Ceriatone Forum

Hi there
I've had my ots (50w S&M) for a few weeks now, and I really like it. However, I'd like a bit more control over the EQ, the mid especially. I'm totally inexperienced at modding amps, and have no idea what I would have to change. I'd like to have the option of scooping the mid. Has anybody done this mod? Is it possible? I suppose another option would be to have an external EQ in the loop? Any Ideas would be much appreciated.
Cheers :)

Im thinking you just dont know how to tweak EQ on this amp. This amp has a HUGE amount of mid control. It uses a 250K mid pot, marshall uses 25k, fender uses 15K in the blackface. A Larger mid pot value will give you more mids and therefore a larger tweekability range. The OTS can go from a flat EQ (not achievable on marshall or fender, no matter what the mids will be scooped never flat) to a full scoop like a blackface fender.

The downside to having lots of mids means that the treble and bass controls are less effective. To get more control over this you need to scoop mids which will give the bass and treble a larger range.

Also if all that tweekability isnt enough you have a mid boost and jazz/rock switch which will further change your sound and give you more possibilities. The OTS have a very effective tweekable EQ, probably the most tweekable passive EQ in an amp today. Active EQ is the only thing that will give you a bigger range as you can boost or cut frequencies (passive only cuts) similar to a graphic EQ pedal.

Make the mid cap 0.05uF. If that's not enough; make the slope resistor 100k.

cheers guys, very helpful :)

Hi Erwin, I added a switch on the mid cap, so when its on its about 0.045uF, and when it's off its back to it it's origional state. It makes a big difference, but I'm glad I made it switchable cause I'm lovin both sounds  :) Thanks for the info. . .although I can see that I'm gonna end up with a lot of switches on the back of the amp hehe..Am I right in thinking that the slope resistor is right next to the mid cap (left and slightly down on the layout diagram) with a value of 150k?
Cheers again!

yes i believe that is the correct resistor, mine is around 74k. My custom amp that is being built will has a switch to go from 30k/100k.

How is that being done? Putting a big coupling cap before it? or using a switch capable of 500v DC? I've though about it, but would like to do it with a mini toggle and I don't believe they are rated high enough unles I am mistaken.

From what I understand the slope resistor sees very little voltage. The highest voltage goes through the filter caps into the power tubes which see about 465V, preamps see around 200V, PI about 300. The tone stack sees very little voltage IIRC

Yes correct that is the slope resisor, making iit switchable requires a capable switch. It's , from a electronic point of view, directly connected to the plate of the tube and sees around 200V.

+- the signal amplitude.