marshall 8020,8040

[ghoshsubha444@gmail.com]

Hello,

I am new to this site. actually I am trying to build a solid state guitar amp of marshall type. do marshall valvestate 8020,8040 worth trying? 8040 even have a tube. i never worked with tube. so 8040 is bit harder for me.

basically i need this: Guitar to amp(clean and distortion channel) --fx loop-- power amp. so i need to drop the reverb circuit.

http://www.drtube.com/schematics/marshall/8020.pdf
http://www.drtube.com/schematics/marshall/8040-iss8.pdf

Thanks

[J M Fahey]

Start by building the Marshall Lead 12 preamp , coupled to any power amp you like , from 10W to 100W.
Killer sound.

Have a good reading of this thread:
http://www.ssguitar.com/index.php?topic=2749.0

To show that I do what I preach, in the end there's a small demo of an amp I built long ago, using such combination.
And, no tubes needed, of course, to get excellent sound.

[ghoshsubha444@gmail.com]

Start by building the Marshall Lead 12 preamp , coupled to any power amp you like , from 10W to 100W.
Killer sound.

Have a good reading of this thread:
http://www.ssguitar.com/index.php?topic=2749.0

To show that I do what I preach, in the end there's a small demo of an amp I built long ago, using such combination.
And, no tubes needed, of course, to get excellent sound.

Hello Mr Fahey,
Thanks for your reply.. Yea I have checked your post. Is that you playing the guitar??Very Cool

By the way this is the youtube link for 8020:
http://www.youtube.com/watch?v=eQyvi8iVT2w
Sound good to me. Though a bit complex than lead 12. Whats your thought? If you please verify 8020 to see if at all the schematic is promising or if there any flaws. after confirmation I will redraw the circuit in circuit maker and again will post here.

another thing to ask. 8020 schematic contains 1875power amp . practically what I was looking for.

[J M Fahey]

1) no, I don't play
2) didn't like the 8020 very much.
The distorted channel has no tone controls!!
Only Contour and presence.
In fact, it is a distortion pedal built "fixed" into an amp (so far, not bad) *BUT* (and that's a big "but") , it goes straight to the power amp !!!
Normally that is poor practice, no flexibility at all.
Usually sound is either muddy or fuzzy.
I'd rather build a normal channel, anyone you like, and stick some distortion in front of it, the "regular" way.
3) it uses hard to find M5201, a proprietary "TL072 with built in switching and logic"
4) and you'll need to design amd build a quite complex PCB.
5) keep looking around, you will find other more practical designs to guide you.
Even older SS Marshalls.
Try to avoid specialized ICs, prefer what uses, say, TL072, switch with Fets or transistors or standard very common switchers, such as CD4016/4066/4053 , etc.
And I'd split the PCB in a couple functional blocks, so later it's easier to "mix and match".
Say:
PSU (4 diodes+2 big caps + resistors/zeners for +/-15V)
Power (1875/TDA2050)
Clean preamp. may be the Lead 12 which can also sound distorted or something like Rodd Elliott's "Guitar Preamp" which is a "clean Fendery" one.
Distortion: your choice, from an MXR Dist+ to, say, a JackHammer .

[ghoshsubha444@gmail.com]

Ok Mr Fahey, Let me try firstly Rod Elliot project 27. But please clear certain facts--

some quotes from rod's site

1.
"A photo of the Revision-A preamp is shown below. You'll see that there are two dual opamps, but the schematic only shows one. This is the main part of the Rev-A update - the output section now has gain (which is easily selected), and a better buffered low output impedance. The remainder of the circuit is unchanged. Full details of the new version are available on the secure site for those who purchase the PCBs."

2.
"The diode network at the output is designed to allow the preamp to generate a "soft" clipping characteristic when the volume is turned up. Because of the diode clipping, the power amp needs to have an input sensitivity of about 750mV for full output, otherwise it will not be possible to get full power even with the Master gain control at the maximum setting. "

now my questions...

1. The power amp mentioned there is transistor based. so can i directly use preamp out to lm1875/lm3875 etc?
or any interface is required?
2. same thing about if i add fx loop, fx loop in will directly goes to power amp in?
3. I see every commercial amp use +-15v supply for preamp compared to 9v for pedals. What is the benefit of using bipolar supply?
4.many people suggests ROG projects. Now are they meant to be used as a preamp? though they use 9 v supply.
5. i have earlier checked with my friends amp that adding dist pedal infront of clean channel sound thin.

[J M Fahey]

"A photo of the Revision-A preamp is shown below. You'll see that there are two dual opamps, but the schematic only shows one. This is the main part of the Rev-A update - the output section now has gain (which is easily selected), and a better buffered low output impedance. The remainder of the circuit is unchanged. Full details of the new version are available on the secure site for those who purchase the PCBs."

The schematic he *shows* is fine and the one I'm referring to.
Simple and elegant.
Rodd redesigned and improved it, fine with me, it's *his* design after all.
But the "public" one is good

"The diode network at the output is designed to allow the preamp to generate a "soft" clipping characteristic when the volume is turned up. Because of the diode clipping, the power amp needs to have an input sensitivity of about 750mV for full output, otherwise it will not be possible to get full power even with the Master gain control at the maximum setting. "

It's not a very good clipper, but "better than nothing".
You can skip it, or add a switch to disable it at will.

1. The power amp mentioned there is transistor based. so can i directly use preamp out to lm1875/lm3875 etc?

Yes.

or any interface is required?

wouldn't hurt, but not necessary.

2. same thing about if i add fx loop, fx loop in will directly goes to power amp in?

same as above

3. I see every commercial amp use +-15v supply for preamp compared to 9v for pedals. What is the benefit of using bipolar supply?

If available, much simpler biasing and coupling, more headroom.

4.many people suggests ROG projects.

Well, not me.
In general, I find them quite poor "design", if that word can be applied at all.

Now are they meant to be used as a preamp? though they use 9 v supply.

I think thet are meant to be used as pedals.
yet, they can drive a sensitive "power amp" , such as an LM386 .

5. i have earlier checked with my friends amp that adding dist pedal infront of clean channel sound thin.

It depends on the amp.
Most pedals driving an entry level, 10W with 6" speaker or 15W 8" speaker, small cabinet, open back, *will* sound thin.
Yet, a horrible buzzy Fuzz Face, driving 3 to 8 100W Marshall stacks, with 8x12" Celestions each, can be chest thumping
Jus ask Jimi Hendrox.

That said, the Metal Zone pedal has *monster* bass boost and mid cut, to sound "big" with little combos.
Yet hardly a Pro will use it, for the same reason; with a "real" amp it becomes too artificial sounding.