• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

2 amps with 1 set of speakers?

webelo

Member
2007-10-19 6:54 pm
I know this probably isn't the right place for this... but you guys seem to know a lot.

my question: Is it possible to hook up two amps to one set of speakers (I'm not referring to bi-amping) and be able to select between the two of them?

My plan is to have a full set of surround sound speakers with a surround sound receiver for playing movies in 6.1 and have pair of monoblocs for playing music thru the floorstanders. All home theater components (dvd, cable, etc) will be hooked up to the receiver and the stereo components (phono, cd, etc) will be hooked up to a pre-amp, then the monoblocs.

I've done some searching on the net and have come across anything definitive.
 

cbutterworth

Member
2006-10-03 11:02 pm
I asked a similar question on the AudioCircle site around six months ago.

The advice that I recieved was that it would be risky. The amps would see the other low impedence of the other amp as the load resulting in smoke and sadness. :bawling:

I am sure that a switch could be used, but according to replies to my posting from Hugh Dean (Aspen Amplifiers) and Frank Van Alstine, it is not worth the risk of switch misuse causing catastophic failure of your amps.

I suppose, there may be solutions to your two amps / one pair speaker issue. Why do you want to use two amps? For me, it was easy as my second amp is a cheap Sherwood amp that I only wanted to use for TV, DVD, radio, etc, which would save me routing these sources through my Aikido preamp and AKSA power amp. In the end, I decided that tube life would be very long, and I have a second set of my desired tubes "on-ice." For this reason, I play everything through my main system.

When I finally get around (ie. have funds and space) to build and install a tube power-amp, then I expect that I'll have to do what most other folk probably do - that is to simply change amps via disconnecting and reconnecting speaker cables.

Charlie
 

webelo

Member
2007-10-19 6:54 pm
two amps... a DIY stereo tube amp for music, because I'm pretty sure I can build a tube amp that'll sound better than my solid state receiver. However, I can't build a receiver that will decode 6.1 surround sound, dolby digital, pro-logic, etc.

So, I want one amp for music and one for movies.

However, my movie and music listening space is the same, so I only want to buy one set of decent speakers too save on space and money.

Could I simply build a switch box? Are there schematics for that?
 

Dan2

Member
2005-09-17 1:24 pm
webelo said:


I'm pretty much a newbie... could you decipher this?


A PIC (Programmable Integrated Circuit) is a chip that you program on a computer, which you can then use to drive relays - or rather drive transistors to drive the relays.

i think what Nordic is saying is have 2 separate sets of relays, and program the PIC so that one amp output is completely disconnected from the speakers before the other amp outputs are connected.
 
What about a relay (4 pole) that selects either the output of the tube amplifier or the receiver? Than there is no way that both amplifiers will be connected in parallel. As Webelo is building the valve amplifier himself he can include this relay in the chassis, and activate it from a voltage derived from, for example, the filaments. An activated relay selects the valve amp output, an desactivated relay (ie, the relay in a turned off tube amp) reroutes the receivers signal to the speaker.

A large wattage 100R resistor across the secondary of the OPT would be a safety measure in case the speaker gets disconnected from the tube amp (either through a loose wire or through a faulty relay). Both should be very rare, but can happen.
 
Hi Renron

I am glad that you (seemingly) understood it. I was almost starting to make a drawing in Paint, but decided I would have to go through some hard English to make my point clear.

The solution is really simple, not needing a microcontroller or any other additional circuit. One may argue about the relay in the signal path, but that would be essential in any kind of 'automatic' setup. I would search for a large industrial relay in a dump store (I have been told that industrial relays with 24VDC coils are not being used anymore, so they should be available).

Erik
 
The scenario that you want to avoid at all costs is accidentally having the speaker disconnected from the circuit, so that each amplifier becomes the "load" for the other.
I actually saw this happen once with a "homemade" switching system in a commercial PA system application. When this complex switching system was inadvertently set up in the wrong configuration, two large 100+ watt Bogen tube amps ended up "driving" each other, with no other speaker load, at all! The resulting destruction was immediate, total, and frankly, rather spectacular!
Had these been solid state amps, the output devices would have probably quickly popped, thus ending the adventure. However, as a testimony to the ruggedness of these Bogen brutes, each fought the other to a flaming death!
 

chrish

Member
2003-10-20 2:43 pm
Sydney
Does the receiver have pre-outs? If it does, use it as your pre amp then you have solved your problem. Allow the receiver to power your surrounds and go from the pre-outs for left front / right front to the monoblocks to the floorstanding speakers. If you need your external pre amp to use your phono, just go from your phono to existing pre to one of the inputs of your receiver.

This might not be the solution you are after (ie receiver in signal path instead of other pre amp), but probably the best practical solution for your situation/setup.

Cheers,

Chris
 

webelo

Member
2007-10-19 6:54 pm
chrish said:
Does the receiver have pre-outs? If it does, use it as your pre amp then you have solved your problem. Allow the receiver to power your surrounds and go from the pre-outs for left front / right front to the monoblocks to the floorstanding speakers. If you need your external pre amp to use your phono, just go from your phono to existing pre to one of the inputs of your receiver.

This might not be the solution you are after (ie receiver in signal path instead of other pre amp), but probably the best practical solution for your situation/setup.

Cheers,

Chris


unfortunately my receiver doesn't have pre-outs.
 

Brett

Member
2002-01-07 6:02 pm
My new system will do 2ch/HT duties. The front speakers will always be driven by the tube amps no matter what I'm listening to; it does make a difference on movies. DVD goes cia digital coax to the receiver, pre outs of receiver to my preamp (VC bypasses in HT mode) and to the front amps.

Several years ago I had a system that was tube and SS. I used the tube amps to listen and the SS amps as background music as the system was on 16hrs/day as I worked from home. I designed all the amps so that the XLR inputs and banana plug speaker outputs were all in an identical spacing, mounted close together. All the connectors were mounted through a small wooden board with a T handle.

When I wanted to swap from one to the other, I simply lifted int from one amp and plugged it into another.

It was sort of like this on the amp, but with two of them XLRs (you could use RCA's, if you really have to).
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=261-354
and a pair of thses and female XLR's on the 'moveable' board. No pics, but it's not a difficult concept.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=090-466

Changeover took 10 secs/channel.
 
stevodude said:
what about a high voltage power lever switch :) old style hehehe...

[IMGDEAD]http://www1.istockphoto.com/file_thumbview_approve/2601445/2/istockphoto_2601445_power_switch.jpg[/IMGDEAD]


Throw the Switch IGOR !


I have pre outs on my Receiver, but, I think going from the Receiver's Pre(s) to the tube preamp would degrade the signal and obfuscate the intention and purpose of the tube preout.

Thoughts?

Ron