Hi LA,
Duncan's software is really good..not only just plugging in new values is interesting it is often a real eye opener as to how the sweeps work, and seeing the interaction. For me it actually helped visualize what is going on in a graphic way and understand how to set up the amp to sound the way you want in a playing situation.
Duncan's software is really good..not only just plugging in new values is interesting it is often a real eye opener as to how the sweeps work, and seeing the interaction. For me it actually helped visualize what is going on in a graphic way and understand how to set up the amp to sound the way you want in a playing situation.
Sortof :} the in use design has 10 step Switchcraft rotary selector switches with soldered in resistors. This gives fine tuneing around the sweet spot.
Hi LA, I am going to go with the 5E3 simple tone control at least for now. It is the same used in the 6G2 Princeton, and I have a reconed C12R vintage speaker I want to get running with it. The simpler tone circuit is less ''lossy'' I think, but I may need to tweek some values once it gets finished.
Hey Shanx - I threw that one-pot 5E3 together last night, all I saw it do was cut the treble (a good amount), and thereby emphasizing the bass? Bass freqs were unaffected. Is that all I can expect from it? My 3 pot Fender ckt had issues (bad pot, cap or something), didn't get Duncan results. May start going back there, with all new/different components. I run my SigGen up and down and look at amplitude changes on my scope. Time consuming but the best way I have. Good luck, let me know how yours works.
I just attempted to duplicate the 5E3 single pot stack on Duncan's calculator.... set R1 & R3 to 999M (simulate open), R4 to 1 ohm (shorted), R2 to 1M (the single pot), C1 to 500p, C2 & C3 to 10n (in series to give .005uF). All pot does is attenuate a fixed mid hump to zero..... I think I'm messing too much with the algorithms. Oh well.... May just swap some caps on my "real" stack. Which pot effects Treble? Bass?
How I think the circuit works: 0.0005 cap is part of the Hi filter, and the 0.005 the Lo filter. Cutoff freqs are 318Hz/32Hz (Hi/Lo). When wiper goes from the "top", then to "bottom", a) Hi passes everything, then to 318Hz; b) Lo passes only below 32Hz, then rises (passing more and more bass). Oops, this means that going from top to bottom cuts both bass and treble... I am assuming what gets "passed" by either filter is going to ground. What am I thinking??? Help!
Hi LA, Sorry I am just getting back to this..been a busy week. With the 5E3/6G2 I am going to do some tests today on it. The volume/tone controls I think are interactive. But I need to check it further, If volume is full (wiper at top) and tone wiper at bottom (towards .0005 cap) it works like a bright switch, where as you start lowering volume now, more highs bleed through to second stage. A Bright switch does more high pass at low volume and nothing at full volume. There is another ''hidden tone circuit'' which the bright switch or tone control compensates: the capacitance from grid to ground of the next stage. That miller capacitance is shunting highs to ground at low volume settings. That is my theory anyways, it always seemed that without a tone control the higher the volume the more highs seem to pass through. Suggest trying the tone sweep with volume set midway (or 25% 50% and 75%), and that should give a fair idea of what range of tone control you have.
Shanx - thanks for the reply. Been busy myself, but been pondering.... am frustrated by tone controls....duplicated the Duncan 3-pot circuit (no amp, just SigGen, stack and scope. Still couldn't get the same results. Tried just a lo-pass RC network, still not seeing any bass control.... Used a 38K on input and 1M load, still nothing. Doing something wrong. Maybe my SigGen. Will do a baseline on it! Rethinking my preamp design (one input, 3 gain stages), will go back to only two (per 5E3), maybe use the free 1/2AX7 for a tremolo. No tone stack, but a Brite switch. I've seen 3 ways to do it: increase the 68K input to stg 1 grid; lower the cathode cap in the 2nd stg; and lower the coupling cap to the 2nd stg grid (from Tone Lizard and Mission Tweedy). Want to start building a chassis, but need to play with the breadboard a lot more. FYI - I was looking at my in-amp tone stack with my scope on the treble pot wiper, before the vol pot (ala AA764), so no vol control (just one stage of gain). Good/not good?
Jamesecox - glad to hear it worked for you. I won't use any solid state devices in my designs, I want to duplicate and understand the original Fender circuits. May spend more time on this later, but have shelved it for now and am playing with vibrato circuits (have a new post - 2 stages instead of three).
I just worked up a quickie preliminary model in LTspice, which I highly recommend for working up tone control schemes. Here are a few screenshots:
Format is Vol 1, Vol 2, Tone; Tone pot is linear, Vol 1 and 2 are log. Settings are on a scale of 0-10, min to max. I used a -6dBu input as input. I did not model the sections after the tone stack.
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The volume controls interact with the tone control, regardless of which channel you are using, so you may want to at least build up that part of the second channel for best results.
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