I have built the venerable Elektor Supra Phono stage..(circuit shown here...http://www.diyaudio.com/forums/group-buys/266887-supa-phono-preamplifier-pcb.html)
I have the original data and build info and it quotes input impedance as 49k/280pf then says this is adjustable via C1 and R1.
C1 is 4p7 so how can loading be both 280pf and 4p7 ?
If the input capacitance is 280 pf then adding any cable capacitance would result in a value almost too high for any modern cartridge..
If it is 4p7 then ???
Any illumination would be appreciated.🙂
I have the original data and build info and it quotes input impedance as 49k/280pf then says this is adjustable via C1 and R1.
C1 is 4p7 so how can loading be both 280pf and 4p7 ?
If the input capacitance is 280 pf then adding any cable capacitance would result in a value almost too high for any modern cartridge..
If it is 4p7 then ???
Any illumination would be appreciated.🙂
The input impedance of the phono amplifier is 56K||4,7pF.
The correct input impedance and capacity for an pick up is usually written in the manual (of the pick up).
The correct input impedance and capacity for an pick up is usually written in the manual (of the pick up).
Thank you for that.
My cartridge is a Nagaoka MP-150 which is listed as 47k||<150pf.
Using 300mm Van Den Hul 502 interconnect @75pf/mtr plus whatever tonearm cable is (Well Tempered Arm. Classic original) lets say 50pf ? Then total loading is 4p7+22+50=76.7 give or take a smidgen.
Using the Vinyl Engine calculator...Cartridge Database Tools - Vinyl Engine
This puts resonance at 23 kHz and optimum loading of 89R does that seem correct..? anyone..?
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Is that a MM or MC system?
4p7+22,5pf (for the cable) + 50 pf (for the tonearm cable).
56K is the input impedance of the phono stage.
1/56K + 1/R = 1/47k
R=292 444 Ohm
4p7+22,5pf (for the cable) + 50 pf (for the tonearm cable).
56K is the input impedance of the phono stage.
1/56K + 1/R = 1/47k
R=292 444 Ohm
Most of the input capacitance will be from parasitic capacitance in the input transistors.DRONE7 said:
I'm not sure what the 4p7 cap does, as it will be swamped by the transistors. Maybe it is just a placeholder for those with Ortofon cartridges who may need to add extra capacitance.
Hi,
I'm with DF96 on 4p7 being a place holder, and have to question
the lack of of any effective radio suppression on the phono input.
I don't know what that calculator is calculating but the result
is 89K not 89R. FWIW adjusting the 47K load is often more
effective than playing with parallel capacitance.
rgds, sreten.
I'm with DF96 on 4p7 being a place holder, and have to question
the lack of of any effective radio suppression on the phono input.
I don't know what that calculator is calculating but the result
is 89K not 89R. FWIW adjusting the 47K load is often more
effective than playing with parallel capacitance.
rgds, sreten.
Calculators like that can be misleading- the electrical response is only half the story since it ignores the mechanical response. These interact to give you an overall flat response when the loading is correct. I'd follow the manufacturer's loading recommendations, then check frequency response with a test record or two if you're unsure.
When I see all those transistors in parallel I think big Miller effect capacity. I admired the 2SK147 jfet because of it's low noise but it had a big interdigitated gate and 15 pF gate to drain capacity. Big Miller effect.
Thanks all for the illuminating replies !
To summarise...The multiple transistors and resulting Millar effect/capacitance means the quoted value of 280pf by the circuit designer is likely correct..? Yikes !
The 4p7 is the lowest commonly available place-holder but anything here should be added to overall capacitance..?
So my loading as it stands is 284.7+22+50=361.7pf and the relatively high 613mH of the MP-150 means the resonance will be well within the audible band ?
If so I may have to visit the loft and unpack some older cartridges for experimenting.
Any other suggestions or comments on these assumptions would be most welcome. 🙂
To summarise...The multiple transistors and resulting Millar effect/capacitance means the quoted value of 280pf by the circuit designer is likely correct..? Yikes !
The 4p7 is the lowest commonly available place-holder but anything here should be added to overall capacitance..?
So my loading as it stands is 284.7+22+50=361.7pf and the relatively high 613mH of the MP-150 means the resonance will be well within the audible band ?
If so I may have to visit the loft and unpack some older cartridges for experimenting.
Any other suggestions or comments on these assumptions would be most welcome. 🙂
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Again, it's important to NOT ascribe anything significant to the electrical resonance! It's only half the picture, and a misleading half if you don't know what the mechanics are. And you don't (nor likely does anyone else here).
Your capacitance (remember to add in the cable capacitance) is far too high if the manufacturer indeed recommends 150pF. Look for a different preamp with low input C to optimize this cartridge.
Your capacitance (remember to add in the cable capacitance) is far too high if the manufacturer indeed recommends 150pF. Look for a different preamp with low input C to optimize this cartridge.
Thanks SY ! I am grateful to have my wild assumptions confirmed. 😀
Agree with the mechanical comments and having spent a great deal of time trying to optimise this cartridge on my Well Tempered arm (plenty of adjustments here 😉) to no avail I needed to get some insight into electrical loading match/mismatch.
I have another phono stage but suspect from listening that this too is incompatible.
Will try another cartridge but am open to recommendations of other phono stages I could build ! 🙂
Agree with the mechanical comments and having spent a great deal of time trying to optimise this cartridge on my Well Tempered arm (plenty of adjustments here 😉) to no avail I needed to get some insight into electrical loading match/mismatch.
I have another phono stage but suspect from listening that this too is incompatible.
Will try another cartridge but am open to recommendations of other phono stages I could build ! 🙂
The mechanics I was referring to won't be much affected by the arm, it's built into the cartridge (tip, cantilever, magnet/iron). What happens is that, if you ignore the electrical response, there will be a droop at high frequencies. The electrical response is then adjusted to peak in the treble at the correct frequency and amplitude so that the overall response (electrical plus mechanical) is flat. If the loading is wrong, the two responses won't be complementary and (depending on the loading) can end up either peaking too much or having a large saddle in the upper midrange.
For the MM I use (Audio-Technical 150MLX), having the load capacitance too high causes a severe HF peak, and not surprisingly, there's lots of reports about the cartridge being "too bright." When the recommended load capacitance is low (150pF or less), matching can be a challenge! I ended up designing my own MM preamp to overcome this issue and (no surprise) the cartridge sounds very tonally neutral rather than bright.
For the MM I use (Audio-Technical 150MLX), having the load capacitance too high causes a severe HF peak, and not surprisingly, there's lots of reports about the cartridge being "too bright." When the recommended load capacitance is low (150pF or less), matching can be a challenge! I ended up designing my own MM preamp to overcome this issue and (no surprise) the cartridge sounds very tonally neutral rather than bright.
and a rolled off top is what I am experiencing with the Nagaoka and the Supra phono stage.
Like sitting behind the speakers instead of in front of them.
No amount of arm adjustment addresses this and now from the comments on this thread I have some insight as to why.
I may not be happy but I am enlightened..🙂
Just unpacked the 'used but not dead yet ' cartridge archive and found a Grado Gold (45mH !) and a long forgotten Koetsu Rosewood ! (ah, the excesses of youth...long before the responsibilities of home and family.)
I plan to try the Grado next as I seem to recall it had a little stylus life left... Changing the Supra gain and loading for the Koetsu could be fun too..😉
I started the Supra build over ten years ago but had to shelve it due to other commitments and house moves 😱
I would at least like to hear it at its best before I move on to a replacement.!
Many thanks for the continued guidance.
If you model the cartridge as a low pass filter, the formula for the approximate electrical Q is Q=Rl SQRT(C/L). Rl is the load resistor, C the terminating capacity and L the cartridge inductance and SQRT means square root. As you see, the Q increases with increased capacity and load resistance.
But absent knowing the mechanical response, this is not a useful thing to know.
I always tried to obtain the maximally flat magnitude electrical response. I figured there was nothing I could do about the mechanical response because I'm not Mr. Grado or Van Den Hul.
Because the mechanical response is not ideal, the electrical response must be adjusted from its ideal
to compensate for that, and to give a net flat response.
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The only thing that matters is the overall response. Making the electrical response flat is a sure path to subpar results.
Precisely.
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