Matamp/Electric amp schematics

[Nutjob]

thanks Nutjob!, Ill give it a shot this winter, thanks for the links. I read all your posts but are there any other hurdles you've discovered that I need to watch for?

Make sure you use a large enough chassis. This is KEY. I discovered in the end, that the oscillation I had was due to things being too close. I had some chassis made up to the standard Orange OR120 size (~19"x7"x3" i think) which weren't deep enough (front to back). I know the Electrics and later Matamps are 19"x10"x3" or something like that. Allowing for spacing the output transformer further from the input, as well as the bias lines and other HT lines further from the signal lines. I have already transplanted everything from the first clone I built into a larger chassis. Just need to build a deeper cab for it now. The old chassis will become home to a Matamp GT120 clone.

[rocket88]

saw the clips on youtube and it looks and sounds incredible. i was curious thought, when i look at the schematic you drew up the bias taps have 2 resistors missing. one says 10k??? and to the right of it there's just ???, what value should they be? i really want to give this a shot, and dont want to mess it up. lol

[Nutjob]

saw the clips on youtube and it looks and sounds incredible. i was curious thought, when i look at the schematic you drew up the bias taps have 2 resistors missing. one says 10k??? and to the right of it there's just ???, what value should they be? i really want to give this a shot, and dont want to mess it up. lol

Being that I was unsure of the actual resistor values and bias tap voltages, I had no way to calculate what the actual numbers are, I sorta just left that up to interpretation or the builder's discretion. Notice the bias CT is grounded as well as the bridge rectifier, as far as I know, this would double the voltage from the bias taps. I dont think this is the case in the stock amp or I just dont remember, so ignore that CT to ground. In my build, my PT has a 60V bias tap, I just used what I put in the schematic and and omitted the ??? resistor. It biases up just fine. The bias adjustment swings pretty wide on the pots in mine, so if you feel like doing the math, you can tighten it up if you choose to. I use locking pots for bias, so its not a big deal to me.

If you have no bias tap, you can always run your bias from one leg of the secondary before your rectifier, with, say a 39K resistor to knock it down. see below

[rocket88]

Being that I was unsure of the actual resistor values and bias tap voltages, I had no way to calculate what the actual numbers are, I sorta just left that up to interpretation or the builder's discretion. Notice the bias CT is grounded as well as the bridge rectifier, as far as I know, this would double the voltage from the bias taps. I dont think this is the case in the stock amp or I just dont remember, so ignore that CT to ground. In my build, my PT has a 60V bias tap, I just used what I put in the schematic and and omitted the ??? resistor. It biases up just fine. The bias adjustment swings pretty wide on the pots in mine, so if you feel like doing the math, you can tighten it up if you choose to. I use locking pots for bias, so its not a big deal to me.

If you have no bias tap, you can always run your bias from one leg of the secondary before your rectifier, with, say a 39K resistor to knock it down. see below
[ATTACH=CONFIG]22851[/ATTACH]
[ATTACH=CONFIG]22850[/ATTACH]

Cool, thanks for the info. I really want to build this amp, and it will be my first build, so I want to make sure whatever I do is correct. I probably wont be ready to do it for awhile, I think I have a lot more to learn. Any suggestions to find parts, help, tips, etc. You seem like you have tons of knowledge, but I'd feel bad if I keep asking you. lol.

I don't get what the first picture is. I don't see the a standby or power switch on the schematic itself. Btw, I don't see what pots you have for the bias adjustment on the schematic or the type of 6 position switch.

[Beefcake]

First of all Nutjob, I'd like to thank you for getting this schematic out there. I recently built one of these clones and after getting the bugs out, it sounds absolutely fantastic.

I have a couple of remarks on the schematic though.

• The rectifier in the main power supply seems to be wired incorrectly.
• The bias supply, as it is shown in the schematic, would give you a positive voltage, instead of the required negative one.
• I'm not sure about this, but shouldn't the wiper of the Boost pot be wired to the capacitor?

Concerning the main power supply, I think the ground needs to be wired to the rectifier while the connection to the two cap cans needs to come from the middle tap. I did some simulations in multisim and wired up my amp this way. If you wire it like in the original schematic, you only get half the required voltage. Here's how I wired it.



Small note, there is no voltage doubler in this power supply. The increase in voltage is just because the output voltage of a bridge rectifier is the input voltage multiplied by the square root of 2.

To fix the bias supply, you have to reverse all the diodes in the rectifier and reverse the polarity on the caps. If you wire it up like in the original, you're going to red plate your power tubes almost as soon as you power it up (that's what it did for me before I found the issue :-p).



Another small note, this bias supply expects a 50V winding. If someone wants to use a power supply with a 100V bias tap (Hammond 290HX in my case, you'll have to change the values of the resistors.

I really appreciate all the work you put into this, I wouldn't have been able to build this thing without it.

I took the liberty of recording a small sample of mine trying to replicate the Dopesmoker tone using nothing but this amp and a guitar.

[xjbear]

You are the man thanks for taking an interest in this thread, it's been on my build list for a few months and haven't got around to it yet, you have saved me some trouble for sure! What speaker(s) and mic did u record the clip with?

[Beefcake]

You are the man thanks for taking an interest in this thread, it's been on my build list for a few months and haven't got around to it yet, you have saved me some trouble for sure! What speaker(s) and mic did u record the clip with?

I used a Marshall JCM 900 1960B cab with standard Celestion G12T-75 speakers. The mic used was an old vintage Shure, rewired for using XLR, that looks a lot like an SM57 but is not labelled as such.

[xjbear]

I have the exact straight cab, cool I'm glad that gives me a tone reference

[Beefcake]

I don't get the obsession that Marshall fans seems to have with the angled cabs, the straights seem to sound a lot better to my ears.

[xjbear]

Your right on, the bottom cabs are fuller sounding and have sweeter mids. I have a 900 1960b and a 2000 1960bv. I glued some 4"x 3/4" birch bracing inside of the four sides and it made the lows even more firm

[xjbear]

I gotta build it to help drive this mess

Oops sideways? Ill fix it later

[Nutjob]

Apologies for all the errors. I have been aware of them for a long time, just have had no time to make corrections. Although I can confirm from the photos of the original unit, that the secondary PT center tap indeed goes between the cap cans, and the rectifier grounds to chassis. I'll get on that right now.

First of all Nutjob, I'd like to thank you for getting this schematic out there. I recently built one of these clones and after getting the bugs out, it sounds absolutely fantastic.

I have a couple of remarks on the schematic though.

• The rectifier in the main power supply seems to be wired incorrectly.
• The bias supply, as it is shown in the schematic, would give you a positive voltage, instead of the required negative one.
• I'm not sure about this, but shouldn't the wiper of the Boost pot be wired to the capacitor?

Concerning the main power supply, I think the ground needs to be wired to the rectifier while the connection to the two cap cans needs to come from the middle tap. I did some simulations in multisim and wired up my amp this way. If you wire it like in the original schematic, you only get half the required voltage. Here's how I wired it.



Small note, there is no voltage doubler in this power supply. The increase in voltage is just because the output voltage of a bridge rectifier is the input voltage multiplied by the square root of 2.

To fix the bias supply, you have to reverse all the diodes in the rectifier and reverse the polarity on the caps. If you wire it up like in the original, you're going to red plate your power tubes almost as soon as you power it up (that's what it did for me before I found the issue :-p).



Another small note, this bias supply expects a 50V winding. If someone wants to use a power supply with a 100V bias tap (Hammond 290HX in my case, you'll have to change the values of the resistors.

I really appreciate all the work you put into this, I wouldn't have been able to build this thing without it.

I took the liberty of recording a small sample of mine trying to replicate the Dopesmoker tone using nothing but this amp and a guitar.

[Nutjob]

Here we go. Boost control is correct here. Actually, not. the one under Attatched Thumbnails is incorrect:

[Nutjob]

I wish you could delete your posts on this forum. This is the correct one

[Beefcake]

I wish you could delete your posts on this forum. This is the correct one [ATTACH=CONFIG]25595[/ATTACH]

Seems like it's still the same boost control wiring as earlier?