Marshall - DRP-1 Direct Recording Preamp  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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rcustoms
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Post by rcustoms »

somebody in an article said:
The non-boost channel is reminiscent of the old "no master-volume" marshalls and sounds best with the master maxed-out. Crank the gain all the way up...and stick an overdrive in front, too. Boost channel is more like modern marshalls, and will roar with authority. Speaker emulation is pretty darn good, and if you get the bass tone knob up to about 3 oclock you actually get some of that good ol' marshall "thud." It's hard to get the thing to sound really good through headphones, as the line out(headphone out) volume has to be up a bit for the beast to develop full tonality...and then it can be a little too loud for comfort.
Very "tube-y" sounding for a solid state device. Direct to tape it sounds like a Marshall. Much more authentic "marshall" sound than sansamp, etc. It won't replace a JMP-1, but it costs less than 25% of the JMP-1's price. It does a good job of "marshallizing" the front end of an amp, as well. And awhile back I ran an fx send from the console to a 50DB pad and thence to a transformer and into the DRP-1. Cranked up all gains to max and used it as a snare drum effect...with the right balance it nicely livened and "trashed up" a pretty boring snare drum sound. No reason it has to just be a guitar preamp, eh?
The DRP1 is supposed to be used as a direct recording preamp...no waking up the street with your 4x12 when you put down a killer solo at 3:00am!!! All I can say is that it works! No fizz, and using the Line Out puts in the 4x12 emulator (not switchable) and there's very little hum and buzz except on monster gain settings, and then what do you expect!
I think I've got a steal. Brilliant for home recording, no cabs to set up and although the emulator is basic, it's about right. Plug your rack FX into it and use it as a practice amp, or on it's own anywhere (it's battery powered!) or even carry it as a spare pre-amp in case your rack goes down (it's 6" x 4" and weighs about 12 oz!) Every guitarist should try one. I'll certainly be taking it out as a back-up pre-amp in case my JMP-1 ever fails and would have no qualms about using it in a home/small studio environment where it's just impossible to use a miked cab.
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phatt
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Post by phatt »

Hi,, thought I'd throw my hat into the ring :)

Having built a few cab sims for folks here is a few hints;
If the PDF charts from *Kurt Godiksen* are correct then the Marshall Cab sim in the JTM series Amps will give even better response.

There is not enough cut below 100Hz to do a good Marshall sound replication.

My rule of thumb is you need a very steep rolloff below 100Hz.
you need to see a -50-60 dB drop from 100 hZ down to 10 hZ,,, So the JTM is more accurate in the bottom end.

I've taken a snap shot of *Kurt's* page (hope it's alright) :oops: and imposed the curve for you to see the *difference*.
The shape is rather important otherwise you just get too much mud happening when the signal gets big.
A lot of folk assume marshall have big bass when in truth it is the lack of bass below 100 hZ that makes the bottom end tight.

My hints;
Put A Hi-z passive styled tone stack ***in front*** of distortion (pick one) then the Cab sim circuitry,,,, you will get a lot closer faster with less to build.
Marshalls (good ones) had a midrange honk that is unique,,,,, Easy to see why when you look at the blue curve. :thumbsup
Cheers, Phil.
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rcustoms
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Post by rcustoms »

great ,what happen if we use the cab sim present in the tech 21 character series and made some mods
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Post by darthoverdrive »

This has been an interesting thread. While searching to find more about the JTM cam sim I came across this article on different cab sims.

http://www.hexeguitar.com/diy-cabsims_e

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Post by tasteless »

Wow ,Nice find !
Thanks Man. :thumbsup

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Post by rcustoms »

INSIDE
shot1.JPG
shot1.JPG (45.14 KiB) Viewed 5193 times
shot2.JPG
shot2.JPG (36.87 KiB) Viewed 5193 times
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Post by rcustoms »

DRP-1 LIKE AMP PHOTOS, I USE A LINE 6 AMP CHASIS.
PREAMP-DRP1
REVERB TANK DRIVER UNIT
TDA 7293 IC BASED POWER AMP
2 LINE 6 CELESTION SPEAKERS
AMP1.jpg
AMP1.jpg (25.26 KiB) Viewed 5155 times
AMP2.jpg
AMP2.jpg (32.56 KiB) Viewed 5155 times
AMP3.jpg
AMP3.jpg (20.41 KiB) Viewed 5155 times
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Post by Lobo »

Sound sample pease!!!!!!!! :thumbsup

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rcustoms
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Post by rcustoms »

soon as posible
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andregarcia57
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Post by andregarcia57 »

anyone have a photo of part of the original PCB?
I've got one here that is not working and boost trails are burned.
thank

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Post by lolbou »

Here you go :
DRP-1 - main.jpg
DRP-1 - jacks board.jpg
:wink:
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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andregarcia57
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Post by andregarcia57 »

lolbou wrote:Here you go :
DRP-1 - main.jpg
DRP-1 - jacks board.jpg
:wink:

Thanks

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Post by fretzburner »

Hi.the original schematic 2nd opamp is non-inverting while the one from rcustoms is inverting.is this and error?
thanks

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Post by Dirk_Hendrik »

Rcustoms version is correct.

However,
You just spotted a major error in the factory schematic :thumbsup
http://milas.spb.ru/~kmg/files/schemati ... otated.jpg

And, as a ps, you cannot make a non-inverting opamp amplifier this way.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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Post by fretzburner »

Thanks for the verification,as i checked all my schematics here from different circuits only that DRP factory schematic uses that configuration.I spotted it because i'm doing a perf layout based on the DRP schematic and rcustoms layout. Now i can continue finishing the perf.

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Post by andregarcia57 »

my original key pedal is broken where can I find a new one?
thanks
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Post by lolbou »

Switch? Seems to be the unusual type. I did succeeded once to get a switch for my Valvestate out of Marshall Support. My local shop did contact the french distributor, and it did arrive in a week. Give it a try?
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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Post by J0K3RX »

Nice work rcustoms!! I just saw this thread and now I am very interested... Great work! Any sound samples? I guess I can go on youtube and find some. Is the cab sim is as good as you say?

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Post by rcustoms »

J0K3RX wrote:Nice work rcustoms!! I just saw this thread and now I am very interested... Great work! Any sound samples? I guess I can go on youtube and find some. Is the cab sim is as good as you say?
sound good ,the circuit is that marshall use in many devices and other companies use very similar clones like hk red box ,the amazing sound comes from the preamp itself tons of loud .the amazing sound comes from the preamp itself ,tons of power, and the eq stage work very well.this device is a really mad dog.
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Post by jmpj45 »

I know this is a old thread but how do you hook up the head phone amp.

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