ODS 124 - revisited for the 21C

[talbany]

Sorry this is all I have

No Worries Tyler thanks for posting those!

Tony

[Charlie Wilson]

Thanks Tyler
It looks as though the shots you have he's changed the value of cathode resistors to (530.17 ohms) 820/1.5k
BUT? he also changed the value of the plate resistors as well to 320k 100k+220k..If you take a look at #38 it appears he did the same to those plates as well..He's changed both RP and RK values..Someone want to do the math?

BTW.I think it's the same amp #38..
Tyler you got any more
Tony

Tony, the bands on the series plate resistor look a little orange to me. Maybe 430k.
CW

[talbany]

Thanks Tyler
It looks as though the shots you have he's changed the value of cathode resistors to (530.17 ohms) 820/1.5k
BUT? he also changed the value of the plate resistors as well to 320k 100k+220k..If you take a look at #38 it appears he did the same to those plates as well..He's changed both RP and RK values..Someone want to do the math?

BTW.I think it's the same amp #38..
Tyler you got any more
Tony

Tony, the bands on the series plate resistor look a little orange to me. Maybe 430k.
CW

I looked at them on 2 seperate monitors and they still look red to me? Sometimes these color bands can be deceiving..
I see Red/Red/Yellow on the plates and Grey/Red/Brown on the cathodes..I am wondering if Dumble even did this mod now??.What do you think?

Tony

[Stephen1966]

I see Red/Red/Yellow on the plates and Grey/Red/Brown on the cathodes..I am wondering if Dumble even did this mod now??.What do you think?

Tony

I see the same.

[Charlie Wilson]

Tony, when I tilt my lap top monitor back they look red so I'll go with the 220k. Yeah looking at the way they were put on there I was wondering about that mod. If it is Dumble, I think it is his, I'm sick of people asking for more gain, there you go, get out of here gain mod.
CW

[talbany]

I'm sick of people asking for more gain, there you go, get out of here gain mod.

[gonzomode]

Is this one of the Dumbles sold by the Roy brothers in Germany late 70s? According to an article I read in a german magazin years ago, these Dumbles were produced in a small batch(a dozen or so) with identical circutries. I‘m relativly new to this amps, but my first impression is this is not a mod Dumble did. Maybe the first Kitty Hawk „prototype“

[talbany]

Is this one of the Dumbles sold by the Roy brothers in Germany late 70s? According to an article I read in a german magazin years ago, these Dumbles were produced in a small batch(a dozen or so) with identical circutries. I‘m relativly new to this amps, but my first impression is this is not a mod Dumble did. Maybe the first Kitty Hawk „prototype“

https://ampgarage.com/forum/viewtopic.p ... 80#p425180

[Stephen1966]

Greetings all, I've just posted the first draft of the FET boost circuit in the first post. This is a version of Martin Manning's work in his post Footswitch-able FET Boost https://ampgarage.com/forum/viewtopic.php?f=5&t=31084. Once again, I'd appreciate it if you could give it the once-over and see if I got my ideas straight. I think I have it all in order but it's always possible I've either misunderstood or overlooked something.

Cheers,

Stephen

[Charlie Wilson]

I don't see anything posted.
CW

[Stephen1966]

I don't see anything posted.
CW

It's at the bottom of the first post on the first page. It's being downloaded (4x so far). Let me know if you still don't see it, I might need to take it up with the moderators.

[talbany]

Well since I basically hijacked your thread. I am not exactly sure what your asking?
I implemented Martins FET boost relay circuit,works great and the switching is simple!.The footswitch basically grounds out (de energizing) the relay coil and light on the foot box, switching the inputs through the relay,super simple and works. Wire it (or draw it) up exactly as drawn and you should be good to go.
Good Luck

Tony

[Stephen1966]

Well since I basically hijacked your thread. I am not exactly sure what your asking?
I implemented Martins FET boost relay circuit,works great and the switching is simple!.The footswitch basically grounds out (de energizing) the relay coil and light on the foot box, switching the inputs through the relay,super simple and works. Wire it (or draw it) up exactly as drawn up and you should be good to go.
Good Luck

Tony

It's all good...

This is what has basically done my head in these past few days. "Grounds out" is opening a path to ground? When the FS switches to a route to ground, the circuit... de-energises? I thought it was the other way round! As in the ground from the pedal, leads back to the negative terminal on the power board; opening the circuit and energising the coil(s). Martin's design is great but I want to implement it slightly differently. In M's design the DPDT pot switch only appears to control whether the circuit routes through the pedal or not: a Manual/Pedal switch, like those on the back panel for the OD and PAB.

The FET circuit in my understanding, can only be closed (relay de-energised) either by the footswitch, or by not plugging the pedal in and switching from Manual, to Pedal. Switching to Manual energises the coil and activates the boost, by opening the circuit (to ground), switching to Pedal - without a pedal - would leave the circuit closed (no route to ground). These seem to be the only way we can activate/deactivate the FET boost. To get around this, I placed a simple (on-off) switch carrying the +12V supply before the coil. This switch, and its indicator LED, isn't in Martin's design. Please correct me if I am wrong.

The thread is becoming a juggernaut but following xtian's suggestion, I'm putting all the files for download in the first post... I think I have Martin's concept squared away in my head and this is what I drew up and posted there. The schematic is ODS FET FS 1.1. But because of the changes I want to implement, I just wanted to run it by the members first to check my thinking before firing up the soldering iron.

Stephen

[erwin_ve]

Stephen looking at your schematic on the fet:
the manual switch you want as a extra is very simple: you can wire that like the pab manual switch as seen in the layouts. It grounding the 12v through the relay at a switch rather than turning the 12v on and off.
I've done that many times complementary to Martin's Fet relay and works great.
You can take the switch wire anywhere you like in the chassis and connect the switch to a ground point.

[martin manning]

In M's design the DPDT pot switch only appears to control whether the circuit routes through the pedal or not: a Manual/Pedal switch, like those on the back panel for the OD and PAB.

The FET circuit in my understanding, can only be closed (relay de-energised) either by the footswitch, or by not plugging the pedal in and switching from Manual, to Pedal. Switching to Manual energises the coil and activates the boost, by opening the circuit (to ground), switching to Pedal - without a pedal - would leave the circuit closed (no route to ground). These seem to be the only way we can activate/deactivate the FET boost. To get around this, I placed a simple (on-off) switch carrying the +12V supply before the coil. This switch, and its indicator LED, isn't in Martin's design. Please correct me if I am wrong.

The pot pull switch is providing exactly the same function as the manual/pedal switches for OD and PAB, and it will engage the FET boost regardless of whether the footswitch is pugged in or not. I'm not sure why you would want another switch. In the relay control circuits you are free to choose which relay coil state engages the function.

In the 124, the functions are engaged when the relay coils are energized, and I've done the same in the FET boost.

You can also wire the panel switches to ground the relay coil and the footswitch, like this: https://ampgarage.com/forum/viewtopic.p ... 66#p420166. That way you get the footswitch LED to come on (and stay on) which will tell you that the manual switch is engaged.