Structo wrote:
The difference between here and there, at least you don't have to buy $400 worth of books to install Dana's!
The TUT series of books is probably an excellent reference set and are probably good to own, but everytime somebody asks Kevin O'Connor a question he refers them to one of the TUT volumes.
Tom,
Kevin sells budget ps kits complete with instructions, he also backs them up personally as well as on line as PS.com.
As far as KOC referring to his books, it is the old "Give a man a fish and he has a fish for a day, or teach him how to fish and he will have fish for a lifetime". His books generally describe the development and implementation of the design, along with variations for customization.
He is one of the most generous guys out there with information and designs etc.
These kits by Dana & KOC are a great way for novice builders & hobbyists to get started, and kudos to them for their work.
They are also frustrating to us newbies when something doesn't work out, and we lack the deep knowledge to sort it out ourselves. These forums can be very helpful *sometimes*!
That implementation does not look right to me at all. For one the VVr should get the B+ after the first filter cap, I believe. And the control pot does not look right either. where does the B+ from the VVR go to the pot? And why does the VVR pot only control the Bias to the power tubes.? Why is the bias strapped across both wipers of the dual VVR pot ? One is for B+ one is for bias.
I know Dana will help you, but I think you need to reread the installation instructions and look at the install diagram again.
Thanks for the input. I was trying to follow the schematic that Dana kindly provided me which shows B+ to VVR coming from standby switch through diode.
Dana lists 2 implementations: one that controls voltage only on power tubes (which this is) and one that controls all tubes. Both also control bias voltage.
The VVR bias output goes to the Master Volume pot as I am using the Lar/Mar PPIMV circuit, from the Metro forums. Again - this was Dana's suggestion on where to "break into" the bias circuit to add the VVR.
Here is the schematic again with a correction on the OT center tap.
- Bil
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I don't have any experience with these kind of voltage limiting circuits yet, neither have digged into London's Power Scaling, not into Dana's VVR yet...
... but after pure logic it seems, that after the corrected schem above it's the only way to go - but still shouldt be confirmed from Dana!
Sorry to be so late to the show. I am swamped with things at the moment and have been on here from time to time answering PMs but I haven't been checking the forums much.
Anyway it appears you tried the new mosfet and still have the problem. I keep looking at the bias circuit and the connection between the bias and the MV pots. I know it works just fine in a amp by itself but I don't think I have seen anyone try this exact circuit with a VVR. I am wondering if we may need to add a couple of .1 caps, ground the MV connections that go to the bias and run the bias out of the VVR straight to the 2) 2.2m resistors. It may be that the interaction between the 2.2m resistors and the 250k pots are doing something strange. Just a thought. are those really 2.2m resistors or are they 220k resistors?
I have no idea if it will fix the problem but it is something to try.
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No problem, my friend. Very busy here too, trying to wrap up work stuff for a few days off. Still squeeze a few minutes in to work on my amp!
I also feel the circuit might need changing. It is possible to have multiple defective parts, but the odds are reduced. So I will try your suggested changes and report back.
Yes, those are 2.2M in the PPIMV circuit. This version was developed by Larry of Larry Amps (novosibir on the forums) and tested and approved by Mark Abrahamian (rockstah on the MetroAmp forums). Hense the name: Lar/Mar. It is one of the best sounding MVs IMHO. Thank you Larry and Mark!
As I've already said above, I still don't have any experience with the VVR or similar circuits and I never saw any instructions, how to install...
... but if in an amp w/ fixed bias by installing the VVR the bias voltage first is taken off the bias circuit above the trim pot/resistor and then fed into the VVR, and then from another contact at the VVR fed into both the 220K bias resistors on that spot, where they're connected together on the board - then the VVR also must work properly, when installed as shown in Bil's schem above w/ the Lar/Mar PPIMV included.
If nonetheless it doesn't, then the prob must be located elsewhere.
I sent a PM.. but as others have posted, this may be different. I was going on the layout pic.. the bias has a jumper wire to the 220k resistors from the bias circuit. you would have to remove the jumper. feed the bias circuit to the bias in on the VVR.. the Bias out would go to the 220k resistors. And max the pot on the VVR board.
I can't really coment on how it will work with your amp, as i haven't used it with that type MV. I also run the B+ in to the VVR board,then B+ out to the switch.
I have a few pics i saved of one amp..just to show you where i installed it.
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Thanks again Larry & Richie. The "stock" 220K bias resistors are not connected on the ends close to the front panel, so they are out of the circuit, replaced by the MV pot.
So it seems like I am currently wired as Richie suggests: bias to/from VVR at junction of 250K pots (and 15K, 47K & 10mf bias components).
I was trying to follow the schematic that Dana kindly provided me which shows B+ to VVR coming from standby switch through diode.
