65amps SoHo

[Darkbluemurder]

That's exactly what I was thinking. I have to check if I still have 10M resistors at home. I got to get into this amp anyway for more tweaking.

Cheers Stephan

[dorrisant]

Just got one in... Redline. This one's mine, not a customer's. I have wanted one for a while.

Bump is on a pot, not a rotary switch.

I might add a loop

[dorrisant]

More ..

[arjepsen]

how does this schematic stack up against it?

[dorrisant]

how does this schematic stack up against it?

I'll compare it to mine and report back.

[dorrisant]

Using the part numbers from your schematic:

Input resistors are paralleled 68k CCs.

C3 is 0.1uf.

C4 is 47p instead of 69p.

R11 is 10k, not 15k.

R10 does not exist, so jump it out.

The Boost Volume or "Bump" Level pot is 500KA, not 1MA.

R14 is 470k, not 10k.

The Boost Tone or "Bump Tone" pot is 250KA not 1M.

After the PI caps (0.01u) and before the 470ks to ground there is a 470k in series with two 0.0022u caps in parallel connecting the signal paths.

In the VVR circuit the switch hanging off of the 220k (R28) is not in my amp.

Also the voltage divider for the elevated heater CT is not there.

I will not go into the relay power supply, as it is very different from the much simpler circuit I have in mine.

Some of these values are so slightly different that they may not really matter. And I realize that sometimes values are changed in subsequent devices due to the learning curve about the problems that arise. But I would say that the Bump pot values and the 470k vs 10k at R14 would make a bigger difference. I will say that my particular amp is newer in the chronological order simply because I do not have a rotary switch for the bump level.

Take that for what it is worth.

Btw... What is going on with the diodes (Zener/rectifier pairs) after the PI? I know it must be clipping the signal at a certain level of PI output, but how is this functioning here? Any comments or guesses?

[arjepsen]

Thanks.
The schematic was what I could glean from other pictures and info I could find - coupled with a few personal edits.

Some of those values were taken from other gutshots that some kind souls shared with me:
The R10/R11 is a +/- switch on some of the models. The switch just parallels the 15 with the 33 for ~10k.
But very nice to get a concrete value on those pots - I didnt have those.

I'm a little confused about this:

After the PI caps (0.01u) and before the 470ks to ground there is a 470k in series with two 0.0022u caps in parallel connecting the signal paths.

As far as I can tell from the pictures, this is only one side ??
So one side has 2x22nF -> 470k before the 470k to ground and the grid resistor... but doesnt that make it kind of imbalanced?

btw, the diode arrangement is my interpretation of something that I saw in all earlier gutshots - there is some shrinkwrapped stuff going on there. I beleive it is the "paul ruby fix" that some people use for the marshall 18watt.

[Roe]

looks like the first gainstage of the Soho is an ef86 (ala ac30/4) but instead of going directly to the phase invert it runs to an ecc83 and a tonestack?

[dorrisant]

There are a few more differences I missed but are minor. The input circuit is different due to the VVR. Also pins 2 and 7 are unused on the EF86.

I have drawn an accurate schematic and will post it when I measure the voltages. I am on vacation this coming week and hopefully will have a bit of time for that.

[Guy77]

There are a few more differences I missed but are minor. The input circuit is different due to the VVR. Also pins 2 and 7 are unused on the EF86.

I have drawn an accurate schematic and will post it when I measure the voltages. I am on vacation this coming week and hopefully will have a bit of time for that.

Hi Dorrisant. Thanks for posting about this Red Line amp.
After listening to some of them on youtube I realize I need to have one for myself too!! Love how it drives hard!


Cheers
Guy

[arjepsen]

Im trying hard to trace out the bump volume circuit, but I must be seeing it wrong.
Following the wires, It seems to me to go like this:

bump circuit.jpg

But this makes no sense - the 6k8 would never have a connection to ground like this....

[dorrisant]

Here is what I have as far as a schematic...

I am working on a layout at the moment.

EDITED: Schematic Update

[dorrisant]

Unverified layout...

EDITED: Layout Updated

[arjepsen]

Awesome, thankyou for sharing!
I do wonder about the bump level though:
So, you have drawn the 470k resistor in series with the 500kA pot. I have tried this out in my version, instead of the 1M pot and the 10k I had there.
But this arrangement makes the bump level have no effect on the sound...
Also, isnt the other resistor supposed to be 6.8k instead of 68k?

When I look at your layout, you sort of have it placed those two resistors on the relay, the same way I drew it in my last post:
the 470k goes to the middle pin on the relay - the pin that gets switched between the other two.
So in one position it gets switched to ground, in the other it gets switched to the 6k8, paralleling them....
Im hoping Im wrong here - but it seems like the layout and the schematic differ?

[dorrisant]

Yep... You're correct sir. I shouldn't have stayed up so late to do this. I will review both of these and revise. I usually just copy and paste to get the topology right then edit the values. Spaced out on this one! No worries, I won't leave it like this for long.