Talk box build

Gearhead

Realising I have not been very forthcoming with what I'm up to, I have decided to go and share a build with y'all: a tube powered talkbox.

Whatsa talkbox? Remember Peter Frampton's 'Show Me The Way' or Bon Jovi's 'Livin' On A Prayer'? The solos in those songs make use of a wah-like effect that is even more wah than wah. The talkbox pedal simply sends your guitar sound up through a garden hose type tube to your mike. allowing you to 'shape' the sound with your mouth. Having always been interested in the effect, I realised I should have one when practising wah and keeping on trying to move my mouth rather than my foot (we've all been there I guess).
Technically the thing is simple: a compression driver normally used in horn tweeters is connected between an amp and a hose and there you go. Problem number one is that horn tweeters don't like the amount of bass a normal guitar amp churns out; some types have been known to fail thermally when used directly from a normal amp. There are self-powered types that don't have this issue and that is where my plan comes in.

The goal is to build a boutique tube powered talkbox into a portable and sturdy pedal housing, having true bypass switching to rig mute / hose output. Surely the sound is going to be shaped with the mouth, but is should be cool to begin with - hence the tube amp. Building the amp into a pedal gives a couple of restrictions. No more than two tubes, preferably small ones at that. Simple power supply. Little or no tone controls. Given the high efficiency of compression drivers the amp would need little power - 5W should be more than enough.

First step has been reading up and selecting components. Sent an email to my tube guru Karel who gave me a tip wrt the power supply. Joining a group buy from tubedepot I today had to make up my mind as to tube complement and components around it.
Decided to go for a smallish duo that I think will do well: EF86 and 6AQ5. Most of you will have never heard of these so I will indulge a little: the EF86 is a preamp tube that, unlike almost all others, is not a triode. It is a penthode, and one with high gain at that. It's most known use is in the 1959 Vox AC15 - modern CCx types do not use it anymore. The 6AQ5 is the little brother of the 6BQ5 aka EL84, having virtually the same spec but in a smaller enclosure. Should give 4W at 8% harmonic distortion (all penthode!), the gain of the EF86 being plenty to drive the 6AQ5 into clip.
Power supply will also be interesting. The thing to do apparently is to use a wall-wart 6VAC power supply into the pedal, which would feed the heaters and another transformer. This transformer should be a low wattage 5V power tranny used the wrong way around, making 250+ volts AC. Quickly rectified this will give enough juice to my penthode tone bottles. I have not sourced any psu parts yet.
The output transformer is another thing, I'm going for a 4-5K for about 40mA . I guess I will have to go beg Karel to wind one.
The compression driver is also going to be a hard thing to find. Will keep my eyes open. Yes I can order a Beyma online but that would be rather heavy on the budget.
For components around the EF86 I have looked at the standard application sheets and compared to Vox's take on it. As they seem to have done with all their amps, they up the plate resistor a good bit and adjust the other components to match - a lead I will follow to some extent.

Will post provisional schematics as soon as I have made some. Will keep you posted ?

AlanRatcliffe

Interesting build, though I'm not sure if the valve amp will make a huge difference to sound quality. I love EF 86s - they are very harmonically rich, perfect for fattening up Teles and Strats. The one downside to them is a tendency to microphonics - especially the new ones. Quite a few of the Dr Z amps use them, and I think one or two of the Matchless amps did too. Actually, didn't the Marshall 18W use an EF86?

I've got a spare new production Electro Harmonix EF86 if you want it - I have a Few NOS ones (a Telefunken, a Philips and an AEG), so will probably never use the EH. It's got an hour or two on it, but

Gearhead

Alan Ratcliffe wrote: Interesting build, though I'm not sure if the valve amp will make a huge difference to sound quality.

You're probably right about the quality, but I do not have any knowledge on sand amps and I do not have an overdrive pedal, so I intended to use the valves for creating the tone I want. What I might look into is using the overdriven signal once it is there, so as to have a talkbox pedal that doubles up as an overdrive. For instance by picking up the signal between the power tube and the output transformer, coupling it through a cap to a constant load and calculating that into the overall impedance....
The other aspect of that is there should be some highpass filter before the compression driver to save it from thermal problems. As an overdrive pedal, it should have more or less flat tonal response. A highpass filter on the secundary is going to be heavier and more expensive... Will need to sleep on this.

Alan Ratcliffe wrote: I love EF 86s - {..} The one downside to them is a tendency to microphonics - especially the new ones.

Thanks for the heads up, I will make sure they are mechanically uncoupled from the compression driver. Being in the floorboard, that should leave the tube relatively still.

Alan Ratcliffe wrote: I've got a spare new production Electro Harmonix EF86 if you want it - I have a Few NOS ones (a Telefunken, a Philips and an AEG), so will probably never use the EH.

I just ordered a new EH.... That is, if MikeM is not too busy with his new Twin to order the parts for us all.

Gearhead

Gearhead wrote: What I might look into is using the overdriven signal once it is there, so as to have a talkbox pedal that doubles up as an overdrive.

Another couple of thoughts occurred to me:
- If I sell my GP-8 with floorboard, I will no longer have a tuner output at my feet. In other words, a tuner output on the talkbox would be nice... a tap that comes to mind is with a suitable trimpot in series with the EF86 cathode bias resistor...
- if I sell my Mesa Boogie Studio preamp as well AND if the talkbox should have a tone stack and overdriven output, I would not need to lug a rack along. On top of that, it looks to me like that EF86 (at 1W anode dissipation) would have no problem coping with the limited insertion loss of a Tweed era tone stack while still being able to drive the 6AQ5 into clip....
- I wanted to use two small small power trannies: one 230V->6V and one 230V->5V reversed to get 6V heater supply and 276V unrectified high voltage. The 5V toroidal is very hard to come by and I want to go toroidal because of the limited space. I could also go 230V->12V into 230V->12V reversed, which are easily found and relatively cheap (R115@RS-Comp). I would need a higher value sag resistor and would just have to put the heaters in series with a shunt over the EF86....
- the EF86 has a much higher max. plate voltage so I could make a 'front-to-back' power supply with higher voltage on the preamp tube....
- if I do not want the 6AQ5 to see a high impedance at low frequencies I should build in a lowpass filter into a dumping resistor at the same -3dB frequency as the compression driver highpass filter... Still undecided whether to put this in the primary or in the secondary circuit...
- I might add a boost footswitch as well, switching the plate load from 100K to 220K and activating some cathode resistor bypass caps....

Hey if anyone here has good idea or comments wrt the above feel free to post! Soon it will be schematics time...

Gearhead

Gearhead wrote: I would need a higher value sag resistor

You guys aren't paying attention eh? An SE power amp is necessarily a class A and what use is a sag resistor in a class A amp? None. Serves me right for posting here ?

Gearhead wrote: - if I do not want the 6AQ5 to see a high impedance at low frequencies I should build in a lowpass filter into a dumping resistor at the same -3dB frequency as the compression driver highpass filter... Still undecided whether to put this in the primary or in the secondary circuit...

Another idea popped up. In order to get some more low frequencies out of the compression driver, I might add some additional mass in the sonic path. That way I would lower the resonant frequency and be able to use a smaller driver. It would also lower the efficiency but (at >107 dB) we have plenty to spare there...

tonerider

Picked up on this a bit late but anyway!

I've built a few talk boxes in my time and still use one live when playing two of Peter Frampton's songs "Show Me The Way" and "Do You Feel Like We Do". I built my current one around 2003 and it's a real workhorse and it's given me no problems at all through 7 years of live playing.

There are a few things to note when building a traditional style talk box:

Choose a horn driver that can handle as wide as possible a frequency bandwidth, even down to 350Hz and use one with a higher wattage than your amp. (Mine is triple the value)
Build a splitter box with a footswitch that can toggle your guitar amp's speaker output to be routed either to the amp's speaker or to the horn driver (mine sits at my mike stand with a short lead to a dpdt mounted in a round Roland pedal.
Remember, if you use an amp other than your existing stage guitar amp it will be very distracting to yourself on stage since you will be hearing the guitar coming through the amp in addition to the talkbox's sound going from the mic out through the FOH system and also back through your floor monitors. I'm talking from personal experience here. You don't want to hear both.
Take note: Horn drivers don't like being fed a distorted signal so when playing the talkbox use a clean sound, I've found bridge single-coil or humbucker bridge in coil-split mode to be the clearest and the best tone for my own talk box designs.

If you need any help just let me know. I can post pictures if anyone is interested.

Valie

If you want a single ended o/tranny just pm me. It comes out of a Akai valve tape recorder. Used two EL 84's single ended in stereo.

Gearhead

@Andre 1: I don't think the two-amp story will ever be a problem. I will run the guitar into the talkbox and the talkbox tap into the rest of the rig. I should have a footswitch for true bypass vs. tapped and one for mute output.

@ Andre 2: If your talkbox does not like drive it must be because it cannot handle low frequency signals. Just because a driver does not produce volume at a certain frequency does not mean the coil is not moving. The low frequency signal pushes the coil to the end of the stroke while it is outputting your highs. Since no speaker coil is very linear at the end of the stroke, your distorted signal is going to get messed up. My plan is to lower the resonant frequency of the system to, say, 200 Hz and to electrically filter out everything underneath 250. I will of course need to make an impedance compensating filter so the tapped signal will still be relatively balanced.

@Valie: have already ordered tranny but am nevertheless interested in the offer. Will PM later.

tonerider

AH! ?

Yours is a new take on the classic design if I understand you correctly.

You will run from the guitar directly into the talkbox (with a dedicated amp built into it to power the horn driver) ?
At the talkbox you will somehow have a true bypass that will route the guitar's signal either to your guitar amp or to the talkbox ?
Will this not make for a very bulky unit that will be lying at your feet at the mic stand since the tube still has to travel up to the mic (mouth) ?

It seems like an interesting project and has started me thinking as well. Just wondering how I will rig this up live since I have a rack and I go UHF wireless.

You can make out my regular talkbox in my small profile pic on the left here.

AlanRatcliffe

As an aside Gearhead:

I used to use an amplitude modulator for a "talkbox" (one was built in to a Boss SE-50 I had). Use a mic as modulator and the guitar sound as carrier and a highpass filtered sidechain to add a little of the uneffected bypass signal back in to the mix.

Worked very well and you can also then use any electronic signal for either modulator or carrier (I often used to use a drumbox/drum submix as modulator) - similar to using a sidechain as key for a gate, but with more control than the usual on/off. ?

Gearhead

@Andre: you've got the picture. The enclosure I have in mind is a 75x50mm aluminium rectangular tube of about half a metre, running across the top of my floor board. I just bought an FCB1010, so I could control two switches in the talkbox. The big hurdle in the design now is lowering the resonant frequency of the compression driver, I am just going to build the rest first and research the topic, I'm sure the answer will dawn on me.

@Alan: please let me just finish this and not think of alternatives.....

AlanRatcliffe

please let me just finish this and not think of alternatives.....

Gotcha! ?

Gearhead

Long time no progress but I now stumbled onto the Monacor KU-616T compression driver which is meant for 100V use and has 112dB at 75W from 160-6500Hz. If I could use this thing it would require a funny OPT but eliminate the need for any filtering or acoustic manipulation. Now how to get hold of one...

Gearhead

Just ordered a couple of NOS 6EJ7 tubes to replace the EF86 as the preamp pentode. Interesting tube. A dozen times more gain to play with so can put the tonestack and the volume between preamp tube and output tube while still having enough drive. Am hoping the one tube preamp will make the amp have less compression while pushed.

Gearhead

found another example of an oke trying to do the same sorta thing:
http://www.kolumbus.fi/risto.kivioja/RikstoneAmps/CircuitC5.pdf

Nicholas-L

I cant wait to see the end result of this project ?

Gearhead

Even better candidate, fullrange: B&C DCX50. Bit costly, but that's just a matter of saving up ?

Gearhead

Or, a lot more affordable, I could go for a normal driver and put a cone on it to get to the hose...