Onboard buffer for longer phono cable

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Vitodam
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Onboard buffer for longer phono cable

Post by Vitodam » 14 Mar 2019 08:05

Hi all,

Due to the relativelly high output impedance and low signal of cartriges, the length of the phono cable has to be as short as possible.

Onbord or external phono riaa preamp could solve this issue, but then it is not possible to use the phono input of the amp and it requires an extra line level aux input which is rarelly available.

I was thus wondering why not integrating a simple unity gain buffer stage into the turntable, whose input would present the proper impedance to the cartridge, and whose low impedance output would allow using longer cables without loss and be less demanding on the amount and quality of the interconnects, while still using the phono input of the amp.

Do you think that would work?

billshurv
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Re: Onboard buffer for longer phono cable

Post by billshurv » 14 Mar 2019 10:55

Yes it would work. I am actually trying to find time to build one to test. The bit potential advantage of this for MM cartridges is that it completely takes cable capacitance out the equation other than the tonearm internal wiring.

http://www.kallhovde.com/advent/phono-pre-research.pdf Holman recognised this back in 1976.

vanakaru
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Re: Onboard buffer for longer phono cable

Post by vanakaru » 14 Mar 2019 11:03

You add another amplifier stage to very low signal path. How linear you think you will get that and how this will interact with next stage amp in RIAA/Phono stage. I think it is not good idea - too much to go worse.
an extra line level aux input which is rarelly available
I see AUX/Line/Tuner inputs in every amp, but Phono mostly in vintage amps.
I assume your gear is not insanely HiFi so I would rather use high output cartridge(like some Shure 9mV) if you need to to run too long cables or maybe a SUT so you will not add any additional electric circuit to audio path.
Last edited by vanakaru on 14 Mar 2019 11:09, edited 1 time in total.

billshurv
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Re: Onboard buffer for longer phono cable

Post by billshurv » 14 Mar 2019 11:07

A unity gain amplifier stage is very simple and very low distortion and potentially gets around a number of other issues. And will run for months on a battery. Technically it is a sensible solution. But people have their own preferences for a system and I can see how it will grate with those.

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Re: Onboard buffer for longer phono cable

Post by KentT » 14 Mar 2019 16:14

vanakaru wrote:
14 Mar 2019 11:03
You add another amplifier stage to very low signal path. How linear you think you will get that and how this will interact with next stage amp in RIAA/Phono stage. I think it is not good idea - too much to go worse.
an extra line level aux input which is rarelly available
I see AUX/Line/Tuner inputs in every amp, but Phono mostly in vintage amps.
I assume your gear is not insanely HiFi so I would rather use high output cartridge(like some Shure 9mV) if you need to to run too long cables or maybe a SUT so you will not add any additional electric circuit to audio path.

Easiest way to get around the problem. Simple. Buy a good quality MM phono stage. Connect it near the turntable. Run the output to a line in on your pre-amplifier, integrated amplifier, or your receiver.

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Re: Onboard buffer for longer phono cable

Post by billshurv » 14 Mar 2019 16:53

Easiest is relative :). I still think its a really interesting idea and should be tried out. Its 12 components per channel, one of which is a 9v battery so I have no excuse for not building one up for testing.

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Re: Onboard buffer for longer phono cable

Post by Spinner45 » 14 Mar 2019 18:01

Vitodam wrote:
14 Mar 2019 08:05
Hi all,

Due to the relativelly high output impedance and low signal of cartriges, the length of the phono cable has to be as short as possible.

Onbord or external phono riaa preamp could solve this issue, but then it is not possible to use the phono input of the amp and it requires an extra line level aux input which is rarelly available.

I was thus wondering why not integrating a simple unity gain buffer stage into the turntable, whose input would present the proper impedance to the cartridge, and whose low impedance output would allow using longer cables without loss and be less demanding on the amount and quality of the interconnects, while still using the phono input of the amp.

Do you think that would work?
Turntables have been designed around using a 3 to 5 foot dual shielded connecting cord for decades now.
It's the time-tested approach that has worked fine for people, for home use.
That means having the preamp/amp conveniently within arm's reach of the turntable.

In a commercial setting, like a studio for instance, yes, a local RIAA preamp would be used, then the signal fed to to the main preamps.

Anything else is really being unconventional and risky, and not along the lines of Good Practice.

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Re: Onboard buffer for longer phono cable

Post by tep392 » 14 Mar 2019 18:02

This talk of cable length reminds me of some frequency response testing I did on my turntable. I found that I had a 1st order roll-off starting at 12,500 hz, due to the high capacitance of the cheap generic audio cable I was using. That's what I got for pulling an old cable out of a tangled ball of cables I found in the basement. Low impedance cable fixed it.

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Re: Onboard buffer for longer phono cable

Post by billshurv » 14 Mar 2019 22:08

Spinner45 wrote:
14 Mar 2019 18:01


Anything else is really being unconventional and risky, and not along the lines of Good Practice.
Unconventional, definately.
Risky? Why? I can't see any inherent risk in a simple 1 or 2 transistor buffer.
Good practice, tricky one as there is very little in domestic audio that those outside domestic audio would view as good practice. RCA plugs spring to mind as an awful solution. If you step back and ask the question of what is the best way to interface a 500Ohm pseudo-balanced transducer to an amplifier in the 21st century then you would be unlikely to end up with the way we currently do it as being the first choice. RIAA standards for 47k loading were set way back in the past and based on what you could do with cheap tube preamps.

You'd be hard pushed to make a successful commercial product out of this, but for the hobbyist I still think it's something worth investigating. It might actually be an improvement...

Disclaimer: I build my own preamps and do things unconventional ways anyway. Therefore I realise that very few people will agree with me. :)

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Re: Onboard buffer for longer phono cable

Post by tlscapital » 15 Mar 2019 02:03

billshurv wrote:
14 Mar 2019 22:08
Spinner45 wrote:
14 Mar 2019 18:01


Anything else is really being unconventional and risky, and not along the lines of Good Practice.
Unconventional, definately.
Risky? Why? I can't see any inherent risk in a simple 1 or 2 transistor buffer.
Good practice, tricky one as there is very little in domestic audio that those outside domestic audio would view as good practice. RCA plugs spring to mind as an awful solution. If you step back and ask the question of what is the best way to interface a 500Ohm pseudo-balanced transducer to an amplifier in the 21st century then you would be unlikely to end up with the way we currently do it as being the first choice. RIAA standards for 47k loading were set way back in the past and based on what you could do with cheap tube preamps.

You'd be hard pushed to make a successful commercial product out of this, but for the hobbyist I still think it's something worth investigating. It might actually be an improvement...

Disclaimer: I build my own preamps and do things unconventional ways anyway. Therefore I realise that very few people will agree with me. :)
Unconventional my phono set-up is partially that and it works wonderful for me. Risky might not be the most appropriate word, but maybe not so convenient or efficient minding the benefit if any such a tweak should bring. The need for long(er) cable from the turntable to the preamp/amp is nothing I have find to be "problematic" if ever.

Now to have the phono stage as close as it could be to the tonearm base/wires end, is indeed most relevant. What might not be would be to have then longer cable after that. I understand the theory behind there but in my experience, even after the preamp the cable specs do impact the signal fed to the amp accordingly. So should length.

Speaker's cables length I have always find to be more problematic not to have them lying "in the way", one need to have the extra length to pass them through walls, ceilings, floors... Even with "thicker" cable, the issue of signal loss prevails with few extra feet and quality can be noticeably affected if one has a "clear", "neutral" and "detailed" sound signature.

For example I've tested a "small" company humble, cheap and simple build passive step-up transformer that many rate rightfully as a "real upgrade". Reputed to be of the "clear" and "neutral" in sound signature, on my phono set-up it only refrained those very qualities that my actual 18 years old solid state adjustable preamp do really well and better.

Sold it on and the new buyer find it an upgrade. This lead me to believe as I understand that some have poor, mismatching and/or just don't pay attention to their phono stage. Over the decades I have come to hear in comparison what some fitting quality gear can do over some more "generic" ones. So I have decide since to buy what's right to my ear.

Not implying that your is of the "lower" efficiency, but for some bits in the phono chain the "cheaper" option just doesn't sadly do it for me. Where on others they can be a better match. In the amplification process I have had only better experience with "higher" end gear. Since I don't mind second hand I can get to get them cheaper with patience. :P

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Re: Onboard buffer for longer phono cable

Post by audiopile » 15 Mar 2019 03:23

Walked into the Hegeman room at a Chicago CES in 1980/ MAYBE 81 ? - they were running the Dual Turntable that half the show was using that year with a Shure V-15 III or IV (whatever was current then) -Stew's electronics and speakers -(as usual) some of the best I heard at that show. So I'm already a bit of a believer in the primacy of the source and am amazed that's all coming out of a Shure ??? Nan then coyly shows me that there is a extra box behind the turntable -very short leads between the TT and this HIP (Hegeman Input Probe if IRR?) -it's battery operated and then goes into the MM input of a HAPI preamp. This box was a input matching device -at least part of it's function was to eliminate interaction caused by capacitance sensitive carts and phono inputs. Made no difference if you fed a Grado into it -but Stantons,Pickerings , Shures,Goldrings were suddenly able to fake being Decca's that tracked. Along with being a really nice guy -A. S. Hegeman was chronically 20-30 years ahead of everybody else.

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Re: Onboard buffer for longer phono cable

Post by billshurv » 15 Mar 2019 10:43

tlscapital wrote:
15 Mar 2019 02:03

Speaker's cables length I have always find to be more problematic not to have them lying "in the way", one need to have the extra length to pass them through walls, ceilings, floors... Even with "thicker" cable, the issue of signal loss prevails with few extra feet and quality can be noticeably affected if one has a "clear", "neutral" and "detailed" sound signature.
Full agree, short speaker cables are very important. I'm building active speakers to deal with that.
Sold it on and the new buyer find it an upgrade. This lead me to believe as I understand that some have poor, mismatching and/or just don't pay attention to their phono stage.
Very much so. I can be challenging to measure and adjust so a lot of systems are not at their optimum. the CH Precision preamplifier comes with a test record. Press button, play record and phono stage optimises itself for your cartridge. Wonderful and €31000!
Not implying that your is of the "lower" efficiency, but for some bits in the phono chain the "cheaper" option just doesn't sadly do it for me. Where on others they can be a better match. In the amplification process I have had only better experience with "higher" end gear. Since I don't mind second hand I can get to get them cheaper with patience. :P
I haven't bought anything new in about 20 years.

http://www.phaedrus-audio.com/PHLUX.htm these guys have the right idea. Commercial suicide but a good way to go about it.

http://www.phaedrus-audio.com/adamantine.htm is £3000. I can build that for about £150 (and have). This is about as far from RIAA std as you can get.

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Re: Onboard buffer for longer phono cable

Post by tlscapital » 15 Mar 2019 11:10

billshurv wrote:
15 Mar 2019 10:43
http://www.phaedrus-audio.com/PHLUX.htm these guys have the right idea. Commercial suicide but a good way to go about it.
OK, not "vintage" looking and with an external battery, so not to my "standards" gear wise. But yes, I admit it's impressive. Yet on the bottom of their site page/link, their "references" tests in comparison with "generic" USA MM and JAP MC carts for what they are worth, left me weary some...

So I haven't listened to the EURO MM comparison, but the USA MM sounded "dirty" and the JAP MC "tiny" where theirs sounded clean with nice separation and a nice bottom. Like my Denon DL-102 cart... And I mean this after digitalisation recording. So evidently, in comparison with comparison !

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Re: Onboard buffer for longer phono cable

Post by billshurv » 15 Mar 2019 11:19

I personally like batteries. But that is a choice.

I'm also old enough to not be sure what Vintage is anymore. 50s, 60s, 70s or 80s?

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Re: Onboard buffer for longer phono cable

Post by cats squirrel » 15 Mar 2019 11:35

billshurv wrote:
15 Mar 2019 11:19
I personally like batteries. But that is a choice.

I'm also old enough to not be sure what Vintage is anymore. 50s, 60s, 70s or 80s?
vintage (at least for wine, etc) is just the year of the grape, so for hifi kit, it would be the year of manufacture. Vintage does not mean old (although that is what is usually understood!). Old things are just OLD. And just for the record (sorry) retro is a term that describes a new thing made to look as though it was styled years ago. Neither terms help describe hifi kit, IMHO. Old means old. I am old, certainly not vintage or retro!

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