SDM SILVER JUBILEE

[ViperDoc]

While researching the Lerxst Omega amp in conjunction with my channel-switching Marshall investigation, I came across a layout of a Silver Jubilee drawn by SDM on the metro forum. Seems to be a well-respected amp guy, but I know nothing beyond a few forum posts.

Questions:

1) How would you rate this drawing? It could be the best in the world, I just have no idea myself.
2) How does the 2550 compare to the 2204? I've never played a 2550.
3) There is a "black box"-looking device just next to the bias supply on the board. Vas ist das?
4) Is there a schematic for this amp?



Thank you!

[xtian]

1. Looks nice. Is it accurate? No idea.
3. Bias trimmer pot

[martin manning]

1) I would trust that drawing to be accurate much more than I would a Mojo drawing.
2) Google.
3) See above.
4) Google.

[ViperDoc]

1. Looks nice. Is it accurate? No idea.
3. Bias trimmer pot

Thanks, xtian! Makes sense, I've never seen one stand on its side like that. I found some Marshall 2550-5 schematics on EL34world. Might take some time to figure out. How reliable are the Ceriatone layouts?

[Colossal]

All of the Metroamp and SDM drawings are of high quality.

5) what Martin said
6) see #5

[ViperDoc]

Here's a Marshall 2554 25/50 watt schematic. I see that Friedman puts his very-Metro-looking effects loop after his Master volume on his amps. Any problems moving the loop from the 2554's position? It is in between V2A and V2B.

Marshall_25aniv_silverjubilee_25_50w_2554.pdf

[ViperDoc]

Are 220K pots still available? I imagine you’d sub for 250k, but if you’re shooting for accuracy, where would one find those, audio and linear? Thanks.

[sluckey]

For sure. AES has three listed. Probably find them all over the net if you just look.

[Colossal]

Are 220K pots still available? I imagine you’d sub for 250k, but if you’re shooting for accuracy, where would one find those, audio and linear? Thanks.

Be sure to check the part tolerance/precision. You might want a 220k pot but end up with something significantly higher or lower than the nominal value, which can be maddening and wastefully expensive, meaning, you might need to buy a bunch of pots just to find the one that works for your application. Then what to do with all the losers?... Case in point, I wanted a 300k pot for a build and the two I ordered turned out to be 250k. Useless.

[thetragichero]

any reason not to use a larger pot (i seem to always have 1M on hand) and run a 220k resistor along the outer lugs?
that's what I've been doing so if there's a reason not to I'd like to know!

[Colossal]

any reason not to use a larger pot (i seem to always have 1M on hand) and run a 220k resistor along the outer lugs?
that's what I've been doing so if there's a reason not to I'd like to know!

You can, but the taper may or may not be ideal. But it's easy to measure the response with a DMM and plot the data in Excel. I did that to get my 300k pot.

[ViperDoc]

A 1MA pot with "283K" across the outer lugs should get you closest to 220K. What about a 270K and a 10K in series? What taper issues have you noticed when doing that? How much better would that be over a 250K pot and calling it good?

[ViperDoc]

For sure. AES has three listed. Probably find them all over the net if you just look.

Right. At first I was searching for a CTS version, and I couldn't find any. AES seems to have quite a bit of everything, thanks for the recommendation. I've never used them.

[ViperDoc]

Please see OP for this question: What is the purpose of the two LEDs on the board? The two red ones just to the side of the relay on the board. ???

[pompeiisneaks]

I believe the LED's are part of the diode clipping circuit. I'm not super strong on how it does it, but it gives some of the distortion.

~Phil