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Old 5th April 2008, 03:07 PM   #1
wicked1 is offline wicked1  United States
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Default Highs roll off

Hi, I asked this a few weeks ago, and have had time to do more testing, and am sure its a problem...

I built the TubelabSE 300b amp, and the thing sounds muffled. It's as if I've thrown a blanket over my speakers.

I tried fooling myself into thinking the other amps I was listening to had too much highs, or it was just the SET sound, but I've been able to hear other 300b set amps on my speakers, and also a bunch more solid state, and a couple of tube P.P amps.

So, the sound is the same in both channels, so I doubt it's a bad component. I'm sure the design is good.

So.. what could it be? I know my coupling caps are fine. I've used the same things in an amp restore which sounds great.
I'm using cheap Chinese 300b tubes. I have some doubts about my output TX's, but they're smaller than most Ive seen. That would usually mean bass trouble and not treble issues. Maybe they sent me the wrong tx's?
I'm trying to think of what else is common between the 2 channels. The power supply, but I don't know what in it would attenuate the highs.
I'm not using an input pot, and my sound source for this testing is an MP3 player.

I've searched and searched, and can't find much info anywhere about problems w/ highs. All the chat and websites seem to focus on getting clean bass.
So, any ideas, or even links to articles about troubleshooting highs, or theory about the high frequencies would be a great help.

Thanks again!
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Old 5th April 2008, 04:13 PM   #2
wicked1 is offline wicked1  United States
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I just removed all of the jumper wires I had connected for testing, and removed the 5 multi-meters, and now the thing seems to sound better!
I must admit, I didn't listen to it, remove my wires, then listen again.
I was just cleaning up my living room where Ive been doing this testing, and decided to give it one last listen before I bring the amp downstairs to clean it up a bit.

So, this is so tough w/out a test equipment other that my ears which can be influenced by wishful thinking, but it really seems to sound better.

I guess i'll leave the amp up here, and do some more side by side comparisons tonight.

Does it make sense that a bunch of wires, and volt and current test meters could have caused the problem? W/ all the talk about capacitance in wires, etc, I'm thinking maybe it does make sense!
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Old 5th April 2008, 10:05 PM   #3
bigwill is offline bigwill  United Kingdom
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Depending on how things were wired the input capacitance on your meters might have rolled off the highs
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Old 5th April 2008, 10:42 PM   #4
wicked1 is offline wicked1  United States
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The problem is definitely solved.
I had a few friends over, and they could hear a difference the second they walked in the door!

So.. lesson learned.
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