a little OT - Randall amps schematics?

[Marcos - Munky]

I'm looking for the Randall RG-100 and Century 200 schematics. I did a search in Google, but I didn't find nothing. Anybody have them?

[space_ryerson]

Which generation? I have some of them, since I own a bunch of Randalls. I got them the easy way,;I called them! If you call them up and ask, they will give them to you. They are very helpful in that manner.

IMO, the old Randalls are way better than the newer ones. (pre-washburn).

[space_ryerson]

I should also mention that I have 3 randalls from 1987: a rg-80se, and rg-100es, and a rg-200ht (I think that's what it's called. It's a rackmounted head with DI and XLR outs). All three share the same preamp circuits, and have different powe sections. All three sound fairly different. I'm guessing the rg-80 was modded, because it has a lot more guts to the distortion than the other 2, and has that dimebag razor-ness down pat, whereas the other 2 sound more warm. One of these days, I'm going to have to sit down and go through them all with a fine-tooth comb to find out where the difference lies.

[Marcos - Munky]

If you can share the schematics with me, I will be thankful. I just want to take a look in the preamp/distortion part of them. My e-mail is diygescorp@yahoo.com.br.

[Davide]

If you can share the schematics with me, I will be thankful. I just want to take a look in the preamp/distortion part of them. My e-mail is diygescorp@yahoo.com.br.

Me too   !
bardon@libero.it

:wink:  thanks

[space_ryerson]

Schematic sent.

I sent the schematic for the 1980's rg-100/rg-80 amps, which I feel is the best for what you are going after. It was faxed to me on two pages, so there is a split, cutting off a little bit. I will check later to see what got cut off.
I imagine you want to build this into a distortion pedal, so you should eliminate the 'sustain boost' switch, and leave those diodes connected to it grounded. (That's the tone you are after). Also, I think a lot of what makes this circuit have that dimebag/edge like tone is the eq, so I would include the tone stack and the presence in the preamp you would build. I need to check the amp that I have that sounds the best to see if it differs from the schematic.

This actually doesn't like it will be too hard to adapt. Let me know how it goes, since I'm interested in whatever you guys come up with!

[Marcos - Munky]

Thanks a lot. I will take a good look in the schematic. Dimebag used a Furman PQ3 Parametric EQ, and I believe that the heavy sound comes from this EQ, not the amp tone stack, but we need a tone stack in a preamp .

EDIT: another question, which is the channel with more gain?

[space_ryerson]

you want the 'red' channel with the sustain boost on.

[Marcos - Munky]

Thanks. Did you received my e-mail about the parts value?

[space_ryerson]

Yes. I haven't had a chance to open up the amp yet and have a look, but I will a little later.

[Distortone]

I'm interested in any Randall schematic, especially for the older amps. I used to play through the RG-80 some 20+ years ago. "Space" if you wouldn't mind I would love to take a look.

Thanks so much.

Bill Powell

fretbrdwiz@aol.com

[Marcos - Munky]

The parts value aren't readable in the original schematic that you got? I redrew the schematic, just need to put the parts value and build it. After finish the schematic, I will put it in my site, so everybody who have interest in it can build your own preamp. And Bill, I sent the schematic for you.

[space_ryerson]

The schematic I have was faxed to me on two pages, so what is cut off on the scan, is cut off on the fax. I'll try to take a look at the amps later tonight.

I was looking at the schematic, and it said that either tis-58's or 2n5484's can be used for the FETs. I wonder if that contributes to the change in tone for my amps.

[Marcos - Munky]

Check if you didn't put one page a little above the other when you scanned them.

[space_ryerson]

I'm certain I didn't overlap them. When Randall faxed them, those components were cut off. I knew about it when I received them, and had Randall fax it again; but it had the same problem. Apparently, all they have are 8.5x11 copies of the schematics, and even they are cut off. I have no idea why they didn't have a full schematic.

I have been meaning to correct the schematic since then (about 3 years ago....I'm a little bad at getting to these things :lol:). I've had the amps open since then, but I always seem to forget to go locate those couple of components.

I'll have a look tonight.

[adgators89]

I love that tone those amps have.  I used to have one when I first started playing - being a total Pantera / Dimebag fan.  That's actually what got me into playing guitar.  anyway. once the corrected schematic is up on your site, I would love to take a look at it.  I'm fairly new here, and doubt I could build anything out of it yet, but it would be something to shoot for.  Thanks guys for sharing!

[space_ryerson]

Ok, I opened up two of the Randalls to have a look at the cut off components, and what could cause the change in tone between the two amps, since they have an identical PCB. They were made within three months of each other, but have slightly different component brands.

I decided to post the schematic here for everyone.

The two resistors after the tone stack that were cut off in the schematic (r13, r14) were both 1m. The cap (c12)seems to be .005, but it isn't marked clearly. It says '502 1kv' on the better sounding randall, and '472k yp5 1kv' in the other one. I have a dmm, but I don't know how to test capacitance yet, as I am a beginner. (don't worry, I do know how to drain the filter caps, and wear rubber gloves and boots).
I'm assuming that they are two slightly cap values. I should also mention if that is so, then the cap values vary between the two amps on the caps that connect the wiper leg of the gain pots (c19, c5). Again, the caps say  '502 1kv' on the better sounding randall, and '472k yp5 1kv' in the other one. Also, I found that on the cap that connects from the presence pot's 3rd leg to the ground (c14) differs very slightly on the two different models. On the better sounding one, the cap reads .1k 250, and on the other is reads .1k 100. The diodes on the red channel are the same on both amps, but D3 and D4 read 74 91 1n on the actual diodes in both amps. I don't know if this adds up to much. Everything else looked visually the same.

I'm thinking that if the cap values are actually different on the gain controls, after the tone stack and the presence control; than that sounds exactly like what would make the tone difference that I'm hearing. Also, I found that the IC in the reverb circuit differs between a ti 414a and a 714a, but that isn't relevant to the topic.

[Marcos - Munky]

Thanks a lot. I will put the values in my redraw schematic, and it will be online today.

[space_ryerson]

So, what's the rating of the caps marked '502 1kv' and '472k yp5 1kv'? Would that account for a change in tone and distortion amount?

[Marcos - Munky]

The change is very small. The 502 cap is a 0.005uF cap, and the 472 is a 0.0047uF, and a change between these values don't change the sound. Maybe the differences is because of the power amp or the speakers that the amps have.