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Topic: Are Technics SL-1200 G GR RCA shields grounded? (Read 830 times) previous topic - next topic
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Are Technics SL-1200 G GR RCA shields grounded?

Hi,

I'm new at vinyl records, but I'm interested in the following for convert RCA to balanced output.

If you have a Technics SL-1200G or SL-1200GR, could you test with a multimeter if shields (outer part of RCA connector) conduct between these? You'd first unplug the RCA cables and cartridge from turntable to test conductivity.

I read here that is possible use any RCA output from turntable as balanced if it isn't grounded.

I found lot of information about SL-1200 MK2, but not about SL-1200G and SL-1200GR; these look grounded to metallic plate.

Sincerely.

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #1
I don't know, but that's "interesting"....  I've never seen a phono preamp with balanced inputs.

Does the manufacturer supply the special cables?    That's not a "standard" XLR-to-RCA connection.    A standard adapter will connect the ground, and it normally grounds one of the signal-connections on the XLR end (so 2 of the 3 connections are grounded).

If you don't have a multimeter, I assume you can't make custom cables. :(

You'd also need a ground connection between the preamp and the turntable.   Does the turntable have a separate ground connection?   Maybe a screw-terminal connection?

IMO - The best solution would be to find a "repair shop" that's willing to make a modification to add XLR connections to the turntable.   Then you don't have to worry about the existing wiring.   That might have to be cables dangling-out with XLR connectors.    You could make those long enough to reach the preamp, or they can be short and you can use standard microphone cables. 

 The phono cartridge doesn't have a ground so it can easily be wired as balanced.

-----------------------------------------
I'm not sure if there's any real advantage to a balanced connection.   It should help with hum if hum is getting-into the cables or if it's caused by a ground loop.    But, if the cartridge itself is picking-up hum a balanced connection won't help.    The coil in the cartridge is a "better" (worse) hum-antenna than the wires, but they both should be shielded anyway.

P.S.
You can buy a multimeter for about $10 USD.

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #2
The principal benefit the balanced output is that: the output voltage from cartridge is duplicated; it is nice for MC cartridges. You could choose lower gain, lower gain reduce the signal noise ratio. The equation for calculating the gain is the following:

Reference voltage: 0.3.
Cartridge output voltage: v —Use (2 × v) for balanced output—.
Load Gain: R.
Cartridge impedance: r
Cable resistance: c.
Gain at dB.

dB = 20 × log(0.3 ÷ (v × (R ÷ (R + r + c))))

Here you can read my source.

The duplicated voltage output from cartridge never will be greater than maximum input voltage for phono preamp or stage, some manufactures call it as input overload; it's important for avoid clipping.

You can build your own cables or you can buy an adapter. Some turntables don't have enough space for XLR, so is preferred use TRS connectors.

I have a multimeter but I don't have the turntable :-( .

I ask just for learning. :-)

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #3
Quote
The principal benefit the balanced output is that: the output voltage from cartridge is duplicated
No!  Not with a phono cartridge.   A phono cartridge is two generators, one for left and one for right, each with two terminals.  The voltage between those 2 terminals doesn't change if you ground one of the terminals.

With some balanced-to-unbalanced connections you might loose half the signal.  

And, with some differential amplifiers you might get half the gain if you only the inverting or the non-inverting input.  But most differential amplifiers just give you the amplified difference and it doesn't matter if one input is ground

Quote
The equation for calculating the gain is the following:

Reference voltage: 0.3.
Cartridge output voltage: v —Use (2 × v) for balanced output—.
Load Gain: R.
Cartridge impedance: r
Cable resistance: c.
Gain at dB.

dB = 20 × log(0.3 ÷ (v × (R ÷ (R + r + c))))
The gain comes from the preamp.  

If the preamp's input impedance is low relative to the cartridge impedance you get a voltage divider which is an attenuator (and a low-pass filter since the cartridge is an inductance).  But the preamp impedance is normally much lower than the cartridge so this isn't an issue.

The cartridge inductance and the cable & preamp capacitance makes a parallel resonant circuit which could create "apparent gain" at the resonant frequency.   I read about someone doing experiments where adding capacitance boosted the high frequencies and that's the opposite of what I would have expected!    But, if you had a resonant circuit, say around 25kHz, and you increase the capacitance, that would lower the resonant frequency and it could give a boost at 20kHz....   But that's just a "casual hypothesis" and I'm not sure if that's what's happening.

Quote
The duplicated voltage output from cartridge never will be greater than maximum input voltage for phono preamp or stage, some manufactures call it as input overload; it's important for avoid clipping.
It's the preamp output that clips.  Of course that's product (literally) of input voltage and gain.  (Sometimes there are multiple stages of amplification so an internal stage  could clip before the output clips.)

Usually the output voltage is limited by the power supply, with some allowance for voltage loss across the internal components.   "Worst case" is usually with USB powered preamps.  5V USB power means no-more than 5V peak-to-peak, which is 1.75V RMS.   Most preamps have an internal power supply around 12 or 15V, and it's not uncommon to have + and - 12 or 15V since op-amps "like" dual power supplies.   So, most preamps can put-out 10 or 20V before clipping and that should NEVER happen unless you are using a MM cartridge on the MC setting or otherwise doing "something wrong".

Line level is about 1V but it varies on home equipment which is never calibrated.   

Quote
You can build your own cables or you can buy an adapter.
Like I said, a standard unbalanced-to-balanced adapter will ground-out the RCA connection that's normally grounded.   Since you want two signal-inputs and no ground directly to the RCA connector so you'll need a custom adapter.


Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #4
Yes, you are right, the gain is selected for the phono stage or preamplifier. Properly, RIAA equalizer.

And, yes, MM cartridges are very sensibly by capacitance in the cable. I'm not engineer, but you can predict ideal electrical frequency response by software. You can read the following articles about:

I know that is important ground the shield on balanced cables from source to input. But You can use the ground screws for this.

I don't found where read this, the differential circuits sums the negative and positive current and gets the amplification.

Best regards.

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #5
I forgot to tell that: maybe could be nice use a Set-Up Transformer, but I don't suggest use this because it add phase shift.

I know ancient vinyl records have lots of phase shift because master tapes recorders and players adds it.

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #6
Back to the beginning...   It's probably not too hard to cut the ground connection to the RCA connectors on the turntable while leaving the signal connection to the cartridge.  (You still need a special-custom adapter.)

Quote
I'm new at vinyl records,
Before you go too far...   Some people like vinyl and some people even like the sound of vinyl, but technically it's inferior to digital. (noise, distortion, and frequency response)   People who  like the "sound" of vinyl  are obviously not bothered by the clicks & pops or other background noise, or other audio limitations.

Vinyl can actually go higher in frequency than CDs (above the audio range) but CDs are perfectly-flat across the audible range.   And if you like "bass", CDs can go down to zero-Hz!   But zero-Hz (DC), on a CD would be considered a defect.

Personally, I could "live with" the low-level noise but the clicks & pops always annoyed me.   And I do appreciate  the dead-silent background of digital.  

Quote
but you can predict ideal electrical frequency response by software. You can read the following articles about:is.
There are also mechanical characteristics.   If it weren't for mechanical differences every cartridge could be perfect and/or every cartridge could be identical.  ;)

Cartridge manufacturers rarely publishes the inductance or resistance of the cartridge.   Usually they specify the recommended load resistance (47K for MM) and recommended load capacitance. 

Cartridge resistance and inductance can be measured, but most of us don't have an inductance meter, and it's very-low inductance so a multimeter with an inductance feature probably can't do it.

The bottom like is that you have to trust the manufacturer's recommendations, or get a test record and do your own experiments, or since your preamp has capacitance switches, just experiment to see what sounds best!

If you are listening to older records it's not that important because records varied a LOT!   I assume they are better now, but in the vinyl days, most records were "dull sounding" (rolled-off highs) with a few rare good sounding ones.    (I was listening to rock & popular and the rumor was that classical records were generally better.)

Quote
I don't found where read this, the differential circuits sums the negative and positive current and gets the amplification.
If you connect a. 1.5V battery to your multimeter (with no actual ground)  you'll read 1.5V.   If you ground the + or - terminal you'll still read 1.5V.   (If you ground both terminals you are shorting-out the battery and you'll read zero.  :P   )

It's the same with a phono cartridge and preamp.   If you ground one input of a balanced (differential) amplifier it still amplifies the same voltage.

Quote
I forgot to tell that: maybe could be nice use a Set-Up Transformer,
I agree...  I wouldn't do that either...

A transformer can isolate the ground to convert unbalanced to balanced.   But, you wouldn't want a step-up.  Normally those are used to boost the output from a moving coil cartridge so it works with a regular phono preamp without a MC input.    And a step-up transformer also steps-up the impedance.    A 1:1 47K transformer could be used if you can find one, and if you can find a good one (a pair, actually).

But the main thing is...   Phono cartridges are "naturally balanced" already....   There is no ground unless you connect it to ground (which is normally done).

Quote
but I don't suggest use this because it add phase shift.I know ancient vinyl records have lots of phase shift because master tapes recorders and players adds it.
Right!  RIAA record & playback equalization (and NAB equalization on analog tape) introduces phase shifts.    The record and playback phase-shifts could be complementary and could cancel out but they would have to be designed for that and we can't control anything on the recording-side.   And the process of cutting and then playing a record also introduces phase shifts.*

But phase is relative so as long as the phase shift is the same in the left & right channels you won't hear anything.   For example, if you reverse the connections to one speaker it becomes 180 degrees out-of-phase with the other speaker.   The bass soundwaves will be almost completely canceled and (because of reflections and shorter wavelengths) other frequencies cancel and sum in unpredictable ways and you get a "weird-spacey" sound that changes when you move around.   If you reverse the connections to both speakers everything is normal again.


----------------------------------------------------------------
* Different topic, but this combined filtering and phase-shifting makes an (undefined) "all-pass filter".    An all-pass filter introduces different phase shifts at different frequencies without affecting frequency response.    It also doesn't affect the sound...  You can't hear the phase shift (or the effects of phase shift),

These phase shifts change the wave shape (without changing the sound).   The changed wave shape makes some peaks higher and some lower.    

The new-higher peaks make a higher crest factor (the ratio of peak-to-average or peak-to-RMS).   Some people use crest factor to  measure "dynamic range",    These higher peaks don't actually sound louder, but it leads some people to claim the vinyl has better dynamic range than the CD even when they were made from the same master.  (We rarely know if they were made from the same master or not).    CD has more dynamic range capability than vinyl (limited by noise) but that's different than musical dynamics.  BTW - CDs also have more resolution than vinyl (again limited by noise).   

MP3 also changes the wave shape, often boosting some peaks and making a higher crest factof(again without changing the sound of the dynamics).    But in this case, MP3 actually has more dynamic range capability than CDs.


Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #7
I don't know, but that's "interesting"....  I've never seen a phono preamp with balanced inputs.
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Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #8
Many people think or though that vinyl records are better because MM cartridge manufactures suggest higher capacitance for compensate the high frequency falls.

Also MC cartridges manufactures suggest their own Set-Up Transformer for compensate this falling in high frequencies.

With both suggestions the people can hear the sounds that isn't able before. But none master tapes record and player have the same attenuation.

In the past, MC cartridges only do easiest use any RCA cable without care the capacitance. But now with vinyl records coming from digital masters, use a MC cartridges with flat frequency response (if mechanics allow it); this is a nice option.

The humans aren't phase shift deaf, phase shift means that sounds come early (lose information) or late (sounds gaps).

Many people perceive better vinyl because it sounds higher and high frequency sounds can be listened, please read Wegel to know how we perceive the sounds.

Possible in the future I RIP vinyls if I don't found equivalent CD's. I chose this turntable because I read reviews that tell it has the best mechanics characteristics. But now I found the Pioneer PLX-1000 which has better Wow and flutter, if we have a record with frequency at lowest and highest audible frequency response, we can hear these appear and disappear by Wow and flutter.

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #9
Quote
I found the Pioneer PLX-1000 which has better Wow and flutter,
I've NEVER actually HEARD wow or flutter unless something is broken.    When I was in high school & college I worked in a repair shop where I heard broken record players with wow and tape players with flutter. But the most common speed-problem is slow speed, caused by a slipping drive wheel of belt, and in that case you often  get slow speed combined with wow     Sometimes the center-hole in a record is off-center and that creates wow, but that's ra.

I HAVE heard rumble from a cheap turntable with a plastic platter... mechanical noise that gets picked-up by the cartridge and amplified.

Otherwise, the turntable itself doesn't make much difference.    The biggest difference is the cartridge but that's mostly frequency response which can be adjusted with EQ or tone controls.  The biggest problem is the records and there's nothing you can do about that.

Quote
Possible in the future I RIP vinyls if I don't found equivalent CD's.
That's the only reason I kept my turntable. 

A few years ago I digitized a record that I had owned for a long time.   It had been released on CD but was it was out of print and no longer available.    I had spent a few days fixing-up the clicks & pops...  It was in pretty bad shape, and I wasn't done yet, and the result wasn't going to be perfect,   Then I found a used CD copy and it sounded so good compared to the record and  I was so happy that I didn't mind that I had wasted so much time on the record!



 

Re: Are Technics SL-1200 G GR RCA shields grounded?

Reply #10
Yes, some infrasonic came audible when flutter and the lowest bass response came infrasonic when wow; otherwise, some ultrasonic came audible when wow and the highest treble response came ultrasonic when flutter.

I wrote about a ideal test record. You can read here how wow and flutter is calculated and here about human frequencies discrimination.