Marshall JCM1H or JTM1H schematics

Tube or solid-state, this section goes to eleven!
User avatar
Tech28
Information
Posts: 17
Joined: 20 May 2014, 05:51
Been thanked: 1 time

Post by Tech28 »

Tech28 wrote:
jtn191 wrote:Ok, so C15 should be in the signal path...where? Also, I don't see any 4M7 resistor...
Now if you want i will correct the rest i see wrong in the schematic I see posed on this site. But I need those SL5 voltage first. I thought we had
a cool community here. Would only take that dude 15 minutes to check voltages at those three points that I've mentioned.
opps, in my moded picture diagram I made a mistake, its not a 4M7 look at the color bands. But the connection is 100% correct for sure.
Attachments
JTM1 PCB.jpg
JTM1 PCB.jpg (53.38 KiB) Viewed 3808 times

User avatar
Tech28
Information
Posts: 17
Joined: 20 May 2014, 05:51
Been thanked: 1 time

Post by Tech28 »

Thomas_H wrote:Are there any pictures for the jcm1 board?
Yes this is it. The clone is 100% same connection points and same value components. But the clone has two additional components, a resistor and another filter cap just after the full wave rectifier. They both sound great but the clone has better tone more body and better low end
Attachments
20140509_135452.jpg
bottom.jpg
chassis botom.jpg
JCM1 and JCM1 clone.jpg

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Hello guys, I am happy to start posting here in this forum.

You can get some answers from me directly, if required. Most queries are already answered here. More details, (not many are left) I can provide.

Only one detail: The schema that I published is the JTM1 (with approximately 95% accuracy). There are components that are in this conversation are the JCM1. And on this amplifier, I do not guarantee 70% of the scheme, so I do not have correct arguments to discuss about it.

As the Thomas_h said, if someone has the amp, whatever the JCM1 or JTM1, and want to post more detailed images of some parts have not yet been photographed, would greatly help us all.

Thank you.

Matec.

User avatar
jtn191
Solder Soldier
Information
Posts: 162
Joined: 01 Jan 2011, 10:28
Has thanked: 31 times
Been thanked: 22 times

Post by jtn191 »

Thanks Matec. I should clarify that I'm mostly interested in the jtm1 whereas Tech28 is interested in the jcm1

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

To further clarify the subject a bit, I am now posting the schema that is my "interpretation" of the pictures I found on the internet.

100% guaranteed? Of course not. But it can have many hits.

Components with "???" are those who have doubts about their values​​.

Schema JTM1.

Image


The next scheme is the prototype I built. I called HTM1-3.

There are few differences to JTM1, but nothing worse than the sound of the amp.

Schema HTM1-3

Image

Click on the images to see them in full.

Thank you.

Matec

User avatar
Thomas_H
Information
Posts: 46
Joined: 05 Mar 2013, 12:37
Has thanked: 3 times
Been thanked: 18 times

Post by Thomas_H »

Hi Matec,
welcome to the forum, nice to have your participation in this thread!

Tech28 very nice build! Do you have some soundclips?
If you don't mind, could you share your schematic for the JCM1 clone? Or at least what OT are you using?

Cheers,
Thomas

User avatar
fakcior
Breadboard Brother
Information
Posts: 68
Joined: 31 Oct 2010, 12:22
Location: Poland
Has thanked: 4 times
Been thanked: 20 times

Post by fakcior »

Tech28 wrote:
jtn191 wrote:Ok, so C15 should be in the signal path...where? Also, I don't see any 4M7 resistor...

Are you talking about in this schematic? Thats just it there is no 4M7 in connection with the 100n being in the correct location.
Im talking about the pcb in the thread not this schematic that someone posted. Signal comes straight from the 100nf down to the 4M7. one end of the 4M7 goes to ground. Then on the hot side of the 4M7 (same side as the 100nf) makes its way into the tonestack. The 4M7 is located all the way in the lower left hand corner of the pcb in the picture, which is right where the signal enters into tonestack via a 3 pin connecter pin#1 one. You want the correct JTM1 voltages readings through out the circuit ? well tell the dude who posted the SL5 schematic to not be scared and slide out the chassis. Then put a multi meter in high voltage DC mode. Then ground the black lead to the chassis. Then take voltage reading at HT1 which is right in between R6 and R4. Or if you cant reach R6 and R4 take voltage reading from C5N which is also HT1 . Same thing goes for HT2 which is right in between R4 and R5. Same thing for HT3 which is right in between R5 and R3. Look at the resistor labeling on PCB its easy to do. Its not the Tone stack PCB its the one with the tubes on it. Thats all i need. Now I am contributing very accurate INFO on the JTM1 so ask the SL5 dude to contribute a little on the SL5 since he has it right there with him lol. My INFO is 100% correct on every connection point for both JCM1 and JTM1. Plus i will share more that I see wrong in the JTM1 schematic but first tell dude i need those SL5 voltage readings.
If you're talkin about me, I have never had SL5. I just found schematic on Marshall-Roadhouse forum.

Peace

User avatar
Tech28
Information
Posts: 17
Joined: 20 May 2014, 05:51
Been thanked: 1 time

Post by Tech28 »

Matec wrote:Hello guys, I am happy to start posting here in this forum.

You can get some answers from me directly, if required. Most queries are already answered here. More details, (not many are left) I can provide.

Only one detail: The schema that I published is the JTM1 (with approximately 95% accuracy). There are components that are in this conversation are the JCM1. And on this amplifier, I do not guarantee 70% of the scheme, so I do not have correct arguments to discuss about it.

As the Thomas_h said, if someone has the amp, whatever the JCM1 or JTM1, and want to post more detailed images of some parts have not yet been photographed, would greatly help us all.

Thank you.

Matec.
Hi matic. I posted a picture where c15 belongs in the circuit, its a moded Jpeg pic which shows the correct connection. runs straight down to the 4M7. Well at least on the JCM1 it is indeed a 4M7. But on the JTM1 it might not be a 4M7 perhaps the signal is not as hot as the JCM1 is at that point. Cant really tell value in JTM1 pics camera's most of the time alter color if the lighting is not right. It's probably a 1M on the JTM1 where as for the JCM1 it is a 4M7. Depends how hot the signal is coming out the second stage. Shunting that is. Run one end of the 4M7 straight to the second filter cap gound. You can gound it wherever you like but the original PCB has it going straight to the second filter cap ground. You may find better tone with the 100n where it belongs,...... coming off the plate of V1 down to either a 1M or 4M7 shunted to ground one side and into the tonestack PCB. I see you do have it shunted coming out your tonestack PCB though. I never tried it but i wonder if it matters any Shunting on its way into the tonestack, or shunting on its way out would make any difference? Id shunt it on its way in maybe it would dry the tone a little if shunted on its way out after the tonestack? The signal. But you will like it more with the 100n coming off the plate in series into tonestack. No doubt about it

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Hello Tech28.

First, I want to thank you for making this topic very interesting.

I'm not fluent in English enough to get into a conversation about the details of the circuit. I could not exactly understand your arguments, and I apologize for that. :oops:

But I can read schematics perfectly. :hmmm:
You could demonstrate your point of view, doing their version of the circuit diagram that you found on the PCB.

Yes, I probably should have erred on several points of the circuit, by not having the amplifier at hand. So I appreciate it, and much, to see his version of the circuit.

Thank you.

Matec

User avatar
Thomas_H
Information
Posts: 46
Joined: 05 Mar 2013, 12:37
Has thanked: 3 times
Been thanked: 18 times

Post by Thomas_H »

If I understood it correctly, the thing is that C15 is between the V1B anode and the tonestack board, and not shunted to ground as a low pass filter, as shown.
C15 instead filters the DC voltage from the tonestack, I do this when I use the Big muff tone, but with the TMB tonestack there are already the 400V capacitors filtering the DC voltage from the potentiometers.

The 4M7 or 1M resistor is like a grid leak resistor, but in front of the tonestack, setting the output impedance of the previous or the next stage?
That changes the way the tonestack interacts in the circuit. It's like a maxed master volume before the tonestack. The first thing I will do is put a master volume in there, because for an apartment even 1W is enough.

Tech28 if you could help us with the tone board of the JCM1, that could explain if marshall used the traditional TMB values or not.

Cheers,
Thomas

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Hello

If I understand the fix that our friend Tech28 suggested; scheme would thus:

Image

The area inside the circle indicates the new positions of C15 and R36.
Is this correct?

This position is totally acceptable, and actually work as DC filter.
But would not cause significant change in sound.

Tech28
There are several components that I can not see the values​​. Could you, please, read their values ​​to us.

Thank you.

Matec

User avatar
oliver84
Information
Posts: 3
Joined: 17 Sep 2013, 16:33

Post by oliver84 »

Thomas_H, the schematics looks nice but the only problem is its reliability of the schematics as I am also looking for something to verify it and hopefully somebody on this forum will verify it.

User avatar
mrsmash23
Information
Posts: 4
Joined: 10 May 2013, 14:48

Post by mrsmash23 »

Hello guys,
@Matec: I noticed your post on brazilian forum from 20.september ( http://www.handmades.com.br/forum/index ... ic=5841.90 ). Is that verified version of your HTM1 project? Any tips on OT manufacturer?
Thanks in advance!

User avatar
okgb
Diode Debunker
Information
Posts: 768
Joined: 16 Mar 2010, 03:58
Has thanked: 226 times
Been thanked: 38 times

Post by okgb »

I've been meaning to build up a 1 watt [ or so ] amp, so thanks for all the posts
As there are lots of marshall schematics around to compare preamp styles, I'd say
it's the low watt pwr amp & psu unit that are more critical in this case.

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

mrsmash23

We're talking about this scheme? Image



Yes, the scheme in question is proven functional, and is the sound I most enjoyed in my project. The OT that I use, have the values ​​indicated in the scheme.
A tip I have is that the DC resistance of the primary , has less than 500ohms PP , even if that core gets a little bigger.

I should add that the amp is extremely stable, and the noise level is extremely low. The gain is very high, even with single pickups.

Currently , the circuit is JTM1, except for R9 and the full tone stack.

Cheers
Matec

User avatar
mavrim
Breadboard Brother
Information
Posts: 75
Joined: 07 Feb 2015, 01:16
Has thanked: 5 times
Been thanked: 25 times

Post by mavrim »

Thank you Mastec for providing these schematics! Could we get a higher quality schematic, such as PNG or another higher resolution format? JPG format makes it very hard to read values and pinouts. Thank you!

I am interested in the JCM 1 Watt schematic. I reverse engineered a Mahaffay Hi-Lo Plexi and a Little Lanilei 1/4 watt tube amp. I was surprised that both circuits were identical from what I saw. Here is a copy of the schematic I made.

Mahaffay Plexi 1/4 Watt tube Amp (no 33 watt solid state power amp, just pure tube circuitry)
Mahaffay_Quarter_Watt_Plexi_Tube_Amp.png
Mahaffay_Quarter_Watt_Plexi_Tube_Amp.png (10.31 KiB) Viewed 3485 times
This amp has that cranked up marshall sound, but lacks any clean. Single ended design uses a 25K reverb transformer. I built mine using a vintage stancor power transformer that puts out 125v x 2. In regards to output transformers, I was using 25K reverb transformers from Antique Radio Supply. I found cheaper Taiwan 14.5K transformers on ebay that actually sounded better with 4 ohm output connected to an 8 ohm speaker.

For the push pull transformer for the marshall 1 watt design, there is an ebay seller who produces custom transformers. Search Matt's Musical Supplies. I believe it is 22.5K input impedance to 4/8/16 ohm outputs.

User avatar
mavrim
Breadboard Brother
Information
Posts: 75
Joined: 07 Feb 2015, 01:16
Has thanked: 5 times
Been thanked: 25 times

Post by mavrim »

https://www.ebay.com/itm/OT2PP-USA-Push ... 259c1ea35b

https://www.ebay.com/itm/OT5PP-PLUS-USA ... 234682e881

This is the link to 22.5K push pull transformers for the 1 watt amp. He can do custom winding for 4/8, 8/16 or even 4/8/16 ohm outputs. Sellers name is: muzicalmatt

User avatar
mavrim
Breadboard Brother
Information
Posts: 75
Joined: 07 Feb 2015, 01:16
Has thanked: 5 times
Been thanked: 25 times

Post by mavrim »

Mastec, could you provide a DSN schematic file for use with tiny cad? I am starting to gain interest in your HTM 1 watt version.

Mastec, on the JCM 1 Watt schematic, is that a fet transistor at TR1 location? If so, I am trying to go all tube with no transistors. Even the boost appears to be diode/led clipping.

User avatar
Matec
Information
Posts: 32
Joined: 28 Feb 2014, 11:04
Has thanked: 5 times
Been thanked: 17 times

Post by Matec »

Hello mavrim.

First let's clarify the nickname: M-a-t-e-c. Just that. :wink:

Thank you for following my work.
There were many questions.

First things first.

I never put any scheme in .jpg format. All drawings are in .png. If any appear in this format is due to the forum mechanism. Try to open as few as the image in another tab.

Good job what you did with this Mahaffay Plexi. I personally do not know this amp, but from what you said should sound good. One thing the low power amps do not have is clean sound at high volumes. The JTM1 is so.

I'm still doing studies on the primary impedance of JTM1 the OT. :scratch:

In HTM1 it is 18k p-p. Works perfectly. But have made more than a test with the original OT and the impedance was in 10k pp. (Believe it or not.) Also has already been made a prototype with this impedance, and it worked perfectly well.

What is a DSN file? :roll:

Yes, TR1 is a MOS-Fet, and yes, you can use a valve there if you want.

As for the clipping with diodes and LED, well, just do not know how you could do. :hmmm:

Cheers

MATEC

User avatar
mavrim
Breadboard Brother
Information
Posts: 75
Joined: 07 Feb 2015, 01:16
Has thanked: 5 times
Been thanked: 25 times

Post by mavrim »

So sorry about the name typo! I guess I read it wrong and never checked. I have had people call me marvin instead of mavrim.

I am using a free cad program to draw schematic and the file happens to be a dsn extension. Was hoping to get your file and easily work on it in my program.

I was in the process of building a 1 watt tube head into a gutted marshall lead 12 chassis/head cabinet, but wasn't sure about what preamp circuit to use with the firefly output section. Since you started dissecting the JTM, I figure I will start from there and modify as needed. I will post details of the build.

Post Reply