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ABY box for 2 channels on Matchless DC30

PhiloTone

Member
Messages
271
I just got my Radial Bigshot ABY box for my Matchless today to switch and combine channels, but it's not acting as I expected. Switching from "A" to "B" works fine, but the "Y" doesn't really seem like it's doing much. When I switch to "Y" (both channels) it sounds almost identical to "B", but with just a smidgen of high frequency roll-off. I'm running both channels at 11:00. It doesn't seem to be behaving the same as when I jumper the channels with a cable, like I was expecting it to.

Has anyone else been successful using a "Y" box to jumper the channels?
 

Tone Meister

Member
Messages
3,266
I use the Lehle Dual switcher and the Y on it combines both channels for a distinctly different sound on a SC-30.
 

PhiloTone

Member
Messages
271
Well it's at least nice to know that it's supposed to work like a 3rd channel with its own sound. Do you think it's because it's a passive box and splitting the signal is making it too weak? (I am using an EP Booster as my high to low impedance buffer)
 

rmconner80

Cantankerous Luddite
Gold Supporting Member
Messages
4,158
Well it's at least nice to know that it's supposed to work like a 3rd channel with its own sound. Do you think it's because it's a passive box and splitting the signal is making it too weak? (I am using an EP Booster as my high to low impedance buffer)
It could be - I've never gotten satisfactory results out of a Y signal split that wasn't transformer driven. It just sounds weak, loaded, lacking punch and highs.
 

hywelg

Member
Messages
140
They're not wired out of phase, they are naturally out of phase because of the unequal number of inverting gain stages on each channel, hence the phase switch on the rear.
 

WmSchwartz

Gold Supporting Member
Messages
36
Love my HC30, but it's the most sensitive amp I have with regards to anything in the signal chain. That's also the same reason why I like it so much --but everything does seems to affect it more than most. Thankfully there's a wide enough frequency bandwidth to compensate for any high end loss as a result of A/B boxes, attenuators, etc....

With that, I routinely run a jumper between the channels and blend to taste with no polarity issues. The speaker "phase" switch (it should be labeled a "polarity" switch) is a convenience that's only needed when playing in a multiple amp setup and all of the speakers aren't pushing in the same direction.

Now, if it just wasn't so damn loud...

Even at half-power.

-Wm
 

PhiloTone

Member
Messages
271
Now, if it just wasn't so damn loud...

Even at half-power.

-Wm
...then it wouldn't sound like an HC30! ;)



I discovered that the "Y" setting has a more positive affect when I lower the volume on the second channel. It's still a subtle difference, and I wouldn't really call it a 3rd channel necessarily, but more like an enhancer, adding a bit of body, grit, and sustain. But again, the "Y" position is basically useless if I run the gain too high on ch2. Also, the iso transformer on the bigshot takes away some of the transients when engaged, so it's basically useless to me too, though not really necessary for this application anyway.

So now, I find myself hitting "B" if I want more of a classic rock vibe and "Y" if I want modern rock (or lead). Clean, classic, modern....kind of a cool setup, but now I keep forgetting which channel I hit due to the lack of LED's. Ah well, I'll learn to deal. But with a channel switcher this amp is the most versatile (and fun) I've ever played through!
 

Seegs

Member
Messages
10,169
definitely has to be transformer isolated...Framptone is and so is the Lehle Dual...

the Framptone's buffer was a deal breaker for me as it altered my base tone and the sound and feel of my drive boxes downstream in an unacceptable way...and yes I used it with a 96 DC30...

Lehle Dual SGOS (newest version) doesn't have a buffer so when you introduce the extra cable your sound will get a bit duller which is normal...

IME mixing channels is always a compromise and you can't optomize each channel to sound its best and then expect them to work well when blended...it just has never happened that way for me...

Chow,
Seegs
 

Tone Meister

Member
Messages
3,266
Did you actually read the OP? That's the box he using........
Oops! I had read the OP a couple of days ago and had forgotten exactly what he was using. Found this one this morning and thought I'd provide the link in his thread. Sorry about missing that. :hide2
 

rmconner80

Cantankerous Luddite
Gold Supporting Member
Messages
4,158
They're not wired out of phase, they are naturally out of phase because of the unequal number of inverting gain stages on each channel, hence the phase switch on the rear.
Just to clear this up, the two channels are not out of phase with one another.

Right (pentode) channel = 1 total gain stage with one inversion
Left (top boost like) channel = 3 total stages with one inversion.

In other words, either channel has the same number of input signal inversions (only 1), and there is no phase issue.

Explanation of the Left channel stages:

-Stage 1 - input stage comprising a paralleled triode. Unlike a single triode, this arrangement does not invert input signal.
-Stage 2 - second stage, does invert input signal.
-Stage 3 - not really a gain stage; is a cathode follower reproducing at unity or less (but with significantly reduced output impedance); and does not invert.

So total number of inverting stages is identical between the two channels.

Also, the speaker polarity switch wouldn't do anything in the case that they were out of phase - because it would affect both channels.
 




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