He is hinting at the kathode resistance in parallel to the kathode resistor 😉
See MJ (3d) page 78 for formula.
See MJ (3d) page 78 for formula.
If I may, I'd put the volume pot on the input; no sense boosting the output Z. Also Agilent HLMP LED's are good for 30 mA and would do away with the need for resistance and capacitance in the cathode circuit.
I do like bigger output caps, 5 uF/440VAC motor runs by ASC are quite fine.
cheers,
Douglas
I do like bigger output caps, 5 uF/440VAC motor runs by ASC are quite fine.
cheers,
Douglas
Re post 13, 16, 18, 19, 21 and 22 - for the gentlemen in Holland it may be
adequate to quote from the excellent Philips textbook "Precision Electronics":
"The condition 2 π fmin Ck ≫ 1/Rk which is found in some books is incorrect."
The correct formula 2 π fmin Ck ≫ (μ +1)/(ri +Ra) takes the cathode
impedance into account. For the rare case Rk ≪ (μ +1)/(ri +Ra) no capacitor
is required.
adequate to quote from the excellent Philips textbook "Precision Electronics":
"The condition 2 π fmin Ck ≫ 1/Rk which is found in some books is incorrect."
The correct formula 2 π fmin Ck ≫ (μ +1)/(ri +Ra) takes the cathode
impedance into account. For the rare case Rk ≪ (μ +1)/(ri +Ra) no capacitor
is required.
I made a similar Preamp some time ago; I had the 6C19 running at 10mA but with CCS (IXCP10M45 ) for the anode load.
I still have some of them FS: IXCP fixed current high voltage current regulators
At present I’m converting it to DHT…
I still have some of them FS: IXCP fixed current high voltage current regulators
At present I’m converting it to DHT…
The volume control behind the stage is an error. It should be in front, at least with modern (younger than 40 years 😉) sources. Why amplify 2Veff to the max. with an open stage with amplified noise and possible newly created distortion? Only to attenuate it later, including the now introduced distortion? I may assume your digital source is 2Veff output at low Zout? That source needs no gain at all and thus only a straight wire. A phono preamp of very old standards is probably not 2Veff output so upping that level so it is nearly equal to the 2Veff standard of the digital source seems a more optimal choice. Add a third input just in case and a 3 position selector switch and it is done. You will have no volume level difference between analog and digital sources and no degradation of the digital sources.
It would help to keep to standards so any line stage should be able to drive loads till 10 kOhm. Just like almost any modern source can drive loads till 10 kOhm. Inserting a superfluous device in the chain that has higher output impedance than the original sources have is not a technical approach and serves no purpose. A muting relay that shorts outputs at power on/off is a nice extra with no negative side effects. This dictates that one should calculate first with impedances and needed gain (hint: 1x to 3x in many cases) and only then choice of parts.
So effectively no one needs a line stage with modern sources but old sources need higher level. This indicates updating the older phono stages seems a shorter path to results. Maybe the circuit as proposed does do a good job when used exclusively at the outputs of just the phono stage. The setup as it is now will essentially enable the owner/builder to sigh "analog really sounds better than digital" 😀
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It seems opinion is divided. The author of The Valve Wizard books posted:
https://www.diyaudio.com/forums/tubes-valves/239562-volume-control-preamp-stage.html#post3603969
Since bottlehead.com also put on the market a 6v6 preamp with volume control after the stage...I thought I'd try it.
Moreplay Preamplifier kit | Bottlehead
I have zero issues with (perceived) noise. In fact my son who can still hear hiss noted that he could hear nothing since I implemented my pre...whereas before he heard hissss.
You could be right. Merlin could be right. All I know is this quietest preamp stage I've ever had. So apart from what Douglas said about output impedance. For me this before/after is a non-issue.
He is an analog engineer.
https://www.diyaudio.com/forums/tubes-valves/239562-volume-control-preamp-stage.html#post3603969
Since bottlehead.com also put on the market a 6v6 preamp with volume control after the stage...I thought I'd try it.
Moreplay Preamplifier kit | Bottlehead
I have zero issues with (perceived) noise. In fact my son who can still hear hiss noted that he could hear nothing since I implemented my pre...whereas before he heard hissss.
You could be right. Merlin could be right. All I know is this quietest preamp stage I've ever had. So apart from what Douglas said about output impedance. For me this before/after is a non-issue.
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I read it, it is still thinking in high impedance stuff which is old. As said, any modern source has 2Veff output level and a low Zout. In that case the circuit does not make anything better. On the contrary. If you add an open amplifying high output stage to a perfect goods source you have effectively degraded that source.
In the tube world people select a tube at random and then start doing something with it. It would really help to define beforehand (like in any other area of audio or even any other area of design) what the requirements are and to keep to standards.
Todays stuff drives loads till 10 kOhm with ease. So source selection and a 25 kOhm log potentiometer plus the high input impedance power amplifier are sufficient. This is already like this since CD was introduced....
In the tube world people select a tube at random and then start doing something with it. It would really help to define beforehand (like in any other area of audio or even any other area of design) what the requirements are and to keep to standards.
Todays stuff drives loads till 10 kOhm with ease. So source selection and a 25 kOhm log potentiometer plus the high input impedance power amplifier are sufficient. This is already like this since CD was introduced....
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Think of what you need. I think you need equal levels of your sources and no superfluous stuff as a fifth wheel does not do much to a car.
Make a small drawing of signal levels and impedances and define what is needed.
Make a small drawing of signal levels and impedances and define what is needed.
My main source is a dddac 1794 with cinemag output transformer...with low output levels...I think it is 10k:10k... what would be prudent then in my case?
I don't know. Most technical minded people keep to standards as otherwise any chain is custom and any situation has issues and fora are even fuller with questions. Please ask the designer what level etc. Once one deviates from standards nothing is ever usable with other stuff and stuff must be married and voiced etc. and such loss of time. Personally I calculate with the 2Veff standard and have no issues and no line stages etc. Less = more.
However I do know the issue of old high impedance low gain phono stuff but why amplify all sources then? Who needs amplified 10Veff line level to a 1Veff sensitive amplifier? One started with 2Veff sources already, twice the level needed for full output!
However I do know the issue of old high impedance low gain phono stuff but why amplify all sources then? Who needs amplified 10Veff line level to a 1Veff sensitive amplifier? One started with 2Veff sources already, twice the level needed for full output!
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There is a difference. Of course which position works best for you should be decided after listening.
No! Just calculate first, then listen. If you know your sources and impedances and you know your the gain of the power amplifier why add something in between that has no function?
Aha, you just do something at random. Of course you need source selection and volume control but you don't seem to grasp the concept. Good luck then.
You do this by adding gain only to attenuate again besides the source selection and volume control?!
I found this at the website of DDDAC1794 :
with 2,2uF capacitor coupled output:
Output = 1,2V RMS at 1kHz sinewave 0dB signal level
Bandwidth (-3dB) = <1Hz - 96kHz
LF Signal distortion at 0dB signal level d2=0,4%
Output impedance per Deck = 133 Ohm (reduces proportionally by number of decks)
Maximum Fs = 192kHz at 24 bit resolution
No digital filter (allowing for 96kHz square wave reproduction)
Power consumption 12Volt: Mainboard = 10mA - 30mA, per DAC Module (deck) = 100mA
Power consumption 5Volt: USB WaveIO = 385mA
with Sowter 1:2 balanced transformer:
Output = 4,6V RMS at 1kHz sinewave 0dB signal level
Bandwidth (-3dB) = 15Hz - 96kHz
LF signal distortion at 0dB signal level d3=0,07%
Output impedance with 4 Decks = 270 Ohm
Maximum Fs = 192kHz at 24 bit resolution
No digital filter (allowing for 96kHz square wave reproduction)
Power consumption 12Volt: Mainboard = 10mA - 30mA, per DAC Module (deck) = 100mA
Power consumption 5Volt: USB WaveIO = 385mA
Maybe yours is different and it its up to you to find out what you have but one always needs to take into account all parameters. Of all things needed gain is not one of them it seems.
You do this by adding gain only to attenuate again besides the source selection and volume control?!
I found this at the website of DDDAC1794 :
with 2,2uF capacitor coupled output:
Output = 1,2V RMS at 1kHz sinewave 0dB signal level
Bandwidth (-3dB) = <1Hz - 96kHz
LF Signal distortion at 0dB signal level d2=0,4%
Output impedance per Deck = 133 Ohm (reduces proportionally by number of decks)
Maximum Fs = 192kHz at 24 bit resolution
No digital filter (allowing for 96kHz square wave reproduction)
Power consumption 12Volt: Mainboard = 10mA - 30mA, per DAC Module (deck) = 100mA
Power consumption 5Volt: USB WaveIO = 385mA
with Sowter 1:2 balanced transformer:
Output = 4,6V RMS at 1kHz sinewave 0dB signal level
Bandwidth (-3dB) = 15Hz - 96kHz
LF signal distortion at 0dB signal level d3=0,07%
Output impedance with 4 Decks = 270 Ohm
Maximum Fs = 192kHz at 24 bit resolution
No digital filter (allowing for 96kHz square wave reproduction)
Power consumption 12Volt: Mainboard = 10mA - 30mA, per DAC Module (deck) = 100mA
Power consumption 5Volt: USB WaveIO = 385mA
Maybe yours is different and it its up to you to find out what you have but one always needs to take into account all parameters. Of all things needed gain is not one of them it seems.
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Thanks as_audio for elegantly correcting me 🙂
Reason to reread MJ...😀
Nevertheless, in case of a cathode decoupling cap, the value could be much smaller (within reach of higher quality film caps).
My take however is that this line amp will sound best without the decoupling cap, just introducing a bit of feedback. No problem with slight loss of gain.