New Posts New Posts RSS Feed - A trip to the dark side?
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Welcome to the Graham Slee Audio Products Owners Forum

 

Open to all owners plus those contemplating the purchase of a Graham Slee HiFi System Components audio product and wishing to use this forum's loaner program: join here (Rules on posting can be found here)

This website along with trade marks Graham Slee and HiFi System Components are owned by Cadman Enterprises Ltd


A trip to the dark side?

 Post Reply Post Reply Page  <1 34567>
Author
Chris Firth View Drop Down
Moderator Group
Moderator Group


Joined: 16 May 2013
Location: Rossendale, UK
Status: Offline
Points: 1529
Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris Firth Quote  Post ReplyReply Direct Link To This Post Posted: 21 Mar 2023 at 9:20pm
Back to Top
Lucabeer View Drop Down
Senior Member
Senior Member


Joined: 24 Jan 2009
Location: Torino, Italy
Status: Offline
Points: 703
Post Options Post Options   Thanks (0) Thanks(0)   Quote Lucabeer Quote  Post ReplyReply Direct Link To This Post Posted: 21 Mar 2023 at 10:01pm
Originally posted by Graham Slee Graham Slee wrote:

I was thinking about how I would do it for myself and how much it would cost me.


Recently retired, but still the active tinkerer, I see! :-D


Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298
Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2023 at 12:01am
I guess with a larger reservoir capacitor the rectified voltage will have less ripple so less chance of (internal) regulator dropout. In which case, the Technics transformer could be used outside the turntable instead of buying one.

If the DC is connected to the a.c. pins (1 and 2) it will still be DC the other end of the Technics bridge rectifier, bar 1.2V due to two diode drops. And it doesn't matter if it's connected "wrong" polarity, as the bridge rectifier on the board turns it the right way up regardless.

I'm just hoping the donor SL1200 I bought to refurbish two others has the transformer left in.

In which case, I might be able to build it as a "scrap box special" and therefore at no cost. Wink

That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298
Post Options Post Options   Thanks (2) Thanks(2)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 22 Mar 2023 at 9:04am
Originally posted by Chris Firth Chris Firth wrote:

The PSU mods to my deck are covered here https://theartofsound.net/forum/showthread.php?26620-SL-1200-DC-Power-Supply-DIY

Looking at the hand drawn schematic, a few things spring to mind.

The snubber can be replaced by a Zobel (1n + 1k), otherwise the snubber capacitor will, in effect, be trying to short transformer harmonics and the harmonics will win.

The original 1 amp anti-surge fuse between secondary and rectifier should be used.

The DC wires can come straight off the bridge rectifier + and - pins as long as the reservoir capacitor(s) attach first.

By doing it as above, it doesn't need any resistors to form a filter.

One 4700uF reservoir will do: the SL1200 consumes 13.5W, which at the regulated 20V is less than 700mA, and if you take off transformer losses, is probably 500mA.

Ripple: CV = IT, so V = IT/C, and 0.5 x 0.01 / 0.0047 = 1.06V

The "bleeder" can be replaced by a regular 20k resistor, or two in parallel, to discharge the reservoir capacitor when switched off.

Now, as my DC would be floating and with a polarity of "don't care", there is no ground, just send and return. Will a shielded cable do anything much? If one is used, the shield cannot be at any voltage potential or there'll be a short.

If the power supply is constructed in a metal box, then the shield will be a Faraday shield. As long as either polarity is NOT connected to the shield, then all should be OK.

And if constructed in a metal box and used in the UK, it must be mains earthed, and via the shield, the turntable will be mains earthed.

And that can then cause a hum loop. So the shield should be connected at the power supply metal box only. That then "breaks" the EMC standards, but I'd only be making it for my own use, and so long as I never sell the turntable without reinstating it, I'm "safe".

I might have a go. Ermm

That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Graham Slee View Drop Down
Admin Group
Admin Group
Avatar
Retired

Joined: 11 Jan 2008
Location: South Yorkshire
Status: Offline
Points: 16298
Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2023 at 8:49am
Trying to move this topic back on thread -

We are faced with three variables in obtaining an "out of this world" experience from a vinyl record.

The cartridge

The turntable (including arm)

The phono stage, amplifier and speakers.

(should that have been six variables?)

It would therefore be unfair to pick just one item to blame.

Out of the above I understand the phono stage and amplifier the best, because that's been my job (vocation) for a major part of my lifetime.

All of that is actually amplification so depends on the comprehension of amplification.

A 1-volt signal is easy to amplify because it doesn't require much gain in terms of voltage and current, to turn it into a speaker driving signal.

A 5 milli-volt output magnetic cartridge is more difficult because it requires 200 times more amplification than a 1-volt signal.

Noise and interference creep in, because 5mV is nearer to them than 1-volt.

But you must consider that the magnetic cartridge only outputs its rated voltage at one frequency. It has a frequency dependant output.

What doesn't help matters when trying to educate users is the cartridge frequency response plots which sometimes accompany a cartridge showing that it's flat.

It is not flat! The plot is "normalised".

The output of a magnetic cartridge rises at 20dB per decade, so let's try it...

At 5mV at 1kHz, therefore at a decade below, at 100Hz, its output is 0.5mV, and another decade below, at 10Hz, it is 0.05mV.

Therefore, at 50Hz its output is 0.25mV, and at 50Hz, that is the frequency of the electric mains supply.

The RIAA response of the vinyl record helps matters by placing a 12dB shelf in the middle of the frequencies, which boosts the low frequency end by 6dB, thus doubling the 50Hz output to 0.5mV.

The RIAA response of the vinyl record also applies bass boost from 50Hz, so as that is its 3dB inflection point, the actual output will be 0.7mV.

So that's not so bad. 0.7mV is nearly 3 times better than 0.25mV, which is helpful to dig out the 50Hz bass from the 50Hz interference.

Now moving coil...

These tend to be 0.25mV output at 1kHz, so if we follow the above math, then at 50Hz the output will be 0.035mV.

Now, let's take it a bit further, and consider quiet passages of music.

Transients can be up to 5 times larger, so we'll look at 5 times smaller, so divide 0.035mV by 5 and you get 0.007mV.

Now, are there any among you who have had to make an amplifier to measure temperature using a thermocouple? Most find it hard and have to filter out as many frequencies as possible so the temperature display doesn't flicker all over the place.

But you can't do that with music!

So, by removing sources of hum, such as the Technics transformer, yes, you're helping. But that still leaves the rectifier charging current in the wires from the transformer to the rectifier circuit you pop in there, and that's 100Hz. But at 100Hz the output is nearer 0.014mV on quiet parts.

And all the above is bad enough, but then there's the stereo ground loop, which is a whole different kettle of fish that isn't generally understood, but is responsible for the harsher sound. And you can chase it out of the phono stage, but if it exists in the amplifier, the phono stage can't correct that.

And that's why it's possible to get an "out of this world" experience using a ceramic cartridge...
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
Back to Top
Fatmangolf View Drop Down
Moderator Group
Moderator Group
Avatar

Joined: 23 Dec 2009
Location: Middlesbrough
Status: Offline
Points: 8960
Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2023 at 9:09pm
I still remember hearing Graham's ceramic cartridge in his old workshop. Natural and musical sound from the records.
Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
Back to Top
Mikeh View Drop Down
Senior Member
Senior Member
Avatar

Joined: 04 Dec 2018
Location: Yorkshire
Status: Offline
Points: 541
Post Options Post Options   Thanks (0) Thanks(0)   Quote Mikeh Quote  Post ReplyReply Direct Link To This Post Posted: 24 Mar 2023 at 9:25am
Graham's comment about ceramic cartridges made me look a bit further into the old technology. It seems there are still some enthusiasts most seem to be in the US. Prices talked about a few years ago don't apply anymore (no surprise) the days to pick up a decent Sonotone for a few £ are gone.  However, I might take a punt to try out and remind me of the days of flip over stylii.
One question, with such high output from the ceramic cartridge is some form of attenuation needed before input to phonoamp ( Accession(?
Mike

Technics sl1210g with Victor U-2
Accession MM, Majestic + Proprius, Solo ULDE
Cambridge Audio CXC CD player
Lindemann Limetree Bridge streamer
Harbeth P3ESR XD paired with 2x REL t5x
Back to Top
 Post Reply Post Reply Page  <1 34567>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.109 seconds.