Building A Talkbox (need amp circuit)

[Be-Kind-Rewind]

I'm building a talkbox with a 16 ohm horn driver and I can't find a 5 - 10 watt amp for a 16 ohm speaker. Does anybody have a schematic for a nice quality sounding amp that fits these parameters? If not does anyone know if there are computer speakers that have a total of 16 ohm impedance? I can't seem to find anything. Thanks for the help.

[petemoore]

  I would take looks at chipamp datasheets.
  A SE powered LM3875'TF' [insulated body] should easily drive your horn sufficiently loudly [preamp may be needed also],  consider trying out the TBox amp by using battery power, 18V should do it, HF drivers are generally very easy to drive [also easy to pop or fry].
  Depending on the frequency response and power rating of the driver, you may want to consider including a HP filter.
  DIY Audio: Chipamps forum: Power supply threads.
  All amps are only as good as the power supply, by comparison these chips are very very good at 'reflecting a large version of' [esoteric yoda chat for "amplifying"] the sources.

[Gurner]

consider trying out the TBox amp by using battery power, 18V should do it, HF drivers are generally very easy to drive [also easy to pop or fry].

...& if you have a large mouth, consider using 24V. (I made one for my wife - I had to use 38V)

seriously though - I've bought a compression driver specifically for a talk box, but never got around to making it yet.....I concur with most of what peter said, except I reckon the fact the compression driver is all but enclosed and erhmm compressed, it's gonna make driving it a bit of  a current thirsty - and therefore I will be going the way of wall wart vs battery.

[petemoore]

  "Chipamp" is the best part of all these suggestions.
  Power supply is the 'hard part'.
  I used my TBox for a few minutes, a few times, that's why I suggested batteries.
  Considering the amp does other work now, the power supply I built for it gets work too.
  So...mains voltage = lethal potential...I don't like suggesting it.

[Gurner]

  So...mains voltage = lethal potential...I don't like suggesting it.

No different to any other effect/pedal using a wall wart really - and it's not as if the circuit is going in yer gob here - just a plastic tube from the compression driver.

Chipamp is def the way to go, but - unless you work for Duracell - I reckon probably a wall wart too.

[GibsonGM]

There is fun in building the whole deal from scratch I agree, but.....

I use a crappy $50 marshall SS practice amp.  It actually sounds good on its own for the bedroom, but it's only like 5-10W or so.   I put in an interrupt jack at the speaker and when I plug the talkbox driver in, it disconnects the internal speaker.   Plenty loud for a mic to pick up!   Combined with an AMZ buffer/splitter, I can switch from regular amp to this one and be on/off the talkbox very easily.

And it has 3 band EQ to roll off the lows to protect my driver.  Quick and painless, but hey, DIY has its own rewards, too.   You could probably build amp and driver into the same box (as long as you vibration dampen it.  I filled my driver box with expanding foam insulation!  Works great, and if I want the driver back out, it will come out with a knife).

[Gurner]

I've just remembered why i parked my own talkbox project - the thread at the throat of a bog std compression driver is some weird, obscure imperial variant first dreamed up by a guy who drags women back to his crib by their hair for Pterodactyl & chips. I could only find one source for a compression driver  'thread' to vinyl tube adapter ....some far flung place in the USA where apparently they only have mains electricity 3 days a week ....& the concept of posting to the UK forced them to lie down & contemplate Globalization for a few weeks.

[stringsthings]

There is fun in building the whole deal from scratch I agree, but.....

I use a crappy $50 marshall SS practice amp.  It actually sounds good on its own for the bedroom, but it's only like 5-10W or so.   I put in an interrupt jack at the speaker and when I plug the talkbox driver in, it disconnects the internal speaker.   Plenty loud for a mic to pick up!   Combined with an AMZ buffer/splitter, I can switch from regular amp to this one and be on/off the talkbox very easily.

And it has 3 band EQ to roll off the lows to protect my driver.  Quick and painless, but hey, DIY has its own rewards, too.   You could probably build amp and driver into the same box (as long as you vibration dampen it.  I filled my driver box with expanding foam insulation!  Works great, and if I want the driver back out, it will come out with a knife).

that's an excellent mod on a practice amp !

[petemoore]

  You realize that the talk box:
 Gets a split signal [if you want a guitar amp to play].
 Amplifies [and transduces] it enough to travel the tube and bounce around in your mouth [the soundwaves].
 By the time the waves have been tubed', mouth-filtered and reshaped, theres a little bit left over, you can barely hear it.
 A Mic can pick this up, and with a PA Speaker amplifying the 'weak' mic source [or something ''amp'', not included] it sounds like a talk-box.

[Be-Kind-Rewind]

Alright thanks guys. I'll try your guys' ideas out too, but I'm curious about this.

I found it at http://www.techlib.com/electronics/audioamps.html. Is there anyway to change the output impedance to 16 ohms for my driver? My driver takes up to 40 watts, would my driver be safe with this amp? How many watts does this circuit produce?

Simple LM386 Audio Amplifier
This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor. The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum.

[Gurner]

That circuit is a terrible proposal...

1. Input impedance is too low - it'll load your guitar pickup. (or are you feeding in another amp's output?)

2. Just under 1W power @9V & 8 Ohms (nowhere near enough for a talkbox  in my opinion) - Attaching a 16 Ohm driver to it will yield even less power (unless you crank your supply rails up)...so don't go there.

Don't be fooled by the seemingly impressive voltage gain figure - you don't want much voltage gain, you want power output/handling - the limiting factors with respect to the latter is the speaker load, the supply rail & the heat disappation ability of the IC package (which for an LM386 ain't much)

Walk on by.

[petemoore]

  The LM386 amp is a pretty quick, easy, inexpensive wire up, and can serve other purposes...generally no big loss of time/effort to play around with.
  Although the 'diaphram drivers' are generally not too demanding of an amp to control them...
  18V powersupply / Lm3875TF would have more than enough control/power over the driver. A bit more trouble and cost than the LM386 [since both require 'other peripheral' components/chassis or soemthings.
  Also not too bad since it can serve other purposes and is basically one heckuva little amplification device...basically worth playin' around with.
  I've had some luck [both kinds] playing around with printer WW power supplies, they're often 1000 Ma. and 24+ volts, a fair amount to start with...whether the amp you build requires more is where the line is drawn for the PS. Nice thing about the Printer WW's is theyre super cheep or free, and basically safe.

[PRR]

> can't find a 5 - 10 watt amp for a 16 ohm speaker

Use a 8W-20W solid-state amp for 8 ohm speaker. It will just run cooler.

Are you sure you need, or even want, much of a 10-Watt signal stuck into a hole in your head? I think the commercial ones get much less than that?

Do the LM386 for now. 12V will make most of a Watt in 16 ohms. That will be plenty for workshop and small-club tests. Get your setup, connections, splits right. If when you play with a drummer you need more power, then get a bigger amp. 20W practice amps are readily available. As Pete says, the bigger chips on 18V or 24V will give 2W to 4W. 36V total supply on 16 ohms will get you to 10W in 16 ohms, plenty to damage your hearing from the inside.

> the thread at the throat of a bog std compression driver

1) There is a $22 plastic horn, cheap enough to cut-off the mouth and use the butt-end. Jam in a broom-stick, drill for your mouth-tube, slobber with glue/caulk.

2) Two pieces 2x4 lumber 6 or 10 inches long. Use a 1-3/8" spade-drill to go 1/2" into one piece. Drill through for talk-tube. Drop a 1" ID rubber washer in the hole (or slather some caulk). The driver nose goes in the 1-3/8" recess. Put the other 2x4 on back of the driver. Drill some holes and run some 1/4" bolts through both boards to clamp the driver and seal the nose in its recess. A buck of materials, maybe an hour of labor. I have used this idea on road-worthy wood horns.

[GibsonGM]

The old toilet paper tube and some elastics or expoxy works pretty well, too ;o)
Couple brass fittings to make it permanent, and you can remove the 3/8" mouth tube from the box for cleaning.
Remember, all that noise will be in your mouth, and you CAN shake dental work loose!  So pay heed to what PRR wrote about wattage....

[petemoore]

  I just used Silk Soy Milk 2 container-container material.
  The 'shell' holds 2 half gallon container units, one of these is probably enough to make your spiraled-strip-tube.
  Cut a strip, roll it into a spiral, you have a tube in your hand, now use glue and it'll become permanent. Start with the right sized loop [slightly smaller in the ID and OD dimensions than you want to end up with]..layer more wraps to the inside or outside to bring the inside dimension and outside dimension to where you want em.
  Other forms of cardboard or paper mache' techniques can work too, I like the hard cardboard material of Silk containers for many types of projects.

[Be-Kind-Rewind]

Thanks for the ideas everyone. I'll definitely try these out.

[Be-Kind-Rewind]

I found 2 speakers for mp3 players they are a total of 4 watts and it has 2 6 ohm speakers hopefully connected in series. I was wondering if I could connect both of the positive and negative wires to the positive and negative connection on the driver.

[armstrom]

Keep in mind that you generally don't need much power for a talkbox. The LM386 should be fine. Most talkboxes use high efficiency horn drivers which have SPL ratings of over 100dB @ 1W/1M.. Keep in mind that it doesn't need to be THAT loud.. you're feeding the signal directly back into a microphone and out to your PA Something like this would do the trick probably: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=292-2502  good frequency response, low price, 102dB 1W/1M sensitivity...

An ideal solution would have a higher input impedance (this is easily achieved by just adding a JFET buffer on the input) but even without that the circuit should work fine. Think about what you're doing here. You're bypassing your normal guitar signal route to a small amp that's driving a horn driver coupled to a tube stuck in your mouth... are you really THAT concerned with the preservation of a pristine guitar signal? You can barely tell it's a guitar anymore! It might as well be a variable frequency buzzer stuck on the end of a tube... A little loss of high frequency content isn't going to kill your sound. And when the talkbox is bypassed who cares what its input impedance is With all that said, add a jfet buffer to the circuit, they're so easy you might as well do it... better yet, just build a ruby amp and use it to power your horn driver. If you need more power you can always bump up to a bigger amp and repurpose the ruby as a practice amp

-Matt

[RJB510]

Just FYI. I work in hardware and found a really easy way to connect the tube to a talkbox. If you get a bit of 32mm Pressure Pipe fitting, that goes down to 25mm pipe. that is almost the exact size you need to fit on the horn driver thread. Then you can either grind it out a bit so that it slips on and glue it there. OR do what i did and add a bit of oil and being plastic, use the metal thread of the driver to cut its own thread to the inside.
Once thats a solid fit, take it off again, and get yourself a 1/2" irrigation director with a 1" BSP fitting on the end. So that its threaded and you can screw it into your pipe. Measure the size of the shank and drill the 1" end of the pressure pipe adapter to allow you to screw the irrigation fitting into it. Then you can get a pipe on the outside of the irrigation fitting.

Total cost. About $4.

[petemoore]

  the 386 amp may sweat hard just to 'twiddle-buzz' the driver, more like a door buzzer with some pitch control.
  For better driver control an amp with greater potential output is recommended.
  Mostly clean may have dirt added [many SS amps have 'gain' or 'distortion' knob. If not then you can choose your dirt-type, have the amp control the driver 'cool-ly'...fiddle with EQ etc.
  Just the driver and the tube "Offer limitations'' and Eq wierdness on their own.
  OTOH the 386's distortion could be the final choice, even after 'opening up' the amp channel [ie lets clean through] and fiddling with everything [dist/eq/  ] at the preamp.
  The worst thing is an SS amp almost big enough, pushed to distort, getting harder to find these though, making one is more reliable if you wanna have railing output transistor blow your diaphram...just a backwards way to make the point that clean power output to the driver will allow small signal distorters which also compress to be chosen, one split second 'blap' of a power railed amp transistor [of sufficient power, the 386 does this but is still 'kinda small signal' enough not to be known for ever having been able to blow any driver coil]. yepp, haven't read about it lately but SS output distortion is something to avoid, it's the 'almost strong enough' output that gets pushed to rail-clip which should be avoided because it has the potential to whap that coil loose.