I have a Hiwatt Lead 50 that I was sorting out microphonic issues, with the V1 gain stage. I noticed some interesting behavior from the stage, while the amp was on a resistor load.
When inputting audio signal into to the front of the amp, I could clearly hear the signal audibly coming out of the first stage of the amp and turning the preamp gain up made it louder. This is without any speakers attached to the amp, Just a load to protect the OT.
Now, it doesn't seem like an issue that should be fretted over, unless this is in some way stressful to components in the amp, I'm curious as to how and why this actually happens. Is it because the stage is still microphonic, and seeing as a microphone and a speaker can be very similar, the microphonic stage is essentially acting as a extremely inefficient speaker, in some way?
I'm not extremely experienced with amps, but I've never come across this before. Is this something that can happen, or is common with microphonic gain stages, or is it not even related?
Interesting behavior from preamp stage
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Interesting behavior from preamp stage
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martin manning
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Re: Interesting behavior from preamp stage
Are you sure it isn't coming from the OT?
Re: Interesting behavior from preamp stage
Perhaps the tube itself makes the sounds since audio frequency is going through it?
Or maybe the caps? (condenser mic)
I've heard singing inductors before.
Or maybe the caps? (condenser mic)
I've heard singing inductors before.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Interesting behavior from preamp stage
I actually had this happen to me the other day. I was playing around with the first amp I ever built, a Champ-ish thing done up from scratch. Dead simple, 12AX7/6V6/5Y3. Isolated jacks, shielded input. Hammond iron. That ought to narrow it down a little.
I will say I only noticed it with the volume all the way down, not with a dummy load, but I have never had a signal leak through zero volume before so I thought it was interesting. It was definitely coming from the amp and not the cab.
Going to play with it a bit more... You have me curious!
Dave
I will say I only noticed it with the volume all the way down, not with a dummy load, but I have never had a signal leak through zero volume before so I thought it was interesting. It was definitely coming from the amp and not the cab.
Going to play with it a bit more... You have me curious!
Dave
Re: Interesting behavior from preamp stage
+1martin manning wrote:Are you sure it isn't coming from the OT?
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Stevem
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Hhhh
Besides the fact that the OT will sing in any amp was the signal passing thru any ciramic caps?
They can act like little pezio speakers and if you have one like that you need to pack some silicone sealer around it to null that action.
They can act like little pezio speakers and if you have one like that you need to pack some silicone sealer around it to null that action.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Interesting behavior from preamp stage
Can that lead to what some call "ringing"?
Tom
Don't let that smoke out!
Don't let that smoke out!