Phono Pre-amp: What are we testing for?

[watchnerd]

Add rumble filter performance.

at what hz?

 

[tomelex]

Here are some 1983 specs for a Hafler pre-amp phon0 section with test source references

 

[Wombat]

at what hz?

The 1976 IEC RIAA recommended curve added a pole at 7590 uS to reduce the affect of sub-audible frequencies on loudspeakers. This low rate roll-off filter, centered @ around 20Hz, was not universally accepted as adequate or disparaged as affecting the sound, though many were happy to have the protection it offered and mfrs obliged.

A much sharper cut-off is more effective as a means of protection and it can have an in-or-out option.

http://sound.whsites.net/project99.htm

 

[amirm]

Found this nice link on measurements HiFi World performs for phono stages: http://www.hi-fiworld.co.uk/index.php/vinyl-lp/70-tests/106-phono-stage-tests.html

 

[RayDunzl]

Here's a Yamaha P300 with a Grado cartridge, powered, and platter turning, with the stylus in the air, feeding a Behringer Microphono PP400 feeding a Behringer UMC202HD with 24/192 USB capture in Audacity.

Spikes are power and power harmonics, similar to what is seen when any other cable I've used is plugged into the analog input of the UMC 202 HD.

65kHz spike area is from the Plasma TV.

Record level is around -3 to -6dBfs when an album was playing (excluding ticks and pops).

Looks reasonable to me.

 

[Sal1950]

LP is obsolete. I wouldn't waste limited time, funds and effort on it. I know it has a certain status among audiophiles. Are we going to test cassette tape, 8-track,RTR, 78s, Rdat, HiFi VHS sound tracks, and wire recordings?

+1 So much gear, so little time.

 

[Fred Thal]

Are we going to test cassette tape, 8-track, RTR . . .?

I say YES! to that last one.

Why? Remember that we have half a century's worth of legacy recording natively recorded onto analog tape. More transfers still need to be done (or re-done).

Also, over in the high-end world, there's been this burgeoning little niche market called tape.

The hot fad there is to hack into the repro head wiring of even very serious pro machine (like, say, a Studer A820 or A80) and then connect up somebody’s boutique "tape stage" some of which carry very big price tags.

But too many people are blindly doing this without ever making any measurements. Baseline or comparative. I've been shocked at what I have found. It's astonishing or depressing, depending on your point of view.

http://www.whatsbestforum.com/showt...equency-response-of-tape-playback-electronics

 

[amirm]

Hi Fred. Great to have you posting here. Would love to perform such tests. Alas, I have not been able to acquire the equipment to test (my one source backed out). My Otari has stock amplifier and such. While I will measure that, it won't answer the question of the outboard tape amps.

In that thread, you talk about a tape with more tones than usual. Is that tape available for purchase? I hunted around MRL site but could not find anything.

 

[Fred Thal]

Hi Amir,

Yes, see page 4 of the MRL publication "Choosing and Using" for the order numbers.

http://mrltapes.com/choo&u.pdf

Fred

 

[amirm]

Thanks Fred. I had seen that paper before but try as I might, I can't find a sweep with 1/12th octave resolution. Do you mind cutting and pasting the text for the one you are referring?

 

[Fred Thal]

Hi Amir,

If you navigate to MRL's Choosing and Using from your browser, you should see hyperlinks to the relevant MRL papers describing the cal tape options. (Let me warn you. There are many.)

For fast sweeps you'll want MRL publication 313, for slow sweeps, publication 402, for the Sound Technology 1500 Test System tapes, it's publication 211, for the Audio Precision System One, you'll want MRL publication 423.

All of these are mentioned (with their relevant hyperlinks) in the current edition of Choosing and Using (on the MRL website) on page four.

Fred

 

[amirm]

Thanks Fred. The extra information in the other pubs were helpful.

 

[Dimitri]

Here are some 1983 specs for a Hafler pre-amp phon0 section with test source references

Hi everyone!
If nothing else it will be intersting to see how far phone stages have improved since then ( and in some cases ...not )

 

[Soniclife]

From another thread...

We rarely measure phase difference between channels, a very important parameter for some sources. It explains much of the perceived difference in phono preamps, but no one mentions it; just amplitude.

I'm dubious about the difference between channels, but I am interested in phase in phono stages.

 

[amirm]

When I get to them , I will test for it.

 

[restorer-john]

• RIAA curve deviation out to 100KHz, not the usual 20KHz. (comments on bottom end FR)
  
• Overload characteristics for both MC and MM
• Sensitivity for both MC and MM
• Input impedances for MC and MM and their correlation to specs.
• Residual noise (unweighted/A weighted)
  
• S/N for both MC and MM
  
• Maximum output
• Output impedance
• Gain as compared to spec (MM/MC)
• Subsonic/infrasonic slope (dB/Oct and corner freq)- comments on usefulness
• channel balance

That's a good start...

 

[restorer-john]

With the AP you can generate an inverse RIAA curve for sweep purposes? I need to create an outboard passive inverse RIAA network to produce a meaningful deviation result on my old gear and it will top out at 30KHz.

Here's an example of quite comprehensive specs for one of my preamps (circa 1983):

Phono stages peaked around the time of CD's introduction and then gradually disappeared or got cheapened. Today's phono stages are pretty average IMO.

 

[svart-hvitt]

With the AP you can generate an inverse RIAA curve for sweep purposes? I need to create an outboard passive inverse RIAA network to produce a meaningful deviation result on my old gear and it will top out at 30KHz.

Here's an example of quite comprehensive specs for one of my preamps (circa 1983):

View attachment 11219

Phono stages peaked around the time of CD's introduction and then gradually disappeared or got cheapened. Today's phono stages are pretty average IMO.

Do you have examples of commercially available phono preamps of technically outstanding quality?

 

[Sal1950]

Do you have examples of commercially available phono preamps of technically outstanding quality?

I just had a thought, since the Pro-Ject S2 DAC that Amir measured came thru with flying colors, I'm wondering if something from them might also be well designed? The Phono Box S2 (sister design to the S2 DAC?) for under $200 looks like it might be just the ticket though it seems to be a bit hard to find in the US right now.
http://www.project-audio.com/main.php?tech=phonobox&cat=default&lang=en
As I've mentioned before, a phono-pre is a very simple amp/eq box that shouldn't cost very much to get excellent performance once you subtract any audiophool magic dust claims, religious surcharges, etc.

 

[Dimitri]

As I've mentioned before, a phono-pre is a very simple amp/eq box that shouldn't cost very much to get excellent performance once you subtract any audiophool magic dust claims, religious surcharges, etc

It's very funny, I've been having the exact same thoughts about DACs and headphone amps.