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Post subject: Re: ec vibro-champ volume control problem
Posted: Sun Jul 08, 2012 1:18 pm
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colB wrote:
I understand audio taper pots - have used them many times. I'm also very familiar with that article you linked to.
Thing is that it's not very low level or very little change from 1 to 2.5. It's absolutely no output at all. Then clear but quiet sound as I would expect at the start of the taper from 2.5 on the dial.
If the 20% tolerance means that for the part of the taper where the resistance is less than 20% of the maximum value, zero resistance is 'correct' because it is within 20%, then this pot is within tolerance. That would mean the pot is not faulty, just really crappy :|


Look at the vertical scale on the audio pot curve. At 25% of the pot rotation, the voltage across that section of the pot is only 5% of the maximum voltage input to the 2nd stage. If the maximum voltage is 1 volt with the pot set to 100%, at 25% the voltage across the input is only 50 millivolts. That may not be enough to get the second stage of V1 working to create any significant volume. Depending on the tube characteristics, the volume may be effectively zero. I don't see this as a "crappy" pot. Of course, the only way to know for sure is to take measurements. :wink:

colB wrote:
Yes, you're right, how hot the pickups are would certainly be significant.
I've been playing the amp again today, and it sure does sound sweet :D


Excellent. :D

colB wrote:
btw, are there any other forums you would recommend where experienced amp techs hang out that aren't manufacturer specific? I have a Hughes and Kettner Blues Master that I'm just about to start servicing - now that It's not my only amp - It would be good to have somewhere to ask questions if I get stuck.

cheers

Col


Try this one: http://ampgarage.com/forum/

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Post subject: Re: ec vibro-champ volume control problem
Posted: Sun Jul 08, 2012 4:09 pm
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I suppose you could try another amp of the same model for validation of it either working normally or not.

Especially where you plunked down a whole lot of $$ !

Try another to sort out the issue.
Let us know.

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Post subject: Re: ec vibro-champ volume control problem
Posted: Mon Jul 09, 2012 9:06 pm
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Retroverbial wrote:
bluesky636 wrote:
As far as getting distortion, how loud do you have the guitar set? You could have the amp set at "12" and if the guitar is not turned up sufficiently, you will not get any overdrive. If you tell me that you have both controls set to "12" and are not getting any overdrive, then you may have a bad tube.


+1

The V1 gain stage needs every available millivolt of input signal to help saturate the tube. Likewise, the downstream stages (especially the phase inverter) require the highest possible level to start the compression process going into the final drive. Turn your guitar all the way up.

Arjay

+2 Bill's right as usual. That's the way most volume controls should work, except for the HRD series that went from 0 to full tilt before you hit 4 on the volume dial. The numbers are meaningless as for as volume goes. They are for reference. The distortion is what it is, the beauty of the Tweed circuit. But that said, if you're concerned, send it back or A/B the amp with another.

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Post subject: Re: ec vibro-champ volume control problem
Posted: Mon Jul 09, 2012 9:08 pm
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Retroverbial wrote:
bluesky636 wrote:
As far as getting distortion, how loud do you have the guitar set? You could have the amp set at "12" and if the guitar is not turned up sufficiently, you will not get any overdrive. If you tell me that you have both controls set to "12" and are not getting any overdrive, then you may have a bad tube.


+1

The V1 gain stage needs every available millivolt of input signal to help saturate the tube. Likewise, the downstream stages (especially the phase inverter) require the highest possible level to start the compression process going into the final drive. Turn your guitar all the way up.

Arjay

+2 Bill's right as usual. That's the way most volume controls should work, except for the HRD series that went from 0 to full tilt before you hit 4 on the volume dial. The numbers are meaningless as for as volume goes. They are for reference. The distortion is what it is, the beauty of the Tweed circuit. But that said, if you're concerned, send it back or A/B the amp with another. A better alternative would be to build your own. There's plenty of clones out there for a ton less money. :wink:

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