[sanaka]

I made a spreadsheet to simply be organized about parts ordering for my personal PIMETA project, sort of an expanded version of Tangent’s PIMETA parts lists. But it quickly grew to a point where I thought maybe this could even be helpful for others out there, especially noobs like me who are getting an initial handle on stuff. It is the fruit of delving into the tedium of hunting down and sorting through lots of alternative parts options and supply sources, and kind of coagulates much of that chaos, at least for me. It provides a stark reality check on the cash outlay.

In pondering on the interrelated decisions of which opamp/what gains/what feedback resistor values to use, I created another spreadsheet which lays out these relative situations for some various opamps. It makes it easy to dial in precise gain and bandwidth values for the Jung multiloop topology used in the PIMETA amp (and elsewhere). It’s of course not much that can’t be done using Tangent’s electronics calculators, and in fact these are crucial for ballparking new resistor values, but I find having everything layed out at once helpful.

My idea for both these spreadsheets is that the specifics I’ve entered might be helpful, but more importantly that the format is something you can plug other quantities into to suit your own goals. Overall these are largely an expanded rehash of some of what is on Tangent’s website, and just represent my noobie hyperobsessive efforts to impose order on things that probably don’t appear to most of you as so in need of having order imposed on them. But hey, welcome to my world...

I welcome constructive criticism as to if all this is helpful and how it could be made better.

PIMETA Parts List
Multiloop Spreadsheet
(These were made in Excel 97, so I guess you'll need Excel or compatible to open them.)

Peace,
Sanaka

 

[ppl]

Thanks for taking the time to put this together while i only gave it a look over it appeared to have all the info needed.

 

[sanaka]

Thanks PPL. If you happen to peek again at the mutiloop sheet, what do you think about predicating around the bandwidth for chips like the 637 or AD843J? It makes the inner loop gain really high and squashes the available/possible bandwidth for these fast chips (even though I set BW at > 100KHz). In contrast, a 637 in a CMoy at gain 11 has a bandwidth of 7.2MHz! Just a curious observation I have no idea what to make of

Peace,
Sanaka

 

[m0nKeY bUsiNeSs]

I really like the way you did your list. Its a great help to me as Im still picking out a couple extra parts to finish up my pimeta Do you know anything more about that DC 5.5/2.5 mm jack? is it isolated from the chassis?

 

[ppl]

The Bandwidth Tangent mentions is the open Loop Bandwidth of the op amp as configured by the inner loop. This was chosen at 100 KHz so as to result in a constant THD vs Frequency to beyond the Audio range by assuring a constant feedback factor from DC-100KHz @-3dB you can use a op amp with a higher open loop gain and or a Higher GBP and rase the inner loop gain so the -3dB point falls at the same 100KHz or you can use a smaller amount of gain and extend the open loop bandwidth beyond 100KHz. My Listening tests showed that going beyond 100 KHz on open loop bandwidth did not result in Better sound and a higher inner loop gain would allow more feedback to be applied around the Output stage and thus result in Lower THD due to a higher feed back factor. see
http://www.st-andrews.ac.uk/~www_pa/...rt4/page3.html

http://www.st-andrews.ac.uk/~www_pa/...rt4/page2.html

http://ocw.mit.edu/NR/rdonlyres/Elec...0/feedback.pdf

http://ken-gilbert.com/images/pdf/Feedback.pdf

If you read all the above links you will have an understanding of the basic method of feedback. Most of the above references deal with just one loop however this is paramount to understanding complex feedback networks. You may also encounter the writings of the anti feedback crowd as stated by the likes of Audio note.
http://www.audionote.co.uk/anp2.htm

Since we are treating Feedback amplifiers hear I will not talk about no feedback designs, However I would like to point out that very few Amplifiers are completely devoid of the so called Evil negative feedback. A simple emitter resistor in any stage of the amplifier will be Local feedback, just like the local feed back applied around the op amp. I find myself LOL at times when reading about a non feedback claim only to find Local feedback used in each Amplifier’s stage. The correct term that describes such a Circuit is not no negative feed back but however no overall feedback. I almost fell over off my chare as I read the following from Audio note>
"out of date" information into the amplifier. Under transient conditions (which is what music is; transients),” This would be True if the input signal is faster than the Amplifier. With Amplifier bandwidths of modern Amplifiers using high performance Op amps well into the MHz range and rise and fall times in the Niño second range no musical signal is going to be left waiting within the Amplifier proper for an Exit, you can be assured that the musical info will have pass out of the Amp been feed back and difference Nulled out prior to another signal entering the same space. However the audio note article gives a simple explanation of what feedback dose if the prior references were too complex