Schematic for your feedback

[rutledj]

I've been piecing this together from several that I've found on this board and would appreciate it if you could take a look and tell me if you see any glaring mistakes or might suggest different values.

This is just the preamp section so far.

Thanks,
Rut

[fabiomayo]

It seems like a good idea. Maybe two OD channels (HRM and non HRM) instead of two clean could be useful too.

A few points:

1) You're missing the resistor on the PAB switch (22M or otherwise).
2) 22k in the Deep sw input instead of the 270k in the schematics around.
3) 500pF on the V2b grid

Check the ODS-101 schematics for tweak values suggestions. Others may give you more tips on switching out the HRM tone stack.

Hope it works out.

[rutledj]

OK. I added the 22m around the PAB switch (Hope I connected those correctly). Also added the feedback ckt around V2b.

Thanks

[rutledj]

Oops! Somehow lost the file.

[heisthl]

2) 22k in the Deep sw input instead of the 270k in the schematics around.

I was not aware of this - any one else want to jump in and confirm?

[yeahyeah]

I like the idea to add a switchable HRM!!!

has anyone else done this sucsessfuly?? definately looks worth experimenting with.

I think you need to add 270pf snubbers in the OD section, but I'm no expert.

[rutledj]

22k in the Deep sw input instead of the 270k in the schematics around.

I assumed he meant the 2 22m across the relay which some prints seem to have and some don't. What purpose do those serve?

Rut

[heisthl]

[quote="rutledj]
I assumed he meant the 2 22m across the relay which some prints seem to have and some don't. What purpose do those serve?

Rut[/quote]
No I don't think he meant that - the 22Ms are on most every schematic except the D'Lite. They are really anti-pop resistors but you can also set the clean boost volume jump by adjusting them downwards.

[Bob-I]

I like the idea to add a switchable HRM!!!

has anyone else done this sucsessfuly?? definately looks worth experimenting with.

I think Glasssman may have something like this.

I think you need to add 270pf snubbers in the OD section, but I'm no expert.

That's gonna be difficult. The HRM doesn't use snubbers and the non-HRM does.

[fabiomayo]

heisthl is right about the 22M resistors on the PAB.

The Deep switch has two 270k resistors between the network switched (.01uF; 1M; 10k). On your schem you have a 22k and 270k.

[rutledj]

I think I fixed that. Can anyone tell me if the two 22m around the PAB are wired correctly?

[heisthl]

heisthl is right about the 22M resistors on the PAB.

The Deep switch has two 270k resistors between the network switched (.01uF; 1M; 10k). On your schem you have a 22k and 270k.

Doh - I thought you meant 22k was a legitimate value, now I understand you were pointing out an error.

[fabiomayo]

I think I fixed that. Can anyone tell me if the two 22m around the PAB are wired correctly?

No, it's not. It's tough to put in words though. The Deep switch should come from the wiper of the bass pot. The 22M in series with the 270k is wrong. The 22M (or lower value for less boost so I'm told) is there mainly to prevent a pop noise when switching. They should be between the common and the switched pole (or to ground I think).

Consider the ODS-101 schematic and the following pinout of the switch for a better explanation. Compare it to your drawing.

[fabiomayo]

Doh - I thought you meant 22k was a legitimate value, now I understand you were pointing out an error.

that's the pitfall of my bad english


One more thing, Rut. You may want to play with the cathode bypass resistors. I'm not sure but I think most people around here use at least one 5uF in the OD section (the first triode usually).

A while ago Bob-I had a similar project, including a schematic. Don't know if it ever was born or not. Search for it, or maybe try and get his advice on the subject.

[rutledj]

They should be between the common and the switched pole (or to ground I think).

Well, on the prints I've been able to find with those 2 22m, none have dots for the connections so its kinda hard to tell what is connected and what isn't.

If you look at this schematic (https://tubeamparchive.com/viewtopic.php?t=1902
it appears that one side goes to bottom side of treble, middle goes to common of sw, and bottom goes to wiper of bass which also connects to the 270k feeding the Deep ckt. Is that correct?