I built one of these, one pole is passive, one is active in the feedback loop. Works and sounds great!
Hi-Fi RIAA Phono Preamp
A few photos of my project here - http://www.diyaudio.com/forums/analogue-source/217725-porsche-design-phonostage.html
Hi-Fi RIAA Phono Preamp
A few photos of my project here - http://www.diyaudio.com/forums/analogue-source/217725-porsche-design-phonostage.html
Hi,
Yes DF96, one one hand it´s good to reduce HF as soon as possible, hence closest to the input, on the other hand, if the circuit is non-inverting (as most are), a LP-filter at the output would be required to achieve correct RIAA response.
A passive 75-µ filter (or active inverting) as last filter stage - maybe only followed by a Buffer/cable-driver - would achieve correct RIAA response with lower parts number count.
If the circuit has enough headroom to safely cope with any clicks, I´d prefer to put the 75µ-Filter in a later stage.
6L6 ... could You explain the meaning of the 2k2 input series resistor in the linked Stage, other than it adding lots of noise?
jauu
Calvin
Yes DF96, one one hand it´s good to reduce HF as soon as possible, hence closest to the input, on the other hand, if the circuit is non-inverting (as most are), a LP-filter at the output would be required to achieve correct RIAA response.
A passive 75-µ filter (or active inverting) as last filter stage - maybe only followed by a Buffer/cable-driver - would achieve correct RIAA response with lower parts number count.
If the circuit has enough headroom to safely cope with any clicks, I´d prefer to put the 75µ-Filter in a later stage.
6L6 ... could You explain the meaning of the 2k2 input series resistor in the linked Stage, other than it adding lots of noise?
jauu
Calvin
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Can anyone please explain this?!
G'day all, I encountered (and cured) a strange 'hum' issue today that makes no sense to me at all! Those familiar with valve (tube) circuitry will no doubt be aware of the great importance of correct (twisted) heater wiring to avoid hum issues, but does all that apply to typical op amp circuitry?
One of my simple full feedback phono stages had developed a strange 'hum' issue virtually overnight that defied all fault finding. The power supply wiring was three short leads (untwisted) going straight to the split rail power supply, a total length of about 18 inches and about half this length was indeed twisted wiring.
In sheer desperation I quickly twisted the untwisted section and all 'hum' completely disappeared! Two really odd things are apparent here.
'Twisting' the DC power supply wires has never been necessary in the past and indeed one of my other DIY phono stages was wired 'untwisted' with absolutely no hum issues, so can anyone possibly explain what was causing the loud hum on one particular phono stage?
Interestingly enough I've since fully twisted all the power wiring on all my DIY phono stages and a small evident residual 'hum' has disappeared. Needless to say, I am delighted but in all honesty I simply can't understand why this 'hum' was happening in the first place! A rather baffling mystery! Regards, Felix.
G'day all, I encountered (and cured) a strange 'hum' issue today that makes no sense to me at all! Those familiar with valve (tube) circuitry will no doubt be aware of the great importance of correct (twisted) heater wiring to avoid hum issues, but does all that apply to typical op amp circuitry?
One of my simple full feedback phono stages had developed a strange 'hum' issue virtually overnight that defied all fault finding. The power supply wiring was three short leads (untwisted) going straight to the split rail power supply, a total length of about 18 inches and about half this length was indeed twisted wiring.
In sheer desperation I quickly twisted the untwisted section and all 'hum' completely disappeared! Two really odd things are apparent here.
'Twisting' the DC power supply wires has never been necessary in the past and indeed one of my other DIY phono stages was wired 'untwisted' with absolutely no hum issues, so can anyone possibly explain what was causing the loud hum on one particular phono stage?
Interestingly enough I've since fully twisted all the power wiring on all my DIY phono stages and a small evident residual 'hum' has disappeared. Needless to say, I am delighted but in all honesty I simply can't understand why this 'hum' was happening in the first place! A rather baffling mystery! Regards, Felix.
I did a write-up on RIAA a few years ago (I need to do a few more minor updates) that you can read about here RIAA Equalizer Amplifier Design
I'd love to read your article, Bonsai but the 3 times I've clicked on the "RIAA Equalization Amplifiers-Part One.pdf" link in the page which your thread link "here RIAA Equalizer Amplifier Design" ... I get a hang?
Andy
ALL circuits require a source to drive the current. that current flows around a route. In that route there is a load.
The wire going to the load is the flow.
The wire coming back from that route is the return.
ALWAYS close couple those flow and return pairs. There is no exception, except when building a radio receiver and/or a metal detector.
Twisting the Flow and Return of the pair is more effective in reducing interference and parasitics.
This applies to all AC circuits, even inside a PCB, or inside an IC.
This does not apply to DC power.
But our DC power is varying. It can emit interference.
In addition our 5pin amp/opamp has 5 inputs, the dc power and the output are in fact inputs. Read W.Jung if you don't believe me.
A loop anywhere is susceptible to emitting and receiving interference.
Twist all Flow and Return pairs, even the DC where they can become inputs.
The dual polarity DC power to an amplifier has a Zero Volts wire. This carries the Return supply current when the two rails currents are not identical. This makes the two wire DC actually a DC triplet.
Twist this as a triplet all the way from the PSU to the amplifier/opamp.
as he said TWIST EVERYTHING !
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Thank you very much, Bonsai. I clicked on your link ... and then clicked on "Preamplifers" which took me to the same page on your site that I had got to before. This time, though, when I clicked on the RIAA link ... after a short delay it came up - and I have printed it off. So thanks.
Now, on your page you say "I use LTSpice". If you know how to drive LTSpice, I would be very grateful if you could explain to me how to get a table of the 1st 10 harmonic distortion levels ... I have spent a couple of weeks playing around with this but have not been able to achieve it.
I've PMed you my email address; if you're willing to help me then please respond with your email address and I will email you my circuit. You could then add to the circuit whatever commands I am missing (that generate the HD table).
Thanks,
Andy
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