Complete 124 Schematic

ic-racer · Post by **ic-racer** » Mon Jan 07, 2008 3:18 pm

In terms of the relay switching I am going to admit I don't yet fully understand how it is supposed to work. I think that with the foot pedal disconnected the switch will ground (ie close) or open the relay circuit. The switch has to be in the grounded position (ie closed relay coil circuit) for the foot pedal to do anything. Then the foot pedal can open and close the circuit when it is plugged in.

If that is the way it is supposed to work then that one switch won't do anything when the foot pedal is disconnected. I see the picture and I can't see any ground either??? Did HAD just forget to hook it up or is it a 'feature' in that it is always OFF when the foot pedal is disconnected???

odourboy · Post by **odourboy** » Mon Jan 07, 2008 3:42 pm

The switching is pretty basic.

When the panel switch is in pedal mode, it relies on a switch in the foot pedal to provide path to ground (via pin 3 of the XLR) which allows current to flow to activate the relay. Ground pin 2 to activate the OD relay. Ground pin 4 to activate the boost relay. Pins 1 and 5 provide current limited power to light LEDs in the pedal using the same scheme.

When a panel switch is in manual mode, the center pole is grounded and that activates the associated relay.

So as I see it, the OD would work off the panel switch in manual mode, but the Boost switch looks kind of useless. It will disconnect the pedal function, but not activate the relay since that side isn't grounded.

mdroberts1243 · Post by **mdroberts1243** » Mon Jan 07, 2008 4:01 pm

odourboy wrote:The switching is pretty basic.

When the panel switch is in pedal mode, it relies on a switch in the foot pedal to provide path to ground (via pin 3 of the XLR) which allows current to flow to activate the relay. Ground pin 2 to activate the OD relay. Ground pin to activate the boost relay. Pins 1 and 5 provide current limited power to light LEDs in the pedal using the same scheme.

When a panel switch is in manual mode, the center pole is grounded and that activates the associated relay.

So as I see it, the OD should work off the panel switch in manual mode, but the Boost switch looks kind of useless. It will disconnect tde pedal function, but not activate the relay since that side isn't grounded.

Now if you decided for some reason that the default condition was relay energized for PAB 'off' then the switch does the correct thing... it disconnects from the FS in order to release the relay and turn PAB 'on'... problem is that you have to have the FS plugged in all the time to be able to disable PAB. (I'm not suggesting this is likely, BTW).

It is interesting you don't even see any evidence of solder on those switch lugs... so the intent from the beginning was to leave the manual position of PAB switch ungrounded.

Really nice to have a complete reference schematic for 124!

odourboy · Post by **odourboy** » Mon Jan 07, 2008 4:26 pm

mdroberts1243 wrote:
Now if you decided for some reason that the default condition was relay energized for PAB 'off' then the switch does the correct thing... it disconnects from the FS in order to release the relay and turn PAB 'on'... problem is that you have to have the FS plugged in all the time to be able to disable PAB. (I'm not suggesting this is likely, BTW).

It is interesting you don't even see any evidence of solder on those switch lugs... so the intent from the beginning was to leave the manual position of PAB switch ungrounded.

Interesting hypothesis Dr. Roberts! Billy's schematic does not show it that way, but I can not tell from the photos if he got it right or not. (He did capture the weirdness of the boost switch wiring.)

mdroberts1243 · Post by **mdroberts1243** » Mon Jan 07, 2008 6:14 pm

odourboy wrote:
Interesting hypothesis Dr. Roberts! Billy's schematic does not show it that way, but I can not tell from the photos if he got it right or not. (He did capture the weirdness of the boost switch wiring.)

Thanks, but 'md' are my initials not my profession!

odourboy · Post by **odourboy** » Mon Jan 07, 2008 8:14 pm

Sorry Mark. I thought the homage to Dr. D would amuse you.

odourboy · Post by **odourboy** » Mon Jan 07, 2008 10:10 pm

New version 1.4 posted. Added some notes regarding the pre-OD network, PAB panel switch and Can cap used in PS. 'Switched' Main speaker jack now shown.

I think we're pretty close on this IMHO.

Thanks all for your input. Feel free to post/PM any addition comments or errors. I'll try to maintain this.

ic-racer · Post by **ic-racer** » Tue Jan 08, 2008 12:39 am

odourboy wrote:New version 1.4 posted. Added some notes regarding the pre-OD network, PAB panel switch and Can cap used in PS. 'Switched' Main speaker jack now shown.

I think we're pretty close on this IMHO.

Thanks all for your input. Feel free to post/PM any addition comments or errors. I'll try to maintain this.

Its really looking good! The only thing I can add at this point are a couple of insignificant details. 1) accessory AC jack and 2) it looks like the 6v tranny has a non-grounded center tap (shown in one picture). (I did say INSIGNIFICANT...)

At this point now we need someone with layout software that can make up the #124 component layout and chassis diagram...

odourboy · Post by **odourboy** » Tue Jan 08, 2008 3:53 pm

ic-racer wrote:
Its really looking good! The only thing I can add at this point are a couple of insignificant details. 1) accessory AC jack and 2) it looks like the 6v tranny has a non-grounded center tap (shown in one picture). (I did say INSIGNIFICANT...)

Oh my!

I think I'll save those up until we get a few more, or something more serious.

ic-racer wrote: At this point now we need someone with layout software that can make up the #124 component layout and chassis diagram...

I'll leave that one for someone else.

nickt · Post by **nickt** » Wed Jan 09, 2008 12:58 am

Great schematic!

One nit - shouldn't the B+1 be *after* the standby switch?
As drawn the power tube plates would always be live.

odourboy · Post by **odourboy** » Wed Jan 09, 2008 2:10 am

nickt wrote:Great schematic!

One nit - shouldn't the B+1 be *after* the standby switch?
As drawn the power tube plates would always be live.

Blimey mate! Good catch.

I moved the standby switch at one point and forgot to move the B+1.

I can't let this go as is. Schematic has been updated V1.5

sst4270 · Post by **sst4270** » Tue Jan 15, 2008 4:08 pm

I was just perusing the photos of #124 today for the Nth time, and I'm curious...

What's the story with the double boards. In all the threads I've read (and I've spent hours and hours lurking in here and over on the other TW side) no one's ever mentioned the fact that most of the boards are double stacked. (Would it be out of character for Mr. Dumble to have components in between these boards? Along the vein of gooping up everything)

What's going on in between them? The boards weren't removed during the photo shoot (at least as far as the photo record shows), so how are "we" confident about the wiring underneath?

I've never seen anyone recreate the double stacked boards in any posts either...

Comments?

-Steve

Structo · Post by **Structo** » Tue Jan 15, 2008 5:16 pm

I think they are merely for protection.

odourboy · Post by **odourboy** » Tue Jan 15, 2008 7:21 pm

I don't know if it was HADs intent, but the double boards serve nicely to hold leads and jumpers in place when you make component changes. It also makes runing wires under the board a little eaiser - they don't get hung up along the way.

ic-racer · Post by **ic-racer** » Wed Jan 23, 2008 5:39 pm

deleted...(looking at older version of schematic)

The Amp Garage

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Double Boards

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