Is this the correct interpretation of 1959 and 2203 circuit?

[Rp3703]

Is this a correct interpretation of the Marshall 1959 and 2203 circuit(assuming the low input is eliminated on the 2203 circuit).

[pdf64]

Yes, can’t spot any errors.

[shooter]

 
6 input jacks for three tubes is just showing off 

[Rp3703]

It only has 4 inputs with relays to switch between the two configurations. I can’t get it to work right, so I figured I should make sure I’m interpreting the circuits correctly before figuring out how to switch between the two.

[Rp3703]

So if those two schematics are correct, does this switching system make sense? Blue is 1959, red 2203. Let me know if the double connection to V1 pin7 creates any problems.

[nandrewjackson]

Im gonna say, no. That won't get you there.


Example. Let's say we want 2203 mode. We plug a guitar into * bright 1 hi* , the signal goes through the 2nd triode from left, then over to pin 9 of the 2nd relay from left (red lines= 2203), out of pin 13, into *bright 1 vol/gain* into pin 4 of the 3rd relay from left, out pin 8 of that relay, through red line over to pin 7 of V1, and PROBLEM.  because of the cliff jack here, there is only 68K to ground.

[nandrewjackson]

It looks like blue mode should be fine. . .   

[nandrewjackson]

Is this the same as your other post recently that mentions the ONE WIRE MOD? 


I tried to look at that one, but im not familiar with *one wire mod* , so i didn't post a comment.


The blue and red colors on your schematic really help to keep things straight,  in my opinion. 

[pdf64]

Schematics are a lot clearer and easy to follow if layout symbols are avoided.
ie your relays comprise 2 dpdt switches and a coil, putting those symbols all within a layout type footprint box seems to me to be applying an unnecessary constraint, which then requires rather more convolution in lines of connection.
If the boxes were dispensed with, and each dpdt switch moved close to its relevant area (and labelled as appropriate), I would find it much easier to follow the signal paths.
My view is that layouts are one thing, schematics are another, though strongly related they each have differing considerations and constraints.
Good circuit design is best served
by a clearly readable schematic, whilst for that design to function as intended, a good layout design (and hence layout diagram) becomes more important as circuit complexity increases.
Modern Marshall schematics seem to merge circuit schematic and layout together somewhat, such that the schematics are of each pcb, rather than the system as a whole. Multiway interboard connectors are used and shown on their schematics, necessitating arrays of parallel lines of connection to those connectors. These are irrelevant to the actual circuit signal flow, and significantly reduce the schematic’s readability.
Hence I suggest it would be better to avoid the conventions used by that drawing style.

[Rp3703]

ntandrewjackson-First off, yes, I was not able to get either One Wire Mod or 2203 circuit to work so I decided to simplify things and work on one circuit at a time.

Second, so you are saying that the signal is being shunted to ground instead of traveling through the second gain stage. This should be easy to test by putting a patch cable into the two input jacks of channel 2, which should disconnect the ground connection.

Third, here is a video of the One Wire Mod.

In the video, it looks to me like he runs a jumper to those same 68K grid stoppers and somehow his signal still makes it through the second gain stage. Maybe I'm missing something. From what I've read about this mod, the channel 2 inputs are supposed to be left non-functioning once this mod is performed. The only way for that to be possible is if the connection is cut.

On a side note, the tone of the OWM in this video sounds bad, really bad but as he states and as I have read elsewhere, it is suggested to place a 1M resistor on the wiper before running the wire to the second gain stage. I'd be interested in hearing how that sounds. I need to get the 1959/2203 to work first.

pdf64-I agree that removing the relay symbols from the schematic would make it a lot easier to read. I've had to pop a few Advil every time I tried to follow the signal path on my Egnator rebel 30. I decided to draw in the relays on this schematic because I wanted some confirmation on my relay switching circuit along with the amp circuit. Now that I know the relays work fine, I could probably remove them if I come up with any more amp specific circuit questions that require a schematic for explanation.

[Rp3703]

Ok, here is another version of that same schematic without the relay confusion. I also added a switch to disconnect the grid stopper connection to ground. Does this look correct?

[nandrewjackson]

Yes , that oughtta do what you're wanting it to do.

[Rp3703]

2203 mode is squealing and sounds terrible. I was afraid it might be because of the relays, so I unsoldered them and tried twisting the wires together using wire nuts. Still squealing. On the 2203 schematic, there is only one 68K grid resistor but my input jacks have two since I'm using the existing 1959 bright/channel 2 HI input jack. Could this be a possible cause?

[nandrewjackson]

If your wiring is correct, then the squealing is due to layout and wire lead dress.


Move some wires around with chopsticks while the amp is on, *something * *should* indicate a noise source while being chopstick'ed.




Are you using any yellow cylindrical signal caps? They do have a +/- even though theyre not electrolytic.  I'm not 100% on the science, but something about the (-) end being soldered to the outer wrapping? Or the other way around. . . . .

[Rp3703]

Doing some research last night, I am thinking my issue may also be due to grounding. I never connected my grounds directly to the filter caps themselves. I just used the chassis which is aluminum. OOPS! I'll fix that and see what that does.
I did add one Mallory cap. I am pretty sure these are not polarized.

[nandrewjackson]

Yeah, I'm not saying the mallory types are polarized in the same convention as an electrolytic power cap, but its direction might influence the noise level of an audio circuit depending on which way it's  installed. Some brands of the mallory type yellow cylindrical audio caps have a band on the body to indicate this. Don't  dismiss it so easily. It could help.

[DummyLoad]

too many grids and plate ckts. crossing one another and in too close proximity within the relays themselves. you may have better luck switching between to separate preamps.


--pete

[Rp3703]

After spending a week trying to diagnose a PPIMV that was actually just a bad speaker cable, I'm back to trying to figure out how to rewire a 1959 to a 2203.

I have attached two schematic layout drawings of each version. I know it is suggested that the connection from the input jack and the gain pot to V1 be shielded but I have seen plenty of pics of stock marshall 2203's that were wired using regular wire and that is how I'd prefer to do it as well.

Please note my cold clipper connection to the ground side of the 330uf bypass cap. I just want to make sure that cannot somehow cause any issues.

[Rp3703]

So when I wire the amp in the 2203 configuration like I drew, I can only turn the gain knob up a quarter of the way before the volume drops and it makes a cracking sound when strumming the strings. Below the 1/4 turn you get full volume but very little gain.

[shooter]

cracking sound

bad solder connection, loose tube, possibly DC getting in

with the amp on the bench, signal in, gain turned to the crackle setting you should be able to wiggle/giggle and narrow it down

[Rp3703]

It may be also worth mentioning that I am switching between the 1959 and 2203 using a terminal board to reconfigure between the two. I have had this amp wired in 1959 and it works fine though, just not in 2203.

[shooter]

I like the '59 better anyway 
except with ONE input

since the 2203 is a proven amp, I'm still sticken with loose something, or mis-wired something

[Rp3703]

I'm thinking mis-wired. Could it be the two 68K grid stoppers? A stock 2203 only uses one on the HI input and no grid stopper on the LO.

[sluckey]

All those long wires zigzagging and crossing is a perfect recipe for disaster in a hi gain amp.

[Rp3703]

The wires and terminal block are temporary until I can confirm the amp will operate in 2203 configuration. I realize the rats nest is not an ideal layout but I can't imagine that would be the cause of my issue. My original idea was to use relays to switch between 1959 and 2203 but I could never get 2203 to work. I eliminated the relays to reduce the number of possible causes for it not working. The terminal block allows me to quickly rewire between 1959 and 2203 and makes a better connection than the wire nuts I was using previously.

[sluckey]

I totally get that it's temporary. Still...

Here's a very similar project that has been successfully built by a few people...

     http://sluckeyamps.com/misc/Marshall_Dual_50.pdf

[Rp3703]

Yes, it has already been suggested to me to that switching between two separate preamps would work better than reconfiguring a single preamp to do both. That may be the case but right now, I’m just trying to get this thing to work in 2203.

[PRR]

> I can only turn the gain knob up a quarter of the way before the volume drops and it makes a cracking sound when strumming the strings. Below the 1/4 turn you get full volume but very little gain.
> I realize the rats nest is not an ideal layout but I can't imagine that would be the cause of my issue.

Crapping-out as gain is raised is classic oscillation. Rat-nest is classic oscillation.

You have to wire high-gain amplifiers like sanitary plumbing. If even a whiff of septic gets in the well, problems.