Using Dumble overdrive on a fender twin preamp,squealing....

[guitardude57]

Glad you got it under control.

It can be hard to just make one part change and check for difference sometimes. You think, well maybe this will help too....... and this........

How do you like the tone now? OD?

[Structo]

OD1 is where the 68K grid resistor is.

Can you elaborate the bypass cap on the feedback resistor?
I don't believe I have seen that before.

You changed the 220K resistor on the OD entrance?

Yes quality cables make a huge difference in performance and tone.

Be aware that the TSC does not model the Dumble tone stack correctly.

Although the D stack is similar to the Fender stack there are a few differences which make modeling inefficient.

Yet, you can get an idea what the various components in the stack do when changed up or down in value.

[gary sanders]

Yes youre right on the 68k location,i typed that real early this morning,really fast.no tellin what it says.As I searched ALL over past threads on here I found someone had the squeals and did the 220k change.

I REALLY like the new tone.The ODS options were OK but just not for what I play.So now I have the 124 ODS with a Fender Twin pre amp.Less is more sometimes and Im diggin it!Get some clips up sometime.On the bridge pickup it screams (the good kind of scream) and on the neck its so sort of SRV-ish.Havent played my Hendrix strat through it yet but the double coils are dead on with it.And the clean tone is great.I think I will leave it alone for a while.Ive tweaked this thing more than Ive played through it.I only had a 500kpot to put on the bass control but Im going downtown to get a 250k tomorow.it calls for 250k,10k,250k on the schematic so im stickin with that.who knows i may like the 500k better.

As for the bypass cap on the NFB resistor,I saw that on a carvin x100B schematic and thought it wouldnt hurt to try and it sounds good so Im leaving it.used a 150p on the 4.7K,4 ohm tap

[Structo]

Gotcha,

There is a funny phenomena called psychoacoustics that causes us to second guess what we are hearing.
I can't count how many times I made a change and said to myself, ah there it is, I can stop tweaking it.

Then a couple days later think, hmmmm, I think it needs such and such.

We are our own worst enemy!

Glad you're getting it sorted out.

[gary sanders]

Got it all out.the cap parallel to the NFB res did nothing really,i took it off.there were some really hot wires that werent there with the dumble eq,moved them around.my OD v2 plate wire was close to my OD trim pot and that was a big factor in the problem,moved it away and it got a litle better,and the thing that made the biggest difference and hushed it up was .....
when i put the fender stages in place of the dumble,i used a 68k instead of a 33k at the input to the 1st grid.changed it back to 33k and it hushed completely,like someone switched a noise gate on it.now its good at all volumes even with the treble,overdrive and presence wide open.finally....damn it.that was a pain in the ass.now im too tired to play

now i want to add a reverb driver......hey the tank is already in there!

[BobW]

Glad to her you got it going Gary! Post some sound clips when you're ready.

[guitardude57]

Atta boy Gary!

[Structo]

That is weird that the grid stopper would do that.
Generally the higher that resistor is, the more it keeps out.
A lot of amps used the 68K stopper.

[gary sanders]

as i am in the habbit of doing more than one change between tests,it could have just been the wire movement.Just read the valve wizard page on grid bias and saw the point what structo said last.remember,im a noob trying not to get electrocuted!So if thats the case moving those wires really made that much of a difference!also put a good quality trimmer (100k) onn the OD entrance.at first i had the old metal kind with no casing around them.i had no idea there were so many factors in noise and such!

now im curious of the difference of the outputs of these two preamps and why the fender type would make more noise.I may put the 68k stopper back just to see what happens.Im in good habbit of turning away from the amp when i flip the standby on.

[BobW]

Rg plays a role in the frequency response of a common cathode stage.

http://www.aikenamps.com/Equations.htm

The larger the Rg, the more the knee moves to the left. I agree that simply changing from 68K to 33K isn't what made all the difference, but am glad you are happy with your amp.

Gary, Where are you buying your parts in BHM? I gotta take a ride down someday.

[gary sanders]

i messed around a little more and think the wires close to the OD trimmer was the squealer.i moved wires around and put a good enclosed trimmer and it hushed.been playing on it for a week now and decided to leave it as it is.just beginners luck i guess but it sounds so freakn good!!!! i put a switch between a 100k and 150k on the eq dropping R.really cool.if I do anything else to it i will use a relay to do a bypass for the fx loop since i have an extra relay in there cause the PAB is gone.AND I tried to make a video but my camera cant handle the Hz.Im moving my mini studio in soon so I'll make some real audio and post it soon.I really love how the bridge pickup screams but the neck has so much twang and voice to it.i really dont think you can buy amps like this at a store.now watch my second build sound like ass.I want a 100w head just like this one.

I get my parts here.

http://www.acksupply.com/

not near as cheap as mouser but they do stock some chassis,tubes,and even hammond stomp box enclosures for a pretty good price.not a bad deal when you need something asap and cant wait for ups.

[BobW]

Thanks Gary, it looks like they are located right around the corner from Highland Music.