Matchless DC30 power scaling

[soma_hero]

If you remove the standby switch make sure you turn the volume down EVERY time you turn the amp off. The point of the standby is to let the valves warm up before you blast them with 300V. If you turn the VVR down (assuming it's working correctly) then you can let the tubes warm up before you turn up the VVR. Works like an adjustable standby. But that could be more hassle than it's worth, i.e. you'd never be able to pause a session and come right back to it, or even go on standby to switch a guitar and come back to the same settings. You'd have to readjust volume every time to where you "thought" it was at last time.

I'd just figure out a wire route that works well and keep the standby switch.

[ampdoc1]

I convinced the use of standby switches and the reasons behind it are a myth.

See attached.

Also, there is a lot more good information on this guy's site.

ampdoc1

[Yngve]

No luck with the Voxer yet, so I went to try it in my Matchless. Removed the master volume, checked if it worked fine (which it did) and installed VVR in it's place. I got the same problem here too, but the noise suddenly kicks in around 10 o'clock and disappear around 3 o'clock. The low settings doesn't sound too good either, as I would expect a lot more break up from the amp.

It's really hard to solder inside this amp; I don't know if Matchless uses some kind of super solder or if my 30W soldering iron is too weak, but I'm having a hard time to solder up the original joints. I had to solder the grounding for VVR directly to the chassis because of this... I tapped B+ right of pin 8 of the rectifier tube.

I've included a picture. As you can see the B+'s is routed far away from AC. Any hints?

[Yngve]

I forgot to mention about the VVR in the Matchless:

1) I haven't installed the resistors and caps suggested for stopping DC-leakage at very low settings.

2) The hum actually appears at settings between 10 and 01 o'clock; NO noise at any other settings and volume is reduced as expected. The funny thing is that when turning the pot down quickly, no hum appears while sweeping through, but turning slowly makes the noise appear. When turning the knob up, the noise always appears at 10 - 01 settings, regardless of slow or quick turning. Must have something to do with filtering??

[soma_hero]

Ok, I've never tried it without the coupling caps and resistor to ground on the input and volume control. So perhaps that should be your first step? Add those and report back. Make sure the resistor to ground (1M) is on the grid side of the coupling cap or the tube won't be properly referenced.

Since you only get noise during a certain percentage of the rotation that makes me think that the issue isn't wire routing. If it were, I'd imagine you would have noise at all positions. It's hard to believe that 0-200V and 300-350V is stable but 200-300V would cause noise right (or whatever your actual voltages are)?

Try adding the coupling cap/resistor. Next, is this the same circuit board you've taken out of one amp and placed in the other amp? If it is, check your parts. Maybe you put the wrong part in somewhere, although the silkscreen is real easy to follow. Maybe it's just a noisy resistor or diode?

[Yngve]

No I used a different board and parts in this amp. Dana said that cap/resistor mods aren't needed if changing the resistor on the VVR so the minimum voltage gets higher. I would try this first as I would like to keep the Matchless as original as possible.

I wonder if the noise is some kind of oscillator effect? It starts by clicking slowly, and the clicks go faster and faster by turning the knob until it suddenly disappear... I have no idea what causes this

[Yngve]

A picture says more than thousand words; I've made a recording with my cell phone and uploaded to youtube:

http://www.youtube.com/watch?v=hao2A4M08CM

See how the noise kicks in and then disappears without touching the knob...

[soma_hero]

Where did you insert the VVR in the B+ line?

Mine are all setup as follows: Secondary -> Rectifier -> 1st filter cap -> standby switch -> VVR -> OT plates and first dropping resistor -> ...etc...

That's a wild sound you're getting. I have no idea but that definitely sounds like a capacitor problem. Where are you grounding the VVR gnd?

[Yngve]

I inserted it right after pin 8 at the rectifier tube, see the schematic. Haven't measured the voltages yet. VVR grounding is soldered to a point that is mounted directly to the chassis.

[soma_hero]

Grounding could be an issue. Not that you don't have a solid ground connection, but where that ground point is on the chassis. I ran my grounds to the first filter cap ground. Try that, if that's not where your ground connection is. If that doesn't help, try grounding at the PT center tap.

[FunkyE9th]

I would put the the VVR after the 1st filter cap, but before the the choke. The output of the VVR should drive the choke and the plates of the power tubes if you are scaling the whole amp.

Reagrding the extra caps/resitors....If you don't install the extra caps/resistors you will hear the pots sound scratchy when you turn the pots (e.g. the volume pot of your guitar or amp, not the VVR pot) at low voltages. If you don't turn the pots, the amps should be quiet. So I doubt that not installing the extra caps is your issue.

[Yngve]

I would put the the VVR after the 1st filter cap, but before the the choke. The output of the VVR should drive the choke and the plates of the power tubes if you are scaling the whole amp.

Thank you for your help.

If I move the VVR between the 1st filter cap and choke, the output tranny will run at full B+ regardless of any settings on the VVR, isn't that correct? Will this be the correct placement for scaling the whole amp?

I also doubt that not installing the extra caps so far is the issue.

[Structo]

I convinced the use of standby switches and the reasons behind it are a myth.

See attached.

Also, there is a lot more good information on this guy's site.

ampdoc1

Interesting article.
I take it the guy doesn't like standby switches.

How about when you are using SS rectifiers, wouldn't hitting the tubes with the high voltage right off the bat be bad on tubes?

[soma_hero]

Yngve,

I agree you need to put the VVR after the first filter cap. The scheme should go like this: Rectifier -> 1st filter cap -> VVR ->OT wire, choke -> etc.

This way, B+ on the plates gets regulated as well as to the rest of the amp.

My bet is it's your grounding still...

[Yngve]

I will try to get better grounding, and if routing and better grounding fails I will try to move the VVR to after the first filter cap.

Another youtube-clip: http://www.youtube.com/watch?v=ZiqWoCA7hoQ

What can you make of this? Is this oscillating? Poor grounding? Poor cables?