I bought a Marshall MG50cfx amp to play heavier music on it. Looking at the schematic, it does not seem to be that much designed for heavy sound so thought if I can fix this.
The amp has a very weak power supply, I doubt filtering is adequate and will rework it. It is also not shielded well, neither is the transformer. At such gain levels I think it is important to have this reworked too.
The 4558 opamps have a gain of around 500 which I believe will not produce the sound I want so will tweak them to at least 1, 000. However, I thought that adding a tube buffer at the guitar input might produce the sound I want. The output is a TDA7293 which sounds pretty ok, although mounted on a micro heatsink (I have a spare one from an amp project and will replace it). I believe this is why they put a fan.
So, any good buffer designs made for high levels of distortion?
The amp has a very weak power supply, I doubt filtering is adequate and will rework it. It is also not shielded well, neither is the transformer. At such gain levels I think it is important to have this reworked too.
The 4558 opamps have a gain of around 500 which I believe will not produce the sound I want so will tweak them to at least 1, 000. However, I thought that adding a tube buffer at the guitar input might produce the sound I want. The output is a TDA7293 which sounds pretty ok, although mounted on a micro heatsink (I have a spare one from an amp project and will replace it). I believe this is why they put a fan.
So, any good buffer designs made for high levels of distortion?
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First, read everything Rob Robinette has to say. Particularly about safety, start up and trouble shooting
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First, read everything Rob Robinette has to say. Particularly about safety, start up and trouble shooting
</answer>
Thanks but:
- I have experience with tubes, have built several amps
- Have quality measurement equipment incl. a digital scope (hacked Rigol DS1074z unit)
- This guy`s website looks scary (the pictures section)
)
I was looking for a proven schematic of a highly distorting amp line driver that can be used in front of the Marshall guts. I will modify the Marshall as the mod will cost me like EUR30 and should boost its performance considerably but I do not like the hard distortion of solid state so wanted to add a tube overdrive and possibly isolate the solid state overdrive.
one question that arises concerns the computer in it - I believe it senses various voltages across the board, if I throw away the overdrive section, how do I fool it its fine and working?
- I have experience with tubes, have built several amps
- Have quality measurement equipment incl. a digital scope (hacked Rigol DS1074z unit)
- This guy`s website looks scary (the pictures section)
)I was looking for a proven schematic of a highly distorting amp line driver that can be used in front of the Marshall guts. I will modify the Marshall as the mod will cost me like EUR30 and should boost its performance considerably but I do not like the hard distortion of solid state so wanted to add a tube overdrive and possibly isolate the solid state overdrive.
one question that arises concerns the computer in it - I believe it senses various voltages across the board, if I throw away the overdrive section, how do I fool it its fine and working?
How do you know the filtering is a problem, how much will another power transformer give you? Will the chip be able to deliver any more performance with the new caps and transformer?
How will you double the gain of the IC's? What will that do for you and the sound you want to achieve? Why do you think the computer is sensing voltages across the board other than the effect send? How about just selling the amp and getting something better? How are you going to power the tube section?
Two options -
Proven: something like Fred Nachbaur's classic McTube Or steal the first stage from an amp you like (perhaps Soldano stages 2 & 3 or V1 from the JCM800 )
Real question: what do you consider "heavy". I.e. which amps would you like to emulate?
Post script: the MG50 preamp linked above seems to do a pretty sucky copy a marshall. Have a look at the RunOffGroove Thunderbird (sound clips here here and here ), particularly what's going on between the second and third op-amps
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Don´t "listen with your eyes"
Just plug a guitar and play.
Look what kind of sounds did Johan Segeborn pull out of his (he had the 100W version but it´s basically same sound):
YouTube
Power supply is adequate for a 50W amp.
That said, you can double main electrolytics and improve the sound, which will be tighter at higher volume or plain clipping (less residual ripple):
very little improvement beyond that.
The power transformer is adequate.
Not a real problem, since sensitive inputs are well away of the power transformer, at the opposite end of the chassis.
However, I thought that adding a tube buffer at the guitar input might produce the sound I want.
Maybe you can avoid that,there is more gain available.
yes, apparently a fan is cheaper than a heatsink.
Read above
Thanks a lot for your comments. Here`s the story and the plan:
I am total novice, bought my first guitar (an ESP LTD EX-50) and asked a friend for advice on what amp would be suitable for rock and metal. He said get a Marshall, and I did, only later to read tons of bad reviews online.
So what I thought of doing:
- Not touch the transformer, just shield it with a pan, it will cost me like EUR3 here
- electrolytic caps are way too low and I think this amp will be noisy. I will replace them with bigger ones - 6800uF instead othe 1000uF 63V ones, 2200uF ELNA (I have some laying around) instead of the op amp supply, may do a CRC there if there`s space (EUR12 in total for all including some 47uF ones on the headphone output which will be replaced with a larger value to push down the corner frequency)
- Replace the coupling caps with Wima MKS (around EUR11 here)
- shield the case (free, have tons of sticky aluminium foil)
- increase gain of the opamps by tweaking Rf/Ri values and the feedback cap if amp starts to oscillate to something that will produce a gain of 1000 or so
- replace the heatsink with a big one, I have it lying from a past project
Then I read tube amps are much better for what I will do and thought, since I`ve built tube amps before, why not modify the section, have lots of 6N23P tubes (ECC88) laying around since my main ampis a hybrid that uses an 6N23P input. So, thought I can force it into the non-linear part of the curve but have zero experience of making a tube distort badly and thats what I need some input on
Hope that helps!
I am total novice, bought my first guitar (an ESP LTD EX-50) and asked a friend for advice on what amp would be suitable for rock and metal. He said get a Marshall, and I did, only later to read tons of bad reviews online.
So what I thought of doing:
- Not touch the transformer, just shield it with a pan, it will cost me like EUR3 here
- electrolytic caps are way too low and I think this amp will be noisy. I will replace them with bigger ones - 6800uF instead othe 1000uF 63V ones, 2200uF ELNA (I have some laying around) instead of the op amp supply, may do a CRC there if there`s space (EUR12 in total for all including some 47uF ones on the headphone output which will be replaced with a larger value to push down the corner frequency)
- Replace the coupling caps with Wima MKS (around EUR11 here)
- shield the case (free, have tons of sticky aluminium foil)
- increase gain of the opamps by tweaking Rf/Ri values and the feedback cap if amp starts to oscillate to something that will produce a gain of 1000 or so
- replace the heatsink with a big one, I have it lying from a past project
Then I read tube amps are much better for what I will do and thought, since I`ve built tube amps before, why not modify the section, have lots of 6N23P tubes (ECC88) laying around since my main ampis a hybrid that uses an 6N23P input. So, thought I can force it into the non-linear part of the curve but have zero experience of making a tube distort badly and thats what I need some input on
Hope that helps!
Thanks for the schematic Printer2
Mario - my 2 cents worth of options;
1. For Harder distortion within the amp I would try silicon diodes (anti parallel) between the junction of R8 and R9/C11. (Marshall has been known to do this even in their tube amps - see the Slash signature)
2. This is also where I would graft in a 6N23P if that is what you want to try - a lot of work, results not guaranteed, but diy fun.
3. As Thoglette suggested, a real McTube or Butler tubedriver type circuit up front.
Have fun.
Mario - my 2 cents worth of options;
1. For Harder distortion within the amp I would try silicon diodes (anti parallel) between the junction of R8 and R9/C11. (Marshall has been known to do this even in their tube amps - see the Slash signature)
2. This is also where I would graft in a 6N23P if that is what you want to try - a lot of work, results not guaranteed, but diy fun.
3. As Thoglette suggested, a real McTube or Butler tubedriver type circuit up front.
Have fun.
Do you want to play the amplifier? Or play the guitar?
You can make a LOT of GREAT music with that amp.
If you want to emulate your particular Guitar God, the amp is a small part of the sound.
This is a very real problem to consider. One has only so many precious hours of free time, so where should one spend it?
For myself, my answer is to try to spend it on whatever will give me the most happiness. Sometimes that means spending time with my wife, sometimes practising or playing guitar, sometimes building or designing electronics, sometimes going for a walk, reading a book, or entertaining the cat with a piece of string.
So you have a conundrum to ponder: is learning to play guitar is a higher priority for you than tinkering with an already good-enough guitar amp?
I keep one quick-n-dirty DIY solid-state guitar amp by the living room couch, ready for use at a moments notice. It's little more than a cheap class-D power amp module, a couple of thift-store boombox speakers glued together, and a guitar pedal or two to act as a preamp.
It is not a great guitar amp, but it does work, and I find I pick up my guitar and play or practise a lot more often since I built it, because this amp is always ready and waiting.
Meantime, I have a tonne of tube amp ideas, as well as a working (but unfinished) DIY tube guitar amp, plus bits and pieces I built towards another DIY tube guitar amp build. I don't see any of those as a waste of time, but neither are they furthering my development as a guitarist much...it is the cheap and nasty solid-state amp that is my constant practise companion.
-Gnobuddy
You still haven't told us what amplifiers you consider "heavy".
(I presume you've got a guitar with dual or triple humbuckers?)
And I stand behind my previous recommendations (See post #8)
Meanwhile,
a) Replace LED 4 with a small signal schotkey
b) Replace R39 and C21 with the 1N5711/1N4148 and resistor network from the Thunderbird
That explains the Marshall recommendation. Or perhaps Mesa Boogie MkII
The hard option is to build in the first two tubes of the JCM 800 and then feed that into your existing tone stack.
The slightly easier option would be to build it as a micro amp and then feed that into your clean input.
Here's how to do the 5F6A+12ax7 aka JTM-45. To do the JCM-800 would take one more (1/2) valve but the idea's clear enough. You could do a Mesa Boogie but they're more work and have more volts (400+) in the preamp.bb
You've also got to remember that the guitar sound on the records results from multiple tracks taken from different places in the room (and possibly several amps), and stadiums have the same effect. So you might want a touch of reverb or similar to get the same feel in the bedroom/practice room.
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