Weird gain problem with ASL Wave 8s

nathanm · « **on:** 25 Jan 2003, 07:26 am »

I am not sure if anyone reads the ASL forum at HD anymore so I thought I'd take a crack here. I bought a pair of used Wave 8s from a fella here (bob and a bunch of numbers) and one of them is way louder than the other. At first I thought it was the tubes. I bought a set of 4 new ones for it since one was broken in shipping and replaced with a different brand. Then I noticed one amp was louder and assumed unknowingly that the new tube was the culprit.

Nope, even with the new tubes one amp is still way hotter than the other. I measured the speaker outputs of the amps with my CD player playing a -20db 1 KHz test tone with the speakers disconnected. The louder amp read 17 volts and the quiet one read, get this: 6.66 volts! The devil's work!?

Something's definitely not right here! Another interesting bit is that this input was so loud that I could actually hear the CD through the amp itself! I dunno if it was the tubes or the transformers, but I could hear the sound being transmitted mechanically! Yeeow! That's loud!

Any ideas?

JohnR · « **Reply #1 on:** 25 Jan 2003, 08:19 am »

The first thing I would do is swap tubes between the two amps and check again. That will at least eliminate the tubes as the culprit.

Other than that, it's broke

. Do you have a schematic and a voltmeter? Checking the DC voltages around the circuit would be the next thing to do.

It's possible that there's a problem with (one of) the output transformer, or that the feedback network has become disconnected. Opening it up and having a poke around looking for loose connections might yield something.

Hm.... I'm wondering, but... does the lower volume amp sound distorted when you turn it up? That would indicate that one of the output pentodes is not being driven. Perhaps a bad coupling capacitor or connection to it.

nathanm · « **Reply #2 on:** 25 Jan 2003, 06:00 pm »

I've got a voltmeter, but no schematic. Oh yeah, the louder amp also hums (quietly) unless the ground is lifted. Hmm. Maybe the transformer is bad or something. Swapping the tubes doesn't make a difference. But now that I think of it, when I first plugged one of them in it hummed\buzzed REALLY loud one time and then went away.

Yep, I think it's broke!

KevinW · « **Reply #3 on:** 25 Jan 2003, 06:06 pm »

Nathan,
Follow John's advice... have a look inside for loose connections or scorched/burned parts. If that doesn't produce results, perhaps I can help you fix it as an ASL dealer.

nathanm · « **Reply #4 on:** 25 Jan 2003, 09:50 pm »

I did open both amps and look around for anything "funny", but to my untrained eyes I didn't notice anything loose or burned out. My guess is that it has something to do with the transformers. Not sure. I didn't remove the circuit board though, I just took off the bottom cover. Both amps do have a 60Hz hum if you get close enough to the speakers, but the louder amp's hum is considerably louder as well. I've e-mailed Divergent Technologies to ask where I could send it. Thanks for the offer KevinW, I guess I'll see what transpires. With this amp being so inexpensive I would imagine that if I factor in shipping and repair costs it might be cheaper to replace it. Hmmm.