Another Early Strain Gauge

 I came across this cart on the 'bay and it is from an Admial 6F10

One interesting thing about it is the way the cantilever and stylus appear to be formed from a single piece of bent metal.

The other quirk is that it has three terminals with rather high resistances.

The end to end resistance is 150kΩ and the center pin is 100kΩ and  50kΩ to the outers. "Tweaking" the stylus makes the resistance change by 1-10kΩ+ so it really seems to be a strain gauge  and with a date of "Pre-1952" that would make it an early one.  The idea that the three terminals all seem to be connected to gauges has me puzzled an I haven't fully digested the schematic so have at it.

Garrard 301

 I know the inerwebs are filled pictures of beautiful Garrard 301's and by that standard this one is a bit pedestrian.

If you take a step back and see that it is partnered with a vacuum tube based phono stage and amplifier things get a bit more interesting

another 20 steps back reveal that this is then paired with a pair of Tannoy Westminsters in a Japanese restaurant in NYC and suddenly that first picture isn't so pedestrian any more.

Makes me really want to exit my bubble and be one of the lucky folks who gets a table during the 25% seating capacity phase of the pandemic.

Laser Zenith

 I have recently found the need to adjust Zenith by small repeatable increments and it seems that hot glueing a laser to the side of the cartridge proves to be quite effective.

 The need for this type of repeatable precision was so I can plot the change of IMD against Zenith angle and the results are telling.

dave

Cartridge Experiments

 Expanded my bubble with a covid test and a visit for a weekend of listening to cartridge variations in DC.

Thus far the cantilever, diamond profile and suspension have been determined so the primary goal of this session was to confirm results of 10 different variations of tieback and coil winding materials. Comparing copper, silver and gold coil wires was interesting and a consistent sonic pattern of behavior is starting to emerge.  The system was Garrard based with my stacked quad57's and the tonearm for the primary swaps was a Schick and then ultimately the winner was installed in the 12" dymondwood "Chunk" and compared to the previous reference in the 16" magnesium "MegaChunk"

In order to do quick and effective swaps the head shells were all mass loaded to net the same VTF and in the case of the mono carts some substantial mass was required.  Zenith and azimuth were set electrically and the SRA was dialed in by ear for each cartridge to best isolate the variable being compared.  It has become abundantly clear that setup usually dominates the sonic results in comparisons like this so extra care must be taken to assure proper setup.  Once a general feel for the variable being examined was determined the pattern of results correlated nicely to the same set of tests in a different system.  The next step with this batch of cartridges is to repeat the comparison in a third system and then move onto coil formers and magnet types with the ultimate goal being a more finessed version of the field coil.

stay tuned.

Silver and Gold

 I've used this title before around the holidays and this time I'll take it 100% literal.

Being a huge fan of silver wound things and loving the sound of silver wound cartridges I decided to take my game up a notch and see what 0.9999 gold coils sound like. 

It has been posed to me by Dick Sequerra that it is the oxide semiconductor boundaries within wire that that make silver a better sonic choice since silver oxide is a more benign conductor than copper oxide which creates a diode.  Dick made the compelling argument a few months ago that since gold doesn't oxidize at all it should be the ultimate choice for the low level signals found in an MC cartridge coils.

Stay Tuned.

Franken-Schick

 I have been playing a fair bit with cartridge designs lately and have come to the realization that setup (mainly SRA) can have a profound impact on the sound of a cartridge.  When trying to make apples to apples comparisons of different suspension types or silver vs. copper wound coils, small changes in SRA will quickly swamp out the variable you are trying to isolate.  

My 12" Schick has been my goto arm for these comparisons since cartridges installed in headshells are a must for efficient changes. That means for these experiments my Schröder Reference sits idle.  The realization of the importance of matching SRA from cartridge to cartridge had me add VTAF to the Schick for quick and repeatable changes in VTA.  This left me counting turns and computing changes from a known thread pitch. Around four hours ago Jeffrey pointed me to a table he used at a show with a machinists indicator to read out VTA.  

I recalled that I had a similar indicator and to the cad/cam program I went. A few hours later I came up with something that would make my long lost uncle Rueben proud.  The end result tells me the VTA setting to the 0.001" over a 1" range which is just what is needed to dial in 5 different cartridges with different tie-back wire types for my next comparison.

When it comes to simple listening pleasure of a single field coil cartridge the Schröder gets cued up as  the daily driver.

Maggin'

I have been playing with cartridges lately and one of the central points to any cartridge is the magnet.  I built this charging coil to re-magnetize the alnico magnet in a denon 103.

For s sense of scale here it is in relation to a charge coil for the magnet in a Sequerra ribbon.

This is a piece of more contemporary audio history.  JC built the charger for Dick Sequerra to charge the magnets for his ribbon drivers.

 The charger uses an ignitron (yes I insist on mercury even in my cartridges) to dump up to 14,000µf @ 600V into the charge coil.

While running it through its paces I was able to reverse the field in a N52 Neo magnet and in my attempt to see if I was reaching maximum charge this happened when I set the voltage to 400V and got a larger "POP" then expected.

The coil was 10 turns of #16 wire encased in JB weld.  The wire broke into several parts and the JB weld was nowhere to be found.   I have always heard stories how they would often vaporize the charge coil in big magnets.... never thought I would experience it first hand.

SUT Writeup.

I figured it was time to jot down some ideas on how step-up transformers are best applied to MC cartridges.  Hopefully the info at the link is easy to digest and not too much of a veiled ad.

Moving Coil Step-Up Transformer Design Considerations.

as a teaser here is the venerable peerless 4722 compared to a SUT that follows the practices I have laid out.  Please leave comments with any critiques.

From the Archives

The archives in this case being a dust covered cardboard box on a bottom shelf in the far corner of the 'Lab'.

The chassis work by Melissa & Doug represents the 'Early Davey Functionalist' era that predates the 'Drug thru the Hudson' look of the early 21st century.

It is a simple remote controlled 100K linear pot attached to some RCA plugs used explore loading options for MC cartridges.  At one point the concept piqued the interest of a well known Stereophile reviewer but upon borrowing the unit, he was terrified to plug it in to his system so into the archives it went.

The remote controlled pot was the handy work of of our good friend John Chapman and the concept evolved into the Opti-Load which replaces the pot with a relay controlled resistor matrix.

Shameless Plug.

I updated the Intact SUT page to better represent the current state of affairs of what is going on inside the Intact and EM/IA MC Step-Ups.

16" Mag Chunk

Back from Capital Audiofest and settling in.  Until a full show post is ready I'll tease you with a work in progress by the good Dr. Khan.  The past few years we have been using a 12" Dymondwood uni-pivot arm which is affectionately known as "The Chunk"  Not to be outdone we were working towards a 16" table to play some ERC Acetates so a 16" model was started out of a plate of Magnesium.

Two versions are being done, one smooth and one with a pattern much like a nail file to break up resonances.

These things look much more like ninja tools than tonearms but that is part of the fun.  I guess one could take it another direction and say it could be used as a pledge paddle for the EMIA fraternal organization.

Here is a photo with a ST 50 in it for scale.  Next time I head down to DC it should be finished and mounted so stay tuned.

Jeffrey was searching for show coverage on Sunday and it appears as if the first hit was spot on topic.

Ortofon Cutter Head.

Pete at ERC sent me an Ortofon cutter head to look at because it wasn't sounding right.  Since I have been looking at how various stylus profiles fit into the groove it was a perfect thing to get under the scope.

This is a beautifully made piece and here are some pics of the important parts.

In looking at it I saw that the cutting stylus didn't seem to fit snugly in place which could explain the reported dark and lifeless sound.  Below  is the ruby cutting stylus holder with the nicrhrome heating wire.

This tapered piece fits into a bracket attached to the drive system.

this interface didn't seem as structurally sound as it should be and closer examination revealed a problem.  It seems that there was a small 'ding' in the receiver hole making it somewwht less than round.

this minor dent kept one side from seating properly and gaps on either side can clearly be seen.  given that the irregulariy is only about 0.001" it will be quite easy to clean up.

For reference, this is how tightly the other side fits.

In general the aluminum piece does not have the 'watchmakers quality' that the rest of the unit has so I suspect it was a replacement part.   Once I get the word to proceed I will clean it up and get it back to Pete to cut a few lacquers and see if things improved.

stay tuned....