GrindingThud

For CFA2 is it possible to up the gain to 7? I've not figured out how to do it with this circuit.

Ooo, Nutella melt looks yummy!

Nice photos VPI! That was me with the KG pile. It was way noisier than normal, hard to analyze anything.

Ah, looks a little different than what I thought. I'll get the single ended version cased up before I move to the balanced one, which I think I will. Whats a few more boards. Got a lot of puzzled faces at the meet today.... people somehow expect less when all the guts are hanging out. Once jacked in, it was all smiles and amazement. Most people preferred it to the Krell clone.

Omfg, I'm going to need a bigger case. Can you do the phase splitter as a separate board so I can add to what I've got?

I'll have the working unit at the MD/DC/VA meet tomorrow. Amp sounds great! http://www.head-fi.org/t/754656/dc-area-head-fi-meet-george-mason-regional-library-sunday-april-12-2015-noon-5-pm George Mason Regional Library George Mason Meeting Room (on your left right after the entrance). Date: SUNDAY. APRIL 12, 2015 Time: 12:00 Noon to 5:00 PM Location: 7001 Little River Turnpike, Annandale, VA 22003

Single ended input (negative grounded) I get +7.9V at that junction. There are two LM339 in the circuit and both are wired. Takes a few seconds to ramp up from around -10V and trigger the relay on. Pins 1, 2, 13, and 14 of the LM339 should all be at 9V or so when output relay on.

It's on a big sink, so it does not get hot. It does get warm after an hour or so. On the angle alone, it gets very hot in a few minutes.

Wondering if I should put a small series resistor on the input of the amp. At the pot extremes, I'm experiencing some noise, especially when maxxed. Of course it's never that high when listening, or my head would explode. This amp is spectacular!

Now I'm way behind.

Indeed! Catching it again now before Marvel comes on.

This circuit should work single ended with both negative inputs grounded, yes? I'm planning on putting it in the CFA2.

4pin and mo bigger resistor it will be. Agree that resistor never should have opened...I'm thinking they may have been defective in some way or there is enough capacitance to spike it open. Never smoked one in the KSA5 clone or the SS Dynalo. Will go to wire wound non-inductives. I still may be able to get this together enough to bring to a meet next week in VA. Thanks for the kind words....it's a hobby for me and a bit fun.

I'm going to put my wow hat on for this one. It sounds great. Tried it with cheesy iems and its dead quiet with the KSA5 psu. I've got my LCD2.2s on it and it's super transparent. Maybe could use a tad more gain. All was good for quite a while until I lost a 1ohm resistor....I stuffed a 10 in there (all I had) and biased a little lower until replacement comes in. Not sure what happened...maybe shorting the TRS..keeping an eye on that. This may be my new favorite once I get it boxed up. Edit...ok, duplicated the failure and these go nuclear when the TRS is shorted on insert: http://www.mouser.com/Search/ProductDetail.aspx?R=CPF11R0000FKEE6virtualkey61300000virtualkey71-CPF11R0000FKEE6 Need to get better resistors in that position. I'd have thunk these would have survived at 1W...guess not. Keeping an eye on Q27/28 also. They are quite hot to the touch. Updated photo....anchored everything to my test platform.

2nd board is done and mounted. Will test after I eat and then listen in stereo. .

Opamp output is sitting at .455V with final amp output settled at 0.1mV with input shorted Driving the input positive or negative with a 1.5V battery (measured at 1.65V) drives pin 6 to +/-20 Output under those conditions is brought to +/-4.68V non-inverting. Without the servo, final output swings +/-5.8, so about 1.2V of correction. Gain is around 3.5

Yep, working great now. I used 5K instead of 15 because that's what I had laying around. I might have some 14.7s I'll use on the next board. Q27/28 run a little hot but I think only drop a third of a watt.

Oh, shoot, way down there in the chain. Thanks for the clarification, I was thinking about it ass backwards trying to tie it back into the other section!

Ok, I'll try the resistors 1st. So I'd tie the top of R4 by Q2 and bottom of R5 by Q4 back to pin 3 via the 5K pair....that will invert it?

I was just going to swap pin 2 and 3....easy trace cut. Need to wait til Friday for the mod...too much work during the week.

Input pot 10k (shorted for now). I have an interesting issue. I jumpered pin3 to ground (left the offset pins float) on the servo opamp. The output of the amp drifts to just under 2v offset (opamp pin 6 drifts to -19v). Or I can flip it if I drive the output the other way with a battery. -2V offset and 19V pin 6. Is the polarity of the feedback correct?

http://www.mouser.com/Search/ProductDetail.aspx?R=RDEC71E476MWK1C03Bvirtualkey64800000virtualkey81-RDEC71E476MWK1C3B http://www.mouser.com/Search/ProductDetail.aspx?R=FK20X7S1H475Kvirtualkey52130000virtualkey810-FK20X7S1H475K

It lives! Without the servo (still need to add the jumper) it's only got a few mV offset and is dead quiet with cheesy iems Now I've got to figure out the bias....oh, I think I've got it. 150mA across the 1 ohm. Now I've got to get the second channel built. I think this one may be a winner. I'm observing interesting behavior...seems the bias current changes with input pot position. May be because the servo is out, or could be my input wiring. Driving my headphones in mono it sounds great!

Soldering under way. Possible error on board. In the schematic, the positive input of the opa445 is grounded. On the board, pin3 is not connected to anything. Pins 1, 3, 5, 8 are floating. I plan to run a short jumper from pin3 to the nearby .1uf cap ground if it needs it.

Looks like a project weekend! Boards are in. I plan to do one set as throughole and one as SMD. Question...will it mind being run off the KSA 21V supply? My other alternative is the 30V from the Dynahi without modding it.