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Old 18th May 2002, 09:51 PM   #1
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Default Egad is alive!!! (more & questions...)

YES! Just fired the (final) version of my dual JLH '99 and EVERYTHING went smoothly. This is a modified JLH, with increased capacitance values and the ccs mod Geoff proposed to control dc offset. So far i've only fed it with a guitar multieffects, but the sound is crystal clean... can't wait to get it altogheter and plugging a cd player to it!

Now, some impressions:

- "Multilayer" caps: i used two of these (1uF each) in parallel at the input of the amp, and i can't hear any coloration whatsoever. Might be something to consider, specially given their size.
- The ccs mod works flawlessly. I haven't had much time with the 7815 based one (it was on the previous board, which didn't work right), but removing the IC is always a good idea. Recommended mod!
- The bias control on the '96 version is *VERY* good... i set each channel at 2A hot and this varies from 1.9 to 2.01 when cold, stabilizing quickly after that. DC offset is easily set and varies between +/- 10mv cold, staying between +/- 1mv hot. Love it
- Turn-on & off thumps: this bothered me a bit. On cold turn-on, at least one channel gets a 2v spike. It's inaudible (???) but i can't say if that's regular for any amp. The turn-off less severe, but audible. The amp stabilizes in about half a second, and, as far as i've tried, is dead stable after that, even with the rat nest wiring over the case i have so far. My output protection prevents thumps, but still... is this good or bad?
- Cap-X power supply. GOOD, very very very good! I seriously have to reccomend this kind of psu to anyone willing to build a class-a amp. No 60hz hum or noise whatsoever, in fact, i have no way of knowing if it's on rather than a blue led if there's no input connected. The only noise i'm getting is from the transformer when it's sitting near the board, which is a quality custom 400va E-I. Since inside the case the trafo lies near the board, i will have to shield it with something. Any ideas?
- (warning: guitarrist content) Hrmm, the guitar sounds rather good through this amp... class-a wonder?! Sweet sound, good pick attack, even the cheapo distortions of my multieffects sound much better than through my Crate guitar amp. Not so long ago someone was asking about using a ss class-a amp as a guitar amp... i'll definitely will be experimenting with this!

Hopefully i'll have some pics and final impressions in a few days, but so far i'm loving this thing. Gotta love those hot sinks...
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Old 18th May 2002, 10:12 PM   #2
tiroth is offline tiroth  United States
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On transformer shielding: wrapping the coils with copper sheet seems to be a pretty effective low cost mod. Other people have certainly gotten fancier.
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Old 19th May 2002, 12:11 AM   #3
PassFan is offline PassFan  United States
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Hey Lisandro, is that the amp you built with a wood case?
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Old 19th May 2002, 02:26 AM   #4
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Oh yes it is Looks lovely. I'll have pics soon!
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