Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mk_716 on June 24, 2021, 12:24:43 pm
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Hello all,
Kind of a general question for those of you that use an effects loop.
Is there a preference where the jacks and pots are front of the amp vs. back? I can see the practicality for both, but never have used one myself. I'm working on the layout now (6k6 clean with FX - hey Tubenit!) and have enough real estate to put both jacks and pots on the front panel or back, or I can move the jacks to the back and leave the pots on the front. (lot's more wiring across the chassis if I split locations).
Is there an arrangement here that is better/more practical?
Thanks in advance for your advice,
mike
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I've gotten to where I prefer the FX return pot on the front of the amp chassis and the send pot on the back of the amp as I seldom adjust the send pot. Just a preference thing and not something one "should" do.
See the attached example. I typically use a smaller value FX send pot now such as a 50ka or 100ka.
With respect, Tubenit
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Hey Tubenit,
Thanks for that. I was looking for practical advice from someone who uses it and that totally makes sense. I tried looking at manufacturer's approaches and they're mostly on the back but no clear consensus.
Here's what I'm up to. I was going to build the TBM 6k6 but after thinking about I wanted to have a lower power clean amp. (I'm not a big lead player, that's a lead player's amp imho)
I found the schematic for the TBM Clean with FX 6v6 and massaged it using the 6k6 values. I then re-worked the layout so it would fit on the Doug's stock TBM board.
I've not soldered anything yet, but I have the board laid out with the components. I've checked/rechecked this a bunch, probably will OCD this thing for a bit yet.
If anyone notices anything wrong, let me know. I kinda suck at DIYLC but I'm getting better!
mike
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As a rule of thumb guide for layout, any wires that carry highish current or highish voltage AC (such as heater wires or leads/wires connected directly to tube plates) want to be about 1" away from any signal wires, or if these cross signal wires, they should cross each other at right angles. AC pairs (like heater wires) can be situated (or twisted) close together so that EMF between them gets cancelled out. Some people do this differently and claim success at avoiding unwanted sources of interference.
Obviously tube grid and plate pins are closer than an inch to each other, but tubes are designed to function this way. However, in principle you should try and avoid creating a layout which results in more AC parallel wire runs between plate and grid wires that results in unwanted electromagnetic induction (which can cause crosstalk, oscillation etc).
Classic Fender amp layouts have the tube sockets on one side of the eyelet board and all the signal switches, pots, input jacks, etc on the other side, and lead dress that kinda follows this principle. Some newer amp designs break this 'rule', but even in these designs, good layouts ought to follow the same principle IMHO. Not saying you might get away with something different, as it also depends on how noise-sensitive the signal is in your FX loop. Rather, its just something to think about when you're putting your FX loop level pots at the back of your amp chassis next to the tube sockets. YMMV
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Thanks for the insight Tubeswell,
I'm going to put the jacks and the pots in the front. I can avoid criss-crossing the chassis, the wiring will be much cleaner and I've got the room. I've got a donor Bugera V22 chassis and cabinet (12" speaker1). Nearly 22" wide and the exact amount of holes across the front with everything installed.
Thanks all for you help.
m.