Dumble Overdrive Special 3rd Gen Build

[martin manning]

Ready for a smoke test? I'm a fan of test-as-you-build, as opposed to wiring everything up before applying any power. Finding and fixing errors early saves time. Still, the typical start-up does some of that by powering up without tubes and checking voltages, etc.

[desertmouth90]

Ready for a smoke test? I'm a fan of test-as-you-build, as opposed to wiring everything up before applying any power. Finding and fixing errors early saves time. Still, the typical start-up does some of that by powering up without tubes and checking voltages, etc.

So you wire up the Power section first for example?

This one I've just ordered two Tung Sol 6L6GCs for it, and a bright cap, might experiment with that bit.

Also I hit the jackpot a few months ago with a box of vintage Mullard valves for £20! Might have to try a few of those.

[martin manning]

So you wire up the Power section first for example?

More like wire up the power supplies (HV, Bias, Relay) and test them, then complete the power amp and test it (set DC operating point, run signal into the power amp input), complete the preamp, etc.

Nice score on the Mullard tubes!

[desertmouth90]

So you wire up the Power section first for example?

More like wire up the power supplies (HV, Bias, Relay) and test them, then complete the power amp and test it (set DC operating point, run signal into the power amp input), complete the preamp, etc.

Nice score on the Mullard tubes!

Take a look at this! I counted 10x Mullard ECC83s (12ax7s)

[desertmouth90]

Got it all working,

however the OD sounds very muddy for some reason, I think its the output tubes. not sure why.

[alnight]

Congrats! If the smoke is staying inside you're doing alright.

It has been my experience that these circuits are quite sensitive to tubes and bias, so that could be an issue.

I have found for best definition with my hot humbuckers that turning the mids down between 8 and 9 o'clock is the way. Anything more is just mush. Every combination is different, but turning the knobs is easy to try. If you can get it less muddy, that will make fine tuning with the bias and the internal trim pots easier, if it needs it. It can be quite fiddly, but it's rewarding when you get there.

[dbharris]

With the amp on, what resistance do you measure from wiper to ground of the OD entrance trimmer?

Can you post a voltage chart?

-Dan

[desertmouth90]

With the amp on, what resistance do you measure from wiper to ground of the OD entrance trimmer?

Can you post a voltage chart?

-Dan

its a B500k Trim pot, schematic says its should be 350k, so thats what I got it at

[desertmouth90]

Congrats! If the smoke is staying inside you're doing alright.

It has been my experience that these circuits are quite sensitive to tubes and bias, so that could be an issue.

I have found for best definition with my hot humbuckers that turning the mids down between 8 and 9 o'clock is the way. Anything more is just mush. Every combination is different, but turning the knobs is easy to try. If you can get it less muddy, that will make fine tuning with the bias and the internal trim pots easier, if it needs it. It can be quite fiddly, but it's rewarding when you get there.

Yeah it was the valves, one preamp valve was shot so I changed to Vintage Mullards and its sounds good but super high gain is really fuzzy.

Ill try get some video recordings.

[martin manning]

With the amp on, what resistance do you measure from wiper to ground of the OD entrance trimmer?

its a B500k Trim pot, schematic says its should be 350k, so thats what I got it at

Youll need to adjust it until you get the range of distortion tone you want, but how is this pcb configured to replicate the 3rd gen OD entrance?

[desertmouth90]

With the amp on, what resistance do you measure from wiper to ground of the OD entrance trimmer?

its a B500k Trim pot, schematic says its should be 350k, so thats what I got it at

Youll need to adjust it until you get the range of distortion tone you want, but how is this pcb configured to replicate the 3rd gen OD entrance?

I will have a search for other schematics and layouts on it, but for the most part I was faithful to these two.

Clive

[martin manning]

The AA "universal" pcb is not true to the 2nd/3rd gen OD entrance, it uses the simpler 4th/5th gen network. You can dial that 500k trimmer down, but I would go with a 100kB trimmer like 102.

[dbharris]

This is really a low plate skyline circuit, not a 3rd gen. I'm sure you can dial it in to make it sound good.

Basically set the wiper of the OD trimmer to about 20%-35% above ground. Then try small adjustments from there to see what you like.

-Dan

[martin manning]

With a 500k trimmer it will probably be closer to 5% above ground. It looks like it would be possible to get a 2nd gen entrance on that pcb without modifying it.

[desertmouth90]

I have plenty of 100k trimmers

Just set it to 35k?