Randall RG80/RG100 Preamp DIY

[Gabriel]

Mensur.

I got the Randall WarheadX2 preamp original schematic  and a couple of redraws of it, from a friend, in Eagle docs. I know you dont like opamps  but you could help me with the simplification of this one? Most of the work is done but i need some tips. I got some troubles with the power supply.
If you cannot help ( you probably are a busy person) i tanks anyway.

[mensur]

What's the problem with PSU?

[askwho69]

hope mensur has pcb on this one

[Gabriel]

Sorry for the late reply!

I almost lost my own schematics for good due to a bad computer thats going to tilt. For that I'm not able to put my own schematis . I'll take it to a tec to solve the problem and then i'll put my drawings here to you see what i was doing.

1 - here is the original one:http://www.4shared.com/document/sLu8FxGW/x2pre_split.html


2 - In the big picture i was cutting off all the stuff (specially the relys ) that run with 7v in the 1st page leaving only 5 parts that i presume that run with 24v:
(a) A main input(buffer?) that goes to 2 preamps - (b)the clean and the (b1)overdrive (this last one with the option of the (c)Fry boost stuff) - and for the last part the (d)EQ. I also cut of the 3rd page (the loop etc).

I cannot specify more my doubt cuz i'm not able for now to post my drawing as i've said before. But, in main lines, i was wonder if the 7v wires are really needed to make this thing work.

Thanks fot the attention!

[Nicht Bernd]

Hi,

could someone post the pic randallultimate.png again? Imageshack killed it...

[Gabriel]

I hope Mensur don't mind: http://www.megaupload.com/?d=VFD4E6KP

[mensur]

I hope Mensur don't mind: http://www.megaupload.com/?d=VFD4E6KP

I don't mind:
http://img641.imageshack.us/img641/4237/ultimaterandall.jpg

[kin0]

Could you post the one without the 9v adaptor?

[tra]

What charge pump was used to get 24v from 9v?

[mensur]

What charge pump was used to get 24v from 9v?

MC34063

[Amplifuzz]

Mensur, thanks for the updated schematic! Coupla questions:

- What's the 150uH 'L1' component in the voltage adapter?
- If I don't want the extra gain stage and contour circuit, what can I leave out of the schem?
- Is there any way to add a Resonance/Depth control next to the Presence one? It would be handy.

[Gabriel]

I'm not mensur but i can answer a couple of your questions:

1 - Its a inductor (veri similar in apearence with a resistor) it's basic eletronics you know...
2 - he has already answer that: "which can be bypassed [the contour], plus it has additional gain stage for accommodating volume drop due to diode clipping."
3 - i guess it could, but resonace isn't a fancy name for low pass?

[jaysunten]

Hey~
I've been reading all of your posts on the SSamp forum. I have 3 RG100HT .
All of them have really crappy volume drop when the treble is pulled (gain
boost). I looked at your 3 page schematic but can't for the life of me figure
out what part specifically I can use to get the volume back up when the
treble knob is pulled.
Can you point me in the right direction?
Thanks!
jason

I made that amp a few years ago and it's awesome.
Here are my samples:
http://www.esnips.com/doc/d6a08723-1fef-4ab9-afd4-f8520f273388/Randall-RG100ES-Boost-1
http://www.esnips.com/doc/489be47f-e102-49d0-aac5-b09ee8a4870b/Randall-RG100ES-Boost-2---Scooped-Mids
http://www.esnips.com/doc/619f7c75-6446-4b4c-85d6-6bd8258b2137/Randall-RG100ES-Boost-1(Solo)

1.Yes the red channel is the distortion channel
2.Caps are in micro farads (10uF on the source of Q6)
3.Yes they are 4V Zener diodes,(1N914 are clipping diodes,or boost in that amp, but they attenuate the signal a lot).

[teemuk]

Isn't the gain boost function just toggling the silicon diode clippers, of which's forward voltage is much below the forward voltage of the other clipping devices (which, if I remember right, were few back-to-back zeners). Hence the drop in loudness.

To even out the volumes you need to install an additional circuit that either
- Switches on when gain boost is not toggled and attenuates the signal by proper ratio.
- Switches on when gain boost is toggled and amplifies the signal by proper ratio.

[tra]

Here is a semi-verified PCB layout using Mensur's schematic. Passes signal, but the tone stack doesn't seem right. Could be a fault in the layout or my build.  

Link removed due to complaint.