Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on September 11, 2011, 01:30:14 am
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HI guys, Our thoughts are with you today. The VVR has a problem, first i thought i had cooked the mosfet because it was only reading 9 to 27 volts and the amp was badly distorting.I bypassed the VVR to fix a few bugs and now getting a good sound.
I replaced the mosfet only to get the the same distorted sound. I originally made two VVRs the same way and the other is in my MSJ with no problems :dontknow:
The volume is huge(with VVR bypassed) and i'm not getting much travel out of the two gain pots and master vol, i'm thinking that it could be due to the paralleled input. Would increasing the gain pots to 2M help?
Also as a side bit, when the blackmore sw is flicked it engages V3b increases the gain as expected, i was thinking adding a vol pot as per the TOS FATNESS schem. Would i need to remove both 470k resistors and just added the 250k pot. Thanks
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Sorry guys V3b is still wired as per this schem. Thanks :icon_biggrin:
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i'm not getting much travel out of the two gain pots and master vol
I am not sure what that means? IF it means that you would like to have that volume on 5-7 and instead you are getting it on 2-3, then you would use a lower value pot?
IF it means that you have to go to 9-10 to get the volume you need & would want to dial 5-7, then you would increase the pot value.
Parallel a resistor across the outer lugs (to reduce value) or add a resistor to ground to increase value to see what you like? Then you can leave it that way or subsitute another pot with that value.
With respect, Tubenit
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Thanks Tubnit, I was only able to turn the pot to 2-3 and was getting blasted.Having a high gain amp as this,it produces what sounds like a lot more than 18-20w.Thanks
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Hi guys still trying to tame the volume on this beast, I replaced the gain pots with 500k pots,have better result (but not much)on the plexi channel and the other channel is still the same. I then replaced the master vol with 250k pot and no real difference. :dontknow:
I also disconnected half of the paralleled V1 and the vol was the same.
The VVR i am unable to locate the problem,so i will replace it with a PPIMV and see if that gives me any joy. :icon_biggrin:
Any thoughts,thanks
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I was only able to turn the pot to 2-3 and was getting blasted
OK, measure wiper to ground with the pot at around 4.5. Let's say it's at 220k to ground then use a 250k pot
OR if it is at 135k then use a 250k with a paralleled resistor to get it in that range.
On my Carolina SongBird, the trim pot into the OD section is at around 20k to ground from wiper.
with respect, Tubenit
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Thanks T, I'm slowly getting it to where i want it.I replaced the VVR with the PPIMV and is working very well :thumbsup: and i added a 1m pot to the second half of V3 which is allowing some control of the gain :blob10: Now all i need to do is give it some smoothness so i'm thinking of a 820r/1uf bypass on V3b or maybe some other combos ( I even had some thoughts of adding the IRF820 CF and see what it would do :l2: ) Thanks
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I even had some thoughts of adding the IRF820 CF and see what it would do
When I added that to one of my amps, it definitely changed the tone. I would remove the cathode cap on the triode prior to the IRF820 CF to see if you like how that increases the smoothness of the tone also. I found the cathode cap added some graininess to the tone that I didn't care for.
With respect, Tubenit