Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JKRamsey1991 on October 02, 2017, 08:27:48 am

Title: Presence and Resonance Controls
Post by: JKRamsey1991 on October 02, 2017, 08:27:48 am

So I'm building a new amp using an Allen chassis. The amp is a sort of trainwreck with tube rectifier that will be running 6V6s. I have a couple extra pot holes in the faceplate and was looking into adding a presence and resonance control.   

Do you all have recommendations as to what pot values to use? Appears on the trainwreck layout it's a 5kl pot for presence and most resonance controls I'm seeing are 1meg but not sure whether to get audio or linear pots.

Title: Re: Presence and Resonance Controls
Post by: SILVERGUN on October 02, 2017, 09:19:24 am

I have found it valuable to go with a proven design first and then tweak to taste.
Since you're building something like a Twreck, go with the 5K for the Presence
 
The attached snip is from Hoffman's H50/H100 amps, where he uses 5K - linear and 1M - audio tapers
 
There is some great info here on how to DIY (Design It Yourself):
http://www.aikenamps.com/index.php/designing-for-global-negative-feedback (http://www.aikenamps.com/index.php/designing-for-global-negative-feedback)

Title: Re: Presence and Resonance Controls
Post by: mresistor on October 02, 2017, 09:29:56 am

So, say on a 5F6A the presence pot is actually the shunt feedback resistance (variable) . Thanks for posting the Aiken link SG.

Title: Re: Presence and Resonance Controls
Post by: SILVERGUN on October 02, 2017, 09:59:03 am

Quote from: mresistor on October 02, 2017, 09:29:56 am

So, say on a 5F6A the presence pot is actually the shunt feedback resistance (variable)

Exactly...and here's a key takeaway from that article, for anyone else who might be playing along:
The shunt resistor value is usually fixed by the phase inverter design requirements, and the series resistor is then sized according to the desired amount of feedback, given the voltage available at the output. - Aiken
 

Title: Re: Presence and Resonance Controls
Post by: JKRamsey1991 on October 02, 2017, 10:05:06 am

This will be the second amp I've built using this preamp just changing the power amp this time. Power amp on the last one was a copy of my Bassman head. This time it's more in line with a deluxe reverb with only a bit more filtering.

I

Title: Re: Presence and Resonance Controls
Post by: SILVERGUN on October 02, 2017, 11:10:59 am

Quote from: mresistor on October 02, 2017, 09:29:56 am

So, say on a 5F6A the presence pot is actually the shunt feedback resistance (variable)

The way the pot is wired it does not act as a variable resistor in the NFB voltage divider equation, it just shunts a variable amount through the .1uf cap, off the wiper
 
 

Title: Re: Presence and Resonance Controls
Post by: mresistor on October 02, 2017, 09:17:15 pm

gotcha   thanks