solid state DC class-A RIAA schematic needed

[neazoi]

hello,
Is there any schematic out there for a direct coupled class-A RIAA preamplifier? Better to be a capacitor-less circuit...

I have seen this pre-pre preamplifier of the 80s but this is a pre-preamplifier for MC cartridges, to bring them in MM level, not a RIAA one...

 

[neazoi]

Here is the pre-pre

 

[AndrewT]

Hi,
the RIAA characteristic cannot be obtained without capacitors.

The RIAA also has two standards for Bass roll off. Both require a DC blocking cap in the signal route to achieve that.

A DC coupled capacitorless RIAA cannot comply with RIAA standard.

 

[neazoi]

Thank you Andrew!
I have also seen this design of hiraga. It uses 1-2 caps only, but unfortunately the article is in French so I cannot understand the details. It says something like this achiever the RIAA response using passive method...?

I have not seen another similar circuit thought...

 

[alayn91]

Hello,

Here are the details translated, at my best:

Direct coupled transistorized pre-amplifier as decribed in november 85 japonese "Stereo music" revue.
Input stages are symmetrical & differential cascodes and are followed by drivers stages and push-pull output with MOSFET.
Between the linear stages wich gains are respectively 33,6dB & 27,2dB,
the passive RIAA correction takes place with passive components LCR Tango EQ-600P.
Total gain is about 41dB, the average distorsion ratio is 0,002%, between 10Hz & more than 40kHz.
Global harmonic distorsion don't reach 0,002%.

Et voila.

Some infos I found about Tango EQ-600P:
http://digilander.libero.it/paeng/inductive_riaa.htm
And, others with Google !

Regards.
Alain, from France.

 

[knutn]

You may try my oldie: RIAA Amplifier

 

[DF96]

To do RIAA without capacitors means either using inductors (with perhaps greater problems) or some form of digital processing. You might also need perfect records played on a perfect turntable, as you would have no protection against warps and arm-cartridge resonance. You would need battery supplies, as you can't smooth the mains without capacitors.

Why?

 

[neazoi]

Alayn, so it uses an interstage transformer to do the equalization, I got this now, thanks a lot for the translation.

Knuth, It seems an interesting design, does it operate in class-A (I bet so)? Could it be used for high fidelity or is it just for old 60s phono heads? A listening impression would help.

 

[neazoi]

To do RIAA without capacitors means either using inductors (with perhaps greater problems) or some form of digital processing. You might also need perfect records played on a perfect turntable, as you would have no protection against warps and arm-cartridge resonance. You would need battery supplies, as you can't smooth the mains without capacitors.

Why?

Df, I mean no caps on the signal path. And yes my Le monstre amplifier operates on batteries only
I am trying to use high quality components and simple designs to achieve best transparency. And DC mostly offers the best transparency. In some cases DC cannot be done, that is why I have started this thread

 

[knutn]

Knutn, It seems an interesting design, does it operate in class-A (I bet so)? Could it be used for high fidelity or is it just for old 60s phono heads? A listening impression would help.

Yes it is operated in Class A; it was used with my high output MC (about 3.5 mV) for high fidelity listening. But it deserves a better power supply. And yes, it sounded good...

 

[AndrewT]

post4 shows discrete opamps.
They are not RIAA circuit, they are opamps.

 

[neazoi]

Yes indeed. This is probably doing the RIAA equalization

 

[AndrewT]

no.
They are opamps.
If designed properly they will have a wide flat passband.

It's the filter that must be added to the circuit that gives the RIAA filter characteristic.