Talk box question(s)

[fowl]

How do, folks.  Long time listener, first time caller.  I guess a passive talk box is only marginally on-topic here, but I don't know of a better place to ask.

Anyway, I'm going to build one, basically a copy of an old Heil.  The main component will be a JBL D250-X driver, 8 ohms and 100W (150W?) rating.  I have a small SS practice amp I can hook it to, but I would like to be able to run it with my ~40W tube amp too.  I will not be adding a speaker switch, this is not really intended for live performances anyway.

But I only recently noticed that those old Heils had a cap in series with the driver.  Some people say 15uF (bi-polar electro), I saw a picture of one with a 6.8uF, whatever.  I understand the cap is there to create a HPF and protect the driver from low frequencies.  But I have NO idea what that cap does to the 8-ohm load as it relates to the amp.  I'm pretty much an idiot when it comes to impedance, and not asking for a lecture, but is it safe to run a tube amp into such a load?  I have considered getting a 250V film cap, for reliability rather than any sound quality reason, but that may not be the issue here.

Would it be better to just leave the cap out?  Maybe the JBL can handle a 40W guitar amp without the protection?  I' pretty sure the cap would be no problem with a SS amp, but I'd rather protect my tube amp from damage than a $38 horn driver, if you see what I mean.

I also noticed that the old EX Golden Throat boxes used a light bulb in series, rather than a cap, not sure if that's a better idea or not.

Thanks in advance for the help!

[antonis]

Hi & Welcome..

in breef:
We are talking about AC coupling cap, mainly used on single supply rail amp to isolate output from any DC offset, to prevent turn-on thump, to make amp short circuit proof, to protect against any DC faults and to avoid the need for output inductor for stability..


P.S.
Light bulbs are (were) used for current limiting purpose..

[GibsonGM]

Welcome, fowl.  Personally (and other opinions may vary), I didn't trust my 70s driver to NOT die in use, leaving my expensive tube amp with no load and the ultimate problem of frying the OT.  Plus, it's on the floor - cable could get pulled by a dancing drunk, etc. 

So I use a small SS practice amp, just like you have. It isn't high watts, doesn't have to be for the mic to pic up the signal. I put a switching jack on the back of it, so when I plug in the driver it cuts the internal speaker out.    Works GREAT!    My driver doesn't have a cap that I'm aware of, if that helps.   The sound of the amp doesn't do much, IMO.  Doesn't have to, your mouth is doing all the work!

[fowl]

Thanks for the replies.

Antonis, I think such a coupling/blocking cap is already included in any amp that needs it, this one in the talkbox is just to protect the driver though.  I understand the lightbulb filament increases in resistance (and impedance) as current increases, thereby protecting the driver from surges, but I don't know if a tube amp would like to have that on it's output.

Mike, I have the same idea for a switching jack on the back of the SS practice amp.  I think the 100+Watt JBL and a high quality cap should hold up to my tube amp, but I just don't have the knowledge level to know how safe that would be for the tube amp, even when everything is working correctly.

I guess the old 1970s Heils were connected to tube amps very regularly, but maybe people were just getting away with it.  I tried to read up on everything related I could find online before asking here.  There are people out there that say the cap+driver "crossover" load is a bad plan for a tube amp, some people that say they run without the cap and haven't damaged their driver, but there is so little info out there about this, it's hard to come up with a consensus.

The Solen cap I'm looking at is both large and expensive (for a cap), I'd rather not order it if I'm not going to use it.  I'm convinced the cap is safe, and probably unnecessary, for a low-power SS practice amp.  I just don't know about the tube amp.

[PRR]

> JBL D250-X driver.... ~40W tube amp

Please don't. This rig would be louder (at the source) than a Marshall Full Stack. And you want to put it in your mouth??

This could be instant deafness. Even if you "are careful".

The "toneful tube amp" is moot when you have to play it below 1/4 Watt and run it through your mouth.

[fowl]

I didn't say a cranked 40W amp.  As it is right now, I have hooked up the driver to my amp set for miniscule "bedroom" volume, and it's barely audible.  So I'm sure I could manage the volume level with the tube amp.  I just want to know if it's safe for the amp, with the series cap.  Even though I will likely use the little SS amp most often, I would like to at least try it with the tube amp.

[antonis]

I just want to know if it's safe for the amp, with the series cap.

A series cap can do no harm..
(a shunt one can be disastrous..)

[GibsonGM]

I mean....try it, if you must   At a micro level.   I've done so too. I just found no difference whatsoever between an overdriven Marshall practice amp and my Fender 40W (or marshall 18W for that matter).   The 'wonderful, saturated tube tone!' just doesn't come thru the little driver and up the tube.   The real "power amp distortion' seems to be your formants, LOL, and the effect of the mic & PA reamping it.   Just my take.  FWIW, an Ebay amp module could probably drive one very well, no fuss no muss.

I had an A-B switch on the floor, and would just send my guitar to the little expendable (yet, still here...) amp, no effects other than a little overdrive the amp came with. Worked great, was easy for the soundman and all that jazz.  I found if I upped the drive beyond a certain point, it lost all dynamics and sounded kind of...ass...

YMMV!

[fowl]

I just want to know if it's safe for the amp, with the series cap.

A series cap can do no harm..
(a shunt one can be disastrous..)

Cool, thanks.  I'll probably order the 15uF cap then, it seems to be the common value at least for Dunlop-era Heil HT1 talkboxes (from what I read online anyway), and should be sufficient protection for the driver (which is rated down to 400Hz).

[fowl]

I mean....try it, if you must   At a micro level.   I've done so too. I just found no difference whatsoever between an overdriven Marshall practice amp and my Fender 40W (or marshall 18W for that matter).   The 'wonderful, saturated tube tone!' just doesn't come thru the little driver and up the tube.   The real "power amp distortion' seems to be your formants, LOL, and the effect of the mic & PA reamping it.   Just my take.  FWIW, an Ebay amp module could probably drive one very well, no fuss no muss.

I had an A-B switch on the floor, and would just send my guitar to the little expendable (yet, still here...) amp, no effects other than a little overdrive the amp came with. Worked great, was easy for the soundman and all that jazz.  I found if I upped the drive beyond a certain point, it lost all dynamics and sounded kind of...ass...

YMMV!

Right on.  The little SS amp I have is a cheap wal-mart type, it probably doesn't compare well to your Marshall SS practice amp.  I actually have a makeshift talk box rigged to it now (with a low-power driver, and no cap), and while I can get a usable sound with pedals, it still sounds very obviously solid-state even through the vinyl tube.  While I'd like this build to be more "pro" level, able to handle my 40W amp at whatever appropriate volume level, I do plan on building a 5W Champ type amp in the not-too-distant future, and maybe that could serve double duty as a talk box amp.

[Jdansti]

> JBL D250-X driver.... ~40W tube amp

Please don't. This rig would be louder (at the source) than a Marshall Full Stack. And you want to put it in your mouth??

This could be instant deafness. Even if you "are careful".

The "toneful tube amp" is moot when you have to play it below 1/4 Watt and run it through your mouth.

After listening to my Dad's Frampton Live album when I was a kid, I tried hooking up a mono earphone to my guitar amp and putting the earphone in my mouth. Boy was that a hot mistake! 

[GibsonGM]

After listening to my Dad's Frampton Live album when I was a kid, I tried hooking up a mono earphone to my guitar amp and putting the earphone in my mouth. Boy was that a hot mistake! 

[duck_arse]

Right on. ...., it still sounds very obviously solid-state even through the vinyl tube. ....

(I can't see it myself, but) use a glass tube.

[fowl]

but...use a glass tube.

6V6GT it is, then.

Great birds think alike.

[pinkjimiphoton]

> JBL D250-X driver.... ~40W tube amp

Please don't. This rig would be louder (at the source) than a Marshall Full Stack. And you want to put it in your mouth??

This could be instant deafness. Even if you "are careful".

The "toneful tube amp" is moot when you have to play it below 1/4 Watt and run it through your mouth.

please! paul, this is utter nonsense.

totally nonsense.

you NEED volume to get past the attenuation caused by traveling up the hose. 40 watts is actually about perfect, 15 watts is about the minimum needed to drive a talkbox properly.

you NEED to get the volume at least as high as the volume you sing at for it to work well.

it will NOT rattle your teeth. it will NOT make you deaf. shit, even with 100 watts it won't hurt you or damage your hearing. these are old wive tales perpetrated by folks who have never actually used a talk box.

you also don't need a cap, or a series resistor. the cap is for blocking DC if any leaks thru, not for frequency response.

what you need is a full-range driver. community, jbl, whatever. shoot for about a 40 watt rating <in a talkbox, that's plenty for up to 100 watts of amplification in general for a compression driver> 8-16 ohms is fine.
you want a frequency response that goes from around 40hz to 16k or so.

most horn drivers these days are not full range, and tend to roll off the bottom end about where your d string is. hard to get them to work right like that.

as for switching the stage amp... it can easily be done, i did it for years with all my amps .... an a/b switch is literally all you really need. the transient from switching is fast enough to not damage the output transformer <if using tubes> and if ya watch the DCR of a speaker while playing thru it, you'll see the resistance change into conduction at points...
YES, some drunk could unplug it on you by accident. that's the main danger.

i've used an eh 44 magnum to drive mine now for about the last 7-8 years. 44 watts is a good level to drive it at, and you can fit it on your pedal board, and not have to worry about your stage amp.

pm me if ya need any advice, i've been using these things since the late 70's, and the only casualty came from me dropping my original one and breaking the zinc casting at one of the terminals. the new one i built to replace it has over 15 years in now with it being seriously abused with 50-100 watts a nite into a 40 watt 16 ohm driver.

older drivers work better than modern ones. you need that full range, or it just won't work properly.

but don't believe all the baloney about it being "so loud" and all that crap. its total bullshit. listen to people who actually have used these things, not people regurgitating fallacies. you need an absolute minimum of 15 watts to push enough volume thru 6 feet of tubing to hope to get as loud as your vocals. ideally, you want it a bit LOUDER than you sing, in fact.

anyways... good luck, and have fun, and don't listen to folks who never even obviously used one to tell you how dangerous they are... just had my hearing checked, i don't wear earplugs, and can still here a solid 16k at 59 years old after using talkboxes for 45 years or so. facts matter.

[stallik]

I used a monacor wide range driver and a 15w SS amp to get the level the same as my singing voice. Admittedly, my voice is pretty quiet but even when I ran it with a 50w amp, the sound pressure down the tube was nothing to write home about.

Then again, perhaps I was doing something wrong..

[pinkjimiphoton]

sounds to me like you're just describing how it actually is, bro lol....

[fowl]

Yeah I'm sure I can manage volume levels to keep my teeth and ears safe, I have some experience with a talk box already.  I was confused about the load itself, a cap and driver in series, and how safe that is for a tube amp.  Like I said, I don't really understand impedance, but it seems a cap and 8-ohm driver in series would total something different than the driver alone.  I guess it's all frequency dependent, even without the cap, but I don't know if there may be some issue I'm not aware of, like the amp "seeing" an open load down below the cutoff of the HPF.  If that makes any sense.

Jimi, I think the cap is really only there to protect the driver from lower frequencies, as it would in a crossover.  That includes DC (0Hz) of course, but an amp shouldn't be putting DC out the speaker jack anyway, tube or solid state.  It may be the case that this JBL driver is robust enough to take my 40W amp straight on without the protection.  I may put a switch in, cap or no cap.

[Mark Hammer]

"Need" that much volume?  Nah.  The volume required depends on the acoustic conduction of the tube and sensitivity of the mic. 

I have a Danelectro Free Speech pedal.  It uses a 386 amp chip and 3" speaker, for crying out loud.  In fact, if one doesn't attach the tube, you can use it as a "Ruby" type practice amp.  The mic cartridges are electret with inputs and preamp-mixer built into the pedal.  Hit bypass and it's guitar straight through.  Hit effect and the signal consists of whatever the mic cartridges pick up from the end of the tube. No voice-mic-into-the-PA required.

All of that said, the requirements depend on the context.  The Free Speech pedal is terrific for lower volume contexts.  If one is playing at much higher volumes on a crowded stage, the goal becomes one of achieving a a hot and isolated-enough signal going into the voice mic at the end of the tube, such that it is louder than the server trying to shout an order while the band plays.  Hearing the talk-box "effect" becomes a matter of making sure everything coming up the tube is guitar-only, that the tube is reasonably short so as not to lose bandwidth and signal level, that the mic is pretty unidirectional, and that the user can sort of encompass the tube aperture and much of the end of the mic with their mouth.

> JBL D250-X driver.... ~40W tube amp

Please don't. This rig would be louder (at the source) than a Marshall Full Stack. And you want to put it in your mouth??

This could be instant deafness. Even if you "are careful".

The "toneful tube amp" is moot when you have to play it below 1/4 Watt and run it through your mouth.

please! paul, this is utter nonsense.

totally nonsense.

you NEED volume to get past the attenuation caused by traveling up the hose. 40 watts is actually about perfect, 15 watts is about the minimum needed to drive a talkbox properly.

you NEED to get the volume at least as high as the volume you sing at for it to work well.

it will NOT rattle your teeth. it will NOT make you deaf. shit, even with 100 watts it won't hurt you or damage your hearing. these are old wive tales perpetrated by folks who have never actually used a talk box.

you also don't need a cap, or a series resistor. the cap is for blocking DC if any leaks thru, not for frequency response.

what you need is a full-range driver. community, jbl, whatever. shoot for about a 40 watt rating <in a talkbox, that's plenty for up to 100 watts of amplification in general for a compression driver> 8-16 ohms is fine.
you want a frequency response that goes from around 40hz to 16k or so.

most horn drivers these days are not full range, and tend to roll off the bottom end about where your d string is. hard to get them to work right like that.

as for switching the stage amp... it can easily be done, i did it for years with all my amps .... an a/b switch is literally all you really need. the transient from switching is fast enough to not damage the output transformer <if using tubes> and if ya watch the DCR of a speaker while playing thru it, you'll see the resistance change into conduction at points...
YES, some drunk could unplug it on you by accident. that's the main danger.

i've used an eh 44 magnum to drive mine now for about the last 7-8 years. 44 watts is a good level to drive it at, and you can fit it on your pedal board, and not have to worry about your stage amp.

pm me if ya need any advice, i've been using these things since the late 70's, and the only casualty came from me dropping my original one and breaking the zinc casting at one of the terminals. the new one i built to replace it has over 15 years in now with it being seriously abused with 50-100 watts a nite into a 40 watt 16 ohm driver.

older drivers work better than modern ones. you need that full range, or it just won't work properly.

but don't believe all the baloney about it being "so loud" and all that crap. its total bullshit. listen to people who actually have used these things, not people regurgitating fallacies. you need an absolute minimum of 15 watts to push enough volume thru 6 feet of tubing to hope to get as loud as your vocals. ideally, you want it a bit LOUDER than you sing, in fact.

anyways... good luck, and have fun, and don't listen to folks who never even obviously used one to tell you how dangerous they are... just had my hearing checked, i don't wear earplugs, and can still here a solid 16k at 59 years old after using talkboxes for 45 years or so. facts matter.

[pinkjimiphoton]

"Need" that much volume?  Nah.  The volume required depends on the acoustic conduction of the tube and sensitivity of the mic. 

I have a Danelectro Free Speech pedal.  It uses a 386 amp chip and 3" speaker, for crying out loud.  In fact, if one doesn't attach the tube, you can use it as a "Ruby" type practice amp.  The mic cartridges are electret with inputs and preamp-mixer built into the pedal.  Hit bypass and it's guitar straight through.  Hit effect and the signal consists of whatever the mic cartridges pick up from the end of the tube. No voice-mic-into-the-PA required.

All of that said, the requirements depend on the context.  The Free Speech pedal is terrific for lower volume contexts.  If one is playing at much higher volumes on a crowded stage, the goal becomes one of achieving a a hot and isolated-enough signal going into the voice mic at the end of the tube, such that it is louder than the server trying to shout an order while the band plays.  Hearing the talk-box "effect" becomes a matter of making sure everything coming up the tube is guitar-only, that the tube is reasonably short so as not to lose bandwidth and signal level, that the mic is pretty unidirectional, and that the user can sort of encompass the tube aperture and much of the end of the mic with their mouth.

> JBL D250-X driver.... ~40W tube amp

Please don't. This rig would be louder (at the source) than a Marshall Full Stack. And you want to put it in your mouth??

This could be instant deafness. Even if you "are careful".

The "toneful tube amp" is moot when you have to play it below 1/4 Watt and run it through your mouth.

please! paul, this is utter nonsense.

totally nonsense.

you NEED volume to get past the attenuation caused by traveling up the hose. 40 watts is actually about perfect, 15 watts is about the minimum needed to drive a talkbox properly.

you NEED to get the volume at least as high as the volume you sing at for it to work well.

it will NOT rattle your teeth. it will NOT make you deaf. shit, even with 100 watts it won't hurt you or damage your hearing. these are old wive tales perpetrated by folks who have never actually used a talk box.

you also don't need a cap, or a series resistor. the cap is for blocking DC if any leaks thru, not for frequency response.

what you need is a full-range driver. community, jbl, whatever. shoot for about a 40 watt rating <in a talkbox, that's plenty for up to 100 watts of amplification in general for a compression driver> 8-16 ohms is fine.
you want a frequency response that goes from around 40hz to 16k or so.

most horn drivers these days are not full range, and tend to roll off the bottom end about where your d string is. hard to get them to work right like that.

as for switching the stage amp... it can easily be done, i did it for years with all my amps .... an a/b switch is literally all you really need. the transient from switching is fast enough to not damage the output transformer <if using tubes> and if ya watch the DCR of a speaker while playing thru it, you'll see the resistance change into conduction at points...
YES, some drunk could unplug it on you by accident. that's the main danger.

i've used an eh 44 magnum to drive mine now for about the last 7-8 years. 44 watts is a good level to drive it at, and you can fit it on your pedal board, and not have to worry about your stage amp.

pm me if ya need any advice, i've been using these things since the late 70's, and the only casualty came from me dropping my original one and breaking the zinc casting at one of the terminals. the new one i built to replace it has over 15 years in now with it being seriously abused with 50-100 watts a nite into a 40 watt 16 ohm driver.

older drivers work better than modern ones. you need that full range, or it just won't work properly.

but don't believe all the baloney about it being "so loud" and all that crap. its total bullshit. listen to people who actually have used these things, not people regurgitating fallacies. you need an absolute minimum of 15 watts to push enough volume thru 6 feet of tubing to hope to get as loud as your vocals. ideally, you want it a bit LOUDER than you sing, in fact.

anyways... good luck, and have fun, and don't listen to folks who never even obviously used one to tell you how dangerous they are... just had my hearing checked, i don't wear earplugs, and can still here a solid 16k at 59 years old after using talkboxes for 45 years or so. facts matter.

huge difference between a free speech and an actual talkbox, mark.  the free speech is a toy. it works... to a point. but it doesn't produce enough volume to be useful anywhere but a bedroom. a half watt of "power" isn't gonna cut it. i speak of real world applications and from pretty extensive experience over hundreds if not thousands of gigs.
you DO need that much volume. try using a free speech with even a VERY dynamic drummer. it won't cut it.
neither will the rocktron banshee. i bought one, expecting it would be enough. not even close. its a toy. same as the free speech. it will let you try the idea, for sure, but it can't possibly cut it on a live stage.
ideally you need a bit more volume than you sing at. its good to have the headroom so you DON'T have to literally gag yourself <the real and only danger you're likely to face, tbh> and have the mic literally against your lips.
minimum i've found useful... and i'm a total volume nazi to my bands, in fact... is about 15 watts.
40 is better. (me being a volume nazi to a band, proof...lol

)
but here's the thing you ignore... the difference in volume between 15 and 40 watts is negligible. its far less than the paltry 3 db you get difference between a 50 and 100 watt amp. barely noticeable, in fact. it may "sound" like brute force, excessive power, but its not at all.
talking real-world application here, not bedroom. bedroom is fine, yes, you can do it and amuse yourself with it, but if you try to take it to the stage, you'll be seriously disappointed.
optimal length of tube? again, real world dictates that to be around 6 feet minimum generally. often slightly more, as its gotta be lashed to the mic stand, and often a boom, as well, if you're using a pedalboard... which is almost impossible with a basic "straight" stand.
the sensitivity of the mic is less an issue in real world application as well. yes, you can dedicate a microphone to the talkbox only, if you can afford or have two mic rigs... but most folks don't have that, and need to use their normal vocal mic.
if you push the normal vocal mic loud enough to pick up a tiny signal, odds are the foldback system are gonna give you feedback issues, and often huge ones... even with a good engineer. like i said, i tried using the banshee system before abandoning it, and even with pro support, it couldn't handle it... with its own dedicated mic. even worse thru the vocal mic.
i realize you're in part playing devil's advocate, but i'm the devil in this case, and here to try and get you to understand that there's a lot of baloney out there about how this works and real world application.
the myth that it "makes you deaf" or "rattles your fillings" and all that crap is ridiculous.
the simplest physics answers most of this.

if your max output vocally is 85 db, you need to get at least that much at the end of the tube going in your face, not counting the attenuation of the warm, damp, soft interior of the average oral cavity. accoustic conduction of the tube is really about the same. rubber, vinyl, whatever. it all attenuates most of the signal.
the freespeech is a brilliant piece of kit for what it is. but its not useable in a live environment, and no talk box actually has all that circuitry built into it. the little electrets in that thing work, sure. but can't cut it live.

my big question would be, what the hell else would be coming out of the tube other than your guitar signal? say what? lol

its really, REALLY not rocket science here. i'm trying to tell the truth about real world application, not perpetuate internet myth. ya'll can choose what ya want.

btw, Fowl, the cap isn't much of a crossover in them. like i said, main thing is to block dc, according to my late guru bob saunders who helped me build my first one. used to be hard to get drivers like these, and common for amps to blast some dc thru, either from failing OT or transistors. there "should be" no dc component, but there often is in practice. we're dealing with speakers, which are inductances, not resistances. speaker resistance will change with frequency.  if ya put a digital multi on a speaker output, you'd be surprised how often it goes to zero while playing. while a 10 or 12 " speaker can take an occaisional burst of dc, most horn drivers can't handle it at all without giving up the magic smoke.
if you DO choose to use the cap, get a non polarized one, or say, two 33uf ones cathode to cathode to give the equivalent of one 15uf cap. its really only necessary if using a mid driver instead of a full range compression driver.
the cap would be, in an actual crossover, to protect the tweeter, not the bass speaker. same app here. no tweeter to protect, and a 15uF cap isn't gonna really roll off much low end, you could still play a bass thru it with it having no effect.... but anyways...

do you want a toy, or an actual, useable item? that's the choice to be made. peace n chicken grease