active v.s. passive phono

[mashaffer]

Passive RIAA phono preamps seem quite popular for DIY but would there be any advantages to going with active (feedback based) eq?

 

[Merlinb]

In a tube circuit? Not really. Tubes don't have enough open loop gain, meaning you have to fiddle with the poles to get an accurate RIAA response, and it is liable to drift with age.

 

[JonSnell Electronic]

Active has gain, passive only loss.

 

[dreamth]

There are lots of good designs on both sides, its just that their performance aren't obvious to the naked eye...just to the ears.You better try them both , but start with the good ones, don't build some shitty one and judge the whole bunch because of that! It took me literally a whole year to see all the designs available on the internet a few years ago and read thousands of opinions about most of them...It never ends...Just build something that's worth the money first! I started with making some of the most craziest designs, but in the end you better think about the money you spend in this sport!

 

[dreamth]

For some reason this schematic is sold by some, and for free you only find lower resolution pdf...Here's:

Luxman a-3040
It was for free once...If anybody has even a better copy...i'm waiting for years to find it!

 

[mashaffer]

I was thinking that a split active design might have advantages in distortion.and noise performance. Some variation on this Broskie idea.

 

[savu]

I would build a high gain differential cascode of 50dB or so, followed by a low impedance source or cathode follower, followed by a differential 600ohm LCR RIAA followed by a differential SRPP

 

[mashaffer]

For example I did a quick back of the CRT scaling up of Broskie's first stage for tubes I have on hand and get the following. The simulated distortion results are many times better than the best I have seen in anything I have gotten using passive methods.

 

[mashaffer]

And looking at the whole thing tweaked a bit for more gain and using standard values as much as possible it seems like this might be worth investigating further.

 

[rayma]

Active has gain, passive only loss.

I've heard people say this, but it isn't true. The passive circuit uses all
of the available gain (in the bass). It's the active circuit that throws away
(open loop) gain and doesn't use it for amplification, in the feedback margin.

 

[dreamth]

The simpler the better.Focus on cartridge compensation as it is way more important than the riaa network perfection.

 

[rayma]

For some reason this schematic is sold by some, and for free you only find lower resolution pdf...Here's: Luxman a-3040

Is this the same as yours"
LUXMAN A3040 PREAMPLIFIER SCH Service Manual download, schematics, eeprom, repair info for electronics experts

 

[dreamth]

Yes, it is , is just that i can't see the components clearly and their values.Is my PDF reader having a problem?

 

[mashaffer]

I am not as concerned with super precise curve as I am keeping noise and distortion that would color the overall sound under control.

 

[rayma]

Yes, it is , is just that i can't see the components clearly and their values.Is my PDF reader having a problem?

It's a jpeg, so it's not as good as it should be.

 

[cerrem]

I know that some builders swear by a mix of PASSIVE and ACTIVE... Basically with RIAA you have 2 POLES and 1 ZERO ... The ZERO being the TURN-OVER frequency @ 500 Hz... If you properly place your 2 POLES, then ZERO will fall in place by itself ..... Some builder will put the 1 POLE active and the other POLE passive... I think some prefer to put the low frequency POLE in the active Feed-Back Loop and then have the High Frequency POLE as passive....some claim it sounds more natural in the highs and more controlled in the lows..

 

[dreamth]

It's a jpeg, so it's not as good as it should be.

mine is a jpeg shot from the whole schematic, the relevant part for the phono schematic, but it's better than the pdf available on the internet for free.

 

[mashaffer]

I know that some builders swear by a mix of PASSIVE and ACTIVE... Basically with RIAA you have 2 POLES and 1 ZERO ... The ZERO being the TURN-OVER frequency @ 500 Hz... If you properly place your 2 POLES, then ZERO will fall in place by itself ..... Some builder will put the 1 POLE active and the other POLE passive... I think some prefer to put the low frequency POLE in the active Feed-Back Loop and then have the High Frequency POLE as passive....some claim it sounds more natural in the highs and more controlled in the lows..

Or one could even use passive filtering and linear feedback gain stages to drive them. I am not sure that there would be any advantage over the full active filter but it could be another option. One possible advantage is that distortion would not vary as much with frequency.

The Broskie circuit would be easy to modify for the mixed approach you mention. Might be very interesting. Will definitely investigate that.

 

[mashaffer]

Here is a stab at mixed.

 

[rayma]

Or one could even use passive filtering and linear feedback gain stages to drive them.

That was done in the HK Citation I in 1959. Tubes, of course.
http://www.mcshanedesign.net/CitIschm.jpg