One guitar into two amps, how? (what plug?)

[zener]

To elaborate further, I'm going to build two identical TDA2003 amps with identical cabs and identical speakers. The cabs will be built with the feature of being attachable and detatchable to each other to form a single cab. With that I can have a "stereo" amp from two separate but similar amps. The two amps will have their own psu so they are really good to be used stand alone.

Is there any 1/4" adapter-plug that would have one input jack and two output plug or I need to make something more complex to make my endeavor possible?

Any link or pic if ever there's an adapter-plug would surely be appreciated since I haven't seen one.

Thanks for any help.

[zener]

Nah, I think I found what I need. How silly of me to answer my own query :?  :roll:



Am I right?

[toneman]

Or,
wire 2 jacks in parallel on 1 amp.
use 2nd jack as "bridged" input.
kinda like a patch bay on a synth.
Guitar into dual-input amp >
use 2nd cord to 2nd amp from 1st.
no special adapters needed.
Heck, splurge: Put 2 input jacks on both amps..
:-)
tone

[zener]

Yeah, toneman. Why I haven't thought of that? Maybe I'll forget the adapter-plug and go with your suggestion. Thanks. :wink:

Btw, I don't see why I need to have 2 input in both of the amp. Well, unless I want either of them to have the guitar's input. Is that correct and/or there's something else?

[soundguy]

hey zener-

you might consider building yourself a fet buffer/driver so your guitar pickups see the right impedance.  Splitting to two amps via a variety of ways will work just fine, but in my experience usually loads down the guitar pickups quite a bit if you are playing a guitar with passive pickups.  This can be to your advantage, as the tone changes and can sound awesome, but if you want the sound you get from one amp, but in two, you should either look to modifying the value of the pulldown resistors on the guitar input on the amp (assuming there are some) or build a fet buffer that can drive the two amps simultaneously while providing the right impedance load to your pickups.

dave

[zener]

Hmmm... that kinda made everything a bit more complex. But of course, if it will be for the tonal goodness, I'll surely consider it.

The 2 TDA2003 amps I'm going to build will both have a dual opamp preamp/active tone stack, this one:


Hey dave, can you elaborate more on fiddling with pulldown resistors? Also, regarding the fet buffer, do I really need it inspite of the presence of opamp preamp?

Another thing, does the sound from what I initially planned would be like having 2 identical guitars, each plugged into 2 identical amp played at the same time with the same notes/chords/riffs/licks etc.?[/img]

[petemoore]

Pulldowns just 'empty' [very slowly with high resistance] any accumulated [stored] energy in the input or output caps, I find sometimes I don't even need them, but they will reduce the related PoP when using the switch...this is the stored energy being released in the signal path.
 2M2 seems a common starting point for the value of a pulldown, if you're still experiencing popping try something a bit smaller...
 If you go 'so' small, the attenuation may become noticable. If you go too big, it won't provide a low enough resistance path to ground for the caps to actually 'empty'...2m2 usually does it for me, could try 4m7, I don't like going less than 1meg, in such cases it's probably a very leaky cap or some other problem causeing the pops...

[Paul Marossy]

One problem. You could possibly get a hum when the two units share a common signal ground...

[zener]

Hey, pete. I have known what pulldown resistors kicks popping sounds, but thanks anyway. Actually, I should have not asked about pulldown resistors because as what Dave said, it is just if I want to get the the sound of a single amp in two. I realized that two amps, despite identical, have their own respective controls. That lead me to my last question

Another thing, does the sound from what I initially planned would be like having 2 identical guitars, each plugged into 2 identical amp set at identical control settings and played at the same time with the same notes/chords/riffs/licks etc.

Hey Paul. Does hum will automatically come out if I set ANY amp like that or I just need to pray that hum won't come in my planned setting. If the first one is true, then what will I do to get rid of the hum? I have seen an effects manual (can't remember what it was, Zoom?) and it indicates the use of the plug (pic above) to plug the effect into two amps.

Thanks for any help.

[toneman]

most amp inputs are hi-Z anyway.
Don't think 2 inputs in parallel will load your
GeeTar noticeably.
A Jfet preamp at the front of each TDA would eliminate
*any* "loading" of the GeeTar.
Reguarding gnd loops.....
Yes, this "could" B an issue.
I didn't mention it, cause I knew that U were building
these amps from scratch.
A friend of mine wanted to play his GR30 in stereo,
so he bought 2 identical Fender practice amps.
Something like in the 10W class.
L-output 2 1 amp, R-output 2 other amp...
result----bad hummmmmmm,
why?
the 2 chassis were not wired identically.
Even though they were brand new, the pwr transformers
were not wired identically with the same phasing.
Solution1:  reverse 1 of the xfmrs.
Solution2: lift gnd on 1 amp.
My friend did the 2nd.
It worked.  But not what i recommended.
If U pay attention to the phases of the pwr xfmr *when*
U wire the amps 2gether, U shouldn't have any humms.
afn
tone

[zener]

Another hmmmm... Ok, I might be confused plus the fact that I know no EE except from the small amount of stuff I learned here in DIY. Please bear with me.  :oops:  Thanks.

What I've known from a ground-caused hum has something to do with PSU as what I read in GEO. My plan is as simple as to build 2 amps, with 2 separate PSU, of course. Then I want to plug my guitar into these amps at the same time using whatever should be used.

Do i just sound redundant? Sorry if ever. :oops:  

Ok, maybe I'll just take some time to build the amps first then get back here and dig this thread if I will have to ask anything. After all, nothing will be ruined or will go out of hand because the 2 amps are actually, well, 2 amps :roll: .

Thanks.

[ejbasses]

make sure you make buffers to isolate the signals so you wont get ground loops. ground lift switches and separate level controls for the outputs would be a good idea too.

Hey man long time no see!

[Paul Marossy]

What I was getting at earlier is that it is possible that you could get a ground loop when you connect the grounds of the two amps together via the signal ground, since that Y-cord shares a common ground. All grounds are not absolutely the same, at least not in any two amplifiers, even if they are "idenctical". In reality, no two "identical" amps are really exactly the same due to tolerances of the parts, etc.

It may not be a problem at all, but I was just pointing it that it could be a possibility. The suggestion for keeping the phasing the same on the transformers would go a long way in preventing any problems with hum.

[soundguy]

Talking about vintage fender amps, where my experience mostly lies, the input of those amps is designed to present a load on the guitar pickups.  If you jump one channel into another, you get a noticable change in load, or at least I do.  Running two amps in parallel pretty much does the same thing.  I've never done it before, but logic pretty much says to me if you know you are going to constantly be using the two amps together, you might try to modify the front end so that the impedance of the two amps in parallel would be equal to what the guitar would be seeing in series with a single "standard" amp.  The catch here obviously is that where you to use a single amp of your pair, you'd have the wrong input impedance...  Would be something cool to put on a switch, if it was as simple as changing the value of the pull down resistors on the input jacks, that might work well, however I dont know if that would work at all.  Unfortunately Im full of good ideas without the EE experience to really know if any of this shit is practical to work...

Ive used the Zvex SHO many times to buffer a signal to two amps and its a great solution provided you like the tonal stuff that the SHO adds to the guitar, on some guitars this is great but if you have a mid 70's CBS strat, might not be the best sound if you dont like bright guitars...  There are a myriad of simple fet circuits out there that would work to this end, the big question with adding circuitry is how transparent you can make it/how transparent you want to make it, etc....

Of course you can always just try it and see...  If you are gonna run the two amps in parallel without any mod, the smartest thing you can do is find the lowest capacitence/foot cable out there as your high end will suffer first.  In the studio, I recently did a shoot out with a bunch of guitar cables, a topic I always thought was utter horeshit, and honestly almost fell over when I heard the difference between the standard george L cable and the rest of the stuff we tried...  Might be a drastic thing to say, but you can go through the trouble of building a buffer and if you hook it all up with cheap cable that rolls off alot of high end, it might sound similar to two amps parallel with better cable...  

dave