floorboard amp with expression pedals

[Donahue]

hello all,

i am hoping that some of the people on this board can help me with an idea i have. i have an idea of what i would like to build, but no real specific knowledge of how to get from wishlist to finished design. i have a modest amount of electronics knowledge, but i have not built anything audio specific. i would like to build a tube amp, possibly with built in effects. because of the large number of features i would like it to have, i may think of it as two different pieces of equipment, the amp and then the effects portion (also due to size). the basic premise of what i would like is an amp that has expression pedals instead of knobs. i would probably try and build the amp into a floorboard (if feasible) and then just run a extension cabinet as the speakers. the effects would be a similar thought, everything with expression pedals. in the end, there might be as many as 12 expression pedals. because of the physical size, it may make more sense to split this up into two floor boards and then just connect them together, which may make the amp + effect idea plausible. the goal would be something around 25 to 50 watts. the whole thing would likely be constructed of something like 16ga stainless. i know its probably going to be heavy.

the controls that i would like a pedal for:

• input volume
• master volume
• high eq
• mid eq
• low eq
• gain (something smooth and modest)
• high gain (something heavy and crunchy. this is a lower priority)

the effects that i would like a pedal for:

• reverb
• tap delay (the pedal would be volume in the mix)
• tap tremolo (the pedal would be the volume in the mix, this is a low priority)
• maybe some sort of scoop?

other features that would be nice:

• built in tuner
• XLR output
• compressor/gate

i know this is quite a bit to package into a first project, but all i am looking for is ideas and feasibility at this point. along with the pedals, some of these would have a bypass switch and an indicator light.

some questions i have:

• is it feasible to have the power amp in a floor pedal?
• concerns with power supplies?
• would it make sense to have an effects board where some of the effects ran pre-preamp and some ran post-preamp? i am envisioning plugging the guitar into the effects board, which is connected to the amp board with 3 patch cables (two for the effects loop). this way the amp could be used standalone.
• could all of this be done analog or would some have to be digital?
• concerns over heat dissipation?
• is it possible to run two different types of gain/distortion simultaneously?
• any problems with a direct output, assuming speakers are connected too?

what are your thoughts?

[nickb]

My $0.02:

I don't see anything wrong fundamentally with all the things in a single floor unit other than your back my start to complain If you're going to have separate units then, honestly, you might want to consider off the shelf stomp boxes for the fx part of it.

I wouldn't be too concerned about power supplies, power dissipation, or direct output.
It would be very, very hard to do without digital and that includes writing the firmware.
Two types of gain/ distortion? Not sure what you have in mind here. If you really mean to mix two different channel then the design is getting very big.

If I make the assumption that you want the pedals so you can change those controls in a live situation then I think you'll find that you've created a monster. You'll be so distracted by all the control that the performance will suffer. If you really want to have different settings you might consider a patch type setup where a microcontroller is used. The patches could then be smoothly transitioned too. You also mention tap delay and tremolo, that will require also digital control and circuitry.

I think that would make for a pretty advanced project that will be complicated by interface of low voltage to high voltage tube stuff.

[Donahue]

basically, i want to have pedals for everything, because i find messing with knobs while playing to be the distraction. i specifically want pedals for the effects so i can roll in and out the amount of delay, as i use delay quite a bit. i would also like to be able to roll in and out of gain while playing. the eq and master volume could be knobs, but pedals might be cool.

the situation with the gains might be overly complicated, but it might yield interesting results. because of my current amp, i do not have a good high gain distortion, so i mostly end up using more of an overdrive tone. the two sounds are for two different types of music. i for sure want the overdrive tone, but it feels like it would be a shame to build a tube amp and not get that high gain sound too. what i dont know is if i can get that sound i want in only 25 to 50 watts. i play mic'd 99% of the time so i am not worried about volume, just tone. my thought is to run the gain channels in parallel and not series, and somehow mix them back together. right now i can only see needing to use one or the other at a time, but who knows how it might sound with a mix?

if i boil down the idea into what i really want vs what might be nice to have, i want to have a tube amp that has pedals for input volume, and gain, and that has a tap delay with an pedal for blend. i use these three things quite a bit right now. everything else is icing on the cake. my current setup is a line 6 spider iii 75 with their little expression floor board. perhaps if i had all my ducks in a row, i could cannibalize this for some of the wiring. i wonder if i can separate some of the effects portions from the amp itself?

the idea of digital does not intimidate me, it just means more research. it looks like the tap portion of the delay is for sure a digital product. maybe cannibalizing a ready made stomp-box and substituting a pedal for a knob might be a better approach.

i may look into building the extension cabinet and just permanently mounting a mic in it instead of the XLR out on the amp.

[Mick Bailey]

Dave Gilmour has a tube-based FX board and it may be worth researching how it's constructed for some further ideas. I know layout and heat dissipation were design challenges.

Any pot can be put under control of a foot pedal and the preamp section of any amp is straightforward to build into a small space with horizontally positioned tubes. The power amp may be given its own section and again, the tubes laid horizontally (like the JTM60). Toriodal transformers would save space and reduce magnetic leakage to some degree - Laney uses these in many amps. Take a look at how some of the rackmount amps are put together. The Marshall 20-20 or Mesa unit, for example. Tube choice and transformers dictate the height of the enclosure. Could be stepped up at the back with plenty of ventilation, possibly fan-assisted.

Digital tap tempo is now appearing in DIY builds. It's possible to design an all-analogue tap tempo circuit, but this would be more complex than the circuit it's attempting to control.

[nashvillebill]

You could also do like Neil Young does with his 5E3. What's his gizmo called, the Whizzinator?

(It's a pedal setup that mechanically moves the amp's knobs to pre-set positions)