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Old 11th January 2009, 04:07 PM   #1
wicked1 is offline wicked1  United States
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Default noticing way more distortion in my 300b

Hello,
I built the tubelab se about a year ago.
I have been noticing way more distortion at slightly high listening levels, and even at 'normal' levels lately. If I turn it down, it sounds great, but not quite loud enough.

Is there a valid reason for this, or is it most likely psychosomatic or my ears getting more in tune for that sort of thing.

It's bad, though. every solid bass hit becomes a flabby mess... (dono why, but flabby seems like the correct description)
Every build up where many instruments are playing becomes unrecognizable. (not truly unrecognizable, but the definition between tones is lost)

And for a slightly more technical description.. My volume control goes to 20. I used to be able to turn it up to 15 and it would be loud, and I used to think it sounded great at that level. Now I can't go past about 10 w/out noticing distortion.

Is it me or my machine?!?
thanks
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Old 11th January 2009, 04:41 PM   #2
wicked1 is offline wicked1  United States
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I think my edit time has timed out, but I wanted to add;

This is on the same speakers/cables/everything.. I haven't changed anything.

I did test the bias, voltages, etc, and they are all as they should be.
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Old 11th January 2009, 06:42 PM   #3
Jeb-D. is offline Jeb-D.  United States
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The honeymoon is over. You have listened to your gear long enough to notice it's shortcomings. You will now spend eternity building and tweaking gear in attempts to achieve the perfect sound. Welcome to the club

I'm partially kidding, something may have (or not) changed electrically, but the only way to tell is to use test equipment and take measurements. If you plan to stay in this hobby, get a Oscilloscope, and download a PC based spectrum analyzer. I use a program called "Visual Analyser" which does a good job for freeware. You will also need some 8ohm dummy loads and some misc connectors and cables to hook everything up.

Flabby bass and rolled-off highs are typical plagues of SE amplifiers that use no feedback. It effects many, but not all.

Have you changed your speaker placement? What kind of speakers are you running and in what sized room?
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Old 11th January 2009, 07:37 PM   #4
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Have you repositioned either your speakers or your seating location?

Do you have an extra set of tubes? You could conceivably put on 1800 hours over the course of a year if you are playing six hours a day, six days a week. While I would hope a pair of ($$$) 300B should last more than a couple thousand hours, maybe not all of them do.
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Old 12th January 2009, 05:56 PM   #5
wicked1 is offline wicked1  United States
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"The honeymoon is over. You have listened to your gear long enough to notice it's shortcomings."

That is sort of what I figured, but it is SO OBVIOUS now that I hear it. I'd really think something is wrong w/ the amp, except that at lower levels it still sounds great. I did test all the common points.. the voltages are in line, the current is where it should be.

I guess the only way to fix this is to go deaf or spend some money on building a more powerful amp.

-I did try different output tubes. Same thing.. I haven't tried switching the input tubes.. I guess thats a possibility, but I truly doubt those have gone out.
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Old 12th January 2009, 06:28 PM   #6
Jeb-D. is offline Jeb-D.  United States
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You can always bi-wire, bi-amp or use a sub, if the amps mid-range still sounds good at higher levels.

The speakers that the amp is paired with can matter quite a bit as well.
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Old 12th January 2009, 06:33 PM   #7
wicked1 is offline wicked1  United States
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I do have a pair of high efficiency fostex speakers. I do have 2 subs, but I'm not crossing over b4 the amp. That was my next thought.
Unfortunately, that opens a new set of issues. There are some very mixed and heated opinions out there about crossovers.

I'd like to xover at bout 80hz b4 my amp. I dont even need to cross over as my music source has multiple outputs, and already one output goes to the subs. I just need to highpass filter the signal going to my amp.
I thought that would be easy, but after researching it, I need to figure out the resistance of my amp first which looks quite complex!
Maybe Mr Tubelab knows... I dont care if its perfect! I just want to cut off the low lows.
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Old 12th January 2009, 06:39 PM   #8
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My feeling is that a vacuum tube amplifier doesn't "like" to be presented with a passive crossover. You'll end up with a high impedance load beyond the crossover frequency, and vacuum tubes don't always handle high impedance loads gracefully. They would rather deal with a dead short.

If you want to bi-amp, I think you would be better off using an active crossover and filter out the lows before they even get into the amp. If you're really lazy, you might try making a simple RC filter on the input side of the Tubelab SE by adding a capacitor just upstream of R8. It'll only be first order, but maybe it'll work well enough for your purposes.
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Old 12th January 2009, 06:45 PM   #9
wicked1 is offline wicked1  United States
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My history w/ electronics comes from building a HUGE analog modular synthesizer, and I have a LOT of filters in that thing. Maybe I'll try running my audio through one of those, as a test. I've got just about every layout of active filter available. They were designed to color the sound, but only when Q is turned up. I've never done any tests to see how well they can cleanly filter a signal.

My initial idea was to make a simple first order passive filter for the amp, but if you say there could be issues w/ that, I guess I'll skip past that idea.
Ive even got spare PCB's for synth filters I've made sitting in a box..... I guess I'll do some testing to see how well they filter w/out changing the rest of the signal.

(AH shoot.. all that stuff is mono.. I guess i can still test it, and just build 2 channels worth if I need)
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Old 12th January 2009, 06:48 PM   #10
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Quote:
Originally posted by wicked1
My initial idea was to make a simple first order passive filter for the amp, but if you say there could be issues w/ that, I guess I'll skip past that idea.
Shouldn't be any problems using a filter on the input signal to the amp. I'd just shy away from using a passive speaker crossover on the output side. I'm sure others will disagree, and cite particular installations where they have biamped into passive crossovers for years without issue.
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