Recommendations for a killer phono preamp?

I'm looking to build a preamp for transfer/restoration work from vinyl to DAW--from a Stanton 681EEEmk3 to balanced +4dBu. I would like something different from the run of the mill phono amp. One feature I need is the ability to switch the RIAA EQ on and off. I've found click/pop removal is easier sometimes if the noise signal isn't distorted by the EQ--I add the RIAA curve after the fact with a parametric plugin. Sonically I'm looking for something really clean and musical--what a really good pre does for a mic.

My thought is to adapt a mic pre design, modifying the input to properly match a moving-iron cartridge. Then add a bypassable RIAA EQ and a balanced output section.

Does this sound like a worthwhile endeavor? Which of the regularly DIY-ed pres might be a good starting point? (The Stanton 681EEEmk3 already has a warm character in and of itself, BTW.) Any idea how to match an input to the cartridge instead of a mic? Any EQ and balancing recommendations? (On the latter, I stumbled upon a sleeve of Burr-Brown DRV-134A--any good?)

I've finished the physical studio DIY--the siren call of the soldering iron beckons now! :grin: Happy 05 and thanks in advance for any input. :sam: :sam:

--Bob

This one sounds good:

http://stiftsbogtrykkeriet.dk/~mcs/Phono/index.html

- it hasn't killed anyone yet though... :wink:

Best regards,

Mikkel C. Simonsen

Another tube option is this RCA circuit, which seems to have a pretty good reputation. I've been planning to build a pair myself, for transferring my old LPs to CD. Note that the output impedance is high, and you should add a cathode follower output stage if you intend to drive anything of lower impedance than the grid of another tube! If a "consumer-level" (-8dBU nominal), unbalanced output is acceptable, you could use a single 12AU7 or 12AV7, one half as a cathode follower for each channel. Since the plates are at AC ground, there should be little or no added crosstalk between channels.

Schematic
Description

Making the RIAA network bypassable is simply a matter of switching it out and switching in a voltage divider of the appropriate attenuation. If you must have a +4dBU balanced output, you will need additional amplification. You could use two 12AU7s or 12AV7s, one per channel, configured as a common-cathode stage coupled to a cathode follower, driving an output transformer (wired so that it reverses signal polarity, so the output will be in-phase).

You didn't mention whether your cartridge is moving-magnet or moving-coil. You say "moving iron", which I guess could mean moving-magnet, in which case the RCA preamp and MCS's preamp will both do. Moving-coil cartridges are much more akin to ribbon mics, i.e., the output level and source impedance are low. "Typical" moving-mags like to work into about 47K and several tens of pF.

You might be interested to know that broadcast practice in Ye Olden Days was to use special pickups designed for a 600-ohm source impedance, feeding standard mic preamps, followed by passive R-L-C bridged-T, 600-ohm RIAA networks, then another mic preamp if needed to overcome the loss of the EQ networks.

Dave:

I've built this particular circuit as is. It's on page 594 of my trusty RCA Receiving Tube Manual, RC-23.

It's my main record listening preamp and it's a good, very usable build.

Bob;
There is only one answer!
The K&K audio Phono Kit

This kit is a simplified version of the Famous
Vinyl Reference Phono Pre
If you are near CES show in Las Vegas
stop by the Art Audio booth and ask for Kevin C.

This Pre will meet your requirments.
It is the most musical RIAA pre I have ever heard.
OK Pro guys start turning you nose up on the audiophiles here.
But before you do ask MARIK here does this Phono preamp make a good
mic pre? Go ahead and ask him, do not take my word for it, I dare you!

Bob what ever you do not use any of that op-amp crap you will hate your sonic results!

adrianh

[quote author="buttachunk"]check this out;
http://cache.national.com/ds/LM/LM833.pdf[/quote]
I have actually just made a phono pre based on the LM833 app. note - not the datasheet. The app. note circuit uses two op.amps. per channel instead of one.

Here's the (still untested) result:



What op. amps. would be good for this sort of circuit? It looks like the LM833 isn't bad at all, but how about something like the OP275?

Best regards,

Mikkel C. Simonsen

[quote author="mcs"] What op. amps. would be good for this sort of circuit? It looks like the LM833 isn't bad at all, but how about something like the OP275? [/quote]

Actually, I think that the LM833 is a very, very underrated opamp. Maybe because of it's low price, people think that it can't be that good..?

To my ears, it competes sonically with the NTP M100 discrete opamp (though with much lower output driving capability)

Try the '833 first. I'm pretty sure you won't be disappointed..

Jakob E.

Here's some sites with lots of options....

http://members.aol.com/sbench101/

http://www.bonavolta.ch/hobby/en/audio/audioel.htm

Gerry

[quote author="mcs"]What op. amps. would be good for this sort of circuit? [/quote]If you are going the silicon route, then I?d suggest using a real audio op amp. :wink:

Take a look are page 4 of the pdf. Pretty simple to build, but you?ll need a good PSU.

http://www.johnhardyco.com/pdf/990.pdf

I've always been a fan of a preamp I first ran into in the '70's.

It uses three opamps, one for moderate gain in the first stage, into a 75uS
passive roll-off, into another gain stage, 10dB or so, into the, what is it 3180?
rolloff, with a pole for the flat spot, then into a third amp that made up the last of the gain.

The split passive networks made it real easy to screw with, like NAB for tape playback...

And yet another solid-state option to consider:

There's a Hafler preamp out there that is reputed to have a superb-sounding phono stage. I don't recall the model name or number, but perhaps someone here will oblige with more info or even a schematic.

Thanks for the pointers! :thumb:

My current preamp is one I built into the turntable itself, with so-so opamps (one of the TL0x series--I'd have to crack it open to recall exactly which one), relay-driven RIAA switching and Burr-Brown DRV134 balanced output drivers terminated in a pair of XLR's on the back. Although it's pretty clean (at least now that I've cured it from picking up radio stations,) I'm not really enthused about its overall tonal quality.

I was initially considering trying different op-amps and/or a passive EQ approach instead of the inverse-RIAA feedback loop. The passive idea got me to thinking about whether other types of "pro-class" amps--discrete, solid-state, Class-A (think Neve) might be applicable and give better results.

Now that some of you have mentioned tubes, it's taken me down a simultaneously attractive and frightening path. I'm drawn particularly to this one that was mentioned: http://stiftsbogtrykkeriet.dk/~mcs/Phono/index.html. A couple questions though. There's a conflict in tube numbers between the text and the schemo in this and the original source article: Are they 6's or 12's? The other question is in regards to the bypassability of the RIAA curve--C3/R4/R5 and C4/R9/R10 are the obvious targets of opportunity, but what to replace them with to maintain gain and maintain a more-or-less-flat frequency response? I know there's impedance, Miller capacitance and whatnot that factors into all this. :? It's just been way too many years since I did tube design! I guess opamps are just too easy!

In refreshing my brain about tube theory, I came upon tubecad.com. Any comments on the phono amp articles on the homepage there; particularly part two which addresses non-feedback passive designs? I can't quite discern if there's a really working design plan there, much less know how to reliably disable the EQ.

Also my need for balanced outputs is rather compelling. In a tube type preamp of the likes of above, is it just a matter of adding the iron (what and where?) or should I look at something like a phase splitter/cathode follower? (this preamp idea is turning into a pretty nice space heater too :wink Are there any failure-mode or other protection considerations when interfacing high-voltage tube gear to solid state recording gear?

Thanks

--Bob

[quote author="stickjam"]Now that some of you have mentioned tubes, it's taken me down a simultaneously attractive and frightening path. I'm drawn particularly to this one that was mentioned: http://stiftsbogtrykkeriet.dk/~mcs/Phono/index.html. A couple questions though. There's a conflict in tube numbers between the text and the schemo in this and the original source article: Are they 6's or 12's?[/quote]
The ones you have. The only difference is the heater voltage (6 vs. 12V) and price. The 12V types are often cheaper. I use 12SL7 and 6SN7 myself, as they were the tubes I had when I built it.

The other question is in regards to the bypassability of the RIAA curve--C3/R4/R5 and C4/R9/R10 are the obvious targets of opportunity, but what to replace them with to maintain gain and maintain a more-or-less-flat frequency response?

Click to expand...

I think just disconnecting C3 and R10 should do it.

Best regards,

Mikkel C. Simonsen

I just found this one: balanced in and outs. hmmmm...

http://www.tubecad.com/july99/page10.html

-Bob

Thanks Mikkel!

I hadn't seen that LM833 App Note PDF- I thought I knew all the Nat Sem app notes!

...there's a trnasformerless dual LM394 mic amp in the back there too.

I'm still wondering what phono pre to build myself- sand or hollow state??

choices!

:grin:

Mark

I would go for the hollow state option, if you have the space and money...

Here's the schematic of my LM833 phono pre. I chose the values to get E12 cap values and E24 resistor values.

http://stiftsbogtrykkeriet.dk/~mcs/Phono1_sch.gif

Best regards,

Mikkel C. Simonsen

Thanks Mikkel,

Yes, that was my feeling too- all the tube phono pre's I've heard have felt cleaner/more dynamic (especially in the top end- cleaner sounding??) Some op-amp phono pre's I've made/heard sound a bit pushed!

I was going to copy the phono stages of some of the tube hi-fi pre's I've heard, but that RCA looks interesting! And some of the Elektor books I've got have some good ideas too...

Mark

I like this one, the El Cheapo:

http://www.fortunecity.com/rivendell/xentar/1179/projects/aaphono/aaphono.html
http://www.users.nac.net/markowitzgd/phonopre.html

Not that Cheapo cos of 637 but sounds very good to me.

:guinness:
Fabio

[quote author="Bauman"]I like this one, the El Cheapo:
http://www.fortunecity.com/rivendell/xentar/1179/projects/aaphono/aaphono.html
[/quote]
Why nearly all the noise curves at the audio looks like the frequency
axe have reversed 0 and infinity.
Every joung child knows some about surface phenomenon and 1/f noise.
And then in good audio circuit best noise performance is not at 100 Hz,
but at 10 kHz.

And peoples still do simulations and prints that unrealistic results.
That results looks like Alice in wonderland for me. It may be nice
on the paper, but reality is different.

Stop these fairy- tales for ever.

xvlk

[quote author="stickjam"]I'm looking to build a preamp for transfer/restoration work from vinyl to DAW--from a Stanton 681EEEmk3 to balanced +4dBu. I would like something different from the run of the mill phono amp. One feature I need is the ability to switch the RIAA EQ on and off. [/quote]

Hagerman Bugle. Do not be fooled by the low price tag. This is possibly as good as it gets for clean and transparent without spending a fortune.

http://www.hagtech.com/bugle.html

The eq is passive, and could be switched out and replaced with a pad of correct level and impedence.