Helium

Did you trim snap-in capacitors leads underneath PCB? Seems that PCB is quite low and may be touching bottom cover. Once I made same stupid mistake. Without load PSU was OK, but when I connected amp section, it exploded quite spectacularly.

Any specific reason why you would put tube unbal-bal converter in front of CFA? Just to make it as complicated as possible? There will be ~100 more parts in signal path, hardly they will make amplifier sound better.

I would use different layout. Move transformers and grlvs to the front. Move cfa to the rear. Keep DC protection board where it is at the front. Use extension shaft to mount volume pot at the rear close to inputs. Side notes: move ac inlet to the left or right, it doesn't have to be on the center, it gives nothing. Stack the upper cfa higher so that transistors are distributed more evenly over heatsinks area. Move inputs closer to center (and to the pot) and move speaker terminals to outer edge of the chassis. Cause your speakers will be placed to the left and right and maybe quite far away from the amp. Consider stacking transformers on top of each other, you have 120mm clearance if you don't use steel chassis. That way you will have space to mount grlvs horizontally. After all I don't think that amp with bjt output transistors is good to drive speakers. I would consider omitting speaker terminals completely.

Here they are. Consider 2-storey layout, where CFA boards are mounted on top with each other and to L-brackets on heatsinks. This is what I have in mind for my CFA3 project.

This is how 3U heatsink looks like with brackets installed.

Well, I myself don't like mounting trafos on aluminum plate. Dissipante comes with 3mm anodized top and bottom plates, mounted with 4 small screws m3. For me this structure is not very good to sustain weight of trafos. Moreover, if you use steel chassis to mount everything inside, you can do without any holes in bottom plate (except those for feet).

I used modushop dissipante quite a few times. I doubt that you will be able to mount boards on side heatsinks this way. Have you accounted for steel support brackets that take up significant area of the heatsinks, and use of steel chassis on the floor? Since you are mounting transformers on the floor it's good practice to use steel chassis (sold separately) to get extra rigidity.

Ok, no one is issuing orders (except that taking a breath can be regarded such). Why such tone?

Not sure if DIY forum where people come together to share interests is an appropriate place for such things. There is too much hostility and hate in life nowadays, don't bring it in here.

Wait a minute, are you telling that no drift is something wrong? From my experience there is some drift (0.5~1VDC without servo, and ~200mVDC with optoservo installed, both balance and offset), and I wish it wasn't there.

If not sold, are you going to transfer most components to split boards? Out of curiosity, are split boards so much better than wider boards to justify hard work of desoldering and soldering a lot of parts?

Yes, same batch. Seems that Hakko 808 isn't ESD safe. Lesson learnt.

Did anyone experience how vulnerable DN2540N5 are? They are damaged so easily that I had to scratch my head. E.g. desolder it from a donor known good GRHV, actually new (don't ask why, I had to get spares) and it's detected OK in circuit as N-Ch depletion mosfet. I desolder it, test it and BAM it's no longer depletion mosfet, it turns into kind of Voltage regulator. And doesn't work of course. I spoiled 4 pcs already, despite the fact that I know how to desolder and handle components. And only one out of 5 was OK after desoldering.

I checked phase of all windings prior to connecting. Yes, they are not marked, I marked them by myself. And connected both HVs in phase. Yes, it's single -400 board. The other one (+400) is dismounted ATM and waiting for a part for replacement.

Wait a minute please. I see what you mean. Is the transfotmer up to the task? That's most unfortunate if it's not. Is Star ground of everything a cure?

Thank you folks. Yes, currently GRLV has no ground connection with HV ground. Didn't know that non-tying LV and HV grounds is so critical. Usually it ends up with hum/noise, such sort of things. I will fix that and see. I the mean time I adjusted CSS with GRLV 15VDC to 18mA, so AMP boards are presumably good. Currently amp is almost done, need to replace DN2540N5 on +400 PS.

I've ran into an issue building Carbon. I'm using split PS boards + separate GRLV. When I connect PS boards to transformer (without AMP boards) everything is fine, and voltage is +405/-406VDC (bias is a bit low at 563 but that's non-relevant issue and a matter of zener tolerances). But as soon as I connect AMP boards, transformer starts to heat up a lot (I didn't risk to leave it connected for more that 15 sec). Maybe it will start melting. Here is my connection: +400 goes to each AMP's B+ terminal, -400 goes to each AMP's B- terminal (obviously). However GND from each PS from goes to nearest AMP board only and are not tied together or by a sort of star terminal, therefore GNDs are not shorted. Am I missing a point here? Should connecting GNDs of each split boards remedy the transformer heating problem? Easy to check by yourself, one must say, but one of my DN2540N5 went bad and I cannot check it right now. This is my transformer spec (must be plenty of power, so insufficient VA rating must not be a reason?): 1 x AUDIO GRADE WITH EPOXY FILL INTERIOR PRI:230V SEC: > 2x 330V under load (350mA) (separate windings) > 2x 18V under load (500mA) (separate windings) - VA rating around 300VA

It's normal for 15030/15031. I had the same thing. Amp will work anyway and DC offset will be nulled out. If you are uncomfortable with hfe difference, try using 2sa1930/2sc5171, much closer to each other by hfe. Seem still obtainable if you search.

Wow Soviet) A good old wine) Correct me if I'm wrong, but like AMP series, thread all the way down to gasket (rarely beautifully looking) implies that the gasket is left outside the panel. I usually like to put connector inside the case (this is low voltage Neutrik Speakon, but same idea).

Hi starcat. What are P/N of the connectors and housings and pins you are using? I'm tempted to try these. As far as my quick search revealed, pins and wire entry seals don't come in bundle and are sold separately, aren't they? My concerns is that CPC series seems to be rated for 250VDC/VAC only, and that there is no space between the thread and the gasket, which means that the gasket itself will be outside the panel/case. Any considerations?

Where are you? I've got lots of them, new, maybe 20 of each.

Lol the above board seems to incorporate amb's sigma22)) Unlike Kevin, Ti is definitely not happy when this happens))

Check this video by Haas: You may want a special tapping drill to make thread go deeper in the limited depth of blind hole.

Thanks, I've already start thinking angle grinder FTW to butcher my nice completed T2 PCB. Just kidding, I would do it on CNC if that happened. Kevin, so how do I wire, simply each PS board to each channel (=half T2 board)? I'm afraid I will encounter heavy ground loops.

Quick question. Do I need to cut T2 PCB in halves to separate GNDs if I'm making dual PS, one for each channel (double the number of PS boards and double the number of transformers)?