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.

If you want all of the sordid details have a look at the link below.

http://www.intactaudio.com/forum/viewtopic.php?t=1660

and for an update on some old dirty laundry check this out:

what comes around...

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.