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zoi 6th May 2012 10:30 PM

Amp for talkbox
Hey guys,

This is my first post and I apologize if this is a newbie question.

I'm looking to build an all-tube talk box and I'm trying to figure out what tube configuration I need.

I need enough gain to raise the level of an electric guitar pickup output (phono level?) to loud enough drive a speaker around 4-6". The output will be channeled through a plastic hose that will be mic'd at the mouth end (dynamic mic, likely sm57) and sent to a mixing board or a guitar amp.

I've been reading about 12ax7 preamps and this appears to be a good choice, but I have no idea about what to use for the power stage. What do you guys recommend? I don't need any controls aside from volume. It's hard for me to estimate the output because I have never built an amp before, let alone worked with one this small.

Thanks in advance for your help!

kevinkr 6th May 2012 10:37 PM

:cop: This belongs in Instruments & Amps, so I'll move it there.
(See header at top of Tubes / Valves forum and I & A for reason why.)

gingertube 7th May 2012 03:09 AM

Would you believe !!!!!
The local guitar god here in south Oz uses a Mullard 5/10 HIFI Monoblock Power Amp (EF86 to 12AX7 splitter to 2 x EL84 in push pull Ultralinear giving 10W maximum output) for exactly this function.
That suggests a clean amp is what you need and you don't need much power. Also the input sensitivity is not huge, probbaly 200mV to 300mV for full output.

phase_accurate 7th May 2012 06:30 AM

And usually large horn-drivers are used for that purpose. you might have to search a littel in order to find one that is up to the tast and that doesn't cost a fortune - but there are such drivers around.
And you will have to protect it from overexcursion by the use of a high-pass.



nazaroo 11th May 2012 07:40 PM

Okay, just a few safety issues:

Doing it this way will involve at least three pieces of amp gear:

(1) guitar amp

(2) 2nd amp for mini-speaker

(3) PA amp.

This is how like 9 out of 10 guitarists were electrocuted:
Hand on strings (Amp1 ground), lips touch mic (PA ground),
Saliva / moisture in tube (Amp2 ground and/or live).

If any one of the 3 amps is:

(a) not grounded

(b) grounded backwards, or to a different power/grid circuit...

BANG. 30 - 600 volts of fun.

This is why they stopped making these things.

Necessary things to do:

(1) Remove "Death cap" and/or ground-lift ****, and properly ground guitar-amp.

(2) Run secondary ground between guitar-amp and PA, and CHECK voltage between the two chassis, and/or current on groundwire.

(3) Design box so that it is impossible for moisture to conduct current from speaker-wires in Talk-box to mouth via moist air tubing.

(4) Make sure moisture / saliva on tube and/or mic stand doesn't short between Amp2 and PA.

Get knowleagable person to check this stuff EVERYTIME you set up your gear for a show.

(5) Pick a different/better way to do the same thing, namely a Voicebox.

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