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
:bawling:

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








;) ;) ;) :)

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....

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

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.

Peranders,

What do you think about AD6810 and AD797?

Greetz,

Adam

AD8610 looks quite impressive, the price? Notice that this chip is SMD only.

AD797 is a typical opamp for phono/mic stage

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

If you don't plan to connect MC pickups AD8610 is quite sufficient, if we talk noise.

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

Here is an image of the PCB:

G