Friday, July 23, 2021

Herculean DIY Autoformer wiring.


 They say a picture is worth 1000 words... well how about how about around 180 wires and 820 solder connections?  Brad from the Boston contingency wired 6 of the 28 position autoformers up for Caroll's home theater system.  I often joke that more than half of the $200 autoformers I have sold sit partially wired in a box on a shelf and this picture might explain why.

Sunday, June 20, 2021

blink blink blink


 I mentioned the Feral Eye a number of years ago and the fate it met from Hurricane Sandy.  It  was brought back to life by steve berger as a PP 10 amp with a 49% nickel phase splitter and last night I got to hear it with a quad of mesh 10's from 1929.  
I'll be he first to admit that historically  I have not been a fan of either push pull or 10's and these days my daily drives are PP 300B's direct feeding stacked quad 57's and last night has me considering revisiting the 10.
The days events were to listen to cartridge variations and the mesh came in at the end of the evening as a treat for a hard days work.

Wednesday, April 28, 2021

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.






Monday, March 22, 2021

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.

Thursday, March 4, 2021

Unsafe At Any Speed

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



 

Wednesday, February 17, 2021

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.

Thursday, February 11, 2021

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


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