Tone Stack - Mid Pot

[guitar54]

How can I trouble shoot the tone stack? My Mid Pot seems to do very little. This is on a Ceriatone ODS 50.

http://ceriatone.com/images/layoutPic/O ... ial-V2.jpg


Thanks - Chris

[martin manning]

Measure ohms from the front end of the mid cap to ground as you rotate the mid pot. If it goes from 0 to about 250k, the pot is working and the connections are good.

[guitar54]

Hi Martin - I know the POT is working correctly - I actually installed a new one since the original was questionable.

What I want to figure out is if I run an audio tone into the amp, how can I follow it to make sure the mid path is working?

OR - maybe you have a better idea.

When I run the Mid pot through through it's full range - I barely hear any difference - that is the symptom.

[martin manning]

Measuring ohms from the mid cap to ground checks the mid path, except for the connection from the mid cap to the slope resistor and bass cap junction, and the mid cap itself, which could be failed open. If you send a signal into the tone stack, you should be able to see (or hear) it at the top of the mid pot as long as the mid pot is turned up.

[guitar54]

Hi Martin - double checked - the signal is getting to the mid POT. But I noticed that when I probe the rock/jazz switch, the signal is getting to the switch (bottom leads which are shorted) from the board - but when I flip the switch up to rock, this takes the mid POT out of the circuit. Is this normal?

Also this is with the preamp boost switch up.

[martin manning]

PAB lifts the tone stack, so if your ineffective mid control issue is only in PAB then that is as expected.

[guitar54]

Thanks Martin. Got it.

Is there a way to trouble shoot the mid such that I can for sure know that it's working? Either via audio generator or other?

As I've said, when I turn the mid pot, there is barely any change - if any at all. And I've tried it with all combinations of switches. I'm convinced there is an issue.

I know it's hard to be a doctor via email or posts, but any other guidance would be awesome!

I wonder how I can check the mid signal all the way through the circuit? That is where I'm sure I'd find if there is an issue or not.

I don't have a scope so I'm using an audio generator with a probe/mini-amp to hear the signal.

Thanks!!!!!

[martin manning]

The maximum mid control effect will be heard with PAB off, Mid Boost off, and with treble and bass controls all the way up. The dip is at about 500Hz, so if you run a 500 Hz tone into it with those settings, and sweep the mid pot, you should hear a volume control effect. If the tone stack doesn't have enough mid scoop for you, you could increase the 0.01uF mid cap to 0.033 or 0.047uF, which is preferred by some Strat players.

[guitar54]

Martin - You are awesome. I am playing a Strat...so I'll follow your instructions and maybe I'll change the cap.

I'll report back...either later or tomorrow.

Thanks again!!!!!

[guitar54]

I just tried the 500Hz tone suggestion - Yes it works. Sweeping the mid did have the volume control effect although on zero - there was still a tone - prob normal?

I think I'm going to try changing that cap....

[martin manning]

For a quick listen just tack something in parallel with the 0.01. The values will add together.

[guitar54]

You read my mind. But I don't have any high voltage caps lying around. Have some ordered.

Again - Thanks so much for your guidance. I'll for sure report back once I get the caps.

The other thing I was thinking of doing was reducing the slope resistor...

It's 150K - thinking of 100k or 82k....

[Structo]

I gotta say, when I built my ODS, I didn't think the mid control did much either.
So it is a subtle tone control but along with bass and treble can round out the tone.

As you get used to it, it will all become clear.

If the bass overwhelms you, install lower value on the cathode bypass caps on V1 and or V2.
Try one stage at a time.

[guitar54]

Thanks Structo! Ya - I think the Mid is just subtle. As for the bass - I like mine - can even use a bit more!

[guitar54]

Update - I put in a .047 uf cap and it for sure helped. I'm happy! Thanks guys for all your help!