Is it bad to mix channels with a twin?

Is it bad to mix channels with a twin?

Postby squire758 » Tue Mar 22, 2011 1:25 am

Ive heard of people using amp selecters/ swtches to go between inputs 1 and 2 on amps but what if you use a Y-cable into both inputs, and plug into that, mixing both inputs? It sounds alright but my lights dimmed a little when I plugged in. :roll:
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Re: Is it bad to mix channels with a twin?

Postby 540EYE » Tue Mar 22, 2011 6:17 am

Hi...
If memory serves well (?).....I think the normal and vibrato channels of a Twin are out of phase with eachother. So if you plugged into both channels with a "Y" cord, there would be cancellation of frequencies and would result in a "thin" sound.

There is a modification that puts the reverb on both channels and doing this will put the channels in phase with eachother. In this form, you can mix the channels w/o phase cancellation.
I know this because I did it to '69 non-master a DSR.

I'm sure there are others (Brad, Waldo) who can shed way more light on this than me.
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Re: Is it bad to mix channels with a twin?

Postby Pete B. » Tue Mar 22, 2011 8:46 am

fwiw, The only time you will have phase cancellation is when the volume of both channels is exactly the same.
Plug into channel 1, run another cord from the 2nd input of channel 1, to the input of channel 2.
With channel 1 volume at 0, turn up channel 2 to a comfortable level.
Now slowly bring up channel one untill all the bass frequencies drop out.
That is the only point you will have phase cancellation.
There is still a great deal of flexability available using both channels, you just have to experiment (mixing dry signal to reverb, tone conteols, etc...).
The other thing you can do is get a phase-inverter to get both channels "in phase" (I've used an old ART Tube Pac that has a phase inverter button on it, but there are many units out there with a phse button or switch).
This will put both channels in phase.
There are pics of Jerry doing exactly this (in this pic he jumps Channel 2 to Channel 1).
http://dozin.com/jerry/74/74.html
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Re: Is it bad to mix channels with a twin?

Postby jenkins » Tue Mar 29, 2011 11:45 am

I feel like I'm missing something her, well obviously i am. The twin mist have to b desired before u can donthis right? How can u jump to channel 2 out of the second input of channel 1? How does that input become an output to send a signal to ch 2 unless it's wired as such
Great pic u posted of Jerry doin that
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Re: Is it bad to mix channels with a twin?

Postby JonnyBoy » Tue Mar 29, 2011 12:16 pm

jenkins wrote:I feel like I'm missing something her, well obviously i am. The twin mist have to b desired before u can donthis right? How can u jump to channel 2 out of the second input of channel 1? How does that input become an output to send a signal to ch 2 unless it's wired as such
Great pic u posted of Jerry doin that



I think you are right, it has to be wired that way. I may be wrong, but I believe He would have a clean no reverb signal and a Wet signal both being amplified with 2 separated outputs, to two separate amps or channels. I read that on waldo's site I believe...
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Re: Is it bad to mix channels with a twin?

Postby Pete B. » Tue Mar 29, 2011 2:04 pm

JonnyBoy wrote:
jenkins wrote:I feel like I'm missing something her, well obviously i am. The twin mist have to b desired before u can donthis right? How can u jump to channel 2 out of the second input of channel 1? How does that input become an output to send a signal to ch 2 unless it's wired as such
Great pic u posted of Jerry doin that



I think you are right, it has to be wired that way. I may be wrong, but I believe He would have a clean no reverb signal and a Wet signal both being amplified with 2 separated outputs, to two separate amps or channels. I read that on waldo's site I believe...


The two inputs on each channel are electronically the same point. It is a continuation of the same input signal, not re-wired to be an output. No re-wiring is requiered.
Try it.
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Re: Is it bad to mix channels with a twin?

Postby Laytonco » Tue Mar 29, 2011 2:35 pm

Good words here. I do this on my 74 Fender Super and love the variables you can get tonewise. You get wet/dry mix, you get the thinning of the sound (close volume setting), etc. I really really like it! Been doing it for years and never had any troubles with the amp. And so many amp tech type people have told me it's perfectly safe. Try it, you'll like it!

Peace,

Gil
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Re: Is it bad to mix channels with a twin?

Postby jenkins » Wed Mar 30, 2011 1:47 am

so this is his you can mix the wet & dry channels on one amp?! That's crucial info! I used to always use two amps, one wet one completely dry to get a Jerry tone. I actually still do it a lot bc of how good it sounds. I remember talkin about it on here a couple years ago. Ive always felt that Jerry did something to mix wet and dry channels. I found it really difficult to get a Jerry tone I was happy with on one amp. He just has that tine where there's always perfect reverb but his notes r still nice and crisp. I used to think that was why he had the two twins. & was really surprised when I found out one was a backup.
This is the info I've been looking for for years, info like this is the reason I visit rukind.

So it doesnt have to b rewired at all? Your basically just continuing your input signal to use both channels at once right? I can't believe how simple that is & I've never known it. Did Jerry have the amp rewired later to jump the channels internally without using the cable or did he stop doing that?

Jerry jumped ch 2 to ch 1, is there a difference between this and goin ch 1 to ch 2? Which way do u guys run it? Do all the knobs work? All the tone knobs and the vibrato or how does that work?
I can't wait to try this for some reason I've never even considered this as a possibility but it seems like exactly what I've been tryin to do for grips
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Re: Is it bad to mix channels with a twin?

Postby Pete B. » Wed Mar 30, 2011 8:57 am

Here's a product you might be interested in:
This unit has one input, and two outputs... and one of the outputs is Phase-Inverted, specifically for use with Twin Reverb style amps, so as to put both channells in-phase with each other.
It also has some other neat features.

http://www.barberelectronics.com/LaunchPad.htm
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Re: Is it bad to mix channels with a twin?

Postby SarnoMusicSolutions » Wed Mar 30, 2011 9:30 am

While that photo shows Jer' jumpering over to the normal channel from the reverb channel input, we do know that these Twins had the two preamp sections separated and sent to their own discrete outputs, I believe. So likely Jerry wasn't encountering a phase issue within the Twin itself. Not sure where the non-reverb preamp section was sent, but likely knowing those guys, they compensated for phase somewhere along the way. Possibly Jerry had the two preamps in that Twin head going so he could control two separate signals. Maybe one for his reverb'd stage and WOS sound, and the other direct to tape so they'd have a dry isolated track to mess with later in the studio. Just guessing. But as far as we know, the way they wired those Twin heads, the Normal channel had its own output jack on back, and the Reverb (aka Vibrato) channel had it's own output which for years to come was Jerry's main sound output from the Twin. The Normal channel thingy there is likely some aux output for other purposes... Anyone???

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Re: Is it bad to mix channels with a twin?

Postby SarnoMusicSolutions » Wed Mar 30, 2011 9:35 am

And also to comment on the method of mixing both channels to share the reverb which also brings both channels into phase with eachother; while that's a popular mod it does have a flaw that has made me want to avoid it. The node or point where both preamp sections meet (pre reverb) is typically done by simply connecting the two signal wires. Simple mod, works ok. But since those wires are not typically mixed using mix resistors, they are loading eachother down and that may not be the best thing for signal purity distortion. Then if you do add mix resistors which is the theoretically "correct" method, you then mess with the gain structure of the Twin's preamp. So for those reasons, I've always avoided the rewiring mod for combining of the two channels to share the reverb.

B
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Re: Is it bad to mix channels with a twin?

Postby Pete B. » Wed Mar 30, 2011 10:00 am

I had the "reverb on both channels" mod done on one of my amps, mainly beacuse I wanted to use one channel for Steel and one channel for Guitar.

Maybe someone can get the info on Jerrys rig in that pic from Healy?
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Re: Is it bad to mix channels with a twin?

Postby jenkins » Thu Mar 31, 2011 9:11 pm

So how was jerry actually running his twin?
His main stage sound was the output from the reverb channel coreect?
So was this jumped so it was a mix of both preamps or not?
Where did that separate dry out go? Does anyone know?
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Re: Is it bad to mix channels with a twin?

Postby RiverRat » Wed Apr 06, 2011 6:57 am

Worth noting, with the Alembic input mod in place on the Vibrato channnel, just running to Input 1 has both the 68K grid resistor and the straight path to the grid in parallel. Which effectively yields a result of having no resistance between the input and the grid of V2a. When you plug the cable into input 2, you disengage switch 1 and switch 2 of the 1st Input and now there is only the 68K grid resistor present. If the Alembic Input mod was done to Input 1 of the normal channel, the same thing seen with just input 1 of the Vibrato channel is true, there is effectively no resistance between between the input and the grid.

This might explain the later addition of the mystery black knob where Input 1 of the normal channel was. It could very well be a pot to dial in the resistance of the remaining normal channel sole input impedance so both channels were close to equal.
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Re: Is it bad to mix channels with a twin?

Postby mijknahs » Wed Apr 06, 2011 12:35 pm

SarnoMusicSolutions wrote:And also to comment on the method of mixing both channels to share the reverb which also brings both channels into phase with eachother; while that's a popular mod it does have a flaw that has made me want to avoid it. The node or point where both preamp sections meet (pre reverb) is typically done by simply connecting the two signal wires. Simple mod, works ok. But since those wires are not typically mixed using mix resistors, they are loading eachother down and that may not be the best thing for signal purity distortion. Then if you do add mix resistors which is the theoretically "correct" method, you then mess with the gain structure of the Twin's preamp. So for those reasons, I've always avoided the rewiring mod for combining of the two channels to share the reverb.

B


Brad, you should try it on your Fender and see if you can actually notice any degredation in sound. I did it to mine (so I could have a backup reverb channel with channel 1) and I really don't notice any change in tone. I mostly only use channel 2.

Jim
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