First impression: Herron VTPH-2A phono preamp

Keith just emailed me, here’s what he said.

"Hi George,

Thanks for the note. The output capacitors of the VTPH-2 and VTPH-2A are approximately 7 uF (polypropylene) and the low frequency response is RIAA flat down to 10 Hz (within 0.1dB) into a 10k Ohm output load."

As you can see no problems with bass rolloff as the cap is 7uf and he’s done the measurements flat to 10hz, into the same load as a 10kohm passive represents!
My calculations with 7uf into 10kohm load are -3db at 2hz, perfect!

All looks fine to me for it to be used with a passive preamp, as the gain is very high for this phono stage, so you may as well utilise it all, instead of knocking it back because of the gain in an active preamp, this way you’ll get a definite lower background noise level.

Also Keith said the Distortion: Less than 0.03% at 2.45 volts RMS output at 1kHz at 20k Ohm, this also "to me" bodes well for passive preamp use. If you’ve got’em smoke em! to see how it sounds. We’ll see after this weekend what rob67 thinks of it with the Lightspeed as it mimics a 10kohm passive volume control.

I’ve got other customers of mine with tube phono’s that aren’t spec’d as good as this for passive use, they say it’s the best they’ve heard their vinyl sound, once they got rid of the active preamp.


Cheers George

Wow! So bass rolloff would not be an issue that would result from driving low impedances such as 10K, with Keith’s design. But I would still take to heart his comments recommending against anything less than 20K. And his suggestions that for other reasons 40K or more is preferable with the 64 db configuration (400 ohms nominal output impedance), and 50K or more is preferable with the 69 db configuration (500 ohms nominal output impedance).

Regarding the 2.45 volt figure, while he has conservatively chosen that number for use in specifying distortion, keep in mind that a gain of 64 db will raise the output of a cartridge rated at 0.5 mv under the standard test conditions (that being the rating of the AT-ART9 which I and the OP and some others here use in conjunction with what I presume in all or nearly all cases is the 64 db version of the VTPH2 or 2A) to only 0.792 volts under the standard test conditions. Not nearly enough to drive many power amps to full power, even with the volume control of a passive preamp at max. Although very high volume transients on some recordings can exceed the standard test conditions severalfold, as I understand it.

In any event, thanks for obtaining the good info about the cap.

Best regards,
-- Al

You’ve got the option of 69db of gain Al also have a look at the on line manual/specs.
Also with average gain of amps at around 27db and speakers that are average around 88db you certainly will have enough volume range

Maybe not with low gain amps as the NP Aleph’s and such, and low efficiency speakers such around 82db.

As for the 2.5v output figure into 20kohm at 0.03% distortion this is far less than what a cartridge has as a distortion, they are closer to 1% so to me that doesn’t mean much.

Well see what rob67 has to report re gain, as his Gryphon Antillion amp is around average at 1v sens and his Wilson Sasha speakers are around average at 90db

As I said I have customers with tube phono stages that have lower gain around 48db and 1kohm output impedance they don’t have any issue with not enough volume. I make it a point of asking where the volume control is for normal/loud listening, and they say around 2pm which gives them plenty of range up or down.
Many of my vinyl junkie customers are here on these forums, hopefully they will respond as I can’t remember who has what, as there are over 900 out there.


Cheers George

As for the 2.5v output figure into 20kohm at 0.03% distortion this is far less than what a cartridge has as a distortion, they are closer to 1% so to me that doesn’t mean much.

Hi George,

To be sure it’s clear, the point I was making had absolutely nothing to do with the distortion percentage. I was making the point that the 2.45 volt figure has no relation to how much voltage the phono stage puts out in normal use. It just relates to how much voltage it is **capable** of putting out, without exceeding the distortion spec.

And the 64 db version of the phono stage, which is what most people choose and which is what Keith recommends as being the best version to use with LOMC cartridges that do not have unusually low outputs, will produce an output far less than 2.45 volts under most circumstances. In fact well under 1 volt under most circumstances. Which in turn will be too little to drive many and probably most power amps to full power, even with the volume control at max, unless the preamp provides additional gain.

As I said I have customers with tube phono stages that have lower gain around 48db and 1kohm output impedance they don’t have any issue with not enough volume. I make it a point of asking where the volume control is for normal/loud listening, and they say around 2pm which gives them plenty of range up or down.

Surely that is with moving magnet or other high output cartridges, not with LOMCs!

Speaking more generally, given the credibility Keith has earned over the years as a result of his universally praised design work and sincere dedication to customer support, if he says that 20K is a bare minimum and 40K or more is preferable, that’s good enough for me.

Best regards,
-- Al

if he says that 20K is a bare minimum

He’s quoting, like me saying 47k and 100k is even better is the figure for the Lightspeed to see, when in fact 25kohm is the min correct figure as measured and listened too by our 50 strong audio group, as that gives a 1:10 ratio as the max output impedance of a 10k volume control is 2.5k, were just taking in any unforeseen circumstances like weird cables etc.

We’ll see when Rob67 reports on what he heard, as for now as I said before lesser phono stages are sounding great into this kind of load.

Al do your ears a favour, ditch the dinosaur if you have the gain, and "not" listen to the noise floor of your preamps output gain stage, you’ll be amazed just how black the background of vinyl can sound if you utilise all the phono stage’s gain instead.
He’s given you massive 64db or 69db of gain, use it, some poor saps only get 35db of gain with their phono stages and they have to listen to the preamps output gain stage’s noise.

Cheers George