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Talkbox MOD Answered

ok so, after reviewing James Haskin's TALKBOX  he splits the feed from his guitar amp through a DPDT switch and he mounts it directly onto the guitar amp.... I was wondering how difficult would it be to make a stomp box feature for this?? with maybe a few LEDs to let you know what your running.. i posted this as a question but being new to the site i'm not sure how that worked so i posted here too...


 ALRIGHT!!!!!!!! BREAKTHROUGH!!!! (powered by google/wikipedia) ok so if i have this right (no garuantees) but the the power supply i will use isnt in anyway connected to the speaker or the talkbox... its in essence 2 seperate circuts.. there should be like 8 connections 2 should be the coil and well it should look like this
                [A1]    [A2]                   these two go to the original speaker                                      [C1]   [C2]  these two should be the amp out (this is the armature)
                [B1]    [B2]   this is the out connection to the talkbox  

so when the coil is energized it atracts C1 and C2 (the armature) towards the connection of B1 and B2... ok so i got that the next thing is the LED

where do i attach that? I would have to attach some where between the coil and the switch which if i am not mistaken i need an DPST switch? right?

In all I'm thinking of using a 5v/1A  DPDT relay and i need a 5v/1A AC to DC adapter (something like the guitar pedals use where i can plug it in and out of the stompbox instead of just the wall) and the receptical for that an LED and the necesarry resistors for that (which i now know what to get thanks to ohms law!!)

**wow question about resistors**

1 Amp = 1000 mA   
so in my division its       R = V / I     and my LED is 2v x  20mA 
                   that means ohms law says 3v/0.02 (20mA) = 150 ohms
so i need to have 150 ohms of resistance in the 

**I guess my main question after all of this rambling is do i hook up the LED and resistor on the negative side of the coil like so?
 -                      +
   |                    |
   |                     |
   |                     |
[resistor]         | 
      |                 |
      |                  | 
   [LED]            | 
     |                   |
     |                    |
     |                    |

obviously with a switch between? is that correct?

.  Having the LED and resistor in series with the coil may work, but I'd connect it in parallel.
.  For an audio application, I'd use a 3-wire, shielded cable - one wire from PS to hot side of sw, one wire from coil side of sw to relay coil, one wire from PS negative to LED.
.  You might be able to go with: the resistor to the coil side of the switch and the LED, and the other side of the LED to the box (ground/-/the shield of the power cable).

 also I am trying to use as many spare parts as i can and keep this super cheap... if a relay says Form C (from what i understand this mean DPDT) 5v Single Coil does that mean that i do not have to meet any ampre requirments for the coil to throw the switch??? because i have a 5vDC/700mA power supply that i would love to use for this just to keep things simple... but all the relays i have found either say 5v/1A or they are 5v Single coil and they don't list a ampre requirement??

.  Form C just means that one or more SPDT switches are ganged together (xPDT)
.  The 1A rating is probably for the switch contacts, not the coil. Coils usually have a pretty high impedance/resistance.
.  I don't have a relay handy, but I don't remember any having the coil current on them. You should be able to get that info at the manufacturer's web site. Or, since you are using DC, measure the resistance of the coil and apply Ohm's Law.
. Don't forget a clamping diode across the coil.

 ok... I knew about your first point...
the second one needs me to see what my amps rating is...
the third one is ok...

but your fourth one about the crimping diode....WAY over my head

.  When you de-energize a coil, the collapsing magnetic field induces a reverse polarity voltage spike. A diode, installed "backwards" across the coil, will short out that spike.

.  Not difficult at all - just use longer wires to the switch. Make sure you use high-quality, shielded cable and follow grounding rules to minimize losses, distortion, and hum. Using shielded wire to the LED may be overkill, but I'd do it anyway.

 whats the difference in a switch and a relay?

.  A relay is an electrically operated switch

 i'm sorry wasnt thinking when i posted that... but the thing is.. i want to choose weather or not to go through the speakers or the talkbox i am building it sounds like the relay will be set so when i turn on the amp it automatically goes to the talkbox... and GMOON.. i am using a solid state peavey rage no tubes for me!! thanks bra

.  Let's split this into two parts: activating the relay and wiring the relay contacts.
.  To remotely activate the relay all you need is a power wire to your stomp box, a SPST switch, and a wire back to the relay coil. You can run your indicator LED off of the coil side of the SPST sw (you may need to rectify/reduce voltage going to LED). I'd suggest using low voltage (say, 5V) DC for the relay coil power - it's safer and less risk of inducing hum somewhere - which you should be able to get from the amplifier circuitry.
.  Not sure what would be the best way to wire the switch. If you have very low noise amps, I'd short the input of whichever unit I'm not using.

 OK, so here is the thing... I have a tiny bit of understanding of electronics (enough to make a few cool gadgets in the past) but i always followed diagrams that said put this here solder here so on and so forth... I know you need resistors and whatever to reduce the current to an LED but.. thats all i know!!!! if i wanted to add an LED would it look like the picture i posted???

.  It may be better to use a DPDT relay in place of the DPDT switch and just run power to the remote switch/indicator. You only have to run two wires and there will be less chance of hum/distortion.

 ok so i did solve my original problem though THANK YOU OHMS LAW!!!


8 years ago

Be careful with this technique when using a tube amp.

Tube amps MUST have a load attached to the output transformer at all times (well, when turned on, anyway.) A normal DPDT switch will break the first contact before it makes the second contact--which could fry the OT if you're playing.

One fix--leave a resistor in place across the transformer secondary permanently (parallel with the speaker, but be sure it's before the switch); Something like a 330 or 270 ohm (10W) for an 8 ohm speaker load. 330 ohms is enough resistance to protect the OT, but should have negligible effect on the loudness of the amp.

This is standard practice now for several tube amp manufacturers. If (when) your bass player gets drunk and trips over your speaker cable--the amp doesn't die.

Probably isn't an issue with a solid-state amp, which should be OK with an open circuit on the output.

Speaker cables really don't need shielding. Amps have really low output impedance, so have low susceptible to noise (most speaker cable is essentially the same as two-conductor 120V mains wire.) Definitely don't use a guitar cable or a shielded cable unless it's designed to carry some real current...

Haha. I just noticed you're a bass player... ;-)

 ha good observation... but i have played bass for several years and am broadening my horizons a bit!! a jack of all trades if you will (master of the bass) ahaha no but yea i am a bass player a heart

 this is a test diagram????? HELP!!