Need help understanding circuit

caspercody · Post by **caspercody** » 13 Apr 2021, 23:14

Hello

I want to make a pedal out of the Nobel's Sound Studio (none of the modulations) and I am having trouble determining where the clean, compressor, and outputs are coming from the circuit. I have attached some cleaned up schematics, hoping they will help someone show me where the outputs connect to the eq sections. I can see how the (2) eq sections are connected, I am having issues seeing where the normal guitar tone would come from, compressor output is, and the overdrive section. Here is how I think the rotary switch works for selecting the mode:

S1-F - 440 HZ
S1-E - normal
S1-D - clean A
S1-C - clean B
S1-B - overdrive
S1-A - distortion

Here is description from Nobel of the sounds from each mode:

phatt · Post by **phatt** » 15 Apr 2021, 01:04

Hi Casper,
Yes your switching progression is right.
I own one of these which no longer works but used some ideas to build my own systems.

Normal & Clean 1 run through (S1-A & S1-D) then into Cabsim 1 (IC 104A)
Clean 1 also engages more gain via S1-B (R102,R103) also switches Q102 via S1-E.

Clean 2 changes to Cab sim 2 (IC103A, IC103B & IC104B)
Cabsim 2 is then used for Clean2, Odrive & Distortion.

Past that I was never able to work out exactly what the other switchs engage.
My unit was faulty, Compressor never seemed to work and as it had battery corrosion I never bothered to fix it.

What I can say is that it had something I liked, except for no bass.
I changed C101 for a 10nF or 22nF fixed that.
I built a new unit just using the input section (no Compressor) and cab sim 2 and that is still in use 20 plus years later.
Assuming you want all the positions in a pedal your issue might be the switching.
I found it far easier and more versatile to use separate pedals for Dirt, Compressor.
Hope it helps,
Phil.

phatt · Post by **phatt** » 16 Apr 2021, 03:03

Hi, Just thought a better schematic might help. Clear PDF below pics

Also some pics of what remains of my old SST unit.
Phil.

phatt · Post by **phatt** » 16 Apr 2021, 03:37

Opps,

I just realised that although your sequence of the switch positions is correct your understanding of the what each switch does is not right.
Yes it is rather complex

Switch S1-A & S1-D switch the audio path around, the other 4 switches change the Gain and the Compressor.
And of course Position 1 is the 440Hz signal. Done via S1-C & S1-F.
The Foot switch over rides the OD position and turns on Distortion.
Phil.

caspercody · Post by **caspercody** » 18 Apr 2021, 01:34

Thanks for all the help. I bread boarded all the circuits, and I could not get any sound out the compressor portion. So I used the input and compressor from the Rockman. I then created (2) distortion circuits, one of the Rockman, and the other from the Nobel. Last I created the EQ1 section. Using jumpers I can create the clean section form the Rockman, clean and compressed, but rather treblely. I can then choose form either distortion circuit, and use the dist/overdrive switch on the input of the Rockman. I replaced the trim gain pot with a normal pot, and removed the 2.2K resistor. Then I ran this into the return of my tube amp.

This really is a one trick unit, not really as great as I was hoping.

But I do like the compressor, just want to change it so it does not change the tone so much. Any thoughts on what to change in the circuit to make it a clean compressor? Maybe make the input buffer like what I attached? But is one better then the other?

phatt · Post by **phatt** » 18 Apr 2021, 08:14

Regards to which buffer is better;
Circuit one will likely have better noise performance.
Are you aware, Both of those buffers are for Single supply. Both the Rockman and the Nobels SS1 use split supply so if you are trying to run it from a single supply you might have trouble getting it to work, Maybe use a split supply.

Be aware either Rockman or Nobels you still need a tone control to get the best out of these units.
In my observations these compressors are problematic to setup and there are much easier ways to build a compressor.
Also in my experience having a compressor right at the front is a waste of time much better to insert it later in the signal path, Distortion BEFORE Comp works very well and gives me much better control of levels when swapping Odrive pedals.
Phil.

caspercody · Post by **caspercody** » 18 Apr 2021, 17:14

Thanks on the buffer

Yes, I have a split power supply using a charge pump. I also put a 6 volt regulator at the front of the charge pump circuit.

I do not have the K192a jfet used in the Nobel for the compressor, or what model number it was. I used what I had laying around so it could be that I do not have the correct jfet. I cannot find a substitute when I Google it. Also it seems like a lot of people seem to think their compressor portion did not work

phatt · Post by **phatt** » 20 Apr 2021, 12:26

Regards this
"This really is a one trick unit, not really as great as I was hoping."

It won't impress by itself but don't give up yet.
It's folly to expect tone nirvana from just one magic box, maybe Try a tone circuit after the cab sim as well as a few dirt pedals in front.
You use these things to build your tone. I would suggest you get hold of some simulation program to help you see just how the response curve alters as it passes through a circuit.
If you want you are welcome to some of my circuit schematics to give you ideas.

-------
Re this;
"But I do like the compressor, just want to change it so it does not change the tone so much. Any thoughts on what to change in the circuit to make it a clean compressor?"

Regards comp circuits, If it's changing the tone a lot then something is wrong, without the circuit in front of me tiss impossible to say. Look if you want crystal clear comp you need studio gear. Frankly IME they don't work for R&R guitar.
I think it's safe to say that Optical compressors seem to suit guitar as they are slower.
I've used quite a few comp pedals and even the one optical unit I used was too aggressive.
I use "Mictesters" wonderful optical compressor circuit and no it's not clean which is why I love it cause it just adds that magical little bit of rattle reminiscent of the old valve amps I once used. Even clean they had a little grit when you dig in.

As I mentioned compression in front is defeating the whole point of it use.
The reason why I use comp close to the End of the pedal chain is it keep the dirt pedals from going stupid loud.

It keeps your SPL within a more controllable range. You still get a lift in loudness when you engage your distortion but much more controlled. I play live gigs and I have to have full control of my levels. So My Pedal board is set and forget and I just press a button when needed.
Re the Fet
I mentioned this on the rockman post, the FET's seem to be really touchy to set up why would you bother when you can't get the part and there are much better circuits that are much easier to setup???? You would have to be a masochist to pursue that

But other might have different views

Re buffers;
Yes I use buffers on all my builds,, one only has to look at the schematics of any half decent brand name gear and you will find a buffer at the input.