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In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: Bleeders at shut-down...Posted by anthony on: 6/25/2015
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 Romy the Cat wrote:
Well, they technically not Lpads but juts regular attenuators even though they connected in “protective mode”. You can go with stabilized impedance to maintain the high pass filter over the coupling capacitor to work properly but I do not feel it is necessary. When you make the real amps you will have the attenuator ruining let say between 35K and 36K to set the real tube bias properly.  You will not slide the attenuator from 0 to 50K. The range will be buffered by two resistors up and down and in context of 100K biasing resistor the impedance shift that your coupling cap will see will be near negligible and might manifest a 2-3Hz difference in the slop. Above I told you that I tested the slope with analyzer and I did not detect any meaningful crossover shift while I changed bias. 
 
Now, the type of the resistor is the real bitch question. You do not want rotary switch with great resistors but you rather want a 10-20 turns attenuator. However this is bias and everything you do with bias matters sonically. So, find the best you can get 20 turns attenuators. At the time I did it I had 3 or 4 different types and all of them were as good as fixed resistor. I chose the one that I liked best at that time, I do not remember what it was, I think it was some kind of large 20 turns Vishay for $12. It was however over 12 years back and today you might find better parts. 


Thanks Romy.  I should be able to track something down.  At this stage I am thinking of Bourns 3590 series pots.



 Romy the Cat wrote:
Be advised that quality of soldering and wires and even the layout of the bias wiring in the amp’s chasses is very auditable for whatever reason. I actually was very surprised how sensitive and demanding my 6C33C where for biasing line. I was able to hear the sound change when I loved the proximity of bias wired to mass ground. I am not kidding.

I don't doubt this statement at all.  There are a few ideas for wiring and component layout kicking round in my brain but I think they are for a later stage.



In the 6 Channel Version of Super Melquiades thread at post #89 you mention trouble you were having with some NC relays that you were using to disconnect some power supply bleeder resistors when the amp was turned on.  When the amp is turned off these relays make contact again and they conduct power to drain the power supplies backwards into high wattage 50R resistors.  I can see that this would be a good idea from both safety and cap lifespan perspectives.  Could you please share a little more info about this setup?  Does it still function?

You mention 50R resistors and bridging two 6A relay contacts for each power supply.  What wattage do you use for the resistors?

Regards,

Anthony

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