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Old 25th February 2006, 08:38 PM   #1
Stew is offline Stew  United States
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Default Help Understanding CD Player Output Voltage, etc.

I have a CDP with +/- 5v rails. I'd really like to try AD843's with Brown Dog Adapters for output buffers but I'm not sure if they will work with +/- 5v rails.

The minimum input voltage is +/- 4.5 v according to the datasheet:

http://www.analog.com/UploadedFiles/...65502ad843.pdf

Typical output voltage is +11.5v, -12.6v with a +/- 15v supply so I'm assuming that I should get at least 1.5v (within 3.5v of the rails). I read somewhere that typical CDP outputs are around 2v but the input sensitivity on my preamp is only 150 mv so I'm assuming that 1.5v would be more than enough. I'm not sure if either are good assumptions.

I've also seen recommendations to use at least a +/- 12v supply with AD843 to prevent clipping. I can see where this would be an issue if using AD843 to power headphones but I'm not sure why the higher voltage would be necessary for CDP output buffers.

I'm a novice at all this and would greatly appreciate it if someone would help me understand this.
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Old 25th February 2006, 09:49 PM   #2
6h5c is offline 6h5c  Netherlands
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Hi Stew,

The minimum supply voltage for the AD843 is +/- 4.5V, so the +/- 5V in your player should be enough. What opamps are in there right now?

With the 843 the maximum output would be 3Vtt at +/-5V according to the graph, and most players don't give such a high output. The margin is not very big, but I think it will work. Your player probably has a bit lower output signal already, since the opamps are only on +/- 5V.

In general, opamps tend to sound better at higher supply voltage.
If there's nothing else on the opamp's voltage rails, maybe you can raise the supply voltage a bit by changing the voltage regulators. If there is sufficient voltage available at their inputs maybe you can swap them with 6 or 8V regs?

Another option is a parametric search on AD's website and look for opamps with similar spec's that are optimised for +/- 5V and have rail-to-rail outputs.

Regards,

Ray.
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Old 26th February 2006, 02:15 AM   #3
Stew is offline Stew  United States
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Ray - Thanks for the info! The original opamps were JRC 2068DD for I/V and JRC 5532D output buffers. Currently using AD826 for I/V and AD8620 for buffers. The AD8620's sound great but the bass is weak in my CDP (maybe due to +/- 5v). I originally tried AD826's for both I/V and buffers. That combination had great bass but the upper mids/highs were a little harsh. From what I've read, I'm hoping AD843 will be the best of both.

I will need to raise the Brown Dog Adapters above the capacitors next to the buffer opamps. I could stack sockets but I understand this is not the best approach. Any ideas on a Brown Dog Adapter with longer pins, etc?

Thanks again,
Stew
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Old 26th February 2006, 12:22 PM   #4
6h5c is offline 6h5c  Netherlands
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Hi Stew,

You're welcome!

I have the same problem with the adapters. I solved it by using SMD opamps. I put them on a SMD-to-DIL adapter and use a single-to-dual DIL adapter with two stacked sockets to find the right opamp combo. When I have a good set I solder them on a single-to-dual SMD adapter. It's a bit of a hassle, but it fits perfectly. My player uses one dual opamp per channel.

Regards,

Ray.
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Old 26th February 2006, 12:24 PM   #5
6h5c is offline 6h5c  Netherlands
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This is the single-to-dual SMD adapter.
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Old 26th February 2006, 02:39 PM   #6
Stew is offline Stew  United States
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Ray - Looks like a great idea! Unfortunately, AD843 doesn't come in SMD. I'll have to find a way to raise a single to dual DIP adapter for these.

Thanks again,
Stew
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