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Old 26th August 2003, 04:17 PM   #1
palesha is offline palesha  India
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Default Bridge Amp Testing

I want to test Bridge amp on my computer. I hv DAAS 32. It has unbalanced input. My friend to told me to make one balance to unbalance opamp based circuit. I want opinion of friends of this forum.
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Old 26th August 2003, 05:15 PM   #2
dhaen is offline dhaen  Europe
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Default I agree.

Hi,

Other than with a transformer, it seems to be the only way that you'll measure the true distortion spectrum.
Going unbal to bal requires 3 opamps to do properly. Or there are "off the shelf" chips like INA137 and SSM2143 that do the whole thing. I'd use one of those.

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Old 26th August 2003, 07:13 PM   #3
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Hi palesha,

I have a DAAS32 also (before had the DAASL3+). Since I have it I always thought that a balanced input would be great and so I began a couple of years already to plan some kind of switchbox for it.
Meanwhile there is something similar that I had in mind - the adm "featurebox" - but mine will have much more possibilities, among other things, a balanced input and balanced outputs.
Unfortunately the documents for this project (schematic, PCB-layout, drawings) are finished only to about 75% (as many of my other projects too and I don`t know when I`ll find time to continue this one ).

I`ll use a Burr-Brown INA-103, for the balanced input which I believe is most suitable for this task.

Low Noise, Low Distortion INSTRUMENTATION AMPLIFIER INA103
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Old 27th August 2003, 02:02 AM   #4
palesha is offline palesha  India
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Hi Cocolino,
Thanks! Just give me the circuit & i will do the rest. Then i will send u the same. This way we will make it final. Hope we can jointly go ahead in the matter.
Mahendra Palesha
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Old 27th August 2003, 11:45 AM   #5
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Quote:
Thanks! Just give me the circuit & i will do the rest.
Palesha,

although the hole project is quite progressed finally it`s nothing more that a bunch of more ore less completed fragments and therefore I fear that You can`t see through (after looking at the files I realised the last time I was working on it is more than a year ago and I would need a lot of time only to figure how to proceed again).

However, as I intended first to make a balanced microphone input only, this is the most progressed part of the project. Later on I changed my mind and got the idea to build a complete "featurebox" and among other things, to add a balanced input for line levels also, respectively to use the bal. mic.-input for line-input too (You only do acoustical measurements via mic-input OR electrical measurements via line-input but not both at the same time).

If You`re interested, I have a ready made board for the instrumentation amp for sale (as I changed my mind from an balanced input only to a complete "featurebox" I revised the PCB layout somewhat, so likely I don`t need this first made board anymore).
As You can see in the picture it has even a low noise dual +/-15V tracking regulator on board (LM325N). So all You`d need is a transformer/rectifier and maybe some more filter caps.

There is a small switch and gain can be changed from fixed x1/x10 to variable with a trimpot.

Also there is an offset servo and a cable shield driver according figure 12 and 13 in the application part of the data-sheet (see link from my previous post). The latter two features aren`t really necessary though.

What may be missing and desireable with external connections and measuring amps is an "input-stabilization-network" according figure 2. This could be easily still added on the bottom (solder side) of the PCB near the inputs of the INA103.

Another thing what can be added is an input attenuator when measuring amps at higher output levels that could exceed the INA-103 max. input range: I thought about an x10/600Ohm attenuator for power amps and/ or another higher impedance attenuator for line-level circuits.

Well, after the board was finished during testing I got aware of a small bug in the layout (as I remember) so I would have to check and fix this first in case You`re interested (as You can see on the pic I have desoldered some parts near the regulator already).

Anyway, should You don`t want to have this board IŽll send You the PCB-layout and schematic (somewhat later - I want to fix the bug in the layout drawing first) and You can modify and adapt it to whatever You like. There is only a small problem: my CAD-program is completely unknown and You can`t open the files as they are. IŽd have to convert them in some format You can use. As far I know I can convert to DXF and PCX files - let me know if any of this is of help for You?
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Old 29th August 2003, 01:57 AM   #6
palesha is offline palesha  India
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Thanks Cocolino.
I might get SSM 2141 from the market. My friend suggested me to use 5534-3nos. so that we can use supply upto +/- 20V. Kindly comment or suggest anyother circuit.
Mahendra Palesha
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Old 29th August 2003, 02:57 PM   #7
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Hello Palesha,

the SSM 2141 should be okay for this purpose and when You could get them without trouble IŽd use.
Of course You can build Your own instrumentation amp with 3 individual OP-amps also - but to get the high precision resistors that are required maybe is more difficult and IMO it`s easier to use one of the integrated solutions.
There are several possibilities - you have the choice
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Old 29th August 2003, 03:04 PM   #8
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the ssm2141 is a receiver - balanced in and single ended out.
you will need a ssm2142 or perhaps even better the drv134....
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Old 29th August 2003, 03:23 PM   #9
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Quote:
the ssm2141 is a receiver - balanced in and single ended out.
That`s exactly what Palesha needs and what he wants to do - the DAAS 32 is a PC based measurement system (mainly for speaker testing but it can be used for all kind of audio-electronics as well) and it has single ended inputs only......... and as he also wants to measure bridged amps he don`t need a balanced line driver as the SSM2142.
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Old 29th August 2003, 03:29 PM   #10
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...ok
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