I read an application note on Sowter where someone used a step up transformer for a Moving Magnet Cartridge as well as Moving Coil (where it is almost a must).
What would the detriments be if I had a unit made that took a 47k ohm primary and stepped it up to 235k (1:5 turns ratio)? The active circuitry would produce 25 dB of gain instead of 40 after RIAA to lower the noise floor.
For moving coil mode, I could add taps that step it up even higher.
Edcor makes small signal transformers that look to me as if they can perform this task. Given that they are unshielded, hum I suppose could be an issue if they are not enclosed in a chassis. One reason I like Edcor is they are made in the US, not China or Europe (high shipping costs).
What would the detriments be if I had a unit made that took a 47k ohm primary and stepped it up to 235k (1:5 turns ratio)? The active circuitry would produce 25 dB of gain instead of 40 after RIAA to lower the noise floor.
For moving coil mode, I could add taps that step it up even higher.
Edcor makes small signal transformers that look to me as if they can perform this task. Given that they are unshielded, hum I suppose could be an issue if they are not enclosed in a chassis. One reason I like Edcor is they are made in the US, not China or Europe (high shipping costs).
I suspect you'll find it seriously difficult to find a transformer that can deliver a decent bandwidth while achieving a 47k load! 😱
In fact, I suspect its winding resistance would be so high that the Johnson noise would actually be no better than the noise of the amplifier stage you would have used instead.
In fact, I suspect its winding resistance would be so high that the Johnson noise would actually be no better than the noise of the amplifier stage you would have used instead.
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Transformers
Hi, As much as I like Edcor transformers (great folks there) and use them in my designs exclusively they will not do well at what you are trying. I thought I could do something similar and found that the lack of shielding was a serious problem. To achieve the results I wanted I eventually used ones by Lundahl. They are designed for such applications and are well shielded with Mu metal. Yes there is a considerable price difference, but in this case IMO it is necessary and worth it.
Hi, As much as I like Edcor transformers (great folks there) and use them in my designs exclusively they will not do well at what you are trying. I thought I could do something similar and found that the lack of shielding was a serious problem. To achieve the results I wanted I eventually used ones by Lundahl. They are designed for such applications and are well shielded with Mu metal. Yes there is a considerable price difference, but in this case IMO it is necessary and worth it.
What do you think of the idea of a 1:5 ratio transformer after the RIAA stage? Between the RIAA and transformer is a current sourced cathode follower that allows the driving of 600 ohms. After that is another lower gain stage. Or yet, another CF followed by another transformer.
Hi,
1:5 will step up 47K to 1.2M, no transformer exists that will work well.
The nearest is 1:2.5 giving 47K to 294K, but I can't see the point.
rgds, sreten.
Note a MM is only a "47K" device inductively at high frequencies.
MC's don't have the inductance issues.
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No, what I mean is a cathode follower driving a transformer that steps 600 ohms up to 15000 ohms. This would appear after a passive RIAA stage. Another lower gain stage would appear after the transformer.
I once managed to order nice mic input transformers from ALTRAN directly. They were nice. 200 Ohm primary, 39K secondary. Usually they take big order from "brand names" known for their famous audio transformers. My friend in Israel used one pair of them for MC cartridges, and was impressed by results.
For MM you better go without any transformers. Just a 47K trimpot, because it is a good idea to start EQing before the 1'st stage to increase headroom that is vital due to the nature of scuffs and particles that produce fast and high peaks.
For MM you better go without any transformers. Just a 47K trimpot, because it is a good idea to start EQing before the 1'st stage to increase headroom that is vital due to the nature of scuffs and particles that produce fast and high peaks.
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Hi King!
Try a search fo Susan Parker and her Zeus amplifier. She uses this approach.
Thorsten
It seems like using passive components (transformers) will definitely raise the cost and add engineering shennigans of their own.
The only way to really know what will happen is to try it.
The only way to really know what will happen is to try it.
A transformer fed from 47k would need huge inductance for good LF response. That would mean high number of turns, high DC resistance, higher Johnson noise, large size, high inter winding capacitance, etc.
Yeah.. Why use a transformer when an Op-amp will do? This forum LOVES their OP-Amps. Use as many as possible and stuff it all in a Altoids box. It's not like you're concerned with sound quality or something. ~Oh wait...
The typical coil DCR of a MM cartridge is somewhere around 500 to 1500 ohms, is it not? Coil inductance would be in the 500mH to 1000mH area. What happens when you have a source with Zout of ~3k ohms feeding the primary of a transformer at tiny signal levels?
An HOMC like a Denon DL110 has output impedance of about 300 ohms. Also, the HOMC won't have the coil inductance an MM cart has. Would this be a better candidate for a low step-up ratio input transformer? Maybe 1:4 or something like that? 2.5mV nominal up to 10mV nominal. Would that be worth doing?
An HOMC like a Denon DL110 has output impedance of about 300 ohms. Also, the HOMC won't have the coil inductance an MM cart has. Would this be a better candidate for a low step-up ratio input transformer? Maybe 1:4 or something like that? 2.5mV nominal up to 10mV nominal. Would that be worth doing?
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Take a simple, but expensive and perfect 1:4 turns ratio step up transformer.
The secondary output impedance is 16 times the input impedance.
But that means that the capacitance of a tube amp input stage that is reflected back to the secondary, will be multiplied by 16 x.
A hypothetical triode that has grid to plate capacitance of 2pF, and has an in-circuit gain of 25, will have 1 + Gain = 1 + 25 = 51pF due to the Miller Capacitance Effect.
51pF x 16 = 816pF at the transformer primary.
A Shure Moving Magnet phono cartridge that has a suggested maximum load capacitance of 200pF, will see 816pF load from the transformer primary.
The cartridge will see over 4 times the recommended capacitance.
The numbers may vary somewhat from moving magnet cartridge to mm cartridge, and 1:4 transformer to transformer, but there is no free lunch here.
Transformers, yes.
Transformer for a 47k load rating mm cartridge, no.
Just my opinion
The secondary output impedance is 16 times the input impedance.
But that means that the capacitance of a tube amp input stage that is reflected back to the secondary, will be multiplied by 16 x.
A hypothetical triode that has grid to plate capacitance of 2pF, and has an in-circuit gain of 25, will have 1 + Gain = 1 + 25 = 51pF due to the Miller Capacitance Effect.
51pF x 16 = 816pF at the transformer primary.
A Shure Moving Magnet phono cartridge that has a suggested maximum load capacitance of 200pF, will see 816pF load from the transformer primary.
The cartridge will see over 4 times the recommended capacitance.
The numbers may vary somewhat from moving magnet cartridge to mm cartridge, and 1:4 transformer to transformer, but there is no free lunch here.
Transformers, yes.
Transformer for a 47k load rating mm cartridge, no.
Just my opinion
Thanks for the breakdown of how transformer action would magnify Miller effect. That is a deal killer for MM cartridges, right there.
But what about for a HOMC like Denon DL110, which 1) works well into a 1.5k load, and 2) is a moving coil, so has much lower coil inductance and so is not sensitive to load capacitance.
Going off topic, I know. Sorry about that.
But what about for a HOMC like Denon DL110, which 1) works well into a 1.5k load, and 2) is a moving coil, so has much lower coil inductance and so is not sensitive to load capacitance.
Going off topic, I know. Sorry about that.
I don't understand this. SUTs, "step up transformers" have used for decades with low output MC cartridges and are superior to active gain stages. There's no problem with bandwidth. Look at Denon, Etre, Sowter, RCA, Altec, Tamura, etc.
What is the typical voltage output of a MM cartridge?
Perhaps 5mV at the standard acceleration (I can not even remember the recording industry's standard acceleration number and acceleration units).
Then compare 5mV to the Denon DL110 MC cartridge voltage output at that same standard acceleration.
Suppose the Denon has 1mV, and the MM has 5mV.
You will need a 1:5 turns ratio step up transformer to get the same voltage from the Denon and transformer combination, as the bare bones MM cartridge.
Impedance is the square of the turns ratio, so the impedance ratio is 1:25.
Using the same example triode as my earlier post that has 51pF: 25 x 51pF = 1275pF at the 1:5 transformer primary.
1,275pF at 20kHz = 6,241 Ohms of capacitive reactance across the Denon MC cartridge.
Well, that is far larger than 1,500 Ohms but . . .
What is the Denon's coil inductance? You need to know that, so that you can calculate the resonance of that coil with the 1,275pF.
Resonant frequency = 1/(2 x pi x (Root of (L x C))).
The original post mentioned both MC And MM cartridges.
I suspect that not all MC cartridges have the same issues that other MC cartridges have.
I bet HOMC (High Output Moving Coil) cartridges have more inductance than low output MC cartridges have.
Without a coil inductance specification, we might be in the dark.
Perhaps 5mV at the standard acceleration (I can not even remember the recording industry's standard acceleration number and acceleration units).
Then compare 5mV to the Denon DL110 MC cartridge voltage output at that same standard acceleration.
Suppose the Denon has 1mV, and the MM has 5mV.
You will need a 1:5 turns ratio step up transformer to get the same voltage from the Denon and transformer combination, as the bare bones MM cartridge.
Impedance is the square of the turns ratio, so the impedance ratio is 1:25.
Using the same example triode as my earlier post that has 51pF: 25 x 51pF = 1275pF at the 1:5 transformer primary.
1,275pF at 20kHz = 6,241 Ohms of capacitive reactance across the Denon MC cartridge.
Well, that is far larger than 1,500 Ohms but . . .
What is the Denon's coil inductance? You need to know that, so that you can calculate the resonance of that coil with the 1,275pF.
Resonant frequency = 1/(2 x pi x (Root of (L x C))).
The original post mentioned both MC And MM cartridges.
I suspect that not all MC cartridges have the same issues that other MC cartridges have.
I bet HOMC (High Output Moving Coil) cartridges have more inductance than low output MC cartridges have.
Without a coil inductance specification, we might be in the dark.
Careful attention to original posts can sometimes eliminate so many postings, with the solution provided earlier rather than later.
Just my opinion.
Just my opinion.