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Vintage threads from the first ten years

Re: Master in 5F6A circuit (YBA-1)

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5/26/2000 12:36 PM
frank	Re: Master in 5F6A circuit (YBA-1) I'd go with page # 196 ("type 4")...IMHO I think you'll like that one better!

5/29/2000 3:56 PM

hi guys,

Thanks very much with your help with the 5F6A master volume ideas. I went ahead and installed the post-inverter style dual-1MA pot (based on Bruce Collins' drawing) and it sounds better than my previous single-pot attempt.

At high-volume/low-master settings the amp is pretty "farty" but at mid-vol/low-master things sound really nice. Slight crunch at lower volumes, exactly what I was after!

cheers,
Sean

6/1/2000 7:41 PM

Sean,

I had very similar results. I used the circuit in Mission amps MV circuit with two .1 on each end. At the lowest levels the output was very distorted at any preamp gain of about 3. It was also very grainy and very bright. Using the idea in TUT, I changed one set of caps to 1uf. The restored some bass, but didn't help the distortion and graininess. What did help was increasing the 68K bias feed resistors to the more normal 220K values. I also reduced the preamp gain by going to a 2.2k cathode resistor (instead of the stock 1.5K). The amp is still a little buzzy at high preamp settings. I don't know if it sounded like that originally since it was so loud at those volumes you couldn't stand it for long.

It is also likely (in my way of thinking at least) that when you cranked the non-MV volume, the entire power supply was sagging and reducing the preamp voltage and therefore gain and grittiness with it.

I may try a simpler cross line cut MV and see if I like that a little better. I'd appreciate an email if you resolve this on yours.

Thanks,
Doug.

6/28/2000 5:54 PM
marcel b	Tryed this post PI mod myself. The sound is interesting but no one mentioned that with lower master settings the prescence doesn't work no more Isn't that a problem to you Marcel B.

6/28/2000 9:20 PM
Doug	Hi Marcel, Yes, anything you insert in the feedback loop will effect the NFB and therefore the presence control. The amp I have uses a fixed presence control, so I didn't have this issue in particular, but I did have to tweek the NFB resistor to get the amp sounding decent with this installed. Doug.

7/5/2000 9:13 PM

Doug you're in luck then, I however have a ajustable presence there and hate the fact that it doesn't work anymore when having the master somewhat lowmostly because then you actually need that extra bite in the tone. So my master volume is wired in just before the PI. Not like most of them but I use a 1 Meg pot there that is only connects the sinal to ground via it's wiper so there is no series resistance in your direct signal.It keeps the highs more alive and of coarse my presence keeps working.The overdrive howeever is not that intense but if I want that I just push the power tubes and we're in heaven . IMHO master volumes on any kind of fender amp Tweed, BF or SF is not that great in general. It seems that these amps need to pushed before they wake up don't you agree
Marcel B.

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