ,Alps blue pot and retro style controls all in a $10 tip shop tape deck case with home made front.
Torroid from old midi system to be upgraded as only running on 15v secondaries though still loud enough!
Finally got my case finished so here are some photos.
Ebay spec MK1 amp featuring Yuanjing 3886 board.
Speaker protect and soft start boards ,Alps blue pot and retro style controls all in a $10 tip shop tape deck case with home made front.
Torroid from old midi system to be upgraded as only running on 15v secondaries though still loud enough!
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