Combining two Cracks

[modestmeowth]

What are peoples opinions of combining two kits in a custom case to get a duel mono design like that of the Dark Voice 339?

[Paul Joppa]

Haha - my thought is a complete redesign with shunt regulated stages (converting the unused channel to shunt regulator duty in each amp). Completely unrealistic and over the top of course!

[Paul Birkeland]

It's doable, but you have some tough decisions to make.  We are not all that in love with the sound of paralleled triodes, so you may actually end up with better results from just having two power transformers and one output tube.  If you build the custom chassis with these questions in mind, you could try out a lot of different designs and pick the one that works best for you.

The shunt regulated Crack is something we have built, but it's more complicated than 2 Cracks in one box, more like a BeePre with two Speedballs. 

-PB

[modestmeowth]

It's doable, but you have some tough decisions to make.  We are not all that in love with the sound of paralleled triodes, so you may actually end up with better results from just having two power transformers and one output tube.  If you build the custom chassis with these questions in mind, you could try out a lot of different designs and pick the one that works best for you.

How would one go about adding a second transformer? Thanks!

[Paul Birkeland]

How would one go about adding a second transformer? Thanks!

You'd need a chassis plate that would take two power transformers.

[ironbut]

Wouldn't you end up with ground issues with 2 transformers and a single output tube?

[Paul Birkeland]

Nah, you can just split everything in terms of high voltage.  One B+ rail for the left channel, one B+ rail for the right channel, running both grounds up to T3. 

[Doc B.]

I might back up here and ask what is intended to be gained by the dual mono setup? It's usually done to reduce crosstalk and improve imaging. But headphone guys often want more crosstalk, even going out of their way to make crossfeed circuits, and imaging is not a forte of headphones in general. So it might not be that fruitful.

[mcandmar]

That is curious as it looks like both sides of the outputs tubes are joined together and running in parallel. I assume that would double the power and half the output impedance?

For a Crack wouldn't it be easier to switch to tubes with better separation.  e.g. 6CG7 & 7236, or just buy a S.E.X. amp

[Doc B.]

Yes paralleling the tubes for lower output impedance might have been the reason for doing this. And yeah, I agree, a S.E.X. or Mainline might be a better solution - depending upon what the perceived problem is.

[modestmeowth]

I might back up here and ask what is intended to be gained by the dual mono setup? It's usually done to reduce crosstalk and improve imaging. But headphone guys often want more crosstalk, even going out of their way to make crossfeed circuits, and imaging is not a forte of headphones in general. So it might not be that fruitful.

My hearing is impaired in my right ear so things always sound unbalanced and I was reading that running an amp that was dual mono would fix that.

[Doc B.]

It wouldn't make any difference unless you happened to have one amp that was more quiet than the other. You just need a simple balance control.

[modestmeowth]

It wouldn't make any difference unless you happened to have one amp that was more quiet than the other. You just need a simple balance control.

Could you explain that for me? I was under the impression that running dual mono would allow me to adjust left and right independently.

[Paul Birkeland]

A balance control adjusts the relative levels of the left and right channel.

"Running dual mono" can mean a lot of different things, but primarily would refer to independent power supplies for a left and right channel. 

If you have the ability to drill a couple extra holes in your Crack chassis, you can add a balance pot pretty easily.  If you know how many dB of attenuation you need on the left ear, you could build that into your amp for about 15 cents.

[Doc B.]

Yes, we were under the assumption that you meant dual mono as in two independent amplifier circuits. I see now that you mean a separate left and right volume control. Either separate controls or a balance control would work. Either way could be implemented with one more hole in the chassis, or you could put the balance pot in a separate box ahead of the Crack.