Hello
I am curious if anyone has experience with tweaking the RIAA transfer function of a phono preamp to account for the frequency response of a particular dedicated cartridge.
For example, below is the measured frequency response of a Denon DL103R:
Could a low-Q bandpass filter be inserted in the network to compensate for the drooping response around 6.5kHz? Or is this just splitting hairs over a few decibels?
Best regards,
Benjamin
I am curious if anyone has experience with tweaking the RIAA transfer function of a phono preamp to account for the frequency response of a particular dedicated cartridge.
For example, below is the measured frequency response of a Denon DL103R:
An externally hosted image should be here but it was not working when we last tested it.
Could a low-Q bandpass filter be inserted in the network to compensate for the drooping response around 6.5kHz? Or is this just splitting hairs over a few decibels?
Best regards,
Benjamin
Curious as to how this was measured. Most cartridges really are not flat, the better ones may come within just a couple of dB overall. Since every cartridge is a bit different (sample to sample, model to model, etc.) I suspect this is probably more trouble than it is worth..
Here's the thread I lifted the image from:
Turntable Forum • Denon Dl-103r Any Users Here?
I understand I'm arguably considering what amounts to a tone control, but the concept has me curious. Seems like a worthwhile experiment when one considers the lengths we go to to have .1dB RIAA EQ and optimal cartridge loading. A dedicated phono preamplifier is not too far out...
Turntable Forum • Denon Dl-103r Any Users Here?
I understand I'm arguably considering what amounts to a tone control, but the concept has me curious. Seems like a worthwhile experiment when one considers the lengths we go to to have .1dB RIAA EQ and optimal cartridge loading. A dedicated phono preamplifier is not too far out...
Hi, yeah you could tinker with the HF component/s of the RIAA circuit, and/or the input Resistor and/or Capacitor.
As kevinkr says "I suspect this is probably more trouble than it is worth" though !
As kevinkr says "I suspect this is probably more trouble than it is worth" though !
P.S. I found a chart that I had measured for 103R myself once through active only phono circuitry. That is in stereo pink noise test record track. The FFT was in octave weighting mode, owes to result flat with textbook pink noise signal. Left is black right is red. The last octave differentiation in mechanical resonance shape (tip mass to vinyl, cantilever & suspension behavior) its either manufacturing tolerance between channels or arm/antiskating influence or all of those combined.
Attachments
Looks like about +3, -2dB excluding the most extreme effects of the ultrasonic resonance.. This IMHO is in line with FR tolerance of relatively inexpensive MC cartridges.
I have 3 different Ortofon SPUs and only the Royal N is guaranteed to do substantially better this, my other two probably fall into that window more or less.
DF96's suggestion for a tilting tone control I think is the best fit if you are going to go to any trouble to correct this. Google the Quad 33/34 for details and schematics for a tilting tone control. If you are into tubes SY had a vacuum tube version of the circuit which is somewhere around here.
I have 3 different Ortofon SPUs and only the Royal N is guaranteed to do substantially better this, my other two probably fall into that window more or less.
DF96's suggestion for a tilting tone control I think is the best fit if you are going to go to any trouble to correct this. Google the Quad 33/34 for details and schematics for a tilting tone control. If you are into tubes SY had a vacuum tube version of the circuit which is somewhere around here.
I think I found it:
Funny, I plan on building SY's His Master's Noise when I finish my Lenco build. Was planning on an Audiomods arm with the DL103R, which seems like a good fit for Stuart's phono stage.
Thanks for all the help and Salas for the additional measurements.
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I had done a recent measurement of the 103R after the TT and arm got tweaked and I did not see a tilt again, only better last octave control. http://www.diyaudio.com/forums/analogue-source/129126-simplistic-njfet-riaa-1179.html#post3789529
Erik Margan wrote an article on this subject. He writes for Linear Audio magazine.
http://www-f9.ijs.si/~margan/Audio/Ironing_RIAA.pdf
http://www-f9.ijs.si/~margan/Audio/Ironing_RIAA.pdf
It's always struck me as odd that we go to great lengths to get flat RIAA response, yet some popular cartridges (I won't mention any names) are real turds when it comes to frequency response. I charitably refer to them as having a particular "house sound". The cartridges I like are usually very flat. It seems entirely possible to "fix" some bad ones, but because the response shapes aren't smooth, the circuitry might be complex and applicable to a single cartridge. A tilt control seems useful but I don't know what circuits produce well behaved tilt over the entire audio range.
With moving magnet and related types yes. MC cartridges generally are much less critical wrt capacitance. (within reason)
Capacitance and load resistance matter, but typically only at the very top end. The lower frequency response variations I've seen could only be corrected by shorting the cartridge out entirely and turning on a radio. 😀
Mr. Hagerman has a webpage on cartridge loading. You can theoretically determine the response by modeling the cartridge as a low pass filter and calculating the Q and cutoff frequency. Neither of those calculations are difficult. Mr. Stegal also has a webpage on the subject but he really makes the calculations difficult.
Hagerman Technology LLC: Cartridge Loading
Website of Wayne Stegall - Phono Termination Calculations and Calculator
Hagerman Technology LLC: Cartridge Loading
Website of Wayne Stegall - Phono Termination Calculations and Calculator
The problem with these calculators is that they don't take into account the very significant mechanical resonance. Adjusting for a flat electrical response will not generally result in a flat overall (electrical plus mechanical) response.
I would want to preserve the HF response above 20khz better than Margan does, and a little lag and partial notching could easily give a flat response out to past 30khz in his example.
If I understand Hagerman right, he suggests taking capacitance as low as you can possible get it, then adjusting response with the load resistance. You end up with a very non-standard non-47k. I've never heard of anybody doing that, or how it sounded.
BTW, I measure my carts with a known accurate RIAA preamp and the old CBS STR-100 test record. You can use a meter, but the most reliable method for me has been to record the tracks to the computer at 96k or higher, then measure in software like Audacity.
BTW, I measure my carts with a known accurate RIAA preamp and the old CBS STR-100 test record. You can use a meter, but the most reliable method for me has been to record the tracks to the computer at 96k or higher, then measure in software like Audacity.