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Old 19th April 2011, 08:15 AM   #1
DQ828 is offline DQ828  Australia
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Default A-B Testing

Hi Guys

As a bit of a beginner I'm not sure what I can get away with re connecting things together. I was hoping to do some A-B testing o two amps, using a separate Squeezebox Touch to supply each amp & connecting both amps to one set of speakers at the same time, with the idea of playing music through each amp one at a time. This would save me building a switching device.

If I cannot do that, does anybody have a simple design for a switch?
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Old 19th April 2011, 08:58 AM   #2
luka is offline luka  Slovenia
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I wouldn't drive other amps output with first, I would use switch or relay there
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Old 19th April 2011, 09:48 AM   #3
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Quote:
Originally Posted by luka View Post
I wouldn't drive other amps output with first, I would use switch or relay there
I was hoping to drive the speakers

Wouldn't electrical relays cause some horrible noises when switching?

I assume I would need two double pole relays and wire one amp out put to the two Normally On side of the two relays & the other amp to the Normally Off side of the relays, you can see I'm a genius at all this. )

Last edited by DQ828; 19th April 2011 at 09:56 AM.
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Old 19th April 2011, 10:26 AM   #4
luka is offline luka  Slovenia
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well if you would turn down the volume, then I don't think there would be any noise... if you need to keep constant volumes on both amps, then you will just have to go and switch when you need to... maybe I would also use 10R resistor, for each amp ch to drive when it doesn't have any speaker on

Maybe I am going to far with this, but..
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Old 19th April 2011, 05:17 PM   #5
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Originally Posted by DQ828 View Post
Hi Guys

As a bit of a beginner I'm not sure what I can get away with re connecting things together. I was hoping to do some A-B testing o two amps, using a separate Squeezebox Touch to supply each amp & connecting both amps to one set of speakers at the same time, with the idea of playing music through each amp one at a time. This would save me building a switching device.

If I cannot do that, does anybody have a simple design for a switch?
You can't parallel (connect together) the outputs of power amps - you'll probably damage one or both amps and it will sound horrible at best.

Why not just purchase a cheap speaker selector switch? That will allow only one amp at a time to be connected to the speakers. If any of the amps are tube amps you'll need to make sure you either place a resistor across the output terminals of the amp (20 ohm would probably not interfere with the sound but would prevent over voltage) or just be careful to keep the volume at zero until the speakers are connected.
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Old 20th April 2011, 05:31 AM   #6
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I also would like to A/B two Tripath amps on one set of speakers, but as I understand it, Tripath amps cannot share the right and left negative terminals, as most other amps typically do. I have been looking but have yet to find a speaker selection switch that does not connect the negatives together to save space and cost.

Anybody have a solution to that problem? I'm about to build a switch of my own with a 4-pole DT switch of some kind.

From an eBay site selling the Lepai's:
Quote:
The machine is BTL output, that is to negative side of speaker out is not public grounded (the two speakers cable must independent connect, no grounding together), we must strictly in accordance with the marking of plus or minus cable connection.
The TA2020 is a 20W/ch continuous average two-channel Class-T Digital Audio Power Amplifier IC using Tripath’s proprietary Digital Power Processing™ technology. Class-T amplifiers offer both the audio fidelity of Class-AB and the power efficiency of Class-D amplifiers.
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Old 20th April 2011, 07:58 AM   #7
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Quote:
Originally Posted by sprinter View Post
I also would like to A/B two Tripath amps on one set of speakers, but as I understand it, Tripath amps cannot share the right and left negative terminals, as most other amps typically do. I have been looking but have yet to find a speaker selection switch that does not connect the negatives together to save space and cost.

Anybody have a solution to that problem? I'm about to build a switch of my own with a 4-pole DT switch of some kind.

From an eBay site selling the Lepai's:
I found this online A-B Box For Amplifier Comparisons it talks about sharing as well, but the design could easily be changed to switch both + & -
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Old 20th April 2011, 07:56 PM   #8
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Originally Posted by sprinter View Post
I also would like to A/B two Tripath amps on one set of speakers, but as I understand it, Tripath amps cannot share the right and left negative terminals, as most other amps typically do. I have been looking but have yet to find a speaker selection switch that does not connect the negatives together to save space and cost.

Anybody have a solution to that problem? I'm about to build a switch of my own with a 4-pole DT switch of some kind.

From an eBay site selling the Lepai's:
I seem to recall coming up against the same problem when looking for a speaker selector switch so I just made my own. It's about as simple of a DIY project as you can get.
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Old 21st April 2011, 08:48 AM   #9
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Originally Posted by sampleaccurate View Post
I seem to recall coming up against the same problem when looking for a speaker selector switch so I just made my own. It's about as simple of a DIY project as you can get.
So what did you use for switches? I guess the cheapest thing would be two common AC rated DPDT toggle switches and just throw them simultaneously. But a multi pole rotary would be nicer. Would you have suggestions? It's been a long time since I've parts shopped. Or how about linear multiple-pole push-button switches? A quick glance at available rotary switches, they seem pretty expensive at required ratings.

Ideally, I would like to eventually be able to switch between two amps and also two sets of speakers. Not sure what kind of switches would be suitable for that.
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Old 24th April 2011, 09:53 AM   #10
DQ828 is offline DQ828  Australia
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Well here it is. I haven't tried it yet, but it is testing fine. I need to make some split RCA leads or else I can us my two Squeeze-boxes, synchronised I guess, then wont need the split leads. Any thoughs on what would be the best approach?

I'll be testing an Integra Class A-B amp against a DIY D class, I not sure If I will need a dummy load for the amps when they are not linked to the speakers, but have bought some 8.2ohm 10w wire wound resistor for that purpose if needed. Any thoughts guys on if the dummy load will be needed?

I have a illuminated switch, that switches two 12V 30amp relays, there is a LED so you know when the unit has power, the who thing is powered by my computer backup drive power supply.

I plan on torturing the kids & brothers (or anyone silly enough to get to close to the house) by making then listen to the amps & giving there opinion on which sounds the best to them, they wont know which amp is on, but I will know because the illuminated switch will be way of keeping track. When I try it myself I will try to make my assessment before confirming which is which.

My thanks to the designer, Phil Allison, A-B Box For Amplifier Comparisons
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Last edited by DQ828; 24th April 2011 at 10:12 AM.
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