VVR Install Problems

[RB]

I may be all wet but I believe the 2m2 are depicted incorrectly in the schematic in the above post. I recall the 2m2 being in parallel with the 250k pots so as to create a 220k pot to more closely approximate the 220k fixed resistors. I put this type of mv in a friends plexie a while back. I have been going through my notes, drawings and pictures trying to find the mod I installed but haven’t found them yet. But that’s how I remember doing it.

Randy

[novosibir]

I may be all wet but I believe the 2m2 are depicted incorrectly in the schematic in the above post.

No! The PPIMV mod in Bil's schem is drafted absolutely correct!

Both the 2.2M are 'safety resistors', which currently apply bias voltage to the output grids for the case, that a pot's wiper fails, so that the concerning output tube doesn't jump over the Jordan.

Another reason of course is, that the 2.2M's in parallel to a dimed pot equal the former 220K bias feed resistor's value - means, with the PPIMV pot dimed it's like the PPIMV isn't in the circuit at all!

Read some more about my version of this type of a PPIMV from here onwards:

http://forum.metroamp.com/viewtopic.php?p=78656#p78656

Larry

[bclick]

Hey Larry -

You may remember me begging you for advice on the Metroamp 50 Watt forum with noise issues when I first built this in Aug/September this year. That has not been a big issue on stage as I cannot come close to diming it.

Anyway, original build pics are at:
http://www.clickernet.com/plexi50.htm
VVR mod pics at:http://www.clickernet.com/plexi50-mods.htm
Some other mod pics on page 1 of this thread.

How about the fact that I have 5" of wire between the VVR board and VVR pot? Shouldn't be an issue since this is "high voltage" - not signal.

- Bil

[UR12]

.

How about the fact that I have 5" of wire between the VVR board and VVR pot? Shouldn't be an issue since this is "high voltage" - not signal.

- Bil

It could be a problem, have you tried chopsticking them around? Are they twisted together? Even with high voltage on them they can pick up noise.

[bclick]

Yes, I have moved them around. I started with the VVR pot mounted in the Presence pot position. Then reinstalled the Presence pot, twisted the VVR pot wires and left it sticking straight up into the air from the VVR board.

I am heading to central VA for a week. No Internet for 8 days...

Happy Holidays to All!
- Bil

[bclick]

Hi Dana -

Please clarify the paragraph on page 9 of your instructions, where it says:

"This type installation will turn down all of the voltages in the amp as you adjust the power control on the board. This kind of implementation will require you to move the 1meg resistor on your guitar input jack and the installation of a cap between the input and the grid of the first tube. You also need to install another 1meg resistor and cap between the vol control and the grid of the tube it feeds."

I interpreted this as instructions for the "all tube" implementation and did not do this step. Is this also for the "power tube only" method? If so, coould this be causing the very loud buzz in the center range of the VVR adjustment?

Thanks - Bil

[UR12]

Hi Dana -

Please clarify the paragraph on page 9 of your instructions, where it says:

"This type installation will turn down all of the voltages in the amp as you adjust the power control on the board. This kind of implementation will require you to move the 1meg resistor on your guitar input jack and the installation of a cap between the input and the grid of the first tube. You also need to install another 1meg resistor and cap between the vol control and the grid of the tube it feeds."

I interpreted this as instructions for the "all tube" implementation and did not do this step. Is this also for the "power tube only" method? If so, coould this be causing the very loud buzz in the center range of the VVR adjustment?

Thanks - Bil

Yes, those 1m resistors and caps are only needed for the preamp section of an amp where you are regulating ALL the voltages in the amp and they aren't needed if you are just regulating the Power Amp section as the Preamp in that senerio will be running at normal voltages.

The buzzing has got to be coming from noise being picked up by the wiring going to and from the board. I also noteiced that you had your board mounted right over top of your power transformer windings. I am not sure if it was you or someone else that said that they had inserted a "Shield" between the board and the power tranny . If you haven't tried putting a shield between the tranny and the board you might try that. I usually try and use a piece of single sided PC board with the copper side down towards the tranny and away from the board. You will need to make sure the copper side of the board is Grounded. If all else fails I would be happy to take a look at your amp here if you wanted to ship it out to me. The only costs to you would be the shipping. Just a thought!

[UR12]

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[bclick]

Dana, thanks for the generous offer. I can't part with it that long right now, but maybe someday...

I tried a couple more things. Mounted the VVR pot directly on the board. Used shielded wire on the B+ and bias leads going to main board. Inserted another grounded shield plate between VVR board and transformer.

These reduced the noise quite a bit, but not enough. Still has that weird zzzcchhhing in the mid range of the pot, and just doesn't sound that good.

So at this point, I'm going to chalk it up to experience and move on. I'm reading The Ultimate Tone Vol1 to further my knowledge on this stuff and understand the interactions between components better.

Thanks again for everyone's help.
___________________________

- Bil