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Old 29th December 2010, 12:27 PM   #1
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Default Parallel amp connection to speakers, SS + tube

Hi all-
I want to connect my DIY KT-88 SE amp to my Klipsch KG-4's that are in my HT setup in parallel with my SS Yamaha HT receiver. Will this damage either device? I'd only be using one at a time. The other option is some sort of amplifier selector switch box, kind of like a speaker selector box in reverse.
Anyone have a similar situation where the use different amps on one set of speakers?

Glenn
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Old 29th December 2010, 01:24 PM   #2
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Yes, the tube device would damage the receiver . Use a speaker selector box in reverse. Make sure you have a light permanent load on the tube device to keep the output voltage from going too high if you turn it on with speakers disconnected.
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Old 29th December 2010, 02:00 PM   #3
kevinkr is offline kevinkr  United States
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Back in the day I regularly repaired the consequences of connecting tube and solid state amplifiers in parallel under the proposed usage conditions. The solid state amplifier always lost resulting in blown output devices.

Indianajo has it right, you must use a switch, and as he says it would be a good idea to assure that there is always a light load on the tube amplifier. I think a 100 ohm 1W resistor would be adequate in most cases unless exceedingly careless. (At your own risk)

Make very sure that no amp output grounds are common inside the switch either - it would be best to use a DPDT switch and switch both sides of the speaker load - prevents ground loops, and in the case of a BTL output on a receiver (IMHO probably not that common) would prevent the destruction of the receiver's output stage. It would be best to build your own.
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Old 29th December 2010, 03:09 PM   #4
Pano is offline Pano  United States
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Right. And beware the Radio Shack speaker switch boxes as they have a common ground.
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Old 30th December 2010, 01:29 PM   #5
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Thanks guys, glad I asked!
Time to build an "Amplifier selector box" I like the idea of putting loading resistors in the circuit.
Of course I asked this question because I didn't want to keep switching speaker wires manually every time I wanted to use a different amplifier due to laziness, now I have to build a switch box, oh well
At least I didn't cook my expensive Yamaha HT receiver!

Have a good new years everyone.
Glenn
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Old 30th December 2010, 01:51 PM   #6
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I'd use a relay (with 4 switching contacts), switched by the power supply of your tube amp.
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Old 31st December 2010, 01:05 PM   #7
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That's a good idea!
That way it's automatic
Thanks!

Happy new year!
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Old 31st December 2010, 01:54 PM   #8
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Kinda off topic, but still relevant -

I built an A-B Test Switch from Elliott Sound Products to switch (online) two amps on a single speaker set - all from my comfortable seating position. The Switch Box has Relays to properly switch the speaker leads from one amp to the other.

A-B Box For Amplifier Comparisons

BTW - you would be surprised how close amps can really sound...that time to unhook/reconnect an amp really can sway an opinion...

This thing has saved me gobs of money chasing the "Best" amp.
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Old 31st December 2010, 02:00 PM   #9
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The Elliott device is not acceptable. The grounds should not be combined to be on the safe side. THis device absolutely couldn't be used with a SS bridged amplifier.
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Old 31st December 2010, 02:08 PM   #10
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You are correct...do not connect the grounds as shown...

I had my amp grounds switched along with the positive speaker lead - I think I eiether doubled the number of relays, or did not double up the DPDT relay pins. I have to check.
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