Randall RG100ES Emu

[deaconque]

Hello everyone.  So my latest project is an attempt to emulate the Randall RG100ES (the amp that Dimebag Darrell used for a while).  It is a solid state amp so there shouldn't be much  of a problem however I have a few questions.  I've extracted the Red channel from the Randall schematic, seen below (sorry if the schem seems kind of cramped, I haven't used Eagle in a while).  It seems pretty straight forward but here are my questions:
1. The circuit is supposed to be fed 24V, should I expect any issues running it at 9V other than less headroom?
2. Are the zener diodes, labeled Z1 and Z2, really necessary (I don't understand why they are in the position they're in)?


Here's the original:
http://www.schematicheaven.com/newamps/randall_rg100es-rg80es.pdf

[space_ryerson]

Odd, this is a project that I've been pondering quite a bit lately! I'm a longtime Randall owner, and have pondered building the red channel of an RG into a stompbox. I've even drawn it up a few times, and just never put it together.

The first thing to note is that you will want to change the value of the drain resistors for Q1 and Q2, so that the jfets bias to 4.5v. I suggest using trimpots, since jfets vary greatly, and dialing in 4.5v will be much easier. While Randall did test their transistors, I've noticed some pretty wide fluctuations with the transistors from one amp to the next (I own more than one), which varies the sound quite a bit. Using trimpots will allow you to adjust this optimally. I'd also suggest socketing the transistors, because you might want to try out other ones besides 2N5484's. I've been thinking about trying out J201's, just for comparison. I'm thinking you would probably want to move the master pot to the output in this case.

Another thing to ponder is whether you want to include the whole tonestack or not. This is where I'm pretty divided between using the whole tonestack, or something like a Big Muff tone control with scooped mids, and keep the presence control and Q4.

As an aside, the RG series was designed by a guy named Gary Sunda, in conjunction with George Lynch. Last year I was in contact with Gary over some Randall items, and he is a very nice and generous guy.

[trixdropd]

You've got my interest!!

[MarcoMike]

zeners should be there with a sort of signal limiting puropose. when the signal excedes a certain value, zeners "open" and let it see some ground...

I would keep the 24 V by the way. that is not that difficoult to achieve even from 9V with voltage multipliers. you can build it as it is, try it at 24V and then reduce the voltage and see what happens...

(I was about to ask: does this preamp sound so good?? but googling for dimebag darrel I can see that's probably not my style... pity!)

[deaconque]

Odd, this is a project that I've been pondering quite a bit lately! I'm a longtime Randall owner, and have pondered building the red channel of an RG into a stompbox. I've even drawn it up a few times, and just never put it together.

The first thing to note is that you will want to change the value of the drain resistors for Q1 and Q2, so that the jfets bias to 4.5v. I suggest using trimpots, since jfets vary greatly, and dialing in 4.5v will be much easier. While Randall did test their transistors, I've noticed some pretty wide fluctuations with the transistors from one amp to the next (I own more than one), which varies the sound quite a bit. Using trimpots will allow you to adjust this optimally. I'd also suggest socketing the transistors, because you might want to try out other ones besides 2N5484's. I've been thinking about trying out J201's, just for comparison. I'm thinking you would probably want to move the master pot to the output in this case.

Another thing to ponder is whether you want to include the whole tonestack or not. This is where I'm pretty divided between using the whole tonestack, or something like a Big Muff tone control with scooped mids, and keep the presence control and Q4.

As an aside, the RG series was designed by a guy named Gary Sunda, in conjunction with George Lynch. Last year I was in contact with Gary over some Randall items, and he is a very nice and generous guy.

I was actuallly going to use sockets for the transistors and trim pots for the bias resistors.  i was thinking about going with j201's for the trannies since that's what most amp emus use but sockets will allow for the use of either.  I was also on the fence about the tonestack but i think i'm going to keep it in there and see what it sounds like.

[caspercody]

Also very interested in your results on this.

[deaconque]

i'll be sure to keep everyone updated

[space_ryerson]

I would keep the 24 V by the way. that is not that difficoult to achieve even from 9V with voltage multipliers. you can build it as it is, try it at 24V and then reduce the voltage and see what happens...

(I was about to ask: does this preamp sound so good?? but googling for dimebag darrel I can see that's probably not my style... pity!)

A few years back, another user named Marcos or Munky built it as just a preamp running 24V, and even designed a PCB for it. I'm sure The PCB is either posted on his site or somewhere in the forum.

I like the sound of the preamp, but I'm also into solid state guitar tones. To my ears, the distortion channel is not entirely dissimilar to a JCM-800. George Lynch, Def Leppard, The Edge, White Zombie, and Jose Feliciano all used the RG series amps at some point or another.

i'll be sure to keep everyone updated

Definitely keep us posted!

[caspercody]

I do have these layouts, if you would like to see them?

[deaconque]

I would love to see those layouts  .  Did you ever build it?  How did it sound?

[caspercody]

I did not build them. I am not sure how to attach on this forum, but send me an e-mail and I will e-mail to you.

[space_ryerson]

There are some layouts in this thread. Disregard what I posted in that thread; I really don't know what I was thinking! Oh, I checked my bookmarks for Munky's site...and it was a Geocities site

[deaconque]

There are some layouts in this thread. Disregard what I posted in that thread; I really don't know what I was thinking! Oh, I checked my bookmarks for Munky's site...and it was a Geocities site

bummer

[dan5150]

This sounds like this could be very cool. I knew that George used the RG100 heads, but I wasn't aware that he was involved in the design.

I have never been a big fan of solid state amps, but the RG series was something special.

IMHO, If you are really going for the "RG tone in a pedal" format, keeping it at 9v will enable it to plugged into just about anyone's board...

-Dan-

[deaconque]

This sounds like this could be very cool. I knew that George used the RG100 heads, but I wasn't aware that he was involved in the design.

I have never been a big fan of solid state amps, but the RG series was something special.

IMHO, If you are really going for the "RG tone in a pedal" format, keeping it at 9v will enable it to plugged into just about anyone's board...

-Dan-

My thoughts exactly.  I feel the same about solid state but sometimes you just need a brutal, harsh , in your face kind of distortion that only solid state can give you.

[caspercody]

Any progress on this? I have gone as far as do it up in Eagle, and added a 68k at the input and adding the trim pots. But have not built it yet.

[caspercody]

Also, I built the X2FET, which is a Randall X2 emu. And this is a very easy, and sounds good pedal. Does anyone know the big differences between the X2 and RG100?

Thanks
Rob

[dellamorte]

built one using the layout posted in the link a few posts back, running it off a 24v wall wart. it sounds killer very dimebag when driven by a booster. highly reccomended!!

[dan5150]

Where did you get the info/layout on the X2FET?

[caspercody]

Go to the search tab, and enter x2fet. There is a link to a web site. It is in French, but do not need to have to read French to build. It sounds great, but unity gan is with the volume cranked.