JTM45 cascading gain "one-wire" mod

LarryLarry · 03-03-2007, 04:08 AM

Can anyone explain to me how to do the one-wire mod to cascade the channels on a JTM 45? Preferably using the Ceriatone layout as a base.

Tom Phillips · 03-03-2007, 06:25 PM

Larry,
I don't have a direct answer for you but here is an interesting link that I saved. If you start there and follow the various links posted on the site, you may find the information you need.
http://raw-sewage.net/jtm45ri_mods.html
Tom

LarryLarry · 03-03-2007, 08:54 PM

Thanks Tom. I do have the reference hand drawn schematic (for the mod) but it is barely readable. I'm sure I'll figure it out, and when I do I'll take photos and post them!

hasserl · 03-03-2007, 09:52 PM

Here you go:

http://www.lynx.bc.ca/~jc/marshallAmps.html

LarryLarry · 03-03-2007, 10:14 PM

Yep, that's the reference I already have, thanks...

Tom Phillips · 03-04-2007, 12:47 AM

OK. Now I see what you are trying to do.
It's a bit more than just adding one wire. The Mod makes sense to me. If you want that insane gain that is.
Are you saying that you are not familiar with working from a schematic?
Tom

LarryLarry · 03-04-2007, 01:11 AM

No, it's just that all the writing on the mod schem is blurry.

Ok, so using the Ceriatone layout (cause it''s easy to read) I think I need to do this:

1. Unsolder the lead going to pin 7 of V1
2. Separate the 2 270k resistors (schem shows 470k) leaving the rightmost (Normal channel) still going to pin 2 of V2
3. Ground the 500pF capacitor (schem shows 220pF) that is across the leftmost 270k resistor
4. Solder a wire from the leftmost 270k resistor going to pin 7 of V1

Sound right?

Tom Phillips · 03-04-2007, 01:37 AM

I don’t have the Ceriatone layout so it’s hard to comment accurately.
The lefts & rights seem to be different and I think that the cap should be left open rather than grounded. You need to be careful when looping back the wire after the first gain stage. Probably best to use a shielded cable with only one end of the shield grounded.

LarryLarry · 03-04-2007, 01:51 AM

Here is the Ceriatone layout.

Tom Phillips · 03-04-2007, 02:13 AM

Do you have a clean scematic from Ceriatone?
That's the best way my brain follows signal flow.

LarryLarry · 03-04-2007, 04:31 AM

Ceriatone doesn't use schematics. I was just using the JTM45 reissue and original as references.

Tom Phillips · 03-04-2007, 07:39 PM

Larry,

I think you have it figured out.
I marked up your directions with my comments as I thought it through. My comments are shown in red below. All references are based on the Ceriatone layout. No guarantees but I think this is correct.

1. Unsolder the lead going to pin 7 of V1. (This disconnects the bright input jacks)
2. Separate the 2 270k resistors (schem shows 470k) leaving the rightmost Normal channel, ( The resistor without the capacitor in parallel ) still going to pin 2 of V2.
3. Remove the 500pF capacitor (schem shows 220pF) that is across the leftmost 270k resistor (The one wire mod instructions show this cap disconnected and left hanging. This makes for easy reversal of the mod and makes sure that an original vintage part is not lost. However, since you are working with a Ceriatone, I say just take the cap out for a cleaner mod result)
4. Solder a wire from the leftmost 270k resistor going to pin 7 of V1

Regards,
Tom

Satamax · 03-04-2007, 08:01 PM

You're talking about something like this?

03-03-2007, 04:08 AM	#1
LarryLarry Member Join Date: Feb 2007 Location: Riverside, CA Posts: 29	JTM45 cascading gain "one-wire" mod Can anyone explain to me how to do the one-wire mod to cascade the channels on a JTM 45? Preferably using the Ceriatone layout as a base.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Salvaging valuable tubes - (see "dead" tube post also)	Rob Mercure	Tubes (Valves)	2	02-01-2007 03:13 PM
Standard Amp "body" and "Limit" controls - what the hell are they?	Ptron	Theory & Design	7	10-02-2006 07:32 PM
Cascading Gain Stage	elpops	5 E 3	1	08-24-2006 05:41 PM
Questions about suspect new "Child Media-Monitor" product	Brad1	Lobby	6	07-12-2006 09:06 AM
"best" passive balance speaker simulated line-out?	Chris / CMW amps	Theory & Design	4	06-21-2006 05:52 PM

03-03-2007, 06:25 PM	#2
Tom Phillips Senior Member Join Date: Jun 2006 Location: California, USA Posts: 676	Larry, I don't have a direct answer for you but here is an interesting link that I saved. If you start there and follow the various links posted on the site, you may find the information you need. http://raw-sewage.net/jtm45ri_mods.html Tom

03-03-2007, 08:54 PM	#3
LarryLarry Member Join Date: Feb 2007 Location: Riverside, CA Posts: 29	Thanks Tom. I do have the reference hand drawn schematic (for the mod) but it is barely readable. I'm sure I'll figure it out, and when I do I'll take photos and post them!

03-03-2007, 09:52 PM	#4
hasserl Senior Member Join Date: May 2006 Posts: 717	Here you go: http://www.lynx.bc.ca/~jc/marshallAmps.html

03-03-2007, 10:14 PM	#5
LarryLarry Member Join Date: Feb 2007 Location: Riverside, CA Posts: 29	Yep, that's the reference I already have, thanks...

03-04-2007, 12:47 AM	#6
Tom Phillips Senior Member Join Date: Jun 2006 Location: California, USA Posts: 676	OK. Now I see what you are trying to do. It's a bit more than just adding one wire. The Mod makes sense to me. If you want that insane gain that is. Are you saying that you are not familiar with working from a schematic? Tom

03-04-2007, 01:11 AM	#7
LarryLarry Member Join Date: Feb 2007 Location: Riverside, CA Posts: 29	No, it's just that all the writing on the mod schem is blurry. Ok, so using the Ceriatone layout (cause it''s easy to read) I think I need to do this: 1. Unsolder the lead going to pin 7 of V1 2. Separate the 2 270k resistors (schem shows 470k) leaving the rightmost (Normal channel) still going to pin 2 of V2 3. Ground the 500pF capacitor (schem shows 220pF) that is across the leftmost 270k resistor 4. Solder a wire from the leftmost 270k resistor going to pin 7 of V1 Sound right?

03-04-2007, 01:37 AM	#8
Tom Phillips Senior Member Join Date: Jun 2006 Location: California, USA Posts: 676	I don’t have the Ceriatone layout so it’s hard to comment accurately. The lefts & rights seem to be different and I think that the cap should be left open rather than grounded. You need to be careful when looping back the wire after the first gain stage. Probably best to use a shielded cable with only one end of the shield grounded.

03-04-2007, 02:13 AM	#10
Tom Phillips Senior Member Join Date: Jun 2006 Location: California, USA Posts: 676	Do you have a clean scematic from Ceriatone? That's the best way my brain follows signal flow.

03-04-2007, 07:39 PM	#12
Tom Phillips Senior Member Join Date: Jun 2006 Location: California, USA Posts: 676	Larry, I think you have it figured out. I marked up your directions with my comments as I thought it through. My comments are shown in red below. All references are based on the Ceriatone layout. No guarantees but I think this is correct. 1. Unsolder the lead going to pin 7 of V1. (This disconnects the bright input jacks) 2. Separate the 2 270k resistors (schem shows 470k) leaving the rightmost Normal channel, ( The resistor without the capacitor in parallel ) still going to pin 2 of V2. 3. Remove the 500pF capacitor (schem shows 220pF) that is across the leftmost 270k resistor (The one wire mod instructions show this cap disconnected and left hanging. This makes for easy reversal of the mod and makes sure that an original vintage part is not lost. However, since you are working with a Ceriatone, I say just take the cap out for a cleaner mod result) 4. Solder a wire from the leftmost 270k resistor going to pin 7 of V1 Regards, Tom

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)