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francolargo  
#1 Posted : Monday, February 4, 2008 4:43:57 PM(UTC)
francolargo

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Joined: 4/21/2007(UTC)
Posts: 60
Location: Minnesota

Greetings,

The energy and productivity of the Twisted Pear braintrust is quite impressive! I know that Russ or Brian would graciously answer my e-mail but I pose these questions here in case the answers might help others.

I'm planning to make one power amplifier for two different applications. One is as a higher-power stereo amp - in my case for tight bass in a bi-amp music setup (~200 Hz and lower); two is for less power but four discrete channels in a video surround setup (full freq. range). I already have a TXO-2 that I particularly like, so I have parts coming for two more TXO-2's, which I will integrate into one rack-mount chassis. I plan to route signal inputs using Darwin parts and I'm still thinking about the best way to switch the amplified outputs. I would greatly appreciate your specific suggestions on switching the inputs and outputs:

a) Best topology and choice of output switching parts [e.g. relays vs. quality silver-contact switches]?

How much juice can I steal from the regulated side of the TXPS for control relays without affecting the TXDs?
Could I possibly run a 12 V relay on the TXPS's regulated 10.X volts without compromising it, or better to use a stand-alone supply for any 5V & 12V relays? Left on my own, I'd probably just use TOCO toggle switches to split the outputs from two of the four TXO channels between the output binding posts. The TOCOS toggle switches have low resistance silver contacts, and I would be inclined to employ 2 poles each for minus and plus, for greater current capacity. Thus, in 2 channel mode each output would be the sum of an un-switched TXO and a TXO whose output came through the routing switches. Cludgy?

b) Thoughts on configuring inputs to achieve best stability and fidelity in 2-channel (parallel) mode?

I was going to split the input signals to use all four TXDs available rather than switch asymetrically into an attempted TXO-4 configuration. No doubt the Darwin is a good hardware choice for this job. Can I assume that it is not necessary to isolate each balanced input channel's ground? If not then I thnk I can get by using only one Darwin board.

I look forward to any and all suggestions, especially on the best approach to the required switching!

Best,

Frank in Minneapolis
Russ White  
#2 Posted : Sunday, February 10, 2008 9:04:56 AM(UTC)
Russ White

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Hi Frank,

Sorry I seemed to have missed this post until now.

In short, we simply don't recommend parallel TXO configurations. I just have not found a good way to make them universally stable. This is one reason we no longer offer the TXO-4 configuration.

While it is technically possible to get it to work, there are some practical issues that make it difficult.

That said, I am working on a new project which we will publicize soon which will deliver more power than the TXO-2, and resolve a lot of the practical challenges.

As to relays, any good quality silver contact relay should do fine for input switching. G6H and G6K come to mind. The Darwin uses G6K and would work very well. SE with switched grounds is easy, just use one Darwin per channel (right and left).

Cheers!
Russ

Edited by user Sunday, February 10, 2008 9:05:35 AM(UTC)  | Reason: Not specified

Russ White  
#3 Posted : Sunday, February 10, 2008 9:18:07 AM(UTC)
Russ White

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BTW, I don't think you will actually need to run the amps in parallel. Bi-amping should be adequate.

As for relays to use to switch outputs, I would have to do more research. We have used types like the Fujitsu FBR111U with great results.

Cheers!
Russ
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