mahdi8

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

Ordering my own it is. one sigma22 board bould be enough to power two boards right? I already have a sigma22 wired for 30V. can the amp board be changed to use 30V input?

Is there a groupbuy for the dynalobal board at the moment?

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

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'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

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 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?

Input was grounded using a 1k resistor

More progress now. I haven't found the 55k resistor so I haven't replace the gain. But all the caps has been replaced with a proper 470uf 35v caps. On default 500 ohm resistor that paraller to the trimpot the bias was stuck at 200mV so I changed it to 680 ohm. Adjust the bias the best currently I can get is 78mV for + and 88mV for - on the 20ohm parallel resistor. Output offset is now at 5mV. I thought it would be good enough to retest the hiss. The power supply is using a test DC PSU set at 30V just to make sure the hiss is not from the sigma22. Trim pot is not installed so I still leave the 1k resistor shorted to ground that I used to do the bias set up. Hook up the test headphone and can hear the hiss noise. Can't figure out where its from. Any suggestions on how to troubleshoot this? Its not connected to any source or pot so that shouldn't be an issue. And its connected to a a clean DC test power supply so it won't be PSU issue.

Big set back on my build. Was doing the voltage balance and offset and manage to get around 40mv and 50mv, but can't get lower the servo seems to bring the voltage up every time I reduce the trimpot, so decided to try on a throwaway headphone. There was quite a high noise floor which sound like a ground loop. So then I change the ground in the pot from power supply ground to the source xlr ground. The ground him dissapear but there is still a high noise floor. Couple second later one of the capacitor blows. Turns out the guy I got the board from populated them with a 25v caps rather than 35v caps written on the board. I think this was where the noise was coming from. What do you guys thinks? Really hoping none of the transistor gets fried. Because that would be a real pain to source. Caps are easy. Will replace all the caps and put in the correct voltage.

Got a reply from Khozmo manufacturer looks like replacing the series resistor to 10k is the go

It is the 50k, I am continuing a abandoned project so that's what I got. Anyone think this will be a problem? Prefer to use this or the existing pot would be a waste. In another matter the initial owner says he planned to have it to be 8x gain in balanced. But I rechecked all the resistor in the board are default value. Shouldn't I change the input resistor to be 50k to have 8x gain? That way it matches the volume pot? Or can I replace the series resistor in the pot from 50k to 10k and leave the shunt resistor alone

Building is running well but still quite a bit to go. managed to get a large case to put the amplifier boards and the power supply boards but I still keep the transformer separate in a smaller case. Was going to have 2 of the large case (bought both of them actually) but decided it's too big. Got a 4PDT switch also so will give it a try. Anybody think if there is any issue running output of single ended and balanced simultaneously? I will only put the 4pdt switch on the input. or should I put it in both input and output? https://flic.kr/p/s6KQxM https://flic.kr/p/rrd45N https://flic.kr/p/rrpkdg

I might give 4PDT Switch a try. looks promising

Great so technically I can follow that way and just use one board when running single ended? I might put a switch so I can run 2 single ended input output the same time or running one balanced. That would be perfect. Might need to make a switchboard to handle it

Agree with Pars I can't see how using combo jack will work. Unless you have a balanced to unbalanced switch of some sort? but I think that will make it more complex. How does ground gets wired in a standalone single ended dynahi? Is it a passthrough from the source ground?

Thanks I'll check them out. I'm considering the have the dynahi balanced with 2 unbalanced input and one balanced input with an balanced and unbalanced input switch. The output would be one balanced and one unbalanced. for unbalanced I will wire the left to + board 1, ground to - board 1, right wire to + board 2. Will that work? or any better suggestion to have both balanced input and output configuration?

Looking for a case Idea. What do you guys think putting the Dynahi Balanced in a well ventilated acrylic case? is it a bad idea? Looking for a budget way of making the case and acrylic seems to be the cheapest way since I know someone who has a laser cutter.

Oh no a new board when mine is not finished yet

Thanks parse I'll check those post out. Yes you're right its 2 amp board and 2 power supply board

Hi All, I'm new to Dynahi and hope to learn a lot from here. My last amp built was the bottlehead crack with speedball add on. I've recently purchased a prepopulated balanced Dynahi board with 2 sigma22 power supply. It's never been powered on so I'm trying to find where is the reference of voltage check measurement for the board? Any help would be greatly appreciated. I've been reading the thread but couldn't find it. I might missed it. the board I'm getting is from this design http://gilmore.chem.northwestern.edu/boards/dynahibalbjt.PDF