New build one more problem

[Garveyte01]

Hello everyone, I’ve built a Dumble 124 clone, (well as close as the parts permitted me to). I am a beginner and I cannot figure out why my amp sounds really good clean and in the FET input as well, but when I engage the OD switch on the back panel I am getting clipping real bad. Plate voltages on power tubes are are 472, control grid is about -50 dc volts. I do have a SPDT pedal switches on the back panel. Could this be the issue? Thanks

[Thomas_H]

Hi,
help us by posting the schematic you are using.

If the schematic looks like what I could find https://el34world.com/Forum/index.php?a ... 1353;image,
the problem might be the additional two triode stages that are added to the circuit in the OD mode.
When the switch is at the clean position the signal goes directly to the send/return and to the PI, without the extra gain stages.

Check the voltages and parts around V2. You might have a wrong voltage somewhere, probably due to a wrong resistor or capacitor.

There are also two 100kB trimmers in the schematic. The first one should be set to something about 25K,
so that a lot of the signal is actually dumped to ground, otherwise it will result in an over the top distortion.
The second one can also be tunned to reduce the amount of signal going to the PI.
Playing with these two should be enough to give you a decent range when using the drive potentiometer.

[Garveyte01]

#124 Schematic 1984.pdf

[Garveyte01]

#124 Schematic 3.pdf

[Garveyte01]

#124 Schematic 1984.pdf

Not this one I used a 500k trimmer in the OD so it must have been the non-1984 schematic

[martin manning]

… my amp sounds really good clean and in the FET input as well, but when I engage the OD switch on the back panel I am getting clipping real bad. Plate voltages on power tubes are are 472, control grid is about -50 dc volts. I do have a SPDT pedal switches on the back panel. Could this be the issue?

You have an error, wrong part value, or bad connection in the OD section. The good news is you’ve got most of it working, FET, clean preamp, PI, and power stage. SPDT switches will work fine for controlling the relays.

The schematic that goes with the layout is the non-1984.

It’s best to keep all posts connected to this project in one thread.

[martin manning]

There are also two 100kB trimmers in the schematic. The first one should be set to something about 25K,
so that a lot of the signal is actually dumped to ground, otherwise it will result in an over the top distortion.
The second one can also be tunned to reduce the amount of signal going to the PI.

#124 has an odd OD entrance with a 500k trimmer modified to 350k. I would go with a 100k there like the other ODS, and play with the series resistor if you want to see what the effect of larger resistance to ground is.
The second 100k trimmer is not a level control, it is used to balance the PI.

[Garveyte01]

I got it! Thank you for all your help it was 2 resistors I had at 150k they should have been 1.5k. I’ve made so many stupid mistakes on this but it’s been an absolutely amazing learning experience for me and it makes me want to do more! I’m not thin skinned so I’d appreciate any negative feedback as to what I should do next…I’m thinking about rebuilding it all because I get the feeling it could be so much neater!

Is this crazy, should I remake the preamp board and redo the wiring so it’s neater? Im wondering how much of a difference would it make sonically. I ordered solid wire during my materials gathering, and that has been more difficult to run nice and straight, my wire looks wrinkled. Also is there any pics or tips as to what a step by step process is for a professional. It looks so incredible when I see the inside of an amp that’s so well done it’s awesome!

Also thank you Amp Garage Community!
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[pottedplant]

I got it! Thank you for all your help it was 2 resistors I had at 150k they should have been 1.5k. I’ve made so many stupid mistakes on this but it’s been an absolutely amazing learning experience for me and it makes me want to do more! I’m not thin skinned so I’d appreciate any negative feedback as to what I should do next…I’m thinking about rebuilding it all because I get the feeling it could be so much neater!

Is this crazy, should I remake the preamp board and redo the wiring so it’s neater? Im wondering how much of a difference would it make sonically. I ordered solid wire during my materials gathering, and that has been more difficult to run nice and straight, my wire looks wrinkled. Also is there any pics or tips as to what a step by step process is for a professional. It looks so incredible when I see the inside of an amp that’s so well done it’s awesome!

Also thank you Amp Garage Community!
-

You're further along than I am in terms of experience with a ground up build but I must say it's a little confusing that you're mixing up resistors. The cathode resistors (and plate) are critically important and it seems like you're not really taking the time to see what they are/do. I could be way off so please forgive me for that presumption if I'm wrong. I mean no offense and i can oftentimes assume incorrect things with no context, sorry if that is the case here.

Another mildly alarming thing for me is how nonchalant you are about the lead dress in your amplifier, including questioning whether or not it even matters. In a high gain amp like an ODS the amount of emissive noise inside an amp and the respective phases of this noise are critically important to manage. High frequency oscillation that you cannot hear will manifest as really bad tone or much lower output (or bleed down into the audible range as squealing) because it's robbing the headroom that would otherwise be available for audible frequencies. Just some observations I've made from looking at your build. It's still very impressive and like I said you're further along than me so who knows, it might be harder than it looks and I'll run into the same issues too. The solid core wire is supposed to be better for this build because of what i said before about how you have to carefully manage where everything is going and coming from.

I have a mesa mark 1 clone (made in the 70s or early 80s i think) that i bought not too long ago and when i move the input wire around to different areas inside the amp (the shielded wire is pretty long) the signal drastically changes in terms of output level and squealing. it also flips behavior when i disengage an extra gain stage because the phases have changed. That was an eye opener for me. This wire will cause uncontrollable squealing if it's just a few inches in the wrong place and also create really low noise floor when moved to another place (could be inverted phase noise causing oscillation i can't hear but manifests as quieter idk).

In short, yes wiring matters tremendously in a higher gain amp. In a classic fender it's probably a substantially more forgiving environment which is where I first started learning. Messing around with the shielded wire in my boogie clone showed me that high gain is a completely different animal. It's like elementary vs college level. You have to really control where the wires are to keep oscillation at bay when the amp is turned up loud enough to play a show. That's another thing to consider, at low volume some of these issues may never show up, but turn that volume up and you have a nonfunctioning amp due to squealing etc.

I'm sure some of what I said could benefit from someone else's perspective who has much more experience building amps but i think I'm on the right track in terms of what matters. I figure since you're looking for help it wouldn't hurt to share my perspective. Hopefully it reads the way I meant it, just sharing what I've observed or learned really. What do you think about how it sounds on the clean channel when turned up? I imagine it's pretty nice?

[garveyte]

[sent you a pm

quote=Garveyte01 post_id=473453 time=1740897452 user_id=26628]
Hello everyone, I’ve built a Dumble 124 clone, (well as close as the parts permitted me to). I am a beginner and I cannot figure out why my amp sounds really good clean and in the FET input as well, but when I engage the OD switch on the back panel I am getting clipping real bad. Plate voltages on power tubes are are 472, control grid is about -50 dc volts. I do have a SPDT pedal switches on the back panel. Could this be the issue? Thanks
[/quote]

[Richard1001]

I ordered solid wire during my materials gathering, and that has been more difficult to run nice and straight, my wire looks wrinkled.

To staighten solid core wire, grab both ends of the (bare) wire with a plier (one in each hand) Bring both pliers together and the pull them apart quick and with some force (pulling the wire straight) The result is a wire that's straight as new.