1981 - Inventions DRV  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
User avatar
MilesXC
Information
Posts: 16
Joined: 17 Apr 2011, 10:04
Has thanked: 3 times

Post by MilesXC »

Hi all : ) really intrigued as to what's going on with this one.

From what I can see this is his only product, and the last thing I want to do is step on any toes, so might be too soon for it.
But if anyone can have a go at a block description like we did with the Sick As, that'd be great.

There's a few blurry board shots on his Instagram, and this dudes had a bit of a go https://m.imgur.com/gallery/euZZ3cv

With 4 IC's I'm thinking one for the relay, one for buffer, one for the drive section and maybe a charge pump?

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

I think it's a rat with a opamp preamp, a voltage doubler and a microcontroller for the soft switch relay. Could be similar to the OD820 with a Rat instead of the tubescreamer like circuit.

User avatar
Dirk_Hendrik
Old Solderhand
Information
Posts: 4193
Joined: 03 Jul 2007, 08:44
Location: Old Amsterdam
Has thanked: 232 times
Been thanked: 887 times
Contact:

Post by Dirk_Hendrik »

I am somewhat surprised by the circuit operation description in that article. It countains numerous errors and suggests the author does not understand this himself.
- The clipping stage is made with a non-inverting opamp. Not an inverting one.
- The feedback to the invtering input is done through the dist pot. R6 and C7 have nothing to do with this.
- The distortion, or more precise, gain, is not set by the dist pot and R6 but by the ratio of thye dist pot and the parrallel of the R5+C6 and R4 and C5 nets.
- The main purpose for C4 is to avoid oscillations. Not tone shaping.
- The main purpose for C7 is DC blocking. Not tone shaping and the thing being electrolitic does not have anything to do with that.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

Thanks Dirk. :thumbsup
The publication of half-knowledge and ignorance is the dark side of the Internet.
That is why we must pay careful attention to such stuff.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

Dirk_Hendrik wrote:I am somewhat surprised by the circuit operation description in that article. It countains numerous errors and suggests the author does not understand this himself.
- The clipping stage is made with a non-inverting opamp. Not an inverting one.
- The feedback to the invtering input is done through the dist pot. R6 and C7 have nothing to do with this.
- The distortion, or more precise, gain, is not set by the dist pot and R6 but by the ratio of thye dist pot and the parrallel of the R5+C6 and R4 and C5 nets.
- The main purpose for C4 is to avoid oscillations. Not tone shaping.
- The main purpose for C7 is DC blocking. Not tone shaping and the thing being electrolitic does not have anything to do with that.
pretty much everything he says on the PCB analysis is also probably wrong (to be fair that was also his disclaimer):
Wild guess, IC3 is the input. It's surrounded pretty with components pretty sparsely so this is likely just an input buffer, and the square and circle pads next to it are the input solder points from the input jack. Tbh, the two circle pads on the right could also be inputs but it's inconsequential.
Very wild guess indeed, IC3 is probably the microcontroller, the pads on the left are for the LED, which is pretty clear once you look at the front of the actual pedal, since that is where the LED is located. The pads on the right are for the switch, which is a momentary spst, and also right there next to it in the actual pedal.
Let's talk about the orange circle containing IC1. With the proximity of the symmetric diode pair above it, and their proximity to the volume pot wire pads, this is probably our RAT. The master volume is almost always at the very end of the signal chain. My guess is that this is a dual package IC and, if so, the upper left pin is the output which feeds the clipping diodes and the volume with a shared plane to ground. Note the lack of a drive pot though, who knows, the traces might reroute it somewhere else, but it might just be a fixed gain stage that he relies on the toneshaping before it to tailor how it clips.
This is almost comical, I'm guessing IC1 is the charge pump using the 2x 1n400x or 1n5817 like in the road rage, especially since the cap he highlights seems to be a 100uf, a typical power section cap.
Ok, so, IC4. This one is interesting. The location of the drive pot and the additional clipping diodes are very very very familiar...
I'm guessing this is the Rat "core" of the circuit and there is no tubescreamer, eliminating all but a probably dual opamp IC2 for the input and output buffers like on the OD820 (or preamp and output buffer). Close to the relay are two transistor packages, one being the 78l05 for the microcontroller and the other probably buffer for the relay signal coming from the micro, as some micros cannot deliver sufficient amps to actually switch the relay reliably.

Here's a gutshot from Instagram zoomed in a little. One can almost read the opamps, the two middle ones look like TL072CP to me.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

I've been looking at this a bit more yesterday, and found the OD880 which is quite similar to a RAT with opamp buffers, but without the voltage doubler.

what I don't understand is why on both the OD880 and the OD820 the output buffer/gain recovery is inverting? Maybe there is a good reason for this?

Edit: active LPF, alright. Makes sense on the od880 because it doesnt have a tone control, but on the OD820 its also connected to the volume control :scratch:

User avatar
Groovenut
Resistor Ronker
Information
Posts: 299
Joined: 07 Jan 2011, 16:31
Has thanked: 60 times
Been thanked: 100 times

Post by Groovenut »

Seiche wrote:I've been looking at this a bit more yesterday, and found the OD880 which is quite similar to a RAT with opamp buffers, but without the voltage doubler.

what I don't understand is why on both the OD880 and the OD820 the output buffer/gain recovery is inverting? Maybe there is a good reason for this?

Edit: active LPF, alright. Makes sense on the od880 because it doesnt have a tone control, but on the OD820 its also connected to the volume control :scratch:
On the OD820, U2B is an inverting mixer stage, combining the clipped signal with the clean signal. I would then say U1B is an inverting gain stage to correct the phase, but that is just a guess.

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

On the OD820, U2B is an inverting mixer stage, combining the clipped signal with the clean signal. I would then say U1B is an inverting gain stage to correct the phase, but that is just a guess.
Your guess is right and I fully agree with them.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

You're right, I missed this.

However, on the OD880 the last stage is also inverted but not compensating for anything

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

Seiche wrote:You're right, I missed this.

However, on the OD880 the last stage is also inverted but not compensating for anything
Thank you for the correction.
You are right, I war focused on the OD820.

BTW, the tone circuit shifts the phase between -45° and 45° depending on the tone potentiometer and the signal frequency.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

So getting back to analysis of the DRV, the relay looks like a NEC/KEMET EA2-5NU to me. DPDT and 5V due to the microcontroller. Similar to the TAKAMISAWA NA5W-K which is often used in these kinds of circuits.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

I'm currently working on a workalike (NOT a clone) of my assumptions for this circuit. An opamp preamp pushing a RAT main stage into an opamp buffer similar to the OD880 output stage. With a voltage doubler running at 18v and a soft switch relay bypass with microcontroller based on the coda-effects relay bypass.

We'll see how it sounds :horsey:

User avatar
bugg
Breadboard Brother
Information
Posts: 144
Joined: 11 Feb 2013, 03:10
my favorite amplifier: Fender Twin
Has thanked: 51 times
Been thanked: 336 times

Post by bugg »

The core of the circuit isn't really a Rat.... It's definitely Rat inspired, but it's not exactly the same.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

Do you know more? The number of resistors and caps roughly align.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

Okay, so apparently the PedalPCB "Informant" is a DRV. I've ordered a board, unfortunately the build docs are not available yet, so no schematic so far.

This will be interesting.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

Haven't received the pedalpcb yet but in the meantime I've tinkered with my workalike circuit for a bit and ruetz-modded it. It sounds pretty good so far. Hacked to shit tho because I went straight to pcb without a prototype and made some mistakes lol. I've done a revision, will build that, and if it sounds as good or better than the first one I'll post the verified schematic.

User avatar
Ben N
Cap Cooler
Information
Posts: 506
Joined: 12 Dec 2008, 03:34
my favorite amplifier: Ampeg J12D Jet
Location: Israel
Has thanked: 192 times
Been thanked: 53 times

Post by Ben N »

He had me at "The clipping stage is called an "inverting op amp" because it takes a portion of the output and feeds it back into the clipping stage. " Huh?

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

according to the pedalpcb forum the bypass is a buffered bypass type, so Input buffer is always in the signal.

User avatar
Seiche
Old Solderhand
Information
Posts: 2526
Joined: 01 Nov 2010, 00:16
Location: Germany
Has thanked: 231 times
Been thanked: 189 times

Post by Seiche »

Still no schematic, but here's my "inspired by" pedal. Sounds pretty good so far :D

Edit: this is not a clone or the schematic of the 1981 DRV.
2019inspirations_v2.jpg
2019inspirations_v2_schem.png
The microcontroller is a PIC12F675 loaded with the coda-effects bypass.

User avatar
Jack Deville
Resistor Ronker
Information
Posts: 403
Joined: 02 Apr 2009, 06:21
Completed builds: too many. too many.
Location: Portland, OR
Has thanked: 1 time
Been thanked: 86 times
Contact:

Post by Jack Deville »

Why load down the voltage doubler circuit with a divider when supply could be used to set bias?
I'm a "professional."
Buy my products and make me rich.

www.jackdeville.com

Post Reply