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How about the phono section ?
I thought I'd do a bit of Spice simulation and as a benchmark I compared it with the High Octane phono from here:http://www.diyaudio.com/forums/analogue-source/242387-high-octane-phono-preamp.html
(I replaced the depletion mode FET with a BJT CCS) as they are both simple active discrete circuits and both are said to sound good.
They both simulate good enough, 1) the RIAA error looks to be less than 1dB over the frequency range of interest, 2) distortion is low, 3) & 4) noise at output is comparable (never used this feature in Spice before so not much idea if it's reasonable or not), 5) PSRR looks better for the NAD circuit, 6) the schematics showing a buffered inverse RIAA at input.
I thought I'd do a bit of Spice simulation and as a benchmark I compared it with the High Octane phono from here:http://www.diyaudio.com/forums/analogue-source/242387-high-octane-phono-preamp.html
(I replaced the depletion mode FET with a BJT CCS) as they are both simple active discrete circuits and both are said to sound good.
They both simulate good enough, 1) the RIAA error looks to be less than 1dB over the frequency range of interest, 2) distortion is low, 3) & 4) noise at output is comparable (never used this feature in Spice before so not much idea if it's reasonable or not), 5) PSRR looks better for the NAD circuit, 6) the schematics showing a buffered inverse RIAA at input.
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Hi Gareth,
I'm curious, what would be the reasons for not using a ground-lift resistor?
Thank you for an interesting project!
Cheers,
Valery
What's the point ?
First of all , you would need a speaker that can adequately reproduce <30hz.
I won't discount "punchy". A 3 stage Sansui paired with an EF3 or my leach amp input stage is noticeable (Just barely) ,
as compared to a "blameless" type topology.
But not to the point where one is not "musical".
(We have) explored "why".
-Back speaker EMF.
-the type of feedback network.
This can be measured at the VAS in it's H2/3/5. So it does exist.
My title reads as it is because if you are short of a bit perfect FLAC (and a god like
DAC) ,
you might
not hear any of this regardless.
PS - Phono ? Give up the ghost ....
OS
20 hz ? I surely hope any forum amp could go that "deep". And then there is "punchy".
First of all , you would need a speaker that can adequately reproduce <30hz.
I won't discount "punchy". A 3 stage Sansui paired with an EF3 or my leach amp input stage is noticeable (Just barely) ,
as compared to a "blameless" type topology.
But not to the point where one is not "musical".
(We have) explored "why".
-Back speaker EMF.
-the type of feedback network.
This can be measured at the VAS in it's H2/3/5. So it does exist.
My title reads as it is because if you are short of a bit perfect FLAC (and a god like
DAC) ,
you might
not hear any of this regardless.
PS - Phono ? Give up the ghost ....
OS
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The tube buffer stage
The tube buffer sits between a relatively high impedance potentiometer (level control) and the input of the amplifier.
The cathode follower in the GK-1 is published as having a Zout in the range 130R to 140R although a bit more current through the tube (nominally 8.5mA) would raise gm and lower Zout.
What makes the GK-1 output stage unusual is Hugh's description of a 'drone' follower, another cathode follower driven in anti-phase to the signal carrying tube designed to draw current from the HT supply in anti-phase to the signal tube and hence ensure a constant current draw from the supply (which is a high impedance supply with heavy RC filtering). There is some 'magic' with the arrangement so that the 'drone' tube doesn't do a perfect job at high frequencies, allowing the HT to 'sag' a little to soften the treble without taking away from the bass.
The tube buffer sits between a relatively high impedance potentiometer (level control) and the input of the amplifier.
The cathode follower in the GK-1 is published as having a Zout in the range 130R to 140R although a bit more current through the tube (nominally 8.5mA) would raise gm and lower Zout.
What makes the GK-1 output stage unusual is Hugh's description of a 'drone' follower, another cathode follower driven in anti-phase to the signal carrying tube designed to draw current from the HT supply in anti-phase to the signal tube and hence ensure a constant current draw from the supply (which is a high impedance supply with heavy RC filtering). There is some 'magic' with the arrangement so that the 'drone' tube doesn't do a perfect job at high frequencies, allowing the HT to 'sag' a little to soften the treble without taking away from the bass.
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Bigun,
You know an extraordinary level of knowledge for someone who has probably never heard or seen a GK1!
I replaced this circuit with the GK2 some years later, but changed only the input stage, leaving the tube CF output unchanged. I reduced the parts count considerably, and shrunk the pcb down 40mm but never produced it in kit form. I built several of these pcbs and sold them to local GK1 users, who felt this new version sounded much better.
Good luck with your good project, and thank you for your encouragement for a sole trader!
Hugh
You know an extraordinary level of knowledge for someone who has probably never heard or seen a GK1!
I replaced this circuit with the GK2 some years later, but changed only the input stage, leaving the tube CF output unchanged. I reduced the parts count considerably, and shrunk the pcb down 40mm but never produced it in kit form. I built several of these pcbs and sold them to local GK1 users, who felt this new version sounded much better.
Good luck with your good project, and thank you for your encouragement for a sole trader!
Hugh
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Having seen the GK-1 design I am delighted with it! But it's not for public use here. I am going to take a different path but will capture some of the spirit of the approach - some frequency dependency to the cathode followers distortion profile.
I want:
a) lowest harmonic distortion at bass frequencies to keep it 'punchy' despite potentially larger signal swings for powerful bass passages, with a tad more H2 at higher frequencies
b) a single triode per channel for simplicity
c) good PSRR with a dual-supply (i.e. a B- and a B+)
d) low output impedance (see comment above from 'rabitz')
I have something on paper right now that should achieve this with a very simple hybrid approach but it needs some tweaking.
I want:
a) lowest harmonic distortion at bass frequencies to keep it 'punchy' despite potentially larger signal swings for powerful bass passages, with a tad more H2 at higher frequencies
b) a single triode per channel for simplicity
c) good PSRR with a dual-supply (i.e. a B- and a B+)
d) low output impedance (see comment above from 'rabitz')
I have something on paper right now that should achieve this with a very simple hybrid approach but it needs some tweaking.
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Well here it is. It's a hybrid Taylor Follower. The small cap between base-collector on the bottom transistor controls the frequency dependent current through the bottom of this push-pull arrangement and it works in spice like a charm. Dominated by H2, and the level of H2 being minuscule at 40Hz and quite noticeable at 4kHz.
However I'm getting cold feet on this frequency dependent behaviour, mostly because I don't want to do a lot of prototyping and listening tests before making up a pcb design and I have no experience to confirm that softening up the treble this way will be pleasant (there are always phase shifts involved with this malarky too) - sound reports from the power amp don't suggest that it's required.
However I'm getting cold feet on this frequency dependent behaviour, mostly because I don't want to do a lot of prototyping and listening tests before making up a pcb design and I have no experience to confirm that softening up the treble this way will be pleasant (there are always phase shifts involved with this malarky too) - sound reports from the power amp don't suggest that it's required.
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I see +5dB for the voltage amp, -0.5dB for the Buffer and +31dB for the Power amp.
Those three stages come to +35.5dB.
I usually use +27dB to +29dB for my gain stages and find that is too much.
I have seriously considered looking at re-doing the stability/gain of all my Power Amplifiers to try to get the gain down to +20dB, or even a bit below that. Not bitten that bullet yet.
Do you really need all that gain to throw away in the attenuator?
Those three stages come to +35.5dB.
I usually use +27dB to +29dB for my gain stages and find that is too much.
I have seriously considered looking at re-doing the stability/gain of all my Power Amplifiers to try to get the gain down to +20dB, or even a bit below that. Not bitten that bullet yet.
Do you really need all that gain to throw away in the attenuator?
Nice to see that Ost is still keeping in touch.20 hz ? I surely hope any forum amp could go that "deep". And then there is "punchy".
First of all , you would need a speaker that can adequately reproduce <30hz.
I won't discount "punchy". A 3 stage Sansui paired with an EF3 or my leach amp input stage is noticeable (Just barely) ,
as compared to a "blameless" type topology.
But not to the point where one is not "musical".
(We have) explored "why".
-Back speaker EMF.
-the type of feedback network.
This can be measured at the VAS in it's H2/3/5. So it does exist.
My title reads as it is because if you are short of a bit perfect FLAC (and a god like
DAC) ,
you might
not hear any of this regardless.
PS - Phono ? Give up the ghost ....
OS
Bigun,
If you'd like a buffer similar to the Taylor buffer, but simpler, see attached schematic.
Mr ITO managed to get a patent for this, but the rest of us will recognize it as a `White Cathode Follower'.
I've used a dn2530 depletion mode mosfet, but you could use a triode for M1 if you really want. Don't leave out D1, and the polarity is correct.
Distortion is low, but almost all H2. The power supply will need to be good, as it has low PSRR. Perhaps a CCS feeding a zener plus cap.
Regards,
Paul Bysouth
If you'd like a buffer similar to the Taylor buffer, but simpler, see attached schematic.
Mr ITO managed to get a patent for this, but the rest of us will recognize it as a `White Cathode Follower'.
I've used a dn2530 depletion mode mosfet, but you could use a triode for M1 if you really want. Don't leave out D1, and the polarity is correct.
Distortion is low, but almost all H2. The power supply will need to be good, as it has low PSRR. Perhaps a CCS feeding a zener plus cap.
Regards,
Paul Bysouth
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I think I'd pick the Taylor over the White just to get the better PSRR, but in the end I decided on something simpler.
The Cathode Follower is loaded on a deceptively simply circuit that will 'look' like a resistor to the tube, producing the same harmonic profile without the voltage drop requirements.
This is something new.
The Cathode Follower is loaded on a deceptively simply circuit that will 'look' like a resistor to the tube, producing the same harmonic profile without the voltage drop requirements.
This is something new.
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What is the output level in the sim..?.
Old such designs from Phllips get close to -120dB THD/1V pk with 3 transistors for instance.
Bigun,
re the circuit in post #52
Some time ago I used a similar circuit, but using a DN2530 depletion mode mosfet in place of the triode - it worked extremely well!
You may find that splitting R3 into two resistors and taking the output from the centre is better (though exactly what is 'better' is hard to define). Altering the ratio of the two resistors allows some control over the H2/H3 ratio.
I used it to implement active crossover filters for an amp/speaker system (Hugh did the amp).
There is also a similar circuit by David Berning of the late 1970's that used a triode and a Pchannel jfet. He used it in a range of preamplifiers.
Regards,
Paul Bysouth
re the circuit in post #52
Some time ago I used a similar circuit, but using a DN2530 depletion mode mosfet in place of the triode - it worked extremely well!
You may find that splitting R3 into two resistors and taking the output from the centre is better (though exactly what is 'better' is hard to define). Altering the ratio of the two resistors allows some control over the H2/H3 ratio.
I used it to implement active crossover filters for an amp/speaker system (Hugh did the amp).
There is also a similar circuit by David Berning of the late 1970's that used a triode and a Pchannel jfet. He used it in a range of preamplifiers.
Regards,
Paul Bysouth
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I was working with a 1V pk output.
Hi Paul - this is good to know. Out of interest, do you have more on the David Berning design ?
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Hi Valery,
Now you come to mention it, there would be no harm if I included one. Better to have the option than not. I'll take a look at the pcb layout I have and see if I can't figure out how to include this option.
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Pre-amp pcb
I've started to layout the pre-amp board. It's rather tight. I thought about using only one shunt regulator for both channels (I consulted Salas on the details and he thought it would be fine) but I couldn't quite get happy about the grounding arrangements so I've gone with dual-mono. Not sure if I can squeeze it in yet, will have to see. So far I've created the traces for the heater wiring - that' was the easy one though!
Power connectors on the right hand side, signal connectors on the left hand side. The RIAA amplifiers are independent from the cathode follower.
I've started to layout the pre-amp board. It's rather tight. I thought about using only one shunt regulator for both channels (I consulted Salas on the details and he thought it would be fine) but I couldn't quite get happy about the grounding arrangements so I've gone with dual-mono. Not sure if I can squeeze it in yet, will have to see. So far I've created the traces for the heater wiring - that' was the easy one though!
Power connectors on the right hand side, signal connectors on the left hand side. The RIAA amplifiers are independent from the cathode follower.
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