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Old 18th November 2002, 08:48 AM   #1
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Default op-amp based preamp advice needed

Hello everybody!
I need a good preamp, line and RIAA stage.
As for the line stage, I need approximetely 6 dB of amplification.

I just browsed the solid state forum looking for a simple answer
but, unfortunately I got more and more perplexed


So there are few questions:
- what op-amp for RIAA stage (I thought about AD 797, would
this one be a good idea?), anyone got good shematics for this?

- what op-amp for line level, after reading, reading and reading
the forum I have three favourites: OPA627, AD825 and AD6810.
Simple question, considering the ideal aplication for each three,
which one would be the 'ultimate'???

- I guess I need buffer. BUF634 or antyhing else? Or maybe a discrete buffer? Any schematics welcome.

- Power supply. I guess it's very important. Would battery PS
be a good idea? Where can I get schem. for circuit that would
load batteries when empty?

- Volume control. Actually I want it to be IC-based, but how
about the sund of such ic-based volume regulators?

Sorry for such a lame questions, but finally I have some time
and just want start some soldering

Thanks,

Adam








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Old 18th November 2002, 08:57 AM   #2
Electrons are yellow and more is better!
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If you are looking for a work horse, check out OPA134/2134/4134 from Texas. This opamp can deliver rather much current also. The noise level is sufficient for MM RIAA amps but for a little bit lower noise, check for a opamps with 2-6 nV/SRQHz. Less than 1 nV is needed only for MC pickups.

OP37
LT1028
LT1128
LT1115
AD797
NE5534 (not so bad!)

plus many more....
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Old 18th November 2002, 09:20 AM   #3
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Thanks Peranders,
but I am looking more for a specialized audio op-amps,
dfferent for RIAA and different fo Line levels. I assume that
because the difference in signal level between phono and
line I will need different op-amps to meke the most of the signal
am I right (I mean that the different op-amp will sound the best
in RIAA and different in 'live-level' application)?


Adam
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Old 18th November 2002, 09:32 AM   #4
Electrons are yellow and more is better!
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OPA134 and others are very suitable for audio, read the datasheets to be convinced. Almost any opamp with slew rate >5v/µs will work but some works better. Some opamps are more suitable for "gain" than others. These are often not stable at gain lower than 3-10. Check for instance LT1028.

OPA134 will work for everything except for extremely low noise applications. I have put in OPA134 in my headphone amp (QRV-02) and I am impressed by it's technical clean performace. The step response is perfect down to gains at 1.
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Old 18th November 2002, 10:31 AM   #5
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Peranders,

What do you think about AD6810 and AD797?

Greetz,

Adam
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Old 18th November 2002, 12:43 PM   #6
Electrons are yellow and more is better!
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Quote:
Originally posted by Adam
What do you think about AD6810 and AD797?
AD8610 looks quite impressive, the price? Notice that this chip is SMD only.

AD797 is a typical opamp for phono/mic stage
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Old 18th November 2002, 01:05 PM   #7
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Peranders,
I would have to pay about 8 $ for AD8610. I think
I'll go for this one certain op-amp

As for AD797 - i though about using it in an RIAA
circuit, would this be a good bet?

Greetz,

Adam
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Old 18th November 2002, 01:29 PM   #8
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If you don't plan to connect MC pickups AD8610 is quite sufficient, if we talk noise.
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Old 18th November 2002, 01:38 PM   #9
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Hi Adam,

I have a PCB layout that would let you use either an OPA627 or AD825 with a BUF634(TO 220 package) on the output. Below is the schematic:

G
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Old 18th November 2002, 01:47 PM   #10
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Here is an image of the PCB:

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