Matchless DC30 power scaling

[FunkyE9th]

If you go to sewatt.com, they have a schematic showing how to install the VVR (http://www.sewatt.com/files/sewatt/VVR.pdf). You have to register though. They show it installed after the the 1st filter cap. The idea is to regulate the filtered DC instead of the pulses that come out of the rectifier.

[Structo]

I found it without registering.

Apparently sewatt.com forum is no longer there.

[FunkyE9th]

I just tried the link without logging in. It seems to work, so I guess you don't have to be a member to view it. My mistake...

I was going to attach the file, but I thought the sewatt guys might not like it because they require you to register to view their forum.

I was just at sewatt. It's still there.

[Yngve]

I've installed VVR after the first filter cap on my Matchless, and it works without any hum now

I had to buy a 60W soldering iron, and next is to solder permanent wiring.

Now it doesn't sound quite as good as I hoped as it looses quite some crunch at the low settings but the sound is much warmer than the master volume I removed, so all in all it's an improvement. I was expecting the same amount of preamp break up as when running the amp at full voltage, but that just doesn't happen. I guess the preamp isn't driven as hard when lowering the voltage and maybe that results in less crunch.

[Yngve]

I did some measuring of B+(in) and B+(out) just for the fun of it and found something interesting:

VVR 100%:
B+ in: 325V
B+ out: 319V

VVR 50%:
B+ in: 343V
B+ out: 196V

VVR 0%:
B+ in: 376V
B+out: 29V

So the 6 DCV difference in B+ in and out at 100% is expected (I've read that the VVR circuit drops a few volts), but is the B+(in) supposed to vary from 325 - 376V when turning the VVR from 100% to 0%?

[FunkyE9th]

I did some measuring of B+(in) and B+(out) just for the fun of it and found something interesting:

VVR 100%:
B+ in: 325V
B+ out: 319V

VVR 50%:
B+ in: 343V
B+ out: 196V

VVR 0%:
B+ in: 376V
B+out: 29V

So the 6 DCV difference in B+ in and out at 100% is expected (I've read that the VVR circuit drops a few volts), but is the B+(in) supposed to vary from 325 - 376V when turning the VVR from 100% to 0%?

The transformer has some equivalent output impedance, so as the amp draws less current (i.e. as you dial down the VVR) that output impedance will generate less voltage drop, which leads to a higher B+(in), so it makes sense that the B+(in) is going up. If you were to take out the pres and power tubes, and power up the amp, B+(in) will even be higher because there is no load to draw any current.

[Yngve]

Thank you for your explaination. Seems that it works as it should then

Does your VVR amps give less overdrive at low settings? I mean, do you have to compensate by increasing the preamp gain knob?

[FunkyE9th]

The amps that I have with VVR either has 2 knobs (volume and tone) or 1 knob (volume). Sorry no gain knob. I just turn volume to get the dirt I want and then dial down the VVR to the level I want.

[Yngve]

The amps that I have with VVR either has 2 knobs (volume and tone) or 1 knob (volume). Sorry no gain knob. I just turn volume to get the dirt I want and then dial down the VVR to the level I want.

Oh. Well the Matchless is simular... Volume and tone at the EF86 channel. I always mix volume and gain. So you don't have to compensate for less dirt ( ) by increasing volume when dialing down the VVR? I do... Hmmm...

[FunkyE9th]

Not that I recall. Maybe you are getting less speaker break up as you dial down the VVR pot. You are no longer pushing the speaker as hard, so less dirt, maybe.

[Yngve]

Not that I recall. Maybe you are getting less speaker break up as you dial down the VVR pot. You are no longer pushing the speaker as hard, so less dirt, maybe.

I don't think so, because I used to get more break up at this setting with a cab sim and load. Not pushing the speakers so hard would not be the full explanation.

[John_P_WI]

Yngve,

As explained as the power amp is dialed down, the loading is reduced allowing the voltages to rise. Are you using the VVR on all supplies or only the power tubes? If only the power tubes, measure your pre amp voltages and you will see an increase in them too as the voltage to your power tubes is decreased. This will impact the tone as the increased pre amp voltages will increase the perceived "head room" or distortion character of the pre amp..

John

[Yngve]

As explained as the power amp is dialed down, the loading is reduced allowing the voltages to rise. Are you using the VVR on all supplies or only the power tubes? If only the power tubes, measure your pre amp voltages and you will see an increase in them too as the voltage to your power tubes is decreased. This will impact the tone as the increased pre amp voltages will increase the perceived "head room" or distortion character of the pre amp..

I inserted the VVR right after the 1st filter cap, so that would be scaling the whole amp.

[Yngve]

Now I've AB'd the VVR against a Weber MASS: VVR 100% and MASS at high attenuation against VVR 20% and no attenuation to compare at the same volume, no changes in other settings. There's much less overdrive/grit/crunch with the VVR compared to the MASS. Tone is much better with VVR though, but the decrease in overdrive bugs me.

I also AB'd my Badger 30 with PS against the MASS, and in this situation the overdrive is preserved. Tone is much better with PS than MASS.

Is this only in my setup? Something wrong here perhaps? I've included the schematics for the new VVR placement.

[Structo]

With regards to the 1M pot shown in the VVR Mod schematic.

Does that have to be a wirewound or high wattage pot?