Adding a selectable second output to my GG preamp - help?

[Tlarwa]

I have a Transcendent Sound GG preamp that I built and enjoy very much (heavily modded). I am interested in adding a second output, so that I can either run a second amp in a bi-amp scenario, or to power a second set of speakers, using the same front end. So I'd like to add a switch that would allow me to select amp 1, amp 2 or both amps (for bi-amping). I assume this is doable, but I'm not sure if there is anything I need to be concerned about. Can anyone lend some sage advice? Any advice on how exactly I'd wire that, as well as what switch I would want (I was thinking a toggle on the back of the chassis between the 2 sets of output jacks) would be greatly appreciated. A shot of the internals is attached. As you can see, there is a ton of room on the back of the unit for a switch and another set of output jacks.

Thanks in advance!

 

[paul_b]

This is the easy option. Turn the amp off that you don't want to use.

 

[TriodeLuvr]

That connector will work if both amps are vacuum tube and if the total parallel R and C at the inputs is easy to drive. Coincidentally, I've been thinking about this too. I want to reassign my low-power 6V6 SE amp to headphone use only and add a higher power amp for speaker use. If both amps are high-Z input, there shouldn't be any need to switch the audio path.

Jack

 

[Tlarwa]

Not sure, but it's highly likely that the second amp may be a solid state design. The main amp is my Finale Audio EL84. Will this make a difference?

 

[TriodeLuvr]

Not sure, but it's highly likely that the second amp may be a solid state design. The main amp is my Finale Audio EL84. Will this make a difference?

I suspect the input stage of a SS power amp will distort the signal if the amp isn't powered on. If it has an input control, setting that to minimum might eliminate this problem. It would be useful to see a schematic.

 

[Tlarwa]

Not sure what amp it'll be yet. That's why I was thinking a selectable switch with a second set of outputs might make sense

 

[MrEd]

Glad this topic came up.
I was contemplating this scenario.
Biamp with passive xo plus using my sub ( mini dsp input )
Both amps are tube with 10k input impedance.
That would be three preamp outs..
Is it feasible?

 

[Blackdog]

It's relatively simple if you can drill holes and solder.
A DPDT on/on switch is all you need.
Using an adapter will work, but the "off" amp may present a non-linear load which could distort the signal.

 

[Tlarwa]

It's relatively simple if you can drill holes and solder.
A DPDT on/on switch is all you need.
Using an adapter will work, but the "off" amp may present a non-linear load which could distort the signal.

On the DPDT switch does the center position send the signal to both amps? I assume so.

 

[RPMac]

I have 4 outputs on my BeePre. I have used 2 amps in bi-amp plus a pair of subs without issues (that I know of). The amps are both tube amps with 100K inputs. The subs are auto-on and have a bad turn-on thump, so I added a switch to keep them off until the preamp warms up.
The issue of concern is impedance matching to the output impedance of the preamp. Paul and PJ had a discussion about this on the Bottlehead forum, so I will let Paul explain.
I can’t speak to Jack’s comment about a SS amp connected, but off causing distortion. But any amp connected will have a pathway to ground.

 

[Blackdog]

On the DPDT switch does the center position send the signal to both amps? I assume so.

No. With what I mentioned above, there is no center position.

 

[paul_b]

It's relatively simple if you can drill holes and solder.

This is really the issue for me. The Transcendent preamp has a nicely cut back panel with all the holes lined up. Getting a new pair of holes reasonably well aligned with what's there will be tough!

 

[Blackdog]

Agreed.
I see hack jobs all the time. Drives me nuts when I see misaligned holes.

 

[MrEd]

This is really the issue for me. The Transcendent preamp has a nicely cut back panel with all the holes lined up. Getting a new pair of holes reasonably well aligned with what's there will be tough!

Looks like lots of real-estate there... piece of cake.

 

[Tlarwa]

This is really the issue for me. The Transcendent preamp has a nicely cut back panel with all the holes lined up. Getting a new pair of holes reasonably well aligned with what's there will be tough!

I'm not concerned about drilling the holes ... I'm equipped to do that. And yes, there is plenty of room as well which makes it easier.

 

[Tlarwa]

No. With what I mentioned above, there is no center position.

I really want a center position as well, so I can either run 2 amps at the same time in a biamp setup, or run a single amp at a time to different speakers. Is this possible? Different type of switch?

 

[Chops54]

This is the easy option. Turn the amp off that you don't want to use.

I use the same thing to feed two amplifiers from one of my own GG preamps. One is a valve amp, the other solid state. Only one of them is in use at any time as they share the same loudspeakers. I have tried them both with the other amp connected and disconnected and there’s no audible difference to my ears so I’m happy to leave both connected to the preamp. I have also drilled the rear panel to include two more inputs. I did this by moving the inputs farther across the back panel and drilling another pair of holes in the gap. One of my other GGs also has a tape loop too. I also have a dual gang Dact volume control fitted to the GG in my main system. It was originally dual mono but I could see no good reason for having to turn two knobs when I only have to turn one so I rebuilt it dual gang using parts from a scrap selector switch.

 

[Blackdog]

Different type of switch?

Yes, and quite a bit more complicated wiring.

 

[Tlarwa]

I use the same thing to feed two amplifiers from one of my own GG preamps. One is a valve amp, the other solid state. Only one of them is in use at any time as they share the same loudspeakers. I have tried them both with the other amp connected and disconnected and there’s no audible difference to my ears so I’m happy to leave both connected to the preamp. I have also drilled the rear panel to include two more inputs. I did this by moving the inputs farther across the back panel and drilling another pair of holes in the gap. One of my other GGs also has a tape loop too. I also have a dual gang Dact volume control fitted to the GG in my main system. It was originally dual mono but I could see no good reason for having to turn two knobs when I only have to turn one so I rebuilt it dual gang using parts from a scrap selector switch.

Have you used these connectors with both amps powered on at the same time in a biamp condition? Any issues?

 

[Tlarwa]

Yes, and quite a bit more complicated wiring.

Fair enough, but I don't have an issue with that if it can work and will allow me the flexibility of running 2 amps either independently or at the same time in a biamp condition. Can anyone share with me what the schematic would look like and what switch type it would require? I would be most appreciative.