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Luxman LXV-OT10 Phono Equalizer Amplifier Review and Measurements

SIY

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The only other Luxman product measured here actually did poorly.


In my mind, this has low noise, sky high distortion. Build quality is exceptional for a kit. Documentation is nice. Input overload is poor.

Just as Marantz measures way worse than Denon, it’s certainly possible that Luxman caters to the those who prefer distortion and Accuphase caters to those who prefer the most transparency.

What is interesting is this:


1) It has very similar gain to the LXV-OT10 for the rec out.
2) MM overload was 25 dB (89 mV by my math)
3) MC overload was 30 dB (16 mV by my math)
4) RIAA seems *better* on the LXV-OT10 phono than the pricey L-509X!

If there wasn’t a tube in the stage, I wonder what the overload actually would be for the LXV-OT10.

@SIY, how exactly would I jumper the pins on the 12au7 socket to bypass it?
phono mod.png


Cut where the red Xs are, add wire where the blue trace is indicated.
 
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GXAlan

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Cut where the red Xs are, add wire where the blue trace is indicated.
Looking at your diagram, can I just jumper the grid and anode/plate pins to non destructively test it?

1696302658673.jpeg
 

TonyJZX

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looks like some of their stuff is still available

 

anmpr1

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Why don't we have something like this in the US? Can you imagine a Stereophile x McIntosh hobbyist line of kit products?

For a brief time McIntosh offered their MacKit amplifier (see link below). But that was during an era when everyone and their brother made and sold them. McIntosh was always a more expensive proposition than the usual thing, and I doubt they were really set up to support kit building. I don't have price sheets, but I'm guessing a MacKit was no where near as inexpensive as Dyna, Scott, HK, Eico and the rest. Plus, Mac customers didn't seem to me like the typical DIY types; the company's big competitor was whatever Saul Marantz was selling, and Saul wasn't selling any kits (that I remember).

Stereophile is of course advertising based, and the few remaining kit operations seem to be mostly hobbyist oriented, not mainstream..., thus they don't have the kind of budget for magazine ads. I think Stereophile reviewed a Japanese Elekit once.

Audio pretty routinely ran kit articles for all kinds of DIY components, not just amplifiers (which were more common as kits). The MC (and amplifier) designs of Marshall Leach come to mind, but there were others. Stereo Review reviewed kits, and always offered a blurb about how the thing went together. Sometimes they'd have a reviewer's family member build it, to give the reader an idea how difficult the kit might be for a non-technical person.

Thanks for your review, BTW.

https://skyfiaudio.com/products/mcintosh-mac-kit-30-monoblock-rare-one-year-only-production
 
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GXAlan

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Stereophile is of course advertising based, and the few remaining kit operations seem to be mostly hobbyist oriented, not mainstream..., thus they don't have the kind of budget for magazine ads. I think Stereophile reviewed a Japanese Elekit once.
They did review an Elekit that was built. But those are “real kits” involving soldering and truly building stuff.

The Luxman marketing project is more about assembling stuff…. Looking at the Weiss DAC review, the high levels of distortion may be part of the appeal of a different sound. Once you add the noise and distortion of the cartridge to this phono amp, I bet it would look similar!

It’s sort of like people assembling keyboards by picking out the caps and mechanism.
 

AnalogSteph

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Looking at your diagram, can I just jumper the grid and anode/plate pins to non destructively test it?
Defo not. Grid to cathode, perhaps. Better lift a leg on the 3k9 and 1Meg and 2µ2.

BTW, the blue line should ideally include a series resistor of 220 ohms or so, a 4558 is not a capacitive loading champ.

With this circuit I would explicitly condone opamp rolling. It is absolutely hopeless otherwise. For some not-absolutely-terrible MC input noise, try NJM2068 instead of TL072. For MM, OPA2134/OPA2132 or NE5532 would be good candidates. It seems to be not entirely AC-coupled though. If the output is found to be slamming into the rails, a part with bias current cancellation may be needed. Maybe LM4562... still not a super great option due to current noise, but whatever.

As for the tone control, a 4558 is an alright choice though a 4565 or 5532 would provide better output driving if needed.
 
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GXAlan

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With this circuit I would explicitly condone opamp rolling. It is absolutely hopeless otherwise. For some not-absolutely-terrible MC input noise, try NJM2068 instead of TL072. For MM, OPA2134/OPA2132 or NE5532 would be good candidates. It seems to be not entirely AC-coupled though. If the output is found to be slamming into the rails, a part with bias current cancellation may be needed. Maybe LM4562... still not a super great option due to current noise, but whatever.

As for the tone control, a 4558 is an alright choice though a 4565 or 5532 would provide better output driving if needed.

I probably will just leave the tube engaged then and just measure the differences with op-amp rolling.

Buying op-amps from mouser is pretty cheap with shipping being the major cost. Besides the NJM2068 to replace the TL072, what else would you try. Is the NJM2068 is JFET or bipolar? The manual says that the TL072 must be replaced by a JFET opamp whereas the 4558 can be replaced by a bipolar or JFET opamp.
 

restorer-john

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The FET input TL-072 is fine at the front end, as is the 4558. But it'd be better to just use the 4558 it as a buffer with no L/H messing around.

All in all, it looks like a total waste of money. There is a million MM/MC stages built into vintage 1970s/80s preamplifiers/amplifiers with way better designs and performance.

1696385527113.png
 

AnalogSteph

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The manual says that the TL072 must be replaced by a JFET opamp whereas the 4558 can be replaced by a bipolar or JFET opamp.
I was afraid of that. The pickings among FET input, low noise, DIP package opamps (preferably inexpensive) are pretty slim - basically all cheap low-noise opamps are bipolars, including NJM2068. OPA213x would be miles better than TL072 but still isn't exactly the kind of part I'd use for MC. Perhaps OPA1656 soldered onto an SO to DIP adapter.

I do think the circuit could be "BJT-proofed" fairly easily, but I would want to reverse-engineer the 3 resistor values in the feedback ground leg (pin 2/6 to ground) for that. At this point I am not sure why the capacitor even has a resistor in parallel. I'd think it would be fairly high in value. How much of a problem a few hundred nA of bias current would be to a cartridge, I'm not sure. There are no provisions for AC coupling on the input.
There is a million MM/MC stages built into vintage 1970s/80s preamplifiers/amplifiers with way better designs and performance.
For sure.
 
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GXAlan

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All in all, it looks like a total waste of money. There is a million MM/MC stages built into vintage 1970s/80s preamplifiers/amplifiers with way better designs and performance.

That’s true. I do have my Kenwood L-08C which I need to measure now that I have an inverse RIAA circuit. That’s one of my best phone stages.

The moving coil stage on my PM-10 is pretty quiet as well. I am going to be selling that shortly since I don’t need the HypeX amps with my Meyer Amie’s.

I think all vinyl is a waste of time/money — you are spending a lot of money to get a different sound that isn’t even consistent from play to play.

This works well with my Sharp RP-117 though.
 

restorer-john

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This works well with my Sharp RP-117 though.

Those things are a blast huh? I've got several, picked up for nothing over the years and repaired. Even got some parts (arms/optical sensors etc) if you ever need anything.

Crazy little turntables. Lubricate the motor and the spindle bearing, clean up the tracking grease and the optical wheel encoder, adjust the drawer and they are the perfect turntable for someone who just wants to 'play' some records, pick the tracks they want on both sides and not be too anal about how it sounds. Those short little linear arms will track anything too- even the most warped disc you can think of, all at 1.25grams! Have you got the original AT styli with the cutout for the IR send/receive sensors?
 
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GXAlan

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Those things are a blast huh? I've got several, picked up for nothing over the years and repaired. Even got some parts (arms/optical sensors etc) if you ever need anything.

Oh nice! Right now, everything works OK although the drawer itself doesn’t feel that smooth. It works though without any issues.

I thought the power switch was bad but it just needed some deoxit. :)

all at 1.25grams! Have you got the original AT styli with the cutout for the IR send/receive sensors?

Yes. The sensors work great too. Today’s colored vinyl can interfere with the detection of tracks but it plays fine. My Sony PS-X555ES is very impressive too. That era of Japanese vinyl players are unmatched, although I do have an LP12 which is great too.

1696388690225.png


It measures +/- 1 dB as well, which could also be the limitation of the CBS vinyl disc too.
 

restorer-john

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Right now, everything works OK although the drawer itself doesn’t feel that smooth.

You likely have a cracked nylon loading gear. It's no fun to fix as the entire thing has to be dismantled. I mean everything. The loading gear/rack is in the base of the unit, under the drawer. It will eventually crack all the way through and you'll lose loading altogether as it will skid on the shaft. Just be gentle with it and 'help' the drawer in and out.

But it is 40 years old.
 
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GXAlan

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@AnalogSteph
I took your advice and replaced the TL072 with an OPA1656 x2. Definitely lowers the noise level considerably! Will try to run measurements when I get a chance.
 
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GXAlan

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Op-Amp Rolling

As noted, I mentioned that the harmonic distortion wasn't an issue to me -- the phono preamp sounds great. The problem is that my Monster Sigma 2000 MC which has an output voltage of 0.2 mV resulted in way too much noise, so I wanted to try different op-amps.

Based upon the advice of @AnalogSteph , I picked up a OPA1656 which was modified to fit the DIP8 switch from @Audiophonics. Switching out the TI TL072CP for the TI OPA1656 was a night and day difference. The noise floor went from unlistenable to sounds great. As I've recently sold my Marantz SA-10 (no complaints, just need to reallocate funds towards speakers), I just focused on measuring the LXV-OT10 with the input shorted.

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1698385661423.png


@pkane -- for these tests where I am recording in mono, is the blue what Multitone assumes is the fundamental?
 
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GXAlan

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I made the op-amp rolling a separate thread.
 

solderdude

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Muses 01 seems worth the money in this particular circuit.
If you did not already have the 02 you could just use cheaper opamps in that position.

What would be interesting is to see what the tube contributes to noise floor.
Maybe just a little as it is just a cathode follower and working at low voltages too.
 
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GXAlan

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