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Maybe not the best place to ask, but -- I had a random (simple) DIY phono preamp thought/question

DonH56

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good evening, maybe it may interest a RIAA preamplifier scheme with anti-rumble filter.
The jumpers J1-J2 allow to change the input impedance,
1) 100Kohm-100pf
2) 50Kohm-100pf
3) 50Kohm-200pf
Power supply 12-30Vdc
View attachment 60089

You need to move the capacitors C3, C15 over to provide 50k/100pF and 50k/200pF options... I would try to find film (not ceramic) caps for C5 and C17.
 

DonH56

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Not sure why I was thinking about phono preamps, but I was.
I was thinking about the proliferation of really, really cheap add-on (MM) phono
preamp/EQ boxes that every retail & catalog electronics supplier carried back in the good ol' days. You know, this kinda thing:

View attachment 58722
source: http://www.radioshackcatalogs.com/html/1977/hr040.html

So, in 2020 AD, they call these Little Rats and there are clowns hucksters audiophiles who sell upgraded examples (new caps) for, like, two hunnert smackers. :eek:

The mind boggles.

So, here's what I was thinkin'. There are lots and lots of really good, cheap transistors nowadays. These gizmos were (are) extremely simple -- although I'll admit, I don't even know if they use active or passive RIAA networks (I assume the latter...?).

I'm just wonderin' if anyone's knocked together a drop-dead simple, discrete SS phono preamp along the lines of the "Little Rat" and its peers -- but using modern transistors and capacitors (and resistors, too...)? Seems like it would be a cheap and fun exercise.
One could run it with batteries, off a wall wart (switchmode or linear), simple linear P/S, not-so-simple linear P/S, or a bench/lab P/S (for those who have such things handy -- they're cheap and plentiful; a good investment for tinkerers). It might be way easier to make it quiet compared to DIY with vacuum tubes. I am a big fan of vacuum tubes for hifi (sorry!) -- but not as much for high-gain applications, due to noise and hum issues. Indeed, I do use a soiled-state umm, I mean solid state phono preamp myself! :rolleyes:

I mean, I could google for examples -- but I am really lazy, so I thought I'd ask! :)

Thoughts?

PS Actually I did google around a little bit -- but everything that started simple in DIY threads seemed to get ever more complex as folks tinkered.
I am poised to pull out the very old GE transistor manual(s) I have downstairs and see what sort of circuit(s) might be therein.

I actually had (maybe still have for all I know) one those Realistic phono preamps! Actually a couple; I gutted one and stuck in a new circuit using an LM381, must have been around 1976, 1977.

I could not begin to list all the various phono (and other) preamps I constructed over the years using discrete transistors, op-amps, and tubes. I learned a lot about noise contributors and layout especially with the discrete versions. The hard way, natch.
 

LTig

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Yes I agree the NE5532 is excellent, people are put off it because it cheap but thats only because they mass produce it. You do need to use a bit of gain with it though, I seem to remember it can't be used at unity gain, but thats no problem in a phono pre-amp as it has a good bit of gain.
The 5532 is stable at unity gain which is required in this design (at high frequencies it has unity gain). It's the 5534 which is not stable at unity gain.
 

dunkuk

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Aha, that makes sense as I made a dual mono pre amp, it was about 20 years ago so my memory is a bit hazy!
 

Digital Mastering System

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That's a negative. Most of the little I know about them has come from some of the local hifi gurus here in northern New England.

Self mentions 'electronic cooling' on page 198 -201 (of Small Signal Audio Design), which uses another opamp to lower the noise of the 47K loading resistor. I used this same technique for the damping resistor in high bandwidth low noise ferrite tape head preamps and I know it works. When the rest of the circuit is as low noise as you can make it, this active loading makes a huge difference.
 
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