Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ncusack on June 29, 2011, 01:33:51 pm
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Hello,
Im looking for a bit of assistance from anyone who knows how I would go about incorperating the AMZ tone stack into a single ended 5879 build im planning. For the most part im looking for help scaling the values up so I can use it in a tube amp instead of a pedal. the schematic can be found here.
http://www.muzique.com/lab/tone3.htm (http://www.muzique.com/lab/tone3.htm)
I intend to have a switch on the front panel that will have 3 preset values for the "body" or mid setting. This stack will be fed from a cathod follower so my input impedance should be around 600R. I know all R values in this stack should be higher for tube amp use and that means the cap values will have to drop. I've dabbled with the Duncan big muff stack and have come up with some values.
Zscr = 615R
R1 = 1.5M
R2 = 50.9k(Scooped), 118.3k(Flat),560k(Mid Peak) - (560k with optional 150k or 56k in parallel)
R3= 1M - A
R4 = 1M
C1= 1n
C2= 500p
these values are all larger aside from the scaled caps and it appears to produce similar frequency response to whats on the AMZ website. I'm just wondering if there is anything drastic im missing with my adaptation of this design.
Any and all input is welcome.
Cheers,
Neill
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IIRC somebody put a Big Muff tone stack in a single-ended amp with a 5879 not too long ago. I think that AMZ tone stack is a derivative of the Big Muff. A search for "Big Muff" here might turn up what you're looking for.
HTH
Chip
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Yeah I've been chatting with tubeswell about his ef86 amp that uses a similar tone stack and I found a thread about a project called DaToad but thats a plate driven version of that tone stack.
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> fed from a cathod follower so my input impedance should be around 600R
NO!
The load on a cathode follower can't be any lower than the load you would use on a plate-loaded stage. For the usual values, say 220K or so.
The plate-loaded will sag with lower impedance loads, the CF won't sag much (until loads get much smaller than 220K). That would be the reason to add a CF.
The BMP stack with 100K pot will have heavy treble-drop with a 39K plate source, equal bass/treb with a low-Z source (<10K).
If you like the BMP stack, but want to use it in a tube circuit, the solid-state BMP values should be higher. Start with resistors 2.5 times higher (62K, 100K, 250K pot), caps 2.5 times smaller (1,500pFd and 4,000pFd). That's for "similar"; you may scale all caps otherwise to get other response shapes.
The "input impedance" of such a stack is perhaps 30K. That's a heavy load on a cathode, but a very-heavy load on a plate. Raising all impedances is not a good path becuse they soon get so large they attract buzz and radio. For "clean", you will need at least one gain-stage between this tonestack and your power tube(s).