Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => PC Express and JSchem - Schematics and Layout diagrams => Topic started by: tubenit on December 22, 2013, 09:24:35 am
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CHECK for ERRORS!
This amp has a VERY cranked OD tone to my ears with nice contrast between the clean (on edge of breakup) to OD (very overdriven tone). With the mid boost engaged and OD on, it will sustain remarkably well!
I played around with quite a few different tweaks. Overall, they're just different and not necessarily better. In fact, I think the "original" values may cut thru the mix of a live band somewhat better? Overall, the tweaks gave a tighter more focuses bass tone and lessened the increase of the midboost slightly. There is still a distinct difference.
Revised is 1-'14 schematic. I do think the 1-'14 schematic is somewhat easier to adjust mids and bass with given the mid pot and bass pot being separate. Some values in the LTPI were changed to be more Dumblish. And it has a mod to the FX making it a paralleled FX instead of series. More info about that in ARCHIVES under effects loops.
With respect, Tubenit
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CHECK for ERRORS!
Jack Hester posted a version that uses a concertina phase invertor which frees up a triode to be used as the CF after the 5879.
I think this would make a nice amp.
With respect, Tubenit
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Hi Tubenit
Referring to the TBM 5879 schematic
which is the purpose of the mosfet that follows the 5879 tube and is before the tube of the CF FXLoop ?
Franco
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To my ears, it adds to a smoother tone.
Tubenit
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So it is for flavour reasons, it isn't strictly necessary for electrical reasons in the circuit
Thanks
Franco
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So it is for flavour reasons, it isn't strictly necessary for electrical reasons in the circuit
Correct. Just for smoother tone.
Jeff
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tubenit -
I finished constructing the board for this amp last night, however during my checking - I found that the 200R resistor on the CF grid (gate) is shown ON the layout but NOT ON the schematic. Looking at other amps with this same CF circuit - they have the 200R resistor. Does it need to be added to the schematic for this amp or should it be left off the board? This is my first use of a SS cathode follower so I want to make sure I get it right. :laugh:
If it is of interest, I built your (non-Hoffman) layout as it seemed a bit smaller on a 3/8" spaced "perf" board with eyelets. I am trying out a "centered" ground "plane" idea I had. If it works out (quiet), I probably will use it going forward.
Thanks much for posting these great designs!!
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Does it need to be added to the schematic for this amp or should it be left off the board?
Yes, it should be on the schematic! Sorry about that.
With respect, Tubenit
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Wow thanks for watching this site so closely!!
No biggie at all kind sir. Thanks for all you do!! :icon_biggrin: