Input was grounded using a 1k resistor

I'm going to reduce the since too much gain might be the problem. so I'm thinking to have either 8x or 6x gain on balance.So I'm thinking to get 30.1K with 14pf compensation caps or 40.2K with 11pf. What do you think? is the compensation caps enough? or should I go higher? say 14pf?
 
is 6x balance gain too low for this design?

finished changing the gain now it's set up with 40.2k with 10pF feedback caps. and the noise is still there. So I hook up a CRO and start tracing where the noise is just int the positive side of one board. The input is noise free, the noise shows at the output leg of the gain feedback resistor. Traced also the emitter leg of mpsw56 transistor that is clean but the collector and see the noise is there. the noise then gets amplified by the mje15030 and that is the same level of noise in the output pin.

So I think I can rule out gain issue now. Don't think it's an issue with the feedback caps. or is it?

Just wondering if there is something obvious I'm missing. the bias on + side of the circuit is 76mv and - side is 81mV which I don't think should matter. the output balance fluctuates though normally 0-2mV but sometimes jumps to 20mV

what's the odd of the mpsw56 being fake?

I'm Trying to trouble shoot the circuit now. Which one has the correct resistor and capacitor value? because the silkscreen in dynabal9.zip and dynabalbjt.pdf doesn't match

I am comparing

http://gilmore.chem.northwestern.edu/boards/dynahibalbjt.PDF

with my board that is 

http://gilmore.chem.northwestern.edu/boards/dynahibal9.zip

 

Discrepancy is the 20 ohm resistor is 10ohm in the schematic and the 470uF caps is nowhere in the schmaticand some rersistor that I can't find matching value in the board (for example r6 and r16). I might be looking at the wrong thing but I think it's the latest schematic.

I believe the 20 ohm resistors are paired to get a 10 ohm resistance.

Is the bias is supposed to be 75mV or 0.75V

.75V

Looks like my previous cap blown did effect the mje transistor. When it was all good when the bias was 75mv it was all good. But when I raise the bias all the chip in the positive path got blown. Would need to replace all 8 of them. Would be interesting replacing it with the heatsink in place

you can't do that without a heatsink, not even for 10 seconds

.75V

Is that even for the on board heatsink version?

Edited June 8, 201511 yr by mahdi8

you can't do that without a heatsink, not even for 10 seconds

You meant I can't replace the mje chips without removing heatsink? It's a bit tight for the middle chips but I would have thought it still possible to replace the chip without removing the heatsink

i thought you had the off board version and were testing without a heatsink.

 

.75 volts across 10 ohms is 75ma x 4 output devices is 300ma

no I'm not that adventurous. So the bias for the onboard version is still 0.75 volt. I replaced the 500ohm next to the trimpot to 680ohm. Because I mistakenly thought the bias should be 75mV. I will change it back to 500ohm now since the bias is now stuck at 400mV. 

 

BTW I've read on AMB forum that the on board heatsinkboard should only biased to 375mV because it would be running to hot at 0.75V 

Edited June 8, 201511 yr by mahdi8

I biased the on board version to 0.75, and boy does the on board heat sinks get hot.  How hot is everyone's heat sinks getting?  Also is it normal for one set out output resistors to measure 0.75V while the other set measure 1V?  

Finished fixing up my board today. But the best I can bias my board is 0.69v for + side and 0.71 for negative side. The offset without servo is 80mV and 10mV with servo. Is it good enough? Or I still need to get closer to 0.75v and get offset to 0? Any idea which part I need to change? Should I change the 500ohm resistor to something lower?

more than acceptable numbers. no way to perfectly match the p and n parts

With the servo the offset still drift between 10-20mV is that still fine? I've tried using headphones on balanced the sound is great but on single ended the sound is sucked out especially the mids but strangely low end is fine

it sounds like its only a matter of what offset value with which you yourself are willing to be comfortable. I don't see how this offset would affect the sonic performance in any significant way

Just worried more on breaking the headphones. But I guess I can put in a protector board. On other note can someone share their wiring diagram on successful single ended out of Susy dynahi? I think my issue is grounding issue.

If I use a protector board the only cut of point is 0.5v. Isn't that too high already? Does anyone know any design that cut off below 0.5v? What is the safe cut off point for headphone?

.5 volt sure seems reasonable to me. but all you have to do is change one resistor

to make it anything you want.

Does that mean anything under .5Volt won't kill a headphone?

calculate the power, and its pretty low.

 

now sensitive iem's might be a different story, but you would be

nuts to run those on this amp.

Awsome 0.5V protector board would be fine then

 

BTW On single ended I wire signal and ground to + and - of the board. And on the wiring I wire only the signal part to the headphone jack. The ground I took direct from the source ground. Does that sound correct?

 

I was going to wire the ground of the jack to the - of board one. but I think that won't work on balanced input. Or am I wrong?