I've been looking at many tubed circuits for an MC cartridge.
The 6DJ8/6922 seems to be used by some.
I was wondering if the 6922 can be used without any cathode resistor. Only one resistor from anode to supply ( say 68K ) and one resistor from grid to ground ( say 2 K ).
It seems to work in a simulation but is this a meaningful configuration for an MC input ( max input say 20mV on severe peaks )? I remember seeing some tubes with no cathode resistor somewhere on the web. A zero volt grid bias works for some situations in some tubes. Since MC signals are very low and I assumed they may work in the linear region for low negative swings at the grid , typically less than 2mV max for a cartridge sensitivity of 0.2mV @5cm/sec .
Any opinions?
Cheers.
The 6DJ8/6922 seems to be used by some.
I was wondering if the 6922 can be used without any cathode resistor. Only one resistor from anode to supply ( say 68K ) and one resistor from grid to ground ( say 2 K ).
It seems to work in a simulation but is this a meaningful configuration for an MC input ( max input say 20mV on severe peaks )? I remember seeing some tubes with no cathode resistor somewhere on the web. A zero volt grid bias works for some situations in some tubes. Since MC signals are very low and I assumed they may work in the linear region for low negative swings at the grid , typically less than 2mV max for a cartridge sensitivity of 0.2mV @5cm/sec .
Any opinions?
Cheers.
Use a searching engine - tipe 6922 or mc-hamer if I recal corectly. You will find two almost same designs of mc step up signal circuit. Hampton mc using 84 reg. DC voltage, or another by Frank using ccs PS. Grid to ground should be 10-150 ohm (cartridge ?), anode res. depending on PSU typ (paralel 2x 47kOhm in Hampton). No cathode resistors on boath.
Thanks.
Hi Frank and Marijan,
Thanks for your really fast response. I will try out the circuit. I have to get a pcb made first ( at home ).
I might be able to select the tubes as I have a few at hand. The CCS may be a problem though. I have some other devices. I will try those . But again I might prefer to try a plain resistor.
I remember Hugh saying that he prefered the sound of a resistor load to a CCS load. Am I right ?
Thanks again.
Cheers.
Ashok.
Hi Frank and Marijan,
Thanks for your really fast response. I will try out the circuit. I have to get a pcb made first ( at home ).
I might be able to select the tubes as I have a few at hand. The CCS may be a problem though. I have some other devices. I will try those . But again I might prefer to try a plain resistor.
I remember Hugh saying that he prefered the sound of a resistor load to a CCS load. Am I right ?
Thanks again.
Cheers.
Ashok.
Hi,
Perhaps he said so in general, but here it's essential to have very high PSRR.
Any CCD or JFET having an Idss of 1mA should do as well.
The BF244As I select as well for equal current and low noise.
I never use any PCBs as I feel the can degrade the sound.
Moreover, by using P2P it leaves me room to fool around with the coupling cap and loadresistor for instance.
Marjan built the Hampton MC which should be a fine cct for all but the lowest output MCs.
Cheers,
Perhaps he said so in general, but here it's essential to have very high PSRR.
Any CCD or JFET having an Idss of 1mA should do as well.
The BF244As I select as well for equal current and low noise.
I never use any PCBs as I feel the can degrade the sound.
Moreover, by using P2P it leaves me room to fool around with the coupling cap and loadresistor for instance.
Marjan built the Hampton MC which should be a fine cct for all but the lowest output MCs.
Cheers,
Yes, Ashok,
I did say that! Different sonics......
I've tried both and much prefer resistive loading.
A tube is effectively a variable resistor, a rheostat, with its resistance controlled by a high impedance voltage at the grid.
If the tube operates in constant current (as it does, within narrow confines, with an inductive load as well), then the voltage output at the plate is extremely linear because the control voltage is not changing the current. It's plate voltage output at constant current for different grid voltages after all. This makes for great accuracy, and complete transparency, something many love. However, with a plate resistor, generally fixed between two and four times the plate resistance, both the plate voltage and the current are changing with signal. This ain't so linear...
This means that there is more distortion with a plate resistor. Oddly enough, since the introduced distortion is H2 and H3, both commonly found in music, this richens the sound and many people love the sound, muttering things like, 'Ah, there's that tube sound, don't you love the rich structure of the music?'
For me, it's like wine. People talk red but drink white. They hate distortion, go for vanishingly low figures, but LOVE tubes. And when you remove the hood, you find a string of plate loaded triodes. To me, this is the clincher.
So, my point would be this: why go for a CCS with a tube so you finish with complete transparency, like excellent SS?? I say the hamburger is a washout unless it has egg, onions, hot chilli sauce and a dash of mustard...
Nice circuit, Frank!
Cheers,
Hugh
I did say that! Different sonics......
I've tried both and much prefer resistive loading.
A tube is effectively a variable resistor, a rheostat, with its resistance controlled by a high impedance voltage at the grid.
If the tube operates in constant current (as it does, within narrow confines, with an inductive load as well), then the voltage output at the plate is extremely linear because the control voltage is not changing the current. It's plate voltage output at constant current for different grid voltages after all. This makes for great accuracy, and complete transparency, something many love. However, with a plate resistor, generally fixed between two and four times the plate resistance, both the plate voltage and the current are changing with signal. This ain't so linear...
This means that there is more distortion with a plate resistor. Oddly enough, since the introduced distortion is H2 and H3, both commonly found in music, this richens the sound and many people love the sound, muttering things like, 'Ah, there's that tube sound, don't you love the rich structure of the music?'
For me, it's like wine. People talk red but drink white. They hate distortion, go for vanishingly low figures, but LOVE tubes. And when you remove the hood, you find a string of plate loaded triodes. To me, this is the clincher.
So, my point would be this: why go for a CCS with a tube so you finish with complete transparency, like excellent SS?? I say the hamburger is a washout unless it has egg, onions, hot chilli sauce and a dash of mustard...
Nice circuit, Frank!
Cheers,
Hugh
Hi,
Thank you very much, Hugh.
Odd as it may seem, in the context of my all tubed gear, this CCSed part sounds the most tubey of all when heard in isolation.
Something I don't quite understand but seems to negate the tendency of most MCs towards a rising top end nicely.
Why it sounds like this, especially with a tube that can veer towards stridency like some ECC88s can is beyond me though.
Thanks to the CCS it also gets away with the seemingly rather poor PS whereas the phono stage proper is tightly regulated and has tremendous dynamic range .
So much so that it puts any CDP based system to shame.
Mind you, this circuit is obviously sensitive to layout which is one more reason I'd recmmend P2P here.
Certainly the Hampton is a candidate for improvement too as I think it was originally designed as a mike preamp service?
Again, thank you for the compliment.
I just hope many vinyl addicts will build and enjoy it.
Cheers,
Thank you very much, Hugh.
Odd as it may seem, in the context of my all tubed gear, this CCSed part sounds the most tubey of all when heard in isolation.
Something I don't quite understand but seems to negate the tendency of most MCs towards a rising top end nicely.
Why it sounds like this, especially with a tube that can veer towards stridency like some ECC88s can is beyond me though.
Thanks to the CCS it also gets away with the seemingly rather poor PS whereas the phono stage proper is tightly regulated and has tremendous dynamic range .
So much so that it puts any CDP based system to shame.
Mind you, this circuit is obviously sensitive to layout which is one more reason I'd recmmend P2P here.
Certainly the Hampton is a candidate for improvement too as I think it was originally designed as a mike preamp service?
Again, thank you for the compliment.
I just hope many vinyl addicts will build and enjoy it.
Cheers,
Hi,
Fair enough, an approximation of transparency can be achieved by marrying tubes and SS...in a way but what about dynamic range?
If I were to design SS devices I'd opt for high voltage device as they seem to sound more correct to me.
With tubes I'd go the same road and I'm talking 300VDC+ voltages, the diffrence is often made by the PS.
Cheers,
Fair enough, an approximation of transparency can be achieved by marrying tubes and SS...in a way but what about dynamic range?
If I were to design SS devices I'd opt for high voltage device as they seem to sound more correct to me.
With tubes I'd go the same road and I'm talking 300VDC+ voltages, the diffrence is often made by the PS.
Cheers,
Hi,
In my design, if you can call it mine, 24 to 40 VDC can be had at Vg0 for the ECC88/6DJ8.
Around and about 20dB depending.Why?
You don't need to care about that 47K resistor anyway...
Yes, which is why I insist on matching up to the moon, not just the tubes but the CCSs as well.
There's little point otherwise....
Cheers,
In my design, if you can call it mine, 24 to 40 VDC can be had at Vg0 for the ECC88/6DJ8.
Around and about 20dB depending.Why?
You don't need to care about that 47K resistor anyway...
Yes, which is why I insist on matching up to the moon, not just the tubes but the CCSs as well.
There's little point otherwise....
Cheers,
CCS vs resistor anode load
Hi Frank, Hugh and Sy,
I simulated the amp with a 6DJ8 .
1. The circuit had a 2k resistor from grid to ground and a 39 K resistor from anode to supply of 200 V. Load was 47K with 100pF in parallel ( my MM input stage impedance) coupled by a 1 uF capacitor.
2. The second circuit had a current source using an IRF9640 at the anode. Everything else the same.
The sim showed very low distortion but the CCS ckt had a slight increase in distortion as the harmonics went above the 4th and then started to drop again after the 7th or so.
The resistor load on the other hand kept dropping as the harmonics went up.
Wouldn't this result in a smoother relaxed sound from the resistor loaded circuit ? Or can the sim not be trusted ?
Thanks.
Hi Frank, Hugh and Sy,
I simulated the amp with a 6DJ8 .
1. The circuit had a 2k resistor from grid to ground and a 39 K resistor from anode to supply of 200 V. Load was 47K with 100pF in parallel ( my MM input stage impedance) coupled by a 1 uF capacitor.
2. The second circuit had a current source using an IRF9640 at the anode. Everything else the same.
The sim showed very low distortion but the CCS ckt had a slight increase in distortion as the harmonics went above the 4th and then started to drop again after the 7th or so.
The resistor load on the other hand kept dropping as the harmonics went up.
Wouldn't this result in a smoother relaxed sound from the resistor loaded circuit ? Or can the sim not be trusted ?
Thanks.
Ashok,
Without deprecating Frank's circuit, I believe you are right. Highish levels of H2 and H3, rapidly dropping thereafter, certainly do give a relaxed, full bodied sound, and are the hallmark of triode circuits.
If you listen to a lead guitar without amplification, you are struck by the thinness of the sound from the string. However, pass it through a Fender, with VERY high loading of the plate, and the sound becomes something very different. Many audiophiles like this sound, and indeed it is routinely associated with electric guitar.
The higher harmonics, albeit very low in magnitude, are discerned over a listening session as an almost subliminal unease. They reflect the highly non-linear behavior of current sources; we know that the triode is essentially blameless in the production of higher harmonics, at least past the 5th, and so a reasonable deduction is that this increase is in fact produced by the mosfet. It is not widely known but current sources have huge impact on sonics in routine amplifiers, and care must be taken that the CCS does NOT contribute to objectionable distortion. Any noise appearing on the base/gate of a CCS device will be amplified, as the device is in common emitter/source, so special care is needed to scotch this insidious, broadband noise. (Ashok, you are also seeing broadband noise, not just distortion products).
I feel jfet current sources are not the best, but they are the simplest. Fred Dieckmann has some strong views on CCS, and might be roped into this discussion......
You there Fred?
Cheers,
Hugh
Without deprecating Frank's circuit, I believe you are right. Highish levels of H2 and H3, rapidly dropping thereafter, certainly do give a relaxed, full bodied sound, and are the hallmark of triode circuits.
If you listen to a lead guitar without amplification, you are struck by the thinness of the sound from the string. However, pass it through a Fender, with VERY high loading of the plate, and the sound becomes something very different. Many audiophiles like this sound, and indeed it is routinely associated with electric guitar.
The higher harmonics, albeit very low in magnitude, are discerned over a listening session as an almost subliminal unease. They reflect the highly non-linear behavior of current sources; we know that the triode is essentially blameless in the production of higher harmonics, at least past the 5th, and so a reasonable deduction is that this increase is in fact produced by the mosfet. It is not widely known but current sources have huge impact on sonics in routine amplifiers, and care must be taken that the CCS does NOT contribute to objectionable distortion. Any noise appearing on the base/gate of a CCS device will be amplified, as the device is in common emitter/source, so special care is needed to scotch this insidious, broadband noise. (Ashok, you are also seeing broadband noise, not just distortion products).
I feel jfet current sources are not the best, but they are the simplest. Fred Dieckmann has some strong views on CCS, and might be roped into this discussion......
You there Fred?
Cheers,
Hugh
Real world test
Hi Hugh,
It would be nice if we can discuss this thoroughly .
I did notice that tubes have the least possible distortion with very high anode loads. The resistance is probably closest to being linear though not the highest load. CCS on the other hand can give very high ac loads but as you say , will also contribute their nonlinearities and other characteristics. So an otherwise potentially lower distortion will be swamped by their inherent weaknesses.
What would be interesting is to see how audible this is going to be. Listening tests can be very long drawn out affairs !
I can build the two circuits in the meantime and see if I can hear any differences easily. The resistor load is attractive as it is very simple and can't have any non linear or hf related problems.
I plan to use an Audio Technica AT30 MC cartridge that I currently have. Its a bit old but works well. I also have an AT step up transformer . Will have to do lots of listening I guess !
Thanks,
Ashok.
Hi Hugh,
It would be nice if we can discuss this thoroughly .
I did notice that tubes have the least possible distortion with very high anode loads. The resistance is probably closest to being linear though not the highest load. CCS on the other hand can give very high ac loads but as you say , will also contribute their nonlinearities and other characteristics. So an otherwise potentially lower distortion will be swamped by their inherent weaknesses.
What would be interesting is to see how audible this is going to be. Listening tests can be very long drawn out affairs !
I can build the two circuits in the meantime and see if I can hear any differences easily. The resistor load is attractive as it is very simple and can't have any non linear or hf related problems.
I plan to use an Audio Technica AT30 MC cartridge that I currently have. Its a bit old but works well. I also have an AT step up transformer . Will have to do lots of listening I guess !
Thanks,
Ashok.
Hi,
I measure 23 to 24VDC after the CCS, the B+ is 24VDC.
Gainscaling certainly is....I usually remove the 47K gridleak resistor of the MM stage.
By doing so the 1M bleeder at the output of the headamp becomes the gridleak of the phono preamp.
Soundwise I prefer it that way. I remember hooking up a tuner once to the MC headamp, taking the signal straight to the amp and it sounded rather too sweet to me.
In short, with the CCS it certainly doesn't sound like your typical 6DJ8 at all, no strident ear piercing.
Cheers,
I measure 23 to 24VDC after the CCS, the B+ is 24VDC.
Gainscaling certainly is....I usually remove the 47K gridleak resistor of the MM stage.
By doing so the 1M bleeder at the output of the headamp becomes the gridleak of the phono preamp.
Soundwise I prefer it that way. I remember hooking up a tuner once to the MC headamp, taking the signal straight to the amp and it sounded rather too sweet to me.
In short, with the CCS it certainly doesn't sound like your typical 6DJ8 at all, no strident ear piercing.
Cheers,
Not Frank but i certainly have an opinion on this You can't really use AC at these levels. It does sound different of course and even if you only use DC you'll notice significant difference in sound depending on use or not of regulator, type of regulator and type of capacitors. Apparently the cathode-heater capacitance is sufficient to couple all sorts of garbage.
You can't really use AC at these levels. It does sound different of course and even if you only use DC you'll notice significant difference in sound depending on use or not of regulator, type of regulator and type of capacitors. Apparently the cathode-heater capacitance is sufficient to couple all sorts of garbage.
Heater AC or DC
I have heard that AC sound's warmer than DC, however that might just be some one's BS. It does make since that a low noise dc regulator might be best on the gain stages, however I don't really know.
I have a couple of 50 watt Tube amps that I'm upgrading. I though that maybe changing to DC regulation for the input tubes and phase converter would be an improvment.
I have heard that AC sound's warmer than DC, however that might just be some one's BS. It does make since that a low noise dc regulator might be best on the gain stages, however I don't really know.
I have a couple of 50 watt Tube amps that I'm upgrading. I though that maybe changing to DC regulation for the input tubes and phase converter would be an improvment.
Hi,
Indeed it is...
The easiest way to find out is to simply tap the signal off the DC heater circuit and listen to it.
You won't like the sound of it but it proves that the coupling is for real.
When it works one way, it also works the other way around as it is capacitive coupling.
So, you'd want that heater supply as clean as a whistle especially at this kind of levels.
It does sound different, especially DHT or DHP will even show a different set of curves when you trace them fed from either AC or DC.
In general, I'd like to mix both ways of heating in a system.
Most of the time you just don't have a choice, unless you want to run the heaters off battery supplies, of course, which is a rather clean DC voltage depending on the type of battery you use.
AC is better for the tube's heater as it has a cleaning effect preventing notching. Whether you like AC or DC heating better is a matter of taste but if good signal to noise ratio is important then I'd recommend the use of DC and as Peter says different regulators have different sonic signatures.
Another way to go about is to use both a voltage reg. and a current reg.
It is said to sound the same as AC heating on a DHT without the induced hum penalty.
Personally I haven't tried that yet on my 2A3 amps so it's just hearsay as far as I'm concerned.
For an amp that's not humming I'd put my money elsewhere first...
Cheers,
Indeed it is...
The easiest way to find out is to simply tap the signal off the DC heater circuit and listen to it.
You won't like the sound of it but it proves that the coupling is for real.
When it works one way, it also works the other way around as it is capacitive coupling.
So, you'd want that heater supply as clean as a whistle especially at this kind of levels.
It does sound different, especially DHT or DHP will even show a different set of curves when you trace them fed from either AC or DC.
In general, I'd like to mix both ways of heating in a system.
Most of the time you just don't have a choice, unless you want to run the heaters off battery supplies, of course, which is a rather clean DC voltage depending on the type of battery you use.
AC is better for the tube's heater as it has a cleaning effect preventing notching. Whether you like AC or DC heating better is a matter of taste but if good signal to noise ratio is important then I'd recommend the use of DC and as Peter says different regulators have different sonic signatures.
Another way to go about is to use both a voltage reg. and a current reg.
It is said to sound the same as AC heating on a DHT without the induced hum penalty.
Personally I haven't tried that yet on my 2A3 amps so it's just hearsay as far as I'm concerned.
For an amp that's not humming I'd put my money elsewhere first...
Cheers,
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