Randall Switchmaster RMS 150 - Both Channels Option - Schematic Request

[TomCarlos]

MEF members...

Anyone have a schematic for the Randall Switchmaster 150, AKA "RSM-150"?

This is a two channel amp. Both channels are working but there is an issue with the channel switching. You cannot switch without the foot pedal.

About the foot pedal - the red light works (on the amp and on the footswitch). The red led is for the channel switching and in fact, when you stomp on the button you see the red light on the amp turn on and off. The green led is dead (on the footswitch). I need to replace that. I have some leds kicking around the house. The button (and green led) for the "both channels" is bad and that will be replaced. But I unsoldered the wires and used clips to make the connections. I cannot get the green light on the amp to turn on or off. I am assuming it does not matter if the led on the footswitch works. Unfortunately, there is no switch on the amp for this feature. I tested the male end of the connector to the wires in the switch - there is continuity. So I need to figure out why the "both channels" option is not engaging.


Thanks in advance!!

[J M Fahey]

there is an issue with the channel switching. You cannot switch without the foot pedal..... Unfortunately, there is no switch on the amp for this feature. I tested the male end of the connector to the wires in the switch - there is continuity. So I need to figure out why the "both channels" option is not engaging.

If itīs anything like "other" Randalls, specifically the famous RG100, switching is as primitive and crude as there is, straight Fender Blackface era Reverb switching Technology.

Both Channels are *always* ON; multi pin footswitch simply grounds one or the other.
Poor Technology because switch is on the floor, and you have a long cable joining it to the proper channel output, cable carrying actual unbuffered signal so it both kills highs and allows some interference to get in.
Same as Reverb Fsw which grounds Reverb signal in a Fender amp.

So with Fsw plugged in, you ground one OR the other.

"Both channels ON" simply removes Ground available to Channel Switch so it does not work any more; same as unplugging the Fsw.

So test continuity and switching based on this.

You did NOT show the Fsw/Amp plug/connector, why?

Itīs hard enough to guess as-is, even harder without enough data.

PS: pictures are too small, maybe you uploded thumbnails or selected that mode, please allow full/original size.

[vintagekiki]

PS: pictures are too small, maybe you uploded thumbnails or selected that mode, please allow full/original size.

https://reverb.com/item/27984496-randall-switchmaster-150-80-s

https://www.millrivermusic.com/listing/randall-switchmaster-150-rsm-150-vintage-200w-1x12-guitar-combo-c-1980s/32987756

[TomCarlos]

Update - I bought a schematic from Music Parts dot com; and found some wiring errors and a bad LED in the footswitch.

I will reproduce portions of the footswitch and grounding circuits with a new photo of the switch. I am also waiting for a new switch as one was bad. I'll get back to this in a few days.

Until then... stay tuned...

[vintagekiki]

Until then... stay tuned...

Why information on a spoon?
If not too big a problem upload (share) the complete schematic.
Such is the old good forum practice.
Thanks for the effort.

[DrGonz78]

Why information on a spoon?
If not too big a problem upload (share) the complete schematic.
Such is the old good forum practice.
Thanks for the effort.

When you purchase the schematic on that site they make you agree to not publish the entire content. Now pertinent snippets probably will go unnoticed. Then again people have no doubt uploaded entire schematics and I don’t think it was noticed.

[TomCarlos]

Vintagekiki....

As DrGonz states, there is an agreement when you buy about not publishing the entire schematic. Anyway, I am trying to do the next best thing - show only the sections that we are discussing.

The image below is of the footswitch and the circuitry for the channel switching. As I mentioned in my other post, 1 resistor, 1 LED. This is different compared to the RG-80-SC. I am tempted to remove some of that information so that future viewers are not confused.

Tom

[vintagekiki]

https://music-electronics-forum.com/forum/amplification/guitar-amps/43055-randall-rg100-es

Does anyone know if you plug in the foot switch on the Randall RG100 Es , will it truly separate the channels

[TomCarlos]

Ok... back to the Switchmaster.

I replaced the "Both" switch on the external box. Despite a very loose Beau Cinch connector on the amp, the buttons do what they are supposed to do. I can get "Both" channels to come on or I can switch between the Clean and Distortion channels. The issue now is that neither "Red" LED will turn on.

I've got this thing wired as shown in Post #8. I did order a new panel mount connector. Maybe something is going on there (or dirty contact).

On the Green LEDs, there is 2.5 volts across the panel LED and 3.5v across the footswitch LED. I get nothing across the Reds.

My question is... are the LEDs independent from one another?

[TomCarlos]

Ok... pulling my hair out over what seems to be a simple circuit, but still having an issue.

Disregard the schematics from an early post - I deleted them!!

I replaced the Beau Cinch connector - nice and tight.


- I am back to the Green LEDs work fine on the amp chassis and footswitch. It is the Red LEDs that will not turn on.

- With no footswitch connected, the LEDs are not on but both channels work.

- The buttons on the footswitch do what they are supposed to do. On one side, I can change channels. The other button turns on both channels.

- I checked the LEDS - both are good.

- I checked the polarity to make sure I did not connect them ass-backwards to the 680 ohm resistors and the Cinch connector

- On the chassis socket, center pins, one side is connected directly to the chassis but the other side connects to a black wire that runs back to the power supply.

- I checked the wiring on the Chassis socket. One side is for the circuits and the other for the LEDs. The center pins to go ground (above).

- Right now, the Clean channel is working when the Green LED is turned on.

- If I click on the Channel Select switch, the Distortion Channel works but no Red LED (on either the chassis or footswitch).

- I checked the 680 ohm resistors that connect to the Cinch connector - both resistors are ok.


So my assumption is that if I can use the footswitch successfully to select either or both channels, that part of the footswitch is ok and so is 1/2 of the Cinch connector. There's gotta be a simple explanation for the Red LEDs to not be functioning!! Maybe a mistake in the schematic for the footswitch? I have double checked my wiring to that schematic.

[TomCarlos]

Ok... getting closer. There MUST be an error on the wiring diagram for the footswitch. I disconnected the wires to the "Both" and I can get the Red and Blue to toggle. AND... it appears that BOTH RED LEDs must be connected and working in order to see them lite up.

Let me try and draw what I have and then tackle the "BOTH"....

Sheesh....

[TomCarlos]

Ok... Here is what I have thus far.... One side of the foot switched hooked up so that I can go between Channel A and B with the LEDs working on the pedal and amp chassis.

I am not 100% convinced that the schematic diagram for the foot switch (see prior post) is correct. It just seems odd that one of the pins on the "Both Switch" is open. I know "The Dude" posted a diagram on a different thread for a Randall rg100. And in that thread, he shows the FS-5 foot switch. But I am not sure it is the same. If you look at the schematic for that amp and this one, there is a difference on how the LEDs are driven to light up.

[vintagekiki]

About FS5

https://www.schematicsunlimited.com/r/randall/randall-rg100es-rg80es-amplifier-schematic

https://www.harmonycentral.com/forums/topic/119194-my-rg100es-footswitch/

https://forum.seymourduncan.com/forum/amplifier-central/323440-diy-hack-footswitch-to-just-turn-one-channel-on-off-on-my-78-randall-rg100es

https://music-electronics-forum.com/forum/amplification/guitar-amps/43055-randall-rg100-es?t=41970

https://music-electronics-forum.com/filedata/fetch?id=841834

https://www.guitars101.com/threads/randall-footswitch.44344/

^{Maybe some of the LEDs are connected inversely?}

[dmeek]

Here is a schematic of the LED wiring. The amp and footswitch LEDs are wired in series so both have to be working and the same polarity. The -40 volts shown in post 7 is a lot more than needed, -12 would be better.
Check the 680 ohm resistors.


Edit: The schematics in post 7 look correct to me except the polarity of the LEDs is reversed between the amp and footswitch. The wiring of the Single/Both switch is a little confusing, but it works. All LEDs will be on in Both mode.

[TomCarlos]

Thank you for the additional posts.

I will make another version of my foot switch diagram and turn the Connector 180 degrees and then turn the switch 90 degrees - all in \hope of trying to understand how the circuit works. At first glance, it appears that the Green LED is backwards in the schematic diagram.