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Post subject: 6G3 Deluxe Presence Control
Posted: Thu Dec 26, 2019 9:26 am
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Roadie
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I'm tinkering with a presence control on a 6G3 Deluxe build. Looks like a 6G6 Bassman presence should work fine but I'm not sure what value I should start with for the NFB tail resistor. Anyone tried this?

Thanks, UN

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Post subject: Re: 6G3 Deluxe Presence Control
Posted: Fri Dec 27, 2019 5:55 am
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I never try that.
Presence control is so subtil, I don't need it.


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Post subject: Re: 6G3 Deluxe Presence Control
Posted: Fri Dec 27, 2019 9:26 am
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Aspiring Musician
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Any particular reason you chose the bassman feedback and presence circuit over some of the other 6GXX circuits? I understand that if I were building a an amplifier, I might like to make it something unique, but is there a particular objective you are trying to achieve?

There are others here who might have more useful advice, I readily admit I don't have any personal experience with anything other than a 6G2A Princeton amp. which only has a fixed negative feedback that is introduced at the cathode of a completely different phase inverter that exists in a 6G3 deluxe.

My next question would be did Leo design the bassman for a bass player or a guitar player, and subsequently was the presence control designed with that in mind? Don't know, they all seem to have the same .1 cap combined with various combinations of resistors, either variable or fixed in the feedback circuit.

Personally, I'd love to have an amp that goes from full on gain, to clean jazz tones, but I'm yet to be convinced that such an amp exists. But I hope that someone won't stop trying to invent it.

I apologize in advance, not the answer you're probably looking for. But I truly hope you get the answer you seek.

Cheers,


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Post subject: Re: 6G3 Deluxe Presence Control
Posted: Fri Dec 27, 2019 10:33 am
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vinyl wrote:
My next question would be did Leo design the bassman for a bass player or a guitar player, and subsequently was the presence control designed with that in mind? Don't know, they all seem to have the same .1 cap combined with various combinations of resistors, either variable or fixed in the feedback circuit.

Good question.

The 6G7 Bandmaster (a purpose-designed guitar amp) used a 1500Ω "tail" resistor at the cathode and a 5KΩ linear-taper pot for the presence control circuit. The same values were used in the 6G14 Showman.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 6G3 Deluxe Presence Control
Posted: Fri Dec 27, 2019 4:27 pm
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Roadie
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Joined: Sat Dec 13, 2014 7:34 am
Posts: 245
vinyl wrote:
Any particular reason you chose the bassman feedback and presence circuit over some of the other 6GXX circuits?

Personally, I'd love to have an amp that goes from full on gain, to clean jazz tones, but I'm yet to be convinced that such an amp exists. But I hope that someone won't stop trying to invent it.

Cheers,


No apology necessary. Outside the box. I've tried things before that worked out pretty darn good without a good, logical explanation as to why so......smoke along the way can be indemnification.

Also, the 6G7A Bandmaster and 6G12A Concert have the same basic design as the Bassman for the presence control circuit.

UN


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Post subject: Re: 6G3 Deluxe Presence Control
Posted: Fri Dec 27, 2019 8:55 pm
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Professional Musician
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The 1500 ohm controls the DC voltages in the phase inverter. The presence control only affects AC signals as it has the DC blocking capacitor.
Use the 1500 to maintain the DC voltage balance of the PI. Add the presence circuit to it with no other changes.
The presence control is a tone control for the main stage. Most pickers leave it turned down.


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Post subject: Re: 6G3 Deluxe Presence Control
Posted: Sat Dec 28, 2019 8:36 am
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Roadie
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Posts: 245
I tried different resistors with a 25k linear pot and here's what I got.

4.7k = 22Vdc PI voltage

1.5k = 16.5Vdc PI voltage

2.2k = 17.9Vdc PI voltage

The 2.2k got me almost dead on with the schematic.

This presence control does make a noticeable difference in this 6G3 circuit with it's limited preamp tone only controls. Being it's active in the power amp stage and the channels are interactive, there's good results within the combination.

UN


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