Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on November 17, 2010, 11:09:15 pm

Title: POT Question
Post by: TIMBO on November 17, 2010, 11:09:15 pm

Just trying to sort out some tone stacks. I have two tone stack in my Little booga project both are marshall style. As a general rule a 1Ma  ( a being LOG and L being LINEAL) is used for Volume, Bass and master Volumes and L for Treble, mid and Presence. It is confusing when most schems do not show type or pin connections :sad:
Also If a schem shows a 220k pot say for treble and only 250k are available will 250k make much difference.
As the schem shows the two mid pots are different, will two 25k pots be OK.
While we are on the pot (sorry forgot the S) subject I am unable to source a 10K trim pot for the bias circuit would a small audio pot be ok and what type A or L.
The mix pot also has me stuffed  :cry: Thanks

Title: Re: POT Question
Post by: FranciscoPerez on November 18, 2010, 04:05:27 am

Hi Timbo,

250K instead of 220k won't make much difference. Considering you get a 220k 10% tolerance pot, it could end up being up to 242k, and that's really close to 250k.

Here you have the frequency response of both marshall tone stacks.Note that it's almost identical!!

You might want to give a try at duncan amps tone stack calculator, I find it very useful!
http://www.duncanamps.com/tsc/download.html

(http://img26.imageshack.us/img26/7356/220p.png)
(http://img405.imageshack.us/img405/3495/250c.png)


Regards,

Francisco Pérez

Title: Re: POT Question
Post by: FranciscoPerez on November 18, 2010, 04:09:18 am

A linear 10k pot will do the work of a 10k trimmer.
I'm unable to open .sch files right now, sorry.

Title: Re: POT Question
Post by: TIMBO on November 18, 2010, 04:28:16 am

Thanks for the info,I did look at it once but did not understand how it worked.