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.

Autoformer Frequency Response

 Had a customer ask for details about the frequency response of the autoformers and while I honestly believe a picture is worth 1000 words,  I'll add a few comments.  My general statement about the high frequency behavior is they behave to 100kHz without the need of any sort of loading network.  I like to show plots that cover the areas where a device misbehaves so a pattern of behavior can be identified.  Lots of people will just show a random well behaved sweep and call the device perfect.  I want you to see the squirrels.  Unfortunately plotting around 50 steps in 1dB increments creates an incredible mess so I picked a random sampling to get these plots.

Around 20 years ago I showed a similar set of plots from a step up transformer to Frank Schröder and he commented how the behavior was unacceptable @ 20kHz to which I replied "check the scale" at which point he realized he read 200kHz as 20kHz and his opinion changed. 

The other set of plots that shows important behavior involve the low frequency end of the spectrum and for this it helps to pick the worst case scenario with the +7dB gain setting of the remote autoformer.

The above plot shows the +7dB setting driven from 100Ω, 500Ω, 750Ω, 1000Ω and 1500Ω.  This represents the worst case situation for the low frequency response an with a 1500Ω source the -1dB @ 20Hz is borderline.  It is also interesting to see how the top end extension is also compromised in the +7dB position with the 1500Ω source but if you then move down to the +4dB position things look better and from unity and below all is well. I could have simply showed the Red sweep above from 20Hz-100kHz and called the device perfect but alas perfect transformers do not exist.

Unsafe At Any Speed

Apologies in advance to Ralph Nader for a wee bit of appropriation.  

 

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.

Boptura

 Random said number 5

boptura needs to get me an address.

Festivus

 It is that time again.  Everyone air your grievance below in an identifiable comment and before the year ends Random.org will pick a winner of a pair of the Slagleformer Modules.  We will cover shipping worldwide.

peace.... 

us.

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.

Number 5

 

By my count that means Pete_B needs to send me his address.  

Enjoy!

Black Freeday

 Not many thinks kicking around lately that need new homes but these might appeal to a few of you.

A customer needed some naked speakerformers that went form -3 to -7dB and I inadvertently calculated and wound a pair that were -3.5 to -7.5dB.  Rather than bin them for the copper I figure someone here can put them to good use.  Full details of the concept can be found here.

leave a comment with a way to identify you and random.org will pick the new owner mid next week and of course I'll cover shipping.

dave

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.

Doc Hoyer's garage door opener.

 It would seem that something as trivial as a garage door opener would never find its way to these pages but often it is the trivial that gives a glimpse into who a person really was.

This seemingly Rube Goldberg approach to automatically opening a garage door is a testament to the cleverness that was Dennis R. Hoyer.  I have no idea when this was constructed but given that they date back to 1926 my guess is going to Sears was not an acceptable option for Dennis.

The key to the operation is the drive mechanism and when I first looked at it I simply thought motor pulled the door open and the casters and gravity did the trick to lower the door with the motor providing some resistive force.  Upon further inspection I realized something different was going on since the casters were pointed in the wrong direction.

A closer look at the casters quickly refuted my first idea and for a second I though that the outside collar would spin around but when I realized that it was fixed it became clear that this simply operated like a ball screw on a CNC machine.

The motor turns the shaft and the casters on the collar were clamped tightly enough and set at a pitch to move the mechanism up or down at the desired rate based on motor speed.  There was a stop at full open and closed but no other safety procedures in place. According to his cousin Damian, if anything were accidentally left in-between the open and closed positions, the results were not pretty.

Most people would have simply driven to Sears but thats not how some of the truly great ones rolled.

New Math

 

THERE! I said it, and I have been trying to say it for years.  Now I am going to use my junkie pulpit to try to explain it in simple terms.

The basic rule of transformers is that the transform the load by the turns ratio squared.  This simple function allows an 8Ω speaker to present a 3200Ω load to a 300B by using a transformer with a 20:1 step-down ratio.  This makes the world an easy place to live in and keeps everyone sane UNTIL someone then asks a poor transformer winder for a 10K:600 linestage transformer and a hole is ripped into the space-time continuum.  The conversation typically goes like this:

Customer:  I need an 10K:600 lineout.

Dave:  What will this be driving?

Customer: Interconnects and the input of the amplifier.

Dave:  Do the interconnects have a 600Ω resistor soldered across them?

Customer: No.

Dave:  Does the amp have a 600Ω input impedance?

Customer:  Of course not.

Dave:  What is the amplifier input impedance?

Customer:  I dunno... 100KΩ... 10KΩ worst case.

Dave:  Then what is the purpose of the 600Ω secondary designation?

Customer:  A 5KΩ:10KΩ transformer would have a 1:1.4 step up ratio and I want a 4:1 step-down ratio to lower the output impedance.

Dave:  A 4:1 transformer loaded with 10K will load the tube with 160kΩ

Customer:  No I want 10K.

Dave:  Head hits table.... nappy time.

This is the thing that urban legends are made of.  Everyone treats transformers as if they all are used to deliver power to a load.  This is perfect for the vacuum tube output transformer since the entire purpose of the transformer is to take the high voltage high impedance anode of a tube and get it to a low voltage low impedance to drive a loudspeaker.  Universally applying this to every audio transformer simply leads to confusion and needless conversations like the one above.  I will categorically state that the worst thing you can do to a transformer sonically is to load it.  In the case of the tube-speaker interface this loading is a necessary evil. In just about every other case in audio, transformers are used to deliver voltage to a high impedance and not current to a low impedance.

I do not begrudge the really smart guys from Bell Labs who did the telephone grid at 600-900Ω.  I tolerate the audio engineers who borrowed the 600Ω impedance as a standard so everything played well together when any mismatch could prevent people from properly hearing Duane Allman at the Fillmore East.  Using those numbers today in audio where systems are meticulously curated is just begging for confusion and mediocrity.  

So back the the 10K:600 step down transformer.  The one place in audio where this transformer will really will be loaded with 600Ω is when used to drive the Pultec LCR Riaa module.  For everything else in audio, the 10K:600 has little if any relationship other than being a convoluted way to say the device has roughly a 4:1 turns ratio.  You will find many who insist that the transformer needs to be terminated with its characteristic impedance in order to work as designed.  With vintage stuff, that is often the case, but that is simply due to the fact that it was designed with the intent to be loaded with 600Ω.  

Lets assume a 4:1 ratio transformer is needed.  I can come up with two very different designs based on its intended use.  99 times out of 100 the actual secondary load will be the grid of a tube so the transformer will be operating essentially unloaded.  Rather than use an incorrect device designed for a 600Ω load, why not simply use a device designed to operate into the actual load? 

The proper (according to me) way to specify a transformer that operates in the voltage realm is to state the source impedance, turns ratio and expected load and then the proper device can be wound.  Using this approach takes what many call a black art back to the nicely ordered oblate spheroid we live on.

dave

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.

R.I.P. Art

It has been two months since Art left us and Janet reached out to me to help re-home the Step-Up that he was rotating through his system with his Denon 103.  This is the exact copper 1:15 H that he reviewed in Listening #176.   He preferred the sound of this copper unit compared to the identical silver version.  It has a 1:15 step-up ratio and is suited for cartridges with internal impedances from 20Ω to 50Ω.  The price at the time of review was $2400 and $1800 seems fair.  Payment will go to Janet Dudley directly and the SUT will ship from me with full support.  Physically this unit has been around the block so to speak but the function and sound is 101%.  Current pricing for this version in copper is $2700.  Pop me an email to discuss if this is a suitable fit for your system and by all means spread the word.  (SOLD)

a final reminder of Art's appreciation of the finer / furrier things in life

Doc Hoyer

Audio lost another of its treasures last week when Dennis R. Hoyer passed away in Milwaukee.  If you had a vintage transformer that needed help, Doc was the person to call.  On a recent trip to Milwaukee where I grew up I had the chance to visit his lab as 60+ years of his work was being dismantled.  As I was admiring his winder his cousin Damian put his license plate from 1980 in my hand and suddenly I got all choked up and truly knew who Dennis was.  


His files are a Who's Who of tube audio history

His winder was CNC controlled and built by him

I can't imagine driving around Milwaukee as a teenager seeing that bright yellow TESLA on the back of a Ford station wagon and not realizing I was behind someone truly ahead of his time.