Helium

Is electrolytic capacitors reforming needed? What is common attitude to this procedure? I've got quite a few pcbs that I completed 8-10 years ago. Most projects are from amb and KG. I soldered PCBs, washed them and put aside on the shelf. But life is life, time has passed and finally I thought that this year it's a good time to complete them. Pcbs were never switched on. Caps I used are all good if not the best brands: Panasonic, rubycon, nichicon. Never frozen, never heated. However I'm confused how short the shelf life is according to manufacturers specs: 2 years, maybe 3. I remember receiving caps from mouser that are almost 2 years old, I'm curious what they do after 2 years, dispose them? Anyway, do I need to do anything about caps? Do they really degrade, or is it just a BS from manufacturers to stay on safe side? Maybe 8-10 years are nothing to worry about? I really would avoid desoldering and replacing everything if possible.

Edit: one idea, is maybe log taper of the pot was too steep. Need to try another one.

It's definitely quieter. Reasonable loudness is reached at 15-16 o'clock. Pot is 10k series type, B+/B- is 400vdc, but those don't affect volume. The only change I made is I used TTA004B,Q and TTC004B,Q instead of KSC2690AYS and KSA1220AYS. I doubt that it could be the reason as they are direct replacements. It would be nice to find a solution.

Did anyone experience that BH BJT is quieter than other Stax amps? Like 15 o'clock vs 12-13 o'clock on T2. Is there any way to increase gain?

Could someone explain the rule for choosing VAC secondaries of HV transformer? Rule of 0.707 (400VDC as target + ~10V of voltage drop = 290VAC÷0.707) doesn't apply here? Should we add 30-50VAC (or how many?) for voltage drop and regulation? Thx.

Thanks, spritzer

I've searched but couldn't find answer. Can KGST work with 450v power supply?

Seems that KSA1220AYS may also be replaced with TTA004B,Q? The latter also seems better.

Yep, I myself had to scroll this thread again as Im in the process of building one. I think the mod is referred to this post: But I dont see what resistors were XXohm value in the original design and became 33kohm in the updated design as Im building the latest rev of PS PCB (speaking of original DIY T2).

Can anyone please point this mod for me? I can't find it reflected in the (latest?) schematic or PS PCB. R14, R29, R41 and R53 resistors are all 2.2k, or am I looking at wrong locations?

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.