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Old 6th May 2012, 10:30 PM   #1
zoi is offline zoi
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Default 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!
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Old 6th May 2012, 10:37 PM   #2
kevinkr is offline kevinkr  United States
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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.)
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Old 7th May 2012, 03:09 AM   #3
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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.
Cheers,
Ian

Last edited by gingertube; 7th May 2012 at 03:11 AM.
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Old 7th May 2012, 06:30 AM   #4
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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.

Regards

Charles
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Old 11th May 2012, 07:40 PM   #5
nazaroo is offline nazaroo  Canada
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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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