Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on June 29, 2010, 10:39:49 am
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I changed recently new pots (Alpha) for the amp of my friend.
After that he has noticed that the high frequencies are gone from the amp.
Can the pots have really that big meaning?
/Leevi
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Objectively: Did you change the value or taper of the pots? Even if NO, pots can vary widely from their nominal value, which could possibly alter tone. Subjectively: how different people "hear" an amp; or how the same person "hears" an amp at different times and conditions, can be very subjective.
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No taper/value changes
/Leevi
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This raises the musical question: specifically what was changed to what? A before/after schematic would be helpful.
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The amp was originally built by me. The circuit is the following:
http://www.kolumbus.fi/risto.kivioja/RikstoneAmps/PreAmpC30W.pdf
I just replaced the pots with new Alpha pots (same value as before but different manufacturer)
and changed all the jacks.
Leevi
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The only thing I can think of would be a bad pot (even though new) where the wiper isn't making good contact, or maybe a resistor got overheated while soldering. But don't worry, someone who knows lots more than me will be along soon! :wink:
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Sorry, I misread your earlier post and mistakenly thought you had changed pot values. Is it possible the amp's owner changed something: tubes; where he uses the amp (room ambience); different guitar or speaker; PU's; guitar cable; pedals; poor health; hearing issues? Any of these things and more could alter the tone of the amp; or change the subjective perception of its tone. E.g., if he used to play the amp up high on a stand, he might hear less highs if it's now placed on the floor.
It might be worth putting a meter on the old and new pots if possible. Anyway, there's lots of stories about fixing or improving an amp, only to have the owner not like the result!
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Why did you change the pots in the first place?
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The pots were changed because they crackled. Now I realized that I have changed
the power tubes too. They are from same manufacturer (JJ) as before.
Is it possible the amp's owner changed something
The amp owner has not changed anything.
/Leevi
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Can you put the old pots back in one by one?
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This is very interesting. I had an amp 3-4 years ago. It sounded killer. I changed the pots they had a few bad shafts
After changing the pots the amp never sounded the same and was oscillation prone to V1
Maybe there is more to just changing pots and having the right taper than i now know
Whose to say what we are buying are the right tapers? Just cause it says so possably dose not make it so
We need a time machine. Hit the old warehouse on the right>
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The pots were changed because they crackled. Now I realized that I have changed
the power tubes too. They are from same manufacturer (JJ) as before.
Is it possible the amp's owner changed something
The amp owner has not changed anything.
/Leevi
I've had trouble with JJ6L6GC crackling and I've heard other guys dissing them too- I'm not that confident about them, but I haven't had any problems with their 6V6S.
Re: the pot - could be you had a bad pot like one of the others said. Some pots can develop leakage (which can cause all sorts of weird effects) if they are soldered wrong.
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After using hundreds, I've never had a bad Alpha pot. Now that I said it, I surely will, though! It's possible a pot was labelled wrong in the factory. That's something you could check. My money's on the new tubes. Each batch of tubes coming out of a factory is totally different than the last batch. It's the cost of buying tubes in an IC world. That's why it's a bit foolish to talk about a "favorite tube". It'll be different next month. I buy my tubes from The Tube Store, only because he actually listens to each new batch and will tell you which tube has the characteristics you're looking for. There may be many other places that will do this for you; I just know of him.
Dave