Local feedback on CL2

[Buschman]

I built a D'Lite and did not include the locak feedback on CL2. It seems that most of the non HRM schematics have a LFB. Am I missing out on anything. I like my clean tone. Will it take some raspiness away from the OD. I would just put one in but I do not have the 22meg resistors.

[dogears]

I like the sound of no LNFB. You could add a .02uf cap in series with the entrance to the pre-od network to reduce bass content. .05 is way too big for nonHRM amps. You may need to adjust the gain a little lower as well. One other thing to try, if you use no LNFB, is to lower the .01uf cap on OD1 to .0068 or so. The extra gain and bottom of no LNFB can be counteracted by reducing some bass at this point. Similar to the HRM amps.

I built a D'Lite and did not include the locak feedback on CL2. It seems that most of the non HRM schematics have a LFB. Am I missing out on anything. I like my clean tone. Will it take some raspiness away from the OD. I would just put one in but I do not have the 22meg resistors.

[Bob-I]

My non-HRM amp has the LNFB on a 3 position switch, 22M, off, 44M. I find that I like it best off. I actually sounds a little dull with it on.

[Funkalicousgroove]

If you use the LFB try using the 250pf/220K network across the loop, I've seen this in more than one amp, and it works well.

[Buschman]

Thanks for all the input. I put a .02 entrance cap in place of the .05. I replaced the .01 cap with a .005 on OD1. I put a .01 back in as the mid cap in place of the .02 I had tried. It sounds sweeter now. The tone controls seem to be happier as well. It is a bit gritty on the OD but that is with the masters turned down. It rounds out nicely when the amp is opened up. I also have a different speaker on the way so I will wait to tweak on the OD when the speaker comes I am going to try a 15" Weber Blue.
I just didn't know how much effect the lfb had on the overdrive tone. I am going to run without it.

[ayan]

If you use the LFB try using the 250pf/220K network across the loop, I've seen this in more than one amp, and it works well.

Brandon, what do you mean by the network "across the loop?"

Thanks,

Gil

[Robert]

I think he is referring to the effects loop and placing a 250pF/220k in parallel across the preamp out and the power amp in.

Robert

[ayan]

I think he is referring to the effects loop and placing a 250pF/220k in parallel across the preamp out and the power amp in.

Robert

Ah yes, the thing that 124 has. It add a bit of chime when the loop is not used, but of course it disconnects from the cvircuit when the loop is used. One thing I found is that I like a brightness cap on the master in the amps with NFB, and althought 124 had a small cap, I like 30pF or bigger.

Cheers,

Gil

[Luthierwnc]

The amp I have on the drawing board has the LNFB on a relay switch. It is connected to the same relay ground as the OD relay. When the OD is off, it is open. When the OD is on, the feedback circuit closes. It doesn't take up a lot of room. No plans for the other half of the switch.

I figured I'd want the cleans clean but didn't want to fumble with a panel switch when it was time to put some hair on it.

sh

[glasman]

The amp I have on the drawing board has the LNFB on a relay switch. It is connected to the same relay ground as the OD relay. When the OD is off, it is open. When the OD is on, the feedback circuit closes. It doesn't take up a lot of room. No plans for the other half of the switch.

I figured I'd want the cleans clean but didn't want to fumble with a panel switch when it was time to put some hair on it.

sh

Have you tested this yet? I suspect if you are just opening the loop it is going to pop like crazy.

One of the commercial companies has a method to eliminate the pop, maybe they will share. It is obvious they watch this board.

Gary

[novosibir]

Have you tested this yet? I suspect if you are just opening the loop it is going to pop like crazy.

One of the commercial companies has a method to eliminate the pop, maybe they will share. It is obvious they watch this board.

I don't build Dumble clones anymore (and are waiting for my D'Lite 44 at the moment), but I've built Dumble clones during the late 90', based on Fender SF Dual Showman's and Twin Reverb's, so some experience from this time has remained

Depending on the FB factor, you've decided for use either two 10M, or a 10M and a 22M or two 22M resistors in series to the cap, which is facing to CL2's plate of course. Then simply switch the junction between both the resistors to ground, to disenable the local FB loop! This way it works 'pop-free'

Larry

[glasman]

Have you tested this yet? I suspect if you are just opening the loop it is going to pop like crazy.

One of the commercial companies has a method to eliminate the pop, maybe they will share. It is obvious they watch this board.

I don't build Dumble clones anymore (and are waiting for my D'Lite 44 at the moment), but I've built Dumble clones during the late 90', based on Fender SF Dual Showman's and Twin Reverb's, so some experience from this time has remained

Depending on the FB factor, you've decided for use either two 10M, or a 10M and a 22M or two 22M resistors in series to the cap, which is facing to CL2's plate of course. Then simply switch the junction between both the resistors to ground, to disenable the local FB loop! This way it works 'pop-free'

Larry

Yup, thats the way they do it.

[JimiB]

I guess I gould use the other half of the relay I am using to have the bright on with clean and off with OD to do this. Awsome! I will try clipping an aligator from the junction of the 22M to ground to see which I like better.

[Fischerman]

Sorry to ask such a simple question but does it matter whether the cap or the resistor (i.e. a 22M or whatever) connects to the plate? There are schematics in the Files section showing both ways...some have cap to plate...others have resistor to plate. I didn't think it would matter but maybe it does?

[novosibir]

Sorry to ask such a simple question but does it matter whether the cap or the resistor (i.e. a 22M or whatever) connects to the plate? There are schematics in the Files section showing both ways...some have cap to plate...others have resistor to plate. I didn't think it would matter but maybe it does?

No, that question isn't that simple!

As long as you don't switch the junction between the splitted resistance to ground - it doesn't matter! In any serial circuit it doesn't matter, what is first, second, aso.

But when you intend to disenable the local FB loop by switching the junction between two resistors to ground, the cap has to face to the tube's plate! Otherwise you'd lead a small DC from the plate to ground, what again would be popping and would influence the tube's load line.

Larry