the dual phono preamp experiment

There was a thread recently where I had mentioned the notion of a dual phono preamp for dj use - connecting each of 2 turntables to external phono stage, then running those to a line input on the dj mixer. The thought was that doing so would yield better sound quality - reduced noise floor, better extension on top and bottom, better detail retrieval from music.

I went ahead and built such a thing. See here for photo of internals - https://imgur.com/a/RiZVDD1

I'll mention a bit about my system to give some background. Speakers I tested with are a pair of Dahlquist DQM9C, amp is a F6 diy clone, preamp is a diy Zen Mod Ire Pre (single ended), Allen and Heath Xone:32 DJ mixer, technics 1200mk2 with Shure M44G carts and Nagaoka styli. I also have the Shure Whitelabels, but prefer the drier sound of the M44's.

The dual phone preamp build consisted of a dedicated transformer and linear power supplies for each turntables. Each of these powers one ESP P06 phono stage, followed by a ESP P99 subsonic filter. The preamp and filter were bare PCB's sent from Australia. I got those and populated them, mostly following the BOM's for each. Power supplies were "off the shelf" from Ali Express, transformers from Antek. P06 and P99 details can be found here - https://sound-au.com/p-list.htm

The difference in sound was subtle. Less congested, fuller on the bottom. Detail level about the same as the mixer. My mixer seems to give a slight bump to the bass giving it a "drive" effect. The external stages are absent of that coloration. Though the build I went with was meant to have a 1db bump around 50hz, with option to forego it (which I did). I am currently playing with setting the proper gain. DJ carts have higher output than your standard hifi cart, the 40db gain is too much. I went back and socketed the gain resistors for one of the two stages to see what might be optimal.

The build came to be around $250 for everything, and I did save some money by using a beat-up chassis I had around. Was it worth it? Hard to say. You will get more of a difference by upgrading your cartridge. Though doing so might actually make something like this more worthwhile - this would make your hypothetical high end dj cart sound better still. I've done some recordings of both with phono stage and without, and it's hard to tell which is which when listening to these. Less so when listening. I don't know if this is due to the analog to digital conversion when recording, or just that again the difference is not all that much.

Anyway, thought to share this here. It was fun putting it together, not something you see everyday, not available in the consumer market - unless you buy two separate phono stages. I'm going to play with it a bit and see how I like it, they might end up being split up and sold as two standard phono stages. If any interest I can report back when I dial in the gain, want to more less get it to match what the DJ mixers phono stage is set to. Can also post recordings if there is interest.

That's interesting ! I'd like to see the whole set-up.
You might be able to help me. I have just got a tube amp, this one;
https://www.ebay.co.uk/itm/196979859825
..so I bought some speakers that are more sensitive to go with it, these;
https://www.ebay.co.uk/itm/256709396708
...then I realised that those speakers are part of a system that includes a subwoofer. So I got this;
https://www.ebay.co.uk/itm/156639526700
...now I am worried that because the sub has it's own amp I will be rendering the tube amp pointless by running the left and right speakers out of it. Do I need to be worried ?

arteom
The difference in sound was subtle.

Subtle enough to for listener bias due to the money which was spent?

Just asking 'cos I've seen many fall down that "Hi Fi" rabbit hole and never be able to climb back out...

Interesting project.
Lehmann made a dual version of their Black Cube phono preamp but they discontinued it years ago.

https://www.tnt-audio.com/ampli/bctwin_e.html

jondavey
That's interesting ! I'd like to see the whole set-up.
You might be able to help me. I have just got a tube amp, this one;
https://www.ebay.co.uk/itm/196979859825
..so I bought some speakers that are more sensitive to go with it, these;
https://www.ebay.co.uk/itm/256709396708
...then I realised that those speakers are part of a system that includes a subwoofer. So I got this;
https://www.ebay.co.uk/itm/156639526700
...now I am worried that because the sub has it's own amp I will be rendering the tube amp pointless by running the left and right speakers out of it. Do I need to be worried ?

Looks like a nice amp! I think you should be alright running the amp through the sub, then sub to your main speakers. There might be a bit of a loss in quality, but I'd bet you couldn't pick it out. You might be able to test it, so run it through the sub, but turn the sub volume down all the way. See how the speakers sound. Then skip the sub, wire directly to amp, see how the speakers sound. That all based on assumption that volume on sub being down completely means it's silent.

Are you still using the Omnitronic mixer? That looks like it has two outputs for main - one XLR and the other RCA. Run the RCA to your tube amp, the XLR get XLR to RCA cables (or adapters) and run that to the sub's RCA input.

devin306
arteomThe difference in sound was subtle.

Subtle enough to for listener bias due to the money which was spent?

Just asking 'cos I've seen many fall down that "Hi Fi" rabbit hole and never be able to climb back out...

Yeah I get that and had it in mind as I was making this thing. The only thing I can offer is data from frequency plot spectrum from recordings. Here what I did was match gain of recording to within 0.05db. The way I verified this was by doing "contrast" in Audacity of the same section of recording from both dj mixer and phono preamp through dj mixer. After that I a spectrum analysis of a 10 second section of a recording using both. Here are the results, definitely more open on the top end - https://docs.google.com/spreadsheets/d/1XXE-Fck47UZrzVVN_GM6JJIO0KmPZLgxPhnKnbksnUY/edit?usp=sharing

More of these tests wouldn't hurt to get better sample size. Though how this particular might be interpreted is debatable. More db doesn't mean better sound quality. Honestly I'm not well versed in testing and measuring. It being a phono stage complicates it, as the test material has to come from a record.

I did also ask of what value this all is because in the end it still goes through the dj mixer. The dj mixer will still impart its sound to what you hear. You could have better sound going from the phono stage, but by the time it comes out from the mixer's output it's degraded. I did test for this, recording from phono stage directly and comparing to phono stage to mixer, very little (if any) difference.

chiz
Interesting project.
Lehmann made a dual version of their Black Cube phono preamp but they discontinued it years ago.

https://www.tnt-audio.com/ampli/bctwin_e.html

Nice! They make good stuff. I'd say pricey, but considering this cost about 1/3 of that, it makes sense. What I might pursue with this build is another set of opamps, those are likely to result in most drastic change to the sound. The set I have in now are supposed to be very neutral, which sounds good on paper but can be a bit lifeless in practice.

arteom
Are you still using the Omnitronic mixer? That looks like it has two outputs for main - one XLR and the other RCA. Run the RCA to your tube amp, the XLR get XLR to RCA cables (or adapters) and run that to the sub's RCA input.

I am yes. I like that idea, thanks !...so the signal will emit from the XLR outs at the same time as the phone RCAs ?.....enabling me to run the sub directly from the mixer and the speakers from the tube amp ? Sorry I know that's exactly what you just said, I was just conferming because it seems like too neat a solution. Surely it's not that simple ?....

jondavey
so the signal will emit from the XLR outs at the same time as the phone RCAs ?

I would think so, you might reach out to Omnitronik to confirm. Before you spend the money on cables.

Yes that does work ! There are also another set of DIN out's, so I might be able to record aswell !

jondavey
so I might be able to record aswell !

I'm expecting some new mixes very soon! :)

jondavey
Yes that does work

Nice, how's the tube amp sound?

Zubeldia
I'm expecting some new mixes very soon! :)

I've bought so many new records that I have to go down through three pages before I reach the one's that I actually have to hand, all the others are on the way. I have really luched out on vinyl recently ! Yerah, I need to get a mix done !

arteom
Nice, how's the tube amp sound?

It's lovely ! The 'Monitor audio' speakers really bring it alive ! The subwoofer is too much ! I have to turn it right down to avoide neighbourly complaints !