Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: taylorc315 on August 07, 2015, 10:14:11 am

Title: Volume Control
Post by: taylorc315 on August 07, 2015, 10:14:11 am

Just a quick question about the volume control on my Hoffman 50 watt plexi, I don't seem to have much control over the volume, at about 2 it's very loud on both channels. I am using the correct pot, 1m that it calls for, do I need to change it to a different value to get more adjustment? I do not have a master volume installed maybe I should consider that?

Thanks
Tracy

Title: Re: Volume Control
Post by: sluckey on August 07, 2015, 10:25:41 am

Plexi 50 is a loud amp. It could benefit from a master volume control. The volume pots need to be audio (log) taper. Did you use a linear taper?

Title: Re: Volume Control
Post by: taylorc315 on August 07, 2015, 11:09:59 am

I'm using the pots that came with the kit, so I believe so.

Title: Re: Volume Control
Post by: mat janssen on August 07, 2015, 11:12:08 am

Could it be that you input voltage is too high ?? :smiley:

Title: Re: Volume Control
Post by: taylorc315 on August 07, 2015, 11:23:05 am

Yes the input voltage is good, but to be sure I will check it again.
Thanks

Title: Re: Volume Control
Post by: jojokeo on August 07, 2015, 11:30:55 am

Quote from: taylorc315 on August 07, 2015, 10:14:11 am

Just a quick question about the volume control on my Hoffman 50 watt plexi, I don't seem to have much control over the volume, at about 2 it's very loud on both channels. I am using the correct pot, 1m that it calls for, do I need to change it to a different value to get more adjustment? I do not have a master volume installed maybe I should consider that?

Thanks
Tracy

To answer your question - yes, if you don't feel the pot is giving you the control or sweep you're wanting throughout it's adjustment range then a change "can" be helpful (but can make things worse too). This includes not just the value but the taper also (logarithmic, linear, reverse log, etc.). However, know that in changing the value it will also come with a consequence (for example when used after the plate of a preceding preamp tube) in gain due to the loading affect of the signal incoming to it. If there is a resistor immediately preceding it will also change the amount of voltage signal output from the pot since the voltage divider has been modified also.

Title: Re: Volume Control
Post by: John on August 07, 2015, 12:02:44 pm

Taylor, something very quick and easy to try, that may or may not work, is on your 1M volume pot: take a 1M resistor and connect it across the outer lugs (not the wiper). That will crudely turn that 1M pot into a 500K pot. That will at least give you an idea if that's what you're looking for.


But yeah, a 50 watt amp is gonna be loud. Heck, my 15 watt Harmony rarely gets turn up past 4. In fact, my 5 watter gets run on around 6 without the guitar turned all the way up. You may find that a master volume is just what you need like Sluckey says.

Title: Re: Volume Control
Post by: taylorc315 on August 08, 2015, 08:56:00 pm

Thanks for all the information, I think that I want to do the master volume route. Is there any information here or does anyone have a diagram/schematic for a master volume?

Title: Re: Volume Control
Post by: sluckey on August 08, 2015, 09:50:10 pm

I used a pre phase inverter master on all my Plexi style amps. It's the same as you will find on a JCM-800 2204 amp. Look at page 2 of this pdf...

     http://home.comcast.net/~seluckey/amps/6v6plexi/6v6plexi.pdf (http://home.comcast.net/~seluckey/amps/6v6plexi/6v6plexi.pdf)

Title: Re: Volume Control
Post by: taylorc315 on August 09, 2015, 12:48:16 pm

Thanks Sluckey, that's what I'm going to do

Tracy