o'connor best tube fx loop...in dumbles?

[dogears]

You need to add a voltage divider after the return amp.... Without the feedback you have way too much gain. Also, the grid ground is too high IMO. Try 270k.

[tictac]

Is this what you mean? What kind of values for the divider? Maybe 100K to ground / 220k series?

TT

[dogears]

Not bad..... Maybe 82k/150k I try and simulate audio tapers half way on.... Pretty close. Give it a try. You can raise the PI input back to .02

The divider isolates the PI from the return amp and changes the load on the PI

(I think as I really have no idea what I am saying, I just know it sounds good)

Is this what you mean? What kind of values for the divider? Maybe 100K to ground / 220k series?

TT

[swt]

is it necessary to ground the 1m resistor if you wanna go in series?. why not leaving that open for a normal dumbleator loop in the series position?. maybe the 1meg can be a pot as in the boogies, or a variable resistor/trimmer. the ground at the grid is necesary in lower values, because of the lower output impedance of fxs. the dumbleator is set at 400k aprox, because you should count the 220k to ground, plus the series resistor and cap ( i guess, maybe someone more experienced can chime in). this is becoming an interesting thread, thanks tictac and dogears!!
ps....edit: if you wanna simulate a pot you have to put the series resistor, and THEN the resistor to ground.

[tictac]

Well here's what I ended up with, it sounds good without being overly bassy. I did return to the .02 input cap even though .01 has been a favorite value of mine for years, I'll go with it for a while and see if it grows on me.

SWT said: [ps....edit: if you wanna simulate a pot you have to put the series resistor, and THEN the resistor to ground.]

Not always true; Take a look at the way the effects return pot is wired (input to wiper). to simulate that configuration you need to have the resistor to ground before the series resistor not after. Some call this wiring a pot "backwards"

[It's actually a good way to wire the reverb control in a BF Fender this way, it keeps the load on the mixing stage grid from changing as you turn the reverb down.]
[/quote]

[swt]

yes but i thought you were trying to retaing the dumbleator type of return pot. also the loading on the PI is different that way because to the PI it looks like a bigger resistor to ground. if you put the resistor first, then the load will be the 85k resistor, or something closer to what dumble did...
i still don't get why the 1m should be grounded. did you try lifting that and hear what changes?

[tictac]

The return pot is wired the way it is because it keeps the tone from changing drastically when you turn the pot down, again the return signal is attenuated but the grid load doesn't change.

The 1M is grounded because OConnor designed it that way, we've made a few changes but I saw no need to remove it because it sounds good the way it is.


You'll find most of the people who build Dumble inspired amps don't always build it exactly the way Dumble did but throw in a twist of there own. Even Dogears, who blows the "do it the way Dumble did" horn louder than anyone has come up with some original ideas that you'll never see in a stock Dumble. If I had to choose a stock Dumble or one of Scotts amps I'd probabally choose Scott's (unless I was going to resell it)

Bottom line is we've developed this thing for you now it's time for you to get out there, build it, do some tweaking of your own and report back. And don't be afraid to come up with your own ideas, or use someone elses if it sounds good, do it!

[dogears]

Actually, I only blow that horn for the guys who are new at building. That way you get a baseline..... I do a lot of stuff different, but I arrived at that after years of experimentation.

The return pot is wired the way it is because it keeps the tone from changing drastically when you turn the pot down, again the return signal is attenuated but the grid load doesn't change.

The 1M is grounded because OConnor designed it that way, we've made a few changes but I saw no need to remove it because it sounds good the way it is.


You'll find most of the people who build Dumble inspired amps don't always build it exactly the way Dumble did but throw in a twist of there own. Even Dogears, who blows the "do it the way Dumble did" horn louder than anyone has come up with some original ideas that you'll never see in a stock Dumble. If I had to choose a stock Dumble or one of Scotts amps I'd probabally choose Scott's (unless I was going to resell it)

Bottom line is we've developed this thing for you now it's time for you to get out there, build it, do some tweaking of your own and report back. And don't be afraid to come up with your own ideas, or use someone elses if it sounds good, do it!

[swt]

thank you guys. i'm just about to finish it. i have a exact one that is mine, but with a dumbleator built in... so i can compare both types of loops and their effect on the amp. i'l let you know. thanks again.