Grampian 636 distortion/saturation box - what input transformer? +cutting spring reverb

Help Support GroupDIY:

Urskov

Active member
Joined
Jan 6, 2020
Messages
32
Location
Dnk
Hi DIY'ers

Me and an internet partner are in the middle of making/designing a Grampian 636 without the spring reverb - for pure germanium filth/saturation/distortion, as it was famously used by Pete Townshend. (Eventually I might want to add the spring and make PCBs available)
The Grampian 636 commands extreme prices, so we thought we'd do it ourselves.

Here's what we got so far - schematic. It also has the questions about certain parts of the circuit marked in.
Notice that since this circuit runs on primary -12v, we decided to add a voltage inverter and doubler with a 79L12 voltage regulator.

Here is tons of documentation by Soundgas that themselves made a clone for a whopping 5300 USD o_O
Schematic: https://soundgas.com/wp-content/upl...pian-Reverberation-Unit-Type-636-DEST4328.pdf
Technical specs: https://soundgas.com/wp-content/uploads/2019/01/Grampian-Reverberation-Unit-Brochure_p1.pdf

So our main questions are:
- Have we proceeded correctly with cutting the spring reverb? We want as much of the "mojo" of the circuit for the saturation, so the more of it we can include, the better.
- What transformer can we use for the mic pre? And how do we wire the balanced and unbalanced channels of the mic pre?
 

musipol

New Member
Joined
Jun 28, 2021
Messages
23
Location
Idaho
Let me preface this by saying I have no experience with this Grampian unit. Are you sure you don't need the reverb part of this for the full "mojo" factor? If you take a blackface Fender Deluxe reverb and get rid of the reverb.............you have lost a good part of the "mojo" IMHO. Just my 2 cents. Also, on the schem where you marked add vol control, it should work fine to replace that with a 50k pot wired as a volume control. It would function as a master volume.
 

Urskov

Active member
Joined
Jan 6, 2020
Messages
32
Location
Dnk
Let me preface this by saying I have no experience with this Grampian unit. Are you sure you don't need the reverb part of this for the full "mojo" factor? If you take a blackface Fender Deluxe reverb and get rid of the reverb.............you have lost a good part of the "mojo" IMHO. Just my 2 cents. Also, on the schem where you marked add vol control, it should work fine to replace that with a 50k pot wired as a volume control. It would function as a master volume.
Yeah, I definitely want that in the long run, but for starters it's gonna be part of a vero layout blog for guitar effects.. so we want this layout for simplicity
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
3,325
Dont forget , theres also a lightbulb limiter in the path to the spring on the Grampian .
 

musipol

New Member
Joined
Jun 28, 2021
Messages
23
Location
Idaho
I'm still laughing about that one after opening that up expecting something serious. I think the Mosrite fuzz (at least what I can remember) was about the worst distortion I have ever heard, although opinions vary. At least after those 1N4001's you'll truly have achieved brick wall limiting.
 

Urskov

Active member
Joined
Jan 6, 2020
Messages
32
Location
Dnk
I'm still laughing about that one after opening that up expecting something serious. I think the Mosrite fuzz (at least what I can remember) was about the worst distortion I have ever heard, although opinions vary. At least after those 1N4001's you'll truly have achieved brick wall limiting.
Funny! I love the sound of the Fuzzrite, built one myself... It¨s the sound of La Gadda Da Vidda, not to mention in the soundtracks of countless spaghetti westerns. Piercing and thin, but just right.
 

musipol

New Member
Joined
Jun 28, 2021
Messages
23
Location
Idaho
Yeah, that's the thing.... we all have our various taste's insofar as what sounds good. Whatever works for you. For me I tend to like smoother distortion tones, something more like certain tube amps.
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
3,325
A harmonically simple source like an electric guitar can take quite a bit of THD before it becomes objectionable ,
voice is way less forgiving , at times choral voices can intermodulate and create a horrendous din even if the signal path is completely clean , even percentage points THD in the low end on something like an electric bass remain innocuous enough to most people , conventional drive units wont have a hope of reproducing low bass frequencies with the same magnitude of distortion that your modern ADC/DAC can do in any case .
 

Latest posts

Top