[sdiy] THAT 2155 on sale

Pete Hartman pete.hartman at gmail.com
Sat Apr 18 09:07:25 CEST 2020

Where do you think most of our chips are made these days? :)

You're right they could be bogus.  I haven't tested mine, I have other
projects and this was just a "hm, I'll snag some of these" whim, nothing
serious.  But just because they say "CHINA" on them means very little.


On Sat, Apr 18, 2020 at 2:01 AM Laughing Man <laughingman647 at gmail.com>

> I bought some of the THAT2155's, and not only is the picture of them quite
> literally what they look like, they also didn't picture that back side that
> clearly says "CHINA" on it. I have low hopes, and I don't recommend anyone
> else buy them. Most likely they just purchased a lot from some Ebay seller.
> On Fri, Apr 10, 2020 at 11:57 PM Kylee Kennedy <kmkennedy at gmail.com>
> wrote:
>> I'm with Adam who said use your ears in the diode testing thread.
>> I have an LPG pcb with sockets for the vactrols and while using the same
>> trigger and noise source for all tests just go in and swap vactrols.
>> I go with the vactrols that sound the best. Some I like the ping/bongo
>> sound while others I like for their slower filter sweep long tail response.
>> So I usually end up with two LPG's per panel with different responses.
>> Trial and error,
>> Kylee
>> PS I did go through a period where I would capture the tail response on
>> my Rigol scope single shot capture. Also use my Fluke multimeter to compare
>> their on resistance and off resistance. This did help me remove wildly low
>> resistance variable vactrols.
>> On Friday, April 10, 2020, Laughing Man <laughingman647 at gmail.com> wrote:
>>> I'll give the comparator circuit a shot, though I'm still curious what
>>> the datasheet is referring to in regards to some specific amount of current
>>> being pushed through the LDR. The Excelitas datasheet also mentions that
>>> currents lower than 1mA would result in excessively high resistances.
>>> That's the main thing that's stopping me from being sure I've tested
>>> them right: I'm not sure how I know I've got the right amount of current
>>> flowing through the LDR. If I don't, then the specs won't line up by a long
>>> shot. It seems as if I just have to get a 'golden vactrol' that I know will
>>> work in the situation I want, and just line them up, which is bugging my
>>> scientific side.
>>> On Fri, Apr 10, 2020 at 10:08 AM Ullrich Peter <Peter.Ullrich at kapsch.net>
>>> wrote:
>>>> Hi Pete!
>>>> To show curves from an Arduino you don't need a display, you can do it
>>>> with the serial interface via USB and the Arduino IDE itself by using the
>>>> serial plotter!
>>>> See here:
>>>> https://www.instructables.com/id/Ultimate-Guide-to-Adruino-Serial-Plotter/
>>>> Ciao
>>>> Peter
>>>> http://www.ullrich.at.tt
>>>> ________________________________________
>>>> Von: Synth-diy <synth-diy-bounces at synth-diy.org> im Auftrag von Pete
>>>> Hartman <pete.hartman at gmail.com>
>>>> Gesendet: Freitag, 10. April 2020 17:17
>>>> An: synth-diy at synth-diy.org DIY
>>>> Betreff: Re: [sdiy] THAT 2155 on sale
>>>> On Fri, Apr 10, 2020 at 8:43 AM Oren Leavitt <obl64 at ix.netcom.com
>>>> <mailto:obl64 at ix.netcom.com>> wrote:
>>>> I have an idea for "quick matching" photo cells.
>>>> Basically one op-amp - a comparator with hysteresis (like that of a
>>>> basic LFO)
>>>> 1) Put the photo cell side in a resistor divider and connect to the
>>>> comparator input.
>>>> 2) Connect comparator output to to LED side thru appropriate current
>>>> limit resistor.
>>>> The circuit should self oscillate at an amplitude/frequency determined
>>>> by the LDR's light/dark resistance and lag time characteristics. Plug
>>>> different photocells into same circuit and sort them by matches in
>>>> amplitude/frequency shown on oscilloscope.
>>>> An idea..
>>>> I rather like it.  I've occasionally started putting on paper ideas for
>>>> using an Arduino where an analog output drives the LED and steps from 0 to
>>>> 5V (with appropriate current limiting of course) and an analog input reads
>>>> from a voltage divider including the resistive side.  The idea being to get
>>>> a graph.  But then I got stuck on how to display the graph meaningfully
>>>> without going full blown OLED.  Considered simply sending the output to the
>>>> serial port and letting a computer read the details.  And that really omits
>>>> the time factor, although I could do a 0V -> 5V step and observe the time
>>>> it takes, I guess.  Overall, too complicated, so I never tried to implement
>>>> it.
>>>> I do have a bunch of Silonex Vactrols that would be nice to
>>>> characterize....
>>>> Pete
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