Mistake sounds better, How do I proceed?

[Otsismi]

I recently breadboarded the Matsumin Valvecaster circuit using a Mesa 12at7 that I got at work. When I plugged it into my amp and played I got the characteristic boost and overdrive that so many have demonstrated with their 'Casters. But the gain potentiometer did nothing to the sound.

http://www.google.com/imgres?imgurl=http://www.beavisaudio.com/projects/ValveCaster/MatsuminValveCaster.gif&imgrefurl=http://www.beavisaudio.com/projects/ValveCaster/&h=357&w=606&sz=19&tbnid=FHAsqfzZWwCeAM:&tbnh=75&tbnw=128&zoom=1&usg=__xnQm8_rPgzs6i-zNjA0PaE8MxOc=&docid=hntg1t2-NvgM6M&sa=X&ei=2FEAUt6_A-_d4APH9YHAAQ&ved=0CDQQ9QEwAQ&dur=302

So I revisited it tonight and found that I was connecting the input jack to pin 1 instead of pin 2. Once I corrected the mistake I immediately got a less driven, quieter, overcompressed signal. I asked my roommate to tell me which sounded better, pin 1 or pin 2. We both agree that the input on pin 1 sounds far better.

What is happening here? Is there a way to reconnect the 50k pot to get variable gain from the new circuit? How should I proceed?

[Thecomedian]

I haven't played too much with tubes yet, but I'm going to guess that what is happening is that you're bypassing the first triode set with your signal and only using a single triode. Essentially you could consider that first triode to be "off". They have a similar trick for some amps or boxes where you can select whether to have both sides of the dual triode working or just one. People hear a warmer sound from having only one of the triodes working as opposed to two triodes.

When you say it got quieter, are you comparing that to a 10 volume/gain setting with pin 2 "active"? You might have had the first stage's gain less than 100% open, which would cause one version to sound quieter than the "bypassed" version you made.

if you only want to use a single triode, you might try swapping the gain pot from pin 3/cathode of the first triode stage to pin 8/cathode.

With the pin 3 still connected to ground, I believe your first triode stage will still be passing current, while not being active in affecting the AC signal, since you have no gate control. This might or might not make a sonic difference, since by passing current it will make the tube slightly hotter inside. Try disconnecting the cathode of the first triode completely and using only the second stage and see if the sound changes. You might want to get an audio recording of it, it could be very subtle in difference.

[PRR]

Try this:



I don't know that it will work. But it re-rigs the first stage for "real gain", then allows you to dial-down for optimum-tone between first and second stage. (It is the way most tube guitar amps are rigged.)

Apologies to Beavis.
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> your first triode stage will still be passing current, while not being active in affecting the AC signal, since you have no gate control.

It "affects" the audio because the plate resistance loads the input signal and is non-linear. However "probably" very-very minor. (Other "plate input" riggings can do massive things to signal, gain-control or tremolo.)

And tube guys call that a "grid" though of course it does the same as a FET gate.

[Otsismi]

Interesting. In other news I've recently tried the correct circuit using a 12au7 and it sounds much better. Silly me trying to take short cuts

[alfafalfa]

No offence meant but pin 1 ?  That's the plate.
You're lucky this wasn't a high voltage project. I would advise you to first read up on tube theory ,especially connections.