AO 35 into Spitfire master volume issue

[guitardude57]

I recently picked up a couple of Hammond organ amps (AO 35 and AO 29) and stripped the components off of the AO 35 board.....reconfigured it into a Spitfire.

Sounds real nice.

Only problem is the master volume goes abruptly from almost no level to mass amounts of level with minimal adjustment.

Any suggestions to get more of a gradual volume increase?

All pots are 1 meg audio.

Used ceria layout.

Thanx, Mike

[Structo]

I've tried that Matchless master volume before and didn't like it at all.

The best one IMHO is the Lar/ Mar or another is the bootstrap master.

For your amp the Lar/Mar will work good because it replaces the 220K resistors on the PI.

Just copy this to your amp and connect the wires that is says to go to pin 5, connect those to your 1K5 grid resistors.
I would move those 1K5 grid resistors to the power tube sockets and run the wires from the master volume to those. Better performance, less noise.

[guitardude57]

Thanks Tom!

I guess this is my chance to try the Lar Mar........

[M Fowler]

The Matchless Spitfire is a great gigging amp but depending on which layout you used it may be wired wrong. I ran into that with the two different Ceriatone layouts I have and the two different Ken Watt's layouts.

Once the MV was wired correctly all has been good.

Mark

[guitardude57]

Mark,

What seemed to be wired wrong, on which layout?

This amp seems to be OK, other than a too big cap on V1 Rk........since that is what I had.

I ran over to RS today and picked up a better value. As is, there is no shortage of low freq's. 100uF is responsible for that. The high mids are somewhat missing. I'll swap the cap out this evening. Should be good then.


I used the original board from the AO35......wired up the Spitfire on it.

All in all, a very responsive and organic sounding amp.

The master volume however, sucks.

[M Fowler]

The pot is wired wrong in two layouts it should be the middle and left lug when looking at the back of the pot.

See the attacked layouts.

[guitardude57]

Thanks Mark,

I had the MV wired correct......... still thinking about disconnecting it.
Useless as is.

[M Fowler]

That's strange mine works very well.

The only thing I want to change is the cap used in the switching that has no appreciable audible difference to my ears.

[rp]

Mark,

The 2 wirings of the pot wouldn't affect the sound of the MV just the rotation, clockwise up or counter cw up. If you miswire it would be apparent, no?

The only thing I want to change is the cap used in the switching that has no appreciable audible difference to my ears.

Which cap is this?

Thanks

[M Fowler]

Which cap is this?

The Fat Boost switched cap.

The 2 wirings of the pot wouldn't affect the sound of the MV just the rotation, clockwise up or counter cw up. If you miswire it would be apparent, no?

Can't remember but I'm sure your right the MV didn't work proper so I changed it over.

Not sure what the problem would be with the OP's amp as the MV works very well on my little 18watter. I used the Ken Watt's version which has verticle Heyboer PT so no have to cut large PT holes nice.

[rp]

I've tried that Matchless master volume before and didn't like it at all. The best one IMHO is the Lar/ Mar

Tom,

I'm not a big MV fan, but think the MV on the lightning sounds good - not buzzy, and mine is switched, but I too think it comes up way too fast. Is the LArMar better here?

I might as well ask in what way you think it sounds better too, as I will one day build a Spitfire and might just start with the LarMar.

I'm not going to mod my Lightning, it's the most professional sounding amp I ever pulled off, I'm going to pretend I paid $2300 for it and leave it alone.

[Structo]

When I had tried that MV like in the Matchless, which I believe is called the Cross Line MV, it was too abrupt and not a very gradual attenuation.
Sort of loud, then not so loud.

I have a little push/pull 6V6 amp that I used for a test bed and I have probably made that amp into 4 or 5 different amps, the last being a Rocket.

Anyway, early on I decided I wanted a master volume on it and I tried just about every kind you can think of mostly just to experiment and also to find what worked best for that amp.

The Bootstrapped MV which is very similar to the Lar/Mar worked pretty good.
I think that was what Kenny, then Larry and Mark based their design on.

It has the best range and curve of attenuation that I have tried.

[Darkbluemurder]

I've tried that Matchless master volume before and didn't like it at all.

The best one IMHO is the Lar/ Mar or another is the bootstrap master.

For your amp the Lar/Mar will work good because it replaces the 220K resistors on the PI.

Just copy this to your amp and connect the wires that is says to go to pin 5, connect those to your 1K5 grid resistors.
I would move those 1K5 grid resistors to the power tube sockets and run the wires from the master volume to those. Better performance, less noise.

I second that recommendation.

One caution however: the Spitfire has only one gain stage before the PI. Most of the distortion this amp gets comes from the power tubes. As a result, any PPIMV will not be transparent.

[Gaz]

I remember someone swearing somewhere that this MV only sounds good with cathode bias, and NFB. Don't remember if there was even an explanation, but I liked hearing that cause it sure sounded like crap in my fixed bias NFB amplifier!

[M Fowler]

Gaz you have a spitfire and used the MV right? Does yours work OK?