Maybe some of you guys can help me out with my issues.
Some time ago my Pioneer C-90 died. Have been satisfied for ages, especially it´s MC input, which in my ears sounded fantastic. But life goes on🙂.
I replaced it in a hurry with a second hand Project Tube Box SE II, just to be able to play my records, having bought the new Vincent SAT-7 (which doesn´t have a riaa). It sounds pretty decent with my Sumiko Palo Santos.
I also just for fun bought a Yaqin MS-23, and while waiting for my Silk MC-220A step-up transformers, I tried to plug it directly into the MM input (there are no others), and despite of the missing gain, it sounded surprisingly
good.
Here the Silks arrive, put them in front of the Yaqin, and what a dissapointment. It´s like hearing Joe Bonamassa playing guitar, fantastic technique, but no soul. Then tried the Phono Box in MM position and the Silk´s in front, and WOW......Wide open soundstage, warm and involving sound, the smile getting bigger and bigger.
I discussed this with a couple of friends, who have had the same experience with Lunddahl, Cinemag, Partridge and others. SUT´s in front of Solid State = Super, in front of tube riaa´s the magic dissapears. This made me put my DIY clone of AR´s PH-3 on hold, until I find either an explanation or a solution to this mystery.
Would really like to hear from others who either share this with me or have a solution, I´ve overlooked.
Forgot to say, that I have absolutely no noise issues. Connected correct groundwise, the Silk´s are dead silent with not the slightest hum or noise.
Some time ago my Pioneer C-90 died. Have been satisfied for ages, especially it´s MC input, which in my ears sounded fantastic. But life goes on🙂.
I replaced it in a hurry with a second hand Project Tube Box SE II, just to be able to play my records, having bought the new Vincent SAT-7 (which doesn´t have a riaa). It sounds pretty decent with my Sumiko Palo Santos.
I also just for fun bought a Yaqin MS-23, and while waiting for my Silk MC-220A step-up transformers, I tried to plug it directly into the MM input (there are no others), and despite of the missing gain, it sounded surprisingly
good.
Here the Silks arrive, put them in front of the Yaqin, and what a dissapointment. It´s like hearing Joe Bonamassa playing guitar, fantastic technique, but no soul. Then tried the Phono Box in MM position and the Silk´s in front, and WOW......Wide open soundstage, warm and involving sound, the smile getting bigger and bigger.
I discussed this with a couple of friends, who have had the same experience with Lunddahl, Cinemag, Partridge and others. SUT´s in front of Solid State = Super, in front of tube riaa´s the magic dissapears. This made me put my DIY clone of AR´s PH-3 on hold, until I find either an explanation or a solution to this mystery.
Would really like to hear from others who either share this with me or have a solution, I´ve overlooked.
Forgot to say, that I have absolutely no noise issues. Connected correct groundwise, the Silk´s are dead silent with not the slightest hum or noise.
No, because I haven´t built in the secondary loading yet.
Without any modification, that would be around 470 ohm, where as the 1:20 is more like around 107-110 ohm, and suits my cartridge a whole lot better soundwise.
Without any modification, that would be around 470 ohm, where as the 1:20 is more like around 107-110 ohm, and suits my cartridge a whole lot better soundwise.
If your phono preamp input impedance is 47K, without nothing connected to the MC step up transformers
1:10 ratio = 47K:10 = 470 ohms
1:20 ratio = 47K:20 = 2.350 ohms
That's the impedance seen by your cartridge.
1:10 ratio = 47K:10 = 470 ohms
1:20 ratio = 47K:20 = 2.350 ohms
That's the impedance seen by your cartridge.
It might suit the cartridge better in terms of load impedance, but the source impedance and the specifications of the SUT might not suit.
Try to optimize the load impedance in 1:10, not so difficult.
Pieter was first.
That´s as stated by Sumiko, but not neccesarily a fact in the living room. In 1:10 position, the treble is untamed and too bright.
Instead of discussing theory, I wanted to hear from people with some experience, since I´ve learned, that I´m not alone with this problem. I need to find out the reason.
That´s as stated by Sumiko, but not neccesarily a fact in the living room. In 1:10 position, the treble is untamed and too bright.
Instead of discussing theory, I wanted to hear from people with some experience, since I´ve learned, that I´m not alone with this problem. I need to find out the reason.
Jensen text:
"Thanks for contacting Jensen Transformers.
There is no simple way to calculate the series RC damping networks for
microphone input transformers. Interwinding capacitance is not important,
it is distributed capacitance within the windings that matters, and this is
not an easily measurable quantity. Also, the transformer needs to be damped
with all of the circuit stray capacitances and loads in place around the
transformer. This is especially true with tube circuit designs where the
"miller" capacitance of the first stage may be VERY significant. The
simplest way to determine the proper damping network for a microphone input
transformer is experimentally. The method is actually quite simple and
fast once that you have done it a couple of times and have gotten together
the proper kit of tools to make it easy.
SETUP:
1) Drive the microphone input with a squarewave generator that has a
source impedance of 150 Ohms. This value is approximately in the middle of
the range of source impedances common to most microphones. If you have a
special situation where the microphone is going to have a known, much lower
impedance (say 20 Ohms), use this impedance instead. Make sure that the
output signal from the generator has nice clean, fast edges with no overshoot.
2) Set the generator for a signal level of approximately 0.1 Volts peak to
peak and a frequency of approximately 5 to 10 kHz.
3) Power the microphone pre-amp and adjust the gain to a level about 10dB
below clipping. The level isn't real critical, just make sure that the
pre-amp is operating in a normal gain range and that it isn't clipping.
4) Connect an oscilloscope across the secondary of the input transformer
using a x10 low capacitance oscilloscope probe. You MUST use a x10 probe in
order to prevent adding SIGNIFICANT capacitance across the secondary of the
transformer. Make sure that you have "calibrated" the oscilloscope probe
trimmer capacitor before starting this procedure.
5) Connect a capacitor substitution box in series with a 20k or 50k pot
and place this network across the secondary of the transformer. You may
also want to include a 1k pot in series with the 20k pot as a "fine"
adjustment control. The capacitor substitution box should have a range of
100pF to about 10,000pF for typical microphone input transformers. Extra
capacitors can be added in parallel if you need larger values. Standard 10%
value increments (100pF, 120pF, 150pF etc.) should provide enough
resolution for even "fussy" tweaking.
6) Make sure that the basic impedance determining load resistor is in
place across the secondary of the transformer. This value is typically 1500
Ohms x the turns ratio squared (for example our JT-115K-E uses 1500 Ohms x
10 x 10 = 150kOhms). This resistor sets the input impedance of the
microphone pre-amp.
ADJUSTMENT PROCEDURE:
1) Set the capacitor substitution box to the highest value (1000pF to
10,000pF) and adjust the pot for maximum resistance value (20k to 50k).
2) While watching the oscilloscope, lower the value of the pot. This
should decrease the overshoot of the waveform and reduce the ringing.
Adjust the pot for the highest value that will prevent all the overshoot
and ringing.
3) The objective now is going to be to find the SMALLEST value of
capacitance and the HIGHEST value of resistance that will eliminate all the
overshoot and ringing and leave just a smooth, flat topped squarewave with
a nice fast rising edge.
4) Keep decreasing the value of the capacitance and re-tuning the pot
until you can no longer eliminate the ringing and overshoot by adjusting
the pot. Go back to the last higher value of capacitance and do a final
tweak of the pot and then measure the final resistance value. These values
are your final damping network.
NOTE: Some transformers will have very high frequency, very small amplitude
ringing in addition to the main lower frequency, large amplitude ringing.
You will probably NOT be able to tweak this effect out of the transformer,
but it is usually not anything to worry about because it is so far removed
from the audio frequency range and results in only a small fraction of a
dB of frequency response variation at a point where the transformer
response is already 10dB or 20dB down from reference level.
Dale Roche - Project Engineer "
"Thanks for contacting Jensen Transformers.
There is no simple way to calculate the series RC damping networks for
microphone input transformers. Interwinding capacitance is not important,
it is distributed capacitance within the windings that matters, and this is
not an easily measurable quantity. Also, the transformer needs to be damped
with all of the circuit stray capacitances and loads in place around the
transformer. This is especially true with tube circuit designs where the
"miller" capacitance of the first stage may be VERY significant. The
simplest way to determine the proper damping network for a microphone input
transformer is experimentally. The method is actually quite simple and
fast once that you have done it a couple of times and have gotten together
the proper kit of tools to make it easy.
SETUP:
1) Drive the microphone input with a squarewave generator that has a
source impedance of 150 Ohms. This value is approximately in the middle of
the range of source impedances common to most microphones. If you have a
special situation where the microphone is going to have a known, much lower
impedance (say 20 Ohms), use this impedance instead. Make sure that the
output signal from the generator has nice clean, fast edges with no overshoot.
2) Set the generator for a signal level of approximately 0.1 Volts peak to
peak and a frequency of approximately 5 to 10 kHz.
3) Power the microphone pre-amp and adjust the gain to a level about 10dB
below clipping. The level isn't real critical, just make sure that the
pre-amp is operating in a normal gain range and that it isn't clipping.
4) Connect an oscilloscope across the secondary of the input transformer
using a x10 low capacitance oscilloscope probe. You MUST use a x10 probe in
order to prevent adding SIGNIFICANT capacitance across the secondary of the
transformer. Make sure that you have "calibrated" the oscilloscope probe
trimmer capacitor before starting this procedure.
5) Connect a capacitor substitution box in series with a 20k or 50k pot
and place this network across the secondary of the transformer. You may
also want to include a 1k pot in series with the 20k pot as a "fine"
adjustment control. The capacitor substitution box should have a range of
100pF to about 10,000pF for typical microphone input transformers. Extra
capacitors can be added in parallel if you need larger values. Standard 10%
value increments (100pF, 120pF, 150pF etc.) should provide enough
resolution for even "fussy" tweaking.
6) Make sure that the basic impedance determining load resistor is in
place across the secondary of the transformer. This value is typically 1500
Ohms x the turns ratio squared (for example our JT-115K-E uses 1500 Ohms x
10 x 10 = 150kOhms). This resistor sets the input impedance of the
microphone pre-amp.
ADJUSTMENT PROCEDURE:
1) Set the capacitor substitution box to the highest value (1000pF to
10,000pF) and adjust the pot for maximum resistance value (20k to 50k).
2) While watching the oscilloscope, lower the value of the pot. This
should decrease the overshoot of the waveform and reduce the ringing.
Adjust the pot for the highest value that will prevent all the overshoot
and ringing.
3) The objective now is going to be to find the SMALLEST value of
capacitance and the HIGHEST value of resistance that will eliminate all the
overshoot and ringing and leave just a smooth, flat topped squarewave with
a nice fast rising edge.
4) Keep decreasing the value of the capacitance and re-tuning the pot
until you can no longer eliminate the ringing and overshoot by adjusting
the pot. Go back to the last higher value of capacitance and do a final
tweak of the pot and then measure the final resistance value. These values
are your final damping network.
NOTE: Some transformers will have very high frequency, very small amplitude
ringing in addition to the main lower frequency, large amplitude ringing.
You will probably NOT be able to tweak this effect out of the transformer,
but it is usually not anything to worry about because it is so far removed
from the audio frequency range and results in only a small fraction of a
dB of frequency response variation at a point where the transformer
response is already 10dB or 20dB down from reference level.
Dale Roche - Project Engineer "
Some of the problem may revolve around miller capacitance (input capacitance) in the tube phono stage which is why all of my phono stages use cascode front ends now. The problem is that if for example the input capacitance is 200pF and the SUT step up ratio is 1:10 the cartridge will see 100X the capacitance at the phono stage input, that's starting to be significant or about 0.02uF, add significant cable capacitance between the transformer and the phono stage and it could be much worse..
In theory given the low source impedance of LOMC cartridges the additional capacitance shouldn't be a problem - unfortunately IMVLE I've found that anything I can do to reduce the capacitance on the high impedance side of the SUT seems to improve the HF performance significantly.
Loading can be quite critical as well, you will need to experiment a bit to find the optimum load resistance for the cartridge/SUT/phono pre combo.
In theory given the low source impedance of LOMC cartridges the additional capacitance shouldn't be a problem - unfortunately IMVLE I've found that anything I can do to reduce the capacitance on the high impedance side of the SUT seems to improve the HF performance significantly.
Loading can be quite critical as well, you will need to experiment a bit to find the optimum load resistance for the cartridge/SUT/phono pre combo.
No other way: use the scope, signal generator and phono pre like I did.
http://www.diyaudio.com/forums/analogue-source/290983-jensen-jt-44k-dx-mc-step-up-loading-doubt-7.html
http://www.diyaudio.com/forums/analogue-source/290983-jensen-jt-44k-dx-mc-step-up-loading-doubt-7.html
Thanks for your input, and I will, just haven´t gotten around to it yet. Found a calculator online somewhere, and figured, that 17,8 Kohm parallel on the secondary would give the cartridge a loading of 100 ohm. But still I can´t think, that me and a couple of friends are the only ones to experinec this (SS vs. Tube riaa´s)???
I agree miller capacitance plays a role here.
Can be the resistance of the transformer with the capacitor forms a low pass filter?
Last edited:
No.
There´s absolutely nothing wrong with the frequency extensions, it´s just like some of the "magic" is missing compared to solid state riaa´s.
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