Test Equipment Anonymous (TEA) group therapy thread

[Saskia]

@mansaxel which reminds me: do you still have a need for an ultrasonic ?

[tggzzz]

I'm of the school that says it's a bad design if you can't substitute almost any BJT in a circuit with something very roughly similar and get a working properly biased stable circuit. Sure, you might miss on some critical applications (e.g. THD on low distortion power amplifiers can rely on having the right output transistors to get 0.001% THD rather than 0.01% with any old thing that's to hand) but for most things with non-critical, not pushing the envelope, design criteria then almost anything with suitable V_BCEO, h_FEmin/h_femin, F_t and P_tot ought to work by design.

I don't disagree, but when you are pushing designs to the limit you often end up relying on some "peculiar" parameter that is only found in one device. That is a problem when the device becomes unprofitable to make.

FFI, have a look at some of the discussions on sci.electronics.design. There's some very high quality info there, if you manage to avoid the politics!

Alternatively, have a look at the tables and "designs of the masters" in TAoE and the x-Chapters.

One of the 'designs of the masters' examples they give is the 34401A ADC design. That is notable in that it designs out a lot of the stuff that could lead to critical reliance on component characteristics. Basically it comes down to "the voltage reference must be long term stable and this small set of resistors must be long term stable and this capacitor and op amp need to OK (but not critical)". I cobbled together an implementation of that ADC on a cheap plug-in breadboard with the components I had to hand and an Arduino and was getting readings that were stable to 6 digits over several hour periods.

Of course. Masters can do that.

At the other end of the spectrum is measuring nanovolts and femptoamps where, even designing out as much as you can, you end up relying on the characteristics of some very particular devices and any substitution would fail on either noise or leakage grounds.

There are many other examples, e.g. a 7ns 1.2kV pulse for a Pockels cell, or circuits based on magnetic components, or microwave circuits. Or even MLCC caps, where some specify the DC voltage derating, but most don't.

[BU508A]

Just sniped a bargain:
16 pieces of 1k resistors, Vishay S102C (Y00071K00000T9L) 0.01% for ca. 77 Euro.   

https://www.ebay.de/itm/133490619724

This is what they cost at Mouser's:

https://www.mouser.de/ProductDetail/Vishay-Precision-Group-Foil-Resistors/Y00071K00000T9L?qs=%2Fha2pyFaduhTAh51oKjlKT8xWwBKANFHd60hTXfJ9%2Fs%3D

[Specmaster]

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

This supprized me too to be honest, i was out for 25 years, but kept my lfull icense...
25 years ago all hams were electronics freeks and had the first computers..and the axam had a proper technical one, je allmost needed to know the TRX by its components level.
i am member of a few ham groups... and most of the new hams, just like talking and have no idea about the radio itself..
i was kicked out of a ham group becouse i posted a video of a teardown of a TRX and the modurator received complains it was to technical...
i will never anderstand those hams.

[edit] was not kicked out, but asked to but less technical videos.... i left, that was not my group..

You're right, not that I have ever been a ham but have known a few over the rears. In the early days most hams actually either built their radios or extensively modded them in some way or other. I remember all the great electronics shops having their own dedicated section of their shops and catalogues for ham equipment.

[Cerebus]

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

This supprized me too to be honest, i was out for 25 years, but kept my lfull icense...
25 years ago all hams were electronics freeks and had the first computers..and the axam had a proper technical one, je allmost needed to know the TRX by its components level.
i am member of a few ham groups... and most of the new hams, just like talking and have no idea about the radio itself..
i was kicked out of a ham group becouse i posted a video of a teardown of a TRX and the modurator received complains it was to technical...
i will never anderstand those hams.

[edit] was not kicked out, but asked to but less technical videos.... i left, that was not my group..

You're right, not that I have ever been a ham but have known a few over the rears. In the early days most hams actually either built their radios or extensively modded them in some way or other. I remember all the great electronics shops having their own dedicated section of their shops and catalogues for ham equipment.

Well originally the official reason, in the UK at least, for granting radio amateurs licences was for them to advance the state of the art by experimentation and the construction of novel equipment.

[bd139]

Well originally the official reason, in the UK at least, for granting radio amateurs licences was for them to advance the state of the art by experimentation and the construction of novel equipment.

The unofficial reason is an excuse to buy a £9000 radio you don't know how to use so your dick looks bigger than the other guys who only have £5000 radios.

(I have yet to find evidence of a single QSO or spot by the £9k radio owner  )

[Saskia]

why do the famous roman centurio, biggus dickus, and his beautiful wife, incontinentia, come to mind ...

I must have watched too many British movies ...

[Specmaster]

@bd139, question a couple pages back, what is Q4?

[Cerebus]

Q4 is a 2N3904 - matched pair with Q5 (in theory).

[Specmaster]

Thats what I thought it should be but the legend has overwritten itself. Matched pairs never really remain matched though in reality so I would expect some serious distortion to creep in.

[tonyalbus]

Difference between an operator and a creator. Which is why amateur radio sucks. It's all operators and cargo cults.

This supprized me too to be honest, i was out for 25 years, but kept my lfull icense...
25 years ago all hams were electronics freeks and had the first computers..and the axam had a proper technical one, je allmost needed to know the TRX by its components level.
i am member of a few ham groups... and most of the new hams, just like talking and have no idea about the radio itself..
i was kicked out of a ham group becouse i posted a video of a teardown of a TRX and the modurator received complains it was to technical...
i will never anderstand those hams.

[edit] was not kicked out, but asked to but less technical videos.... i left, that was not my group..

You're right, not that I have ever been a ham but have known a few over the rears. In the early days most hams actually either built their radios or extensively modded them in some way or other. I remember all the great electronics shops having their own dedicated section of their shops and catalogues for ham equipment.

Well originally the official reason, in the UK at least, for granting radio amateurs licences was for them to advance the state of the art by experimentation and the construction of novel equipment.

it was called (direct translation) License for experimetall radio reseurse

[bd139]

Thats what I thought it should be but the legend has overwritten itself. Matched pairs never really remain matched though in reality so I would expect some serious distortion to creep in.

Should be fine enough for this application. Ideally they'd be on the same bit of silicon and actually matched like the now dead and gone LM394 or inside an opamp. But the only thing you're going to have an issue here with is DC offset between the input dividers. And meh to that. This would be an insignificant contributor to the distortion in this application. Saturating the transistors is a risk here as the output range is only about 5V with this circuit 

If we take the whole thing to bits it probably makes more sense...

The core of it is a fairly lame opamp:



And this is just surrounded with a feedback loop to give it some gain and some coupling to make it single supply:



So going back to the original question, Q4 is the input transistor on the non-inverting input in the lamest opamp that the human race has produced 

Edit: I haven't measured THD formally but it's around 0.44% from the simulation assuming you don't saturate the output transistors which is pretty good for a shite design

Edit 2: improvements I could make: Current mirror in diff amp, better VCCS, JFET diff amp. But can't be arsed.

Aaaand back to less interesting things 

[Specmaster]

Why have you produced such an amplifier? I thought you was trying to produce a piece of high fidelity equipment here so that you could hang a pair of decent speakers on it and enjoy some serious music such as The Division Bell for instance at sound levels that would annoy your neighbours to hell. 

[mansaxel]

@mansaxel which reminds me: do you still have a need for an ultrasonic ?

Do I want it? Yep.
Do I need it? Maybe.

I'll make a pass in my toy ultrasonic first, just for shits and giggles, and if I'm still left wanting after that I'll PM you. Don't hold on to them, if someone else wants'em by all means!

[med6753]

Why have you produced such an amplifier? I thought you was trying to produce a piece of high fidelity equipment here so that you could hang a pair of decent speakers on it and enjoy some serious music such as The Division Bell for instance at sound levels that would annoy your neighbours to hell. 

The output of that amplifier wouldn't annoy a mouse. 

[VK5RC]

Just sniped a bargain:
16 pieces of 1k resistors, Vishay S102C (Y00071K00000T9L) 0.01% for ca. 77 Euro.   

https://www.ebay.de/itm/133490619724

This is what they cost at Mouser's:

https://www.mouser.de/ProductDetail/Vishay-Precision-Group-Foil-Resistors/Y00071K00000T9L?qs=%2Fha2pyFaduhTAh51oKjlKT8xWwBKANFHd60hTXfJ9%2Fs%3D

You can get arrested for 'stealing' with a deal like that - top purchase, 👍

[bd139]

Why have you produced such an amplifier? I thought you was trying to produce a piece of high fidelity equipment here so that you could hang a pair of decent speakers on it and enjoy some serious music such as The Division Bell for instance at sound levels that would annoy your neighbours to hell. 

Yes objectively that's the end game but the best way to approach a problem is from the bottom up

[mansaxel]

Ideally they'd be on the same bit of silicon and actually matched like the now dead and gone LM394 or inside an opamp.

Enter ex-soviet union: https://www.ericasynths.lv/media/AS394CH.pdf

"In Soviet Russia, transistors match you!"

But yes, this is stumbling head first into unobtanium component -land.

[PA0PBZ]

Should be fine enough for this application. Ideally they'd be on the same bit of silicon and actually matched like the now dead and gone LM394 or inside an opamp.

BCY87 comes to mind

[mnementh]

Spara, I have found the root cause of poor readings in my HP 3478A. It was the Front/Rear Switch that has gone bust, only the rear works fine. Shall I buy a new switch or a switch contact cleaner ?

      

This is a common failure mode with these. The good news is the switch is a very good candidate for dismantling & manual cleaning; I have a detailed writeup here: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg1911782/#msg1911782

Mine had a tiny bit of grit in it causing intermittent contact. My cleaning process involved a squirt bottle of alcohol and a NEW mascara brush, which are available for a buck or three at any Wally Wurld or similar disenfranchisement department store.

Good hunting!

mnem
 

[BU508A]

https://www.ebay.com/itm/122212630512



    

[mnementh]

On the other side I attended the Keysight webinars about FFT. Interesting stuff, I report here my question and how they answer it:

Q: Does the 10MHz input on the high end Scope improve the FFT performance?
A: Hello Zucca, Thank you for the question. I am not sure if this would provide any improvement, I will check with the factory and get back to you via email.

Further answer:

I assume you refer to the 10MHz common instrument clock, typically used to synchronise instruments and which often come from a high-precision source. I checked with the factory and they state that think this would have very little effect. You wouldn’t notice a few parts/million difference in frequency measurements. Johnnie Hancock will be presenting a virtual seminar in early October on “Understanding Oscilloscope Specifications”. One thing he plans to point out is that although the scope’s time-base accuracy specification is often touted, it is overrated. There are many other factors that go into determining timing accuracy that are much bigger than time-base accuracy. He states the same can be said for frequency measurements in the frequency domain.

If you are referring to the 20MHz filter used in the oscilloscope front-end (hardware bandwidth limit filter): then this will have an effect - if you are only interested in frequency components below 20 MHz, this will definitely help. It should also improve the scope’s noise floor.

FFTs are boring
Here is a nice screenshot, especially when you try to count the number of digits in the frequencies   

FFI see https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3000930/#msg3000930

I was just thinking how tidy my 54645A would look stacked on a similar HP SA... and then you remind me that it not only would look good awesome, but would serve as a counter (independent of my scope) for most of my purposes as well. Now I just wasted 30 min on fleaBay lookin' instead of packin' ta move! 

And I don't even have a address for them to ship it to yet!!!   

mnem

[Specmaster]

Why have you produced such an amplifier? I thought you was trying to produce a piece of high fidelity equipment here so that you could hang a pair of decent speakers on it and enjoy some serious music such as The Division Bell for instance at sound levels that would annoy your neighbours to hell. 

The output of that amplifier wouldn't annoy a mouse. 

Exactly my point, my old Hacker radio has more power 

[mnementh]

It’s just humans. Some of them are wired up wrong. Or have a burned out resistor somewhere.

i hope he is wired enough to properly pack it... . or i end-up with 4 stars and a broken unit, because of this clown...
the tarts are not a problem, i was just supprized, i have 100+ 5 start so it will not show...
how this people think..if they even do..
don't sell the thing i am not forcing you..

You don't have to take it either. This is expressly against the rules on feedback; seller cannot ding you for anything other than abusive communication or late/non-payment. Call customer support, they'll remove it. Take my word; if you let it slide, you'll soon get to where that 99.9% pisses you right off.

mnem
"...I'm mad as hell, and I'm not gonna take this any more!!!"

[Cerebus]

If anybody is a real hard core Keithley fan there's an old Keithley advertising/marketing giveaway mug up on eBay UK. Other than being Keithley related (and brown naturally) it's otherwise unremarkable - no useful reference material like the recent HP mugs.