implementing HT bypass in preamp

[dvenardos]

I am building a six channel passive preamp based on the Goldpoint 2P-6T-3D selector switch and MV-6-20K attenuator.
http://www.goldpt.com/selector.html
http://www.goldpt.com/dims.html

I have decided to implement one of the inputs as an HT bypass so that I have the option of using it with an av pre/pro. However, I am not sure how I would go about implementing a bypass for one input and can't seem to find any information on how to do it.
Anyone implemented an HT bypass?

Thanks,
Don

 

[dvenardos]

No one has done a HT bypass?

 

[h_a]

Using abbreviations does no good 😉

I have to guess what you mean: Hometheater bypass? The same as a tape-out?

Connect the input directly to the bypass-output and you could risc problems with the lowered input impedance (input impedances of preamp + home theater amp in parallel). Depending on your home theater amp it probably does not matter.

You could insert a switch and switch the connection the input is connected to (either to pre or to home theater amp) - that's probably easiest.

Or you could sandwhich a buffer in between.

Lots of possibilities.

Have fun, Hannes

 

[dvenardos]

Sorry, yes home theater bypass. A home theater bypass is a straight pass-thru from one input to the output bypassing the attenuator. The way most commercial home theater bypasses are implemented is that you use the switch to select the bypass input. With only one common output on the switch I don't see how I could wire one input directly to the output. I suppose I could put in a toggle switch that when selected would send the bypass input to the output but then if another input was selected on the switch it would combine the selected input with the bypass input. So, I am wondering how it can be done while still requiring that the bypass input be selected on the switch?

 

[AndrewT]

what is an "av pre/pro"?
Why does it not require an attenuator?

 

[dvenardos]

what is an "av pre/pro"?
Why does it not require an attenuator?

Audio video preprocessor, a preamp with digital decoding.
http://www.outlawaudio.com/products/970.html

This is a way to use an analog only preamp for music and still retain the ability to use an audio video preamp (which is not nearly as good for music) for movies.

 

[dvenardos]

Okay, I think I have it. I can put a toggle switch in-between the switch and the attenuator that will route the output either to the attenuator or to the output. This will effectively make the preamp either a preamp or a switch.

 

[dvenardos]

Looks like I would need a 6PDT toggle switch, but they seem to be pretty hard to find. Anyone know where to find a good quality one in the United States?

 

[sjalloq]

I'm going to be doing this and the easiest way is to have an output switch after the attenuator and input switching. So you have all your inputs, excluding your HT input, being switched into the attenuator. Then the output switch selects either the output from the attenuator or the input from your HT gear. I'm doing it with a relay.

Cheers.

 

[dvenardos]

I'm going to be doing this and the easiest way is to have an output switch after the attenuator and input switching. So you have all your inputs, excluding your HT input, being switched into the attenuator. Then the output switch selects either the output from the attenuator or the input from your HT gear.

That's better, just one set of wires going to the outputs.

 

[dvenardos]

Does it matter.

I am going to get two switches and either

1) Implement as sjalloq suggests and put the second switch after the attenuator and select between the one bypass input and the attenuator and send that to the output.

bypass input--------------------------v
normal inputs ----> attenuator ----->switch----->output

2) Put the second switch before the attenuator and wire the output of the attenuator and the switch to the output only one of which would be active.

all inputs-------->switch------>attenuator----->output
|-----------------------------^


The second option has the advantage of being able to switch all the inputs directly to output so that the preamp can work either as a preamp or a switch but has two sets of wires going to the output only one of which is live at a time. Would this be a problem?