Most recently, two different lat-FET class AB power amps: the Hafler DH-220C (Bob Cordell designed new IPS and OPS circuits for these) I built last summer and updated with an SMPS in January; and vzaichenko TubSuMo monoblocks I completed earlier this year.
Hafler DH-200/220 Mods
Ultra-high performance, yet rather simple - hybrid and more!
Each of those are exquisite amplifiers with finesse and authority.
This VFET amplifier throws some wicked curveballs in perception, which I mostly attribute to the negative phase H2 described in the original Pass article and elsewhere. Not detrimental in any way, but different.
Last edited:
Thanks!
Yes, the small solid core twisted pair got a little too hot as I soldered them. My iron may be set on caliente...
Remember not to use cigarette lighters as soldering irons.
The pots should be in a good starting position already. My initial bias was about 15 Volts. I carefully adjusted the bias to 19 Volts, then let the amp warm up. The bias will increase slightly with temperature, so let the amp burn in for a while (at least half an hour) before final adjustment.
I see people are going for different placements on the output stage. I believe it was 6L6 that brought up the notion that placement took into account other FE boards, so keep that in mind! If you know you won’t be trying the other input stages, it’s all ok. But there may be not enough room for them forcing you to redo thermal paste and wiring.
I’m still undecided on this, but keep that in mind.
I’m still undecided on this, but keep that in mind.
No way I am getting in there again unless it catches fire... (knock on wood).
If one were planning to modify it I would strongly advise to use spades, terminal blocks etc....AND of course respect the initial layout from the build guide.
As per now, Bias is rockstable after something like 30 min at 19.99V, offset right -4,7mV, left -5 with probes red on red / blk on black.
If one were planning to modify it I would strongly advise to use spades, terminal blocks etc....AND of course respect the initial layout from the build guide.
As per now, Bias is rockstable after something like 30 min at 19.99V, offset right -4,7mV, left -5 with probes red on red / blk on black.
Last edited:
I am finding the output boards are asymmetric. I see another amp picture with the same issue. Why can't the output caps be on the same side facing the back panel? The way the board is placed on the T is not the same as you can see from the picture. The drilling is different, so I was going crazy thinking this was done intentionally so that the both output caps would point to the back panel. I was trying all permutations to get the cap on the same side. I suppose the only way to do it is to unsolder the to3 flip the sides (or maybe not now that I think about it..). Redrill the Ts maybe the only way.
Attachments
Perhaps you can consider installing one side upside down if having the cap facing the back panel is that important to you.