Calling all electronic gurus

Crafty

So about 18 month ago i bought a valvestate s80 from this forum. What a lovely thing it was.
Unfortunately she played her last few notes, ☹
I had the head portion in, but all the electronics is fried. I tried myself to fix as well, and she is done. Between me and the experts, it is unanimous.
That said, i'm gong to create new life...
40 watt chipamp is waiting to be built this december.
I need some advice on the preamp sections.
Im planning a preamp based on 12ax7 tubes
Any one got diagrams and or experience? i'm still stuggelng to understand the dynamics.
Do i have 3 stages? Ie, overdrive feeds into preamp, feeds into power amp.
Or do i just have a pre amp with clipping high gain into the power amp?
Then i want 4 effects in series with a button i can bypass or engage.
Chorus/delay
Overdrive
Full on heavy distortion.
Wah (i understand this is tricky, since it is a digital effect)

I'm hoping to tackle this in the holiday season from the 22nd onwards.
Any one with experience/pointers/diagram etc?
Need a basic design before then so that i can have the transformer wound to specs, and source the parts before every one closes.
The power amp parts i have already. I can choose between 40watt chipamp, or duel channel 120watt sold state based on naim nap 200.
I need help on the pre and effects stages.

Crafty

Ps, all of this will be built into the cassis of the s80, along with the 2x 40 watt 12" drivers

GuitarDoge

Please forgive as I have no idea why I am still awake and may not be making much sense.

There is plenty of information and schematics for building full valve amps online, however very little for solid state. I think this has something to do with cost of R&D that companies put into producing solid state amps that model valves compared to what the average person can do.

Solid state guitar amps need to model the tone of a valve and it is very tricky using straightforward solid state components to achieve this well (components that could be used to make hifi amps.)

Your plan could work by using a valve preamp to give it that "proper tone" and then amplifying that with a solid state power amp, however you may be missing many parts of what gives a guitar amp good tone.

Overdrive can be produced by clipping op amps found in overdrive and distortion effect pedals etc, clipping through the preamp section(12ax7s work well for that) or the clipping of a valve power section. Putting a tubescreamer in front of an already cranked valve amp to boost it and get more gain is essentially diodes boosting the signal and clipping a signal then boosted and clipped more by valves. Therefore you don't need to have built in diode overdrive.

As for effects, it might be worth putting a switchable effects loop in between the pre and power stage(schematics can be found for this, using valves and solid state components) and then building your own pedals and using existing pedals to your liking, not limiting your options. There are many, many pedal schematics.

Of course, all of this requires a very decent knowledge of electronics to mix valve and solid state. My best suggestion is if you can, build a full valve amp with that guaranteed tone. However research as much as possible and see what can be done with solid state power amps.

P.S. this is coming from someone who has never built an amp or effect, however has built an audio amp and is studying electrical engineering.

Gearhead

GuitarDoge wrote: My best suggestion is if you can, build a full valve amp with that guaranteed tone.

+1. The step from building a 12AX7 preamp section to a full valve amp is small as long as you stick to EL84 or 6V6; they run at similar voltages to the preamp. Once you start talking EL34 or 6L6 you get the 400+ volts and things get hectic. Don't worry about power, 14-18W is as loud as the VS80 and if you want to go louder you add two more output valves to double up.

This S80 is the 2x12 combo, right? Plenty of space to put two trannies and a choke onto the chassis and still have a full size turret board as well.

The first step to take is to look at what tone you like. From the sound of your comments on the Marshall's tone, you should go for an 18Watt, for which there is plenty of knowledge available on the net as well as on this forum. Then again, you may actually like American overdrive better and opt for a 2x6V6 amp.

Crafty

I'm fairly comfortable with electronics. Except when I do things like putting a power supply board with 110v charged caps on my lap. I tend to talk very dirty then! half a farad takes some time to drain. plenty french escaped my mouth there.
This is my previous audio project.
http://www.guitarforum.co.za/amps-speakers-and-valves/diy-projects/msg231905/#msg231905
Allas, my budget is a lot smaller this time.
I think I will stick with the solid state and valve pre-amp with a gain control in order to induce clipping for now. Hopefully I can get away by spending not more than about 2K. When budget improves, I will try and get my hands on the mars JTM45 kit. Maybe even the smaller one. Scared that 30watts will obliterate the drivers of the S80.

Dave

Hi Crafty, it is very unusual to have an amp such as a Marshall unfixable, if you are based in Jhb and the amp has valves, talk to Bill lange on 0837970346

Crafty

Well the valve portion works fine.
The valve state is a hybrid amp. Thus valve pre-amp, and solid state power amp. However, it seems marshal has included another stage in the middle that is also solid state. It is the power circuit that popped. The chip itself was glowing red, then cracked. This was due to a zener failure just before that. I replaced the chip, and the zeners, but too much other portions was blown as well. Also that chip is very rare. It is no longer in production, and I managed to track one down in pretoria. They sold me their last one. Doubt I will find another one.

This is the pre-amp I'm going to build now.
http://www.instructables.com/id/Guitar-Tube-Pre-Amp/

That will feed into the 50 watt gainclone chipamp.

Gearhead

If you must... Good info on hybrids and gainclones to be had on diyaudio.com, but you probably found them already.

Crafty

Gearhead wrote: If you must... Good info on hybrids and gainclones to be had on diyaudio.com, but you probably found them already.

Haha, power stage is built ?
Tested it on some mordaunt short speakers and sounds great. Very clean, no white noise even on max vol.
very true to the original signal. Maybe slightly bright. So all character will have to be imposed from the pre. I think i will have to include some tone controls as well.

Attila

Ear you go ..... some basics to gain an understanding..... got lots more in-depth stuff... but this will give you the basics.....

https://www.dropbox.com/s/fcxbptgzc1254hj/Tube%20Amp%20Overview.pdf?dl=0

The whole enchilada.....

https://www.dropbox.com/s/1njp7hqgsuwc6e5/Designing%20Valve%20Amplifiers.pdf?dl=0

Crafty

Excellent documents! Thanks a mil!!
Much more info in there than I will ever need. Fantastic resource, and great reference guide when playing with valves.

I bought a 12ax7 from mr valve, and will also get the original EC(something) back that was in my busted marshal amp. Seems like this project is taking off soon ?
Will be curious to compare the sound from the ElectroHarmonix 12AX7 with the original marshal valve.

sharonzaz

Riaan Diedericks

find him on facebook.
drummer and electronic wiz.
not much that he cant fix.

https://www.facebook.com/riaan.diedericks.1?fref=ts