a lot of questions regarding a 2 channel amp... help needed!

[Rickey_Dee]

hey folks!

haven't been here for a long time, now i want to build a new amp, basically a "usual suspect" when i take a look at some 2-channel amps (voodoo, cae, etc...). for the clean i'm thinking of a fender blackface type, the other - oh surprise - a 2203 (i think about a 4 gain stager, with or without CF, haven't decided yet, maybe i have to try what i like best. and each channel should have his seperate controls (bass, mid, treble, gain, master) so far so good.

the main problem here is, because i never had anything to do with 2-channel amps, i don't really know what part of the fender blackface schematic i need here. the preamp and the tone stack, right? also, if i want the ability to add some dirt to the clean channel and think about adding a gain-pot here too, where do i put the gain in the path, and should i add here one more preamp tube? as far as i know - but sure i can be wrong, the input stage and the tone stack use one preamp tube, right?

also, because both channels should have their own volume, i want to put a ppimv there too as a "global master", and i want to put it on the frontpanel. is that ok? i have to mention that i will drill the front holes on the chassis myself, and the controls of the channels will be 2-rows. so from left to right i want to have the following controls: presence - resonance - ppimv master - then 2 rows of bass - mid - treble - gain - volume - and the input jack (a single jack, just the "high" input) of course.

so, and the channels should be footswitchable... jerry recommended me this: http://skipzcircuits.com/CHSW.html" onclick="window.open(this.href);return false;

the point i still don't get, because i don't know s*** about this, where do i split the signal? and where do i wire the kit to the board then? somewhere after the tonestack of the 2203 circuit i GUESS...

i wanted to add a twin reverb layout, but the file is too big, i'll try to add it later. would be great if someone could help me there, showing me what i need from the twin reverb layout and where to implement this and the switching kit into the 2203 circuit... if i also need more tubes, no problem, i can add holes if desired. i just want to make most things clear before adding parts...

thanks a lot so far!! i really hope someone could chime in and help me to realise this. i know, i don't really have a lot of knowledge, but i'm open to learn a lot of things, and this is something i really wanna do!!

rickey

[Thiez]

wow... uhm when i see your questions i'm a bit in a doubt if this project isn't a bit to much for you right now. You allready have some experience on amp building?

But nothing is impossible. soooo lets give it a try. It would always be a compromise. You can't build a marshall and a fender in one amp. Then you have to got two maintrafo's, two outputs, two poweramp sections, two preamps etc etc.
But you can build a marshall 2203 preamp and a fender preamp and then you got to choose between a marshall or a fender powersection.
I hope you can read schematics. This is a schematic of the SLO clone forum. http://www.slocloneforums.com/download/file.php?id=1576" onclick="window.open(this.href);return false;
On page 3 you have the preamp section. It's just to give you an idea to what you can do. It quiet a bit like what you are looking for. Leave the 3rd channel. Just have a look at the first and second channel. You have an input. The input is split to channel one and two. Channel one is a bit fender twin like. An input stage -> tonestack -> gainstage. Channel two is quiet marshally build up. Inputstage -> gainstage -> cathode follower -> tonestack. So basicly this schematic is a verry good base to start you amp from. I hope this gives you an idea of your build.
After the tonestacks you see the channel switching. In this schematic its a ON-ON switch that chooses between signal->preamp or signal->ground. And the other channel you do it vice versa. So when channel one is on, the signal of channel one goes to the powersection and the signal of channel to goes to ground. If you use ON-OFF switches you have to put two contact in. On every channel a NO in the signal chain and an NC to ground.

I'll get a mastervolume after the tonestack in both channels. this way you can compensate the volume differences of the preamps.

After this you go to the PI and powersection.

[Chris_P]

Check out the schematic I posted in the thread 'Parallel, switchable - volumes/Gain' in this forum. Checking out a whole bunch of schematics has helped me quite a bit.

That sounds like a very ambitious build, I just finshed my first build a month or 2 ago. It started out on paper as a 4 gainstager with, footswitchable 4th stage and a volume boost, I too laid out the chassis myself. I learnt SO much building that amp. By the time it came to installing the relays & have the faceplates made up I decided to just do a revised model of the whole amp. Dont get me wrong, its a working amp, sounds great.. I had a great time building it & Im ready to make the MKII version now, 2 months on. But yeh, just get used to calling it a 'prototype'.. by the time you've built it & tweaked it, you might figure out a way to build it better .

Chris.

[Thiez]

Just noticed that you can't see the schematic without register. I have put in on my dropbox.
ALL CREDITS GO TO THE GUYS ON SLOCLONE FORUM. Really nice and technical people there.
http://db.tt/8P8fu1fl" onclick="window.open(this.href);return false;

[Rickey_Dee]

Thanks a lot guys for all the infos!

i already registered on the slo-forum and checked the schematic, and it opened my eyes a bit, altough i'm not THAT good in reading schematics, but i can see what you're talkin about.

so i'm pretty busy until monday, so let's talk along then, but once again, thank you very very much for your informations, i really appreciate this!!

Rickey

[Rickey_Dee]

@chris: yeah, i call it a "prototype" too. i already built an amp couple years ago, a 50w lead. i was thinking about tweaking this one, but i have a 100w chassis here, so... and i already ordered most parts for the amp, so i definitely want to do this, even if it takes a lot more time than the 50w.

ok, thanks again!!

Rickey

[Thiez]

http://music-electronics-forum.com/atta ... 2-hth-.jpg" onclick="window.open(this.href);return false;

This schematic came by on the marshall forum. Maybe it is usefull for you. Bit the same project as you are planning to do, only they added a xtc kinda channel as 3rd.
Don't know if this schematic is tested btw, so it's just a guide you need to check yourself.

[Rickey_Dee]

thanks a lot!!

there are some things i still need to figure out, but this is more because of my unknowledge when it comes to electrical stuff... i'll try to find these out for myself before i start bugging someone here.

but thanks, the schematic seems is a very good starting point for me, except that i will do a 4-gain-stage 800 channel.

i am really not THAT good in reading schematics, i always have a layout here to see what goes where to understand it,but it get's slowly better... so i guess it will be best if i try to make a layout and post it and ask if this will work... is there a program where i can do a layout that will look like one of steve's (sdm's) layouts?

anyway, thanks so far!!

rickey

[Rickey_Dee]

@chris: the footswitchable 4th gainstage is also interesting to me, and how did you do the volume boost?

thanks
rickey

[Thiez]

A schematic is easier to see whats going on in an amp. A layout is easy for building your amp. So if you put a layout together it's best to first make yourself a schematic. So you have both. Easy for debugging etc.

For volume boost you can aslo add a second mastervolume parallel with the existing one and switch between them. This way you have a variable volume 'boost'. You can also add a resistor between the mastervolume and ground which you switch on and off. This way you change the 'voltage divider' of the mastervolume and boost the volume up.