Strain Gauge catridges
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flavio81
Turntable technician
Yo Pio, your AK inbox is FULL. I've emailed you to scb@hi(...) You will find a nice surprise there. Please check that you have received mail from Flavio...
To the rest of the distinguished friends: It seems (in theory) that i've nailed the equalization to be flat within 2dB between 40-10000Hz, which would be a pretty excellent spec for any cartridge. It probably is still within 2dB between most of the 10000-20000Hz range too.
I need to do build the actual thing first, so far i only have tested it on the simulator. I have to check things like keeping noise under control, etc. And of course, i have to listen to the actual thing. Because i have the terrible suspicion that perhaps most LPs are cut with the typical MM cartrdge frequency response in mind (a circa 2-3dB valley in the 3-6KHz range, and a strong HF peak at about 15KHz...)
In any case i will include a control to compensate for this.
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Pio1980
AK Member
I'm putting the SG/PL-L1000 system back into service for a while, I've been off with a BD H-K T60 TT/MM cart project after a DD Mitz LT-30/MC project and DD/LT ReVoX Linatrack/MM project. The contrasts may prove interesting since I have a standard 451-C with a "Vivid" stylus and a 450-C MkII w/OEM Quadratip tweaked by the Prof (judicious damping and mass loading) for fun, both thru my uncomp'ed linear SG front end.
After spinning some Joni Mitchell "For The Roses" and Dixie Dregs "Night of the Living Dregs", followed by the "All That Jazz" soundtrack thru the 451-C/"Vivid"/ PL-L1000 after a couple years hiatus I'm reminded why Peter L. is loathe to put more EQ 'stuff' into the signal chain of custody out of concern for affecting the 'direct' sound characteristic of the SG carts. The nekked SG really doesn't sound bad at all tho' Peter's metal bodied and optimized version of the Pana-Mat SG is no doubt more refined.
The $80 LP Gear 'Vivid' stylus is probably the best cost-effective option to bring your Pana-Mat SG cart carcass back to life; http://www.lpgear.com/product/PAS451QD.html
For a 'beater' record stylus and for mono/vintage LPs and 45s the $30 spherical stylus is a good budget option; http://www.lpgear.com/product/PAS046STDS.html
They also list a Shibata tipped stylus for $150 as the closest replacement for the OEM Quadratip CD-4 stylus.
Peter L. @ Soundsmith does not support or retip Pana-Mat SG stylii, Elite in G.B. 'may' do so.
After spinning some Joni Mitchell "For The Roses" and Dixie Dregs "Night of the Living Dregs", followed by the "All That Jazz" soundtrack thru the 451-C/"Vivid"/ PL-L1000 after a couple years hiatus I'm reminded why Peter L. is loathe to put more EQ 'stuff' into the signal chain of custody out of concern for affecting the 'direct' sound characteristic of the SG carts. The nekked SG really doesn't sound bad at all tho' Peter's metal bodied and optimized version of the Pana-Mat SG is no doubt more refined.
The $80 LP Gear 'Vivid' stylus is probably the best cost-effective option to bring your Pana-Mat SG cart carcass back to life; http://www.lpgear.com/product/PAS451QD.html
For a 'beater' record stylus and for mono/vintage LPs and 45s the $30 spherical stylus is a good budget option; http://www.lpgear.com/product/PAS046STDS.html
They also list a Shibata tipped stylus for $150 as the closest replacement for the OEM Quadratip CD-4 stylus.
Peter L. @ Soundsmith does not support or retip Pana-Mat SG stylii, Elite in G.B. 'may' do so.
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Pio1980
AK Member
I got a few of them off the 'bay for ca $12 ea. Wear 'em out and have fun with the remounts!
The index post-to-tip distance and resolver 'donut' ring position are the critical factors.
flavio81
Turntable technician
Pro tip: By varying the donut ring position, you can change compliance (how much, i don't know). It is mentioned on the patent for the resolver system. On the other hand i guess this could affect sound quality if the position is not so optimal.
Pio1980
AK Member
My guess is that it affects compliance and probably tracking force range. Pana-Mat seems to have 'upped' the TF thru the later iterations tho' the stylii are all interchangable past the original EPC 450, so there may be differences on the resolver position between OEM stylii versions. I do not have an OEM 460-C Quadratip stylus to check against the earlier versions.
I use a Win SG cartridge and think kits the best thing I've ever heard (amongst many other cartridges, I've owned Shure V15V, Audio Technica OC9, Grado Signature and ZYX Universe). I found this site when I was doing a google search to look for some info on SG cartridges - and found some very interesting stuff here.
My audio buddy Chris has a Win cartridge and Pana EPC451C. Chris has got the original Win pre-amp (op-amp based), but he commissioned me to build a replacement pre-amp. Originally I simply copied the Win circuit but used new opamps (OPA 627) in place of the old 1970's prehistoric op-amps an the original. A big improvement. Once I was comfortable with the operation of the WIn, I built a discrete fet-based pre-amp, which sounds much better. Ideally I would build a valve based unit as valves are the best, but the expense to build a good valve unit would be considerably more. My circuit is attached - and I think it sounds very nice. (note - I also posted this at Vinyl Engine).
I borrowed Chris' Pana last week, unfortunately the gain is considerable less than the win - at least 6dB down. So it's back to the drawing board, as Chris wants a pre-amp with enough gain for the Pana, and I won't be able to squeeze 3 times more gain from a single gain stage.
I've looked at the op amp circuits here, they are good but my preference is for discrete circuits. has anyone got a discrete amplifier circuit for a Pana cartridge that they can share?
My audio buddy Chris has a Win cartridge and Pana EPC451C. Chris has got the original Win pre-amp (op-amp based), but he commissioned me to build a replacement pre-amp. Originally I simply copied the Win circuit but used new opamps (OPA 627) in place of the old 1970's prehistoric op-amps an the original. A big improvement. Once I was comfortable with the operation of the WIn, I built a discrete fet-based pre-amp, which sounds much better. Ideally I would build a valve based unit as valves are the best, but the expense to build a good valve unit would be considerably more. My circuit is attached - and I think it sounds very nice. (note - I also posted this at Vinyl Engine).
I borrowed Chris' Pana last week, unfortunately the gain is considerable less than the win - at least 6dB down. So it's back to the drawing board, as Chris wants a pre-amp with enough gain for the Pana, and I won't be able to squeeze 3 times more gain from a single gain stage.
I've looked at the op amp circuits here, they are good but my preference is for discrete circuits. has anyone got a discrete amplifier circuit for a Pana cartridge that they can share?
Pio1980
AK Member
Any discreet linear ckt that can 'do' a mag mic to line level, provided with the bias /blocking network should do it. I very much prefer inverted bias to adding a unity gain inverter stage to one channel to get the proper cross-channel acoustic polarity relationship.
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flavio81
Turntable technician
Hi,
Thank you very much for your schematics!! Care to explain a little bit what's "AOT" and what is the potentiometer adjusting? Also, how much current goes through the SG element? Is there any provision for inverting phase (polarity) at one of the two channels?
For the other friends, currently i'm using a Shure M64 (DISCRETE) phono preamp modified for strain gauge operation. The modification is extremely easy to do and i will post this mod as soon as i have time to show a clear schematic.
Greetings,
Flavio.
flavio81
Turntable technician
Hi Hazard,
I just found that you have posted this circuit to me before on VE, on 8 Feb 2012. These were your notes. I'm including them so Pio/Steve an others can be up to date with your circuit:
********
Notes regarding this circuit:
- Strain gauge element is fed through 8k resistor, this gives about 4ma thru strain gauge. Equally you use a current source but be careful of max voltage rating for your active device (it could see up to 34 volts).
- the strain gauge is direct coupled to the FET - the DC voltage thru the strain gauge sets the DC bias point for the JFET (about 4 volts).
- DC current throught the FET stage is 10mA each phase. Therefore the J310 current source is set for 20mA. AOT = adjust on test.
- the upper cascode resistor does not connect to the DC supply as normal, but instead to the output. Nelson Pass uses this arrangement in Zen V8 and v9. John Broskie (tubecad journal) also uses this arrangement and calls it "ultralinear cascode". I tried both normal cascode connection (upper resistor then needs to be 160k) and ultraliner connection, the ultralinear is a bit cleaner.
- I have also connected a 7 volt zener (not shown) across the strain gauge - just in case something goes wrong, it adds a bit more protection.
- use whatever output caps you like. I actually use a 1:1 output transformer.
I think that covers the design. The sound - with the batteries - sublimely clean and quiet. I love it. Bass is deep and tactile. Treble is extended and clear. Miodrange is smooth. I don't feel the need for any EQ, but YMMV. SOmetimes it feels too clean, like there's something missing - but I think that's because for the first time I am listening to a truly transparent gain stage. I love it (there, I said it again!!).
********
I just found that you have posted this circuit to me before on VE, on 8 Feb 2012. These were your notes. I'm including them so Pio/Steve an others can be up to date with your circuit:
********
Notes regarding this circuit:
- Strain gauge element is fed through 8k resistor, this gives about 4ma thru strain gauge. Equally you use a current source but be careful of max voltage rating for your active device (it could see up to 34 volts).
- the strain gauge is direct coupled to the FET - the DC voltage thru the strain gauge sets the DC bias point for the JFET (about 4 volts).
- DC current throught the FET stage is 10mA each phase. Therefore the J310 current source is set for 20mA. AOT = adjust on test.
- the upper cascode resistor does not connect to the DC supply as normal, but instead to the output. Nelson Pass uses this arrangement in Zen V8 and v9. John Broskie (tubecad journal) also uses this arrangement and calls it "ultralinear cascode". I tried both normal cascode connection (upper resistor then needs to be 160k) and ultraliner connection, the ultralinear is a bit cleaner.
- I have also connected a 7 volt zener (not shown) across the strain gauge - just in case something goes wrong, it adds a bit more protection.
- use whatever output caps you like. I actually use a 1:1 output transformer.
I think that covers the design. The sound - with the batteries - sublimely clean and quiet. I love it. Bass is deep and tactile. Treble is extended and clear. Miodrange is smooth. I don't feel the need for any EQ, but YMMV. SOmetimes it feels too clean, like there's something missing - but I think that's because for the first time I am listening to a truly transparent gain stage. I love it (there, I said it again!!).
********
Sorry, one little detail i missed out - my system (all DIY) is balanced throughout - this circuit does not have a unity gain inverter, rather it is set up as a phase splitter with balanced outputs. Phase inversion is managed by simply reversing the +ve and -ve outputs on one channel (of course you can't do this with a single end output. One of the advantages of balanced operation).
AOT = adjust on test - 15 ohms is approximately correct to provide a CCS of 20mA but needs to be trimmed to get exact value. The potentiometer adjusts the gain of the stage, by reducing the load. I use a 24 position switch which is open circuit on the last step (max volume) down to about 50 ohms (minimum volume). I actually use this a volume control - this stage runs straight into my power amp and I I don't use a pre-amp! This is another advantage of balanced operation.
Pio1980
AK Member
Thnx for carrying this fwd for me and others. At the present the SG player (lightly mod'ed Pioneer PL-L1000/Pana-Mat SG cart either 451-C w/ aftermarket stylii or a mod'ed 450Mk-II with OEM nude square-shank Quadratip) isn't my primary player in the secondary system as I've been flipping 2 other mod-ed good-sounding players for a parity check of the SG system with MM and HOMC carts. So far I prefer them and am trying to work out the differences.
These front end systems direct-drive the power amp thru a stepped attenuator sans active line-level stage via unbalanced runs.
These front end systems direct-drive the power amp thru a stepped attenuator sans active line-level stage via unbalanced runs.
flavio81
Turntable technician
flavio81
Turntable technician
This is what i use: a modified Shure M64 phono preamp. You can take this circuit as a starting point too. Works perfectly although transistors are a bit noisy (should be upgraded to better transistors!).
It should be self-explanatory. Basically is the famous Shure M64 preamp set to "flat" operation. The resistors power up the strain gauge elements with circa 4mA current, as they want it to.
It is just plug and play -- but one of the channels will have its polarity reversed. You can compensate by just wiring one speaker out of phase, for example.
You can just buy a M64 from ebay, etc, and modify it. Piece of cake.
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flavio81
Turntable technician
Hi Pio and friends,
I've located the schematic for my own strain gauge preamp circuit. The one some people out there built.
I'll try to upload them here this week, it seems they were hosted on a place that is not showing the image anymore.