I have an old 211 power amp which I designed but in the end did not build, and I have been updating an old ARC preamp and have been staggered at the difference individual components make to the sound. What resistors did you use, I don't recognise them?
Rich
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I’ve no doubt that the details like parts choices can be a rabbit hole. I usually make a choice at the design or build stage and that’s it.
The low power resistors are Vishay Beyschlag Thin Film, MRS25 Series.
I picked them because I wanted them to be at a reasonable cost, easily available, also the same colour that I see in the website photos of the Kondo units, that they have suitable voltage rating (350V AC, 500V stand-off is claimed in the datasheet) and are generally specified as good quality. You won’t recognise them because they’re dressed up with white epoxy, just like in Kondo, but in my case I can say purely out of fun and not for any claimed scientific or ’sonic’ reason! It was fun reproducing the look and feel.
The low power resistors are Vishay Beyschlag Thin Film, MRS25 Series.
I picked them because I wanted them to be at a reasonable cost, easily available, also the same colour that I see in the website photos of the Kondo units, that they have suitable voltage rating (350V AC, 500V stand-off is claimed in the datasheet) and are generally specified as good quality. You won’t recognise them because they’re dressed up with white epoxy, just like in Kondo, but in my case I can say purely out of fun and not for any claimed scientific or ’sonic’ reason! It was fun reproducing the look and feel.
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I am very impressed by your work! I wonder about the usefulness of grid bias control of the tubes and to what extent you were thinking about this issue during your design process. This off course knowing that Kondo pre amps were indeed your guide. Bias control according to theory should become relevant with tube ageing. Can you comment this and to what extent you think it is could be an improvement on your design (or not) ? Also if you can share with us some updates on your listening experience of your build. Thanks.
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Thank you for the kind words.
My primary aim was to follow in the footsteps of the great Kondo, and his successor. My only deviation from their design has been away from their preferred RIAA correction curve to one that is technically more accurate, and the use of ‘stoppers’ at various grids etc.
I’m quite comfortable with the use of grid leak bias on the upper Cascode (this was your question right ?) given the low signal level at the grid-cathode (low distortion), a large enough anode resistor (stabilizes at low operating current) and the grid cap is sized large enough that the cut off sits around 10Hz. Although tubes age, I don‘t anticipate issues arising from the grid leak biass, rather the aged tube will need replacing anyhow when it gets noisy or too weak.
My primary aim was to follow in the footsteps of the great Kondo, and his successor. My only deviation from their design has been away from their preferred RIAA correction curve to one that is technically more accurate, and the use of ‘stoppers’ at various grids etc.
I’m quite comfortable with the use of grid leak bias on the upper Cascode (this was your question right ?) given the low signal level at the grid-cathode (low distortion), a large enough anode resistor (stabilizes at low operating current) and the grid cap is sized large enough that the cut off sits around 10Hz. Although tubes age, I don‘t anticipate issues arising from the grid leak biass, rather the aged tube will need replacing anyhow when it gets noisy or too weak.
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I have been distracted by my day job and as such listening has taken a back seat. So far, there’s been no changes is my good opinion of the sound of this unit. Give me a bit more time.
I would like to further explore it’s imunity to r.f. interference, I have a neighbour with a tall antenna mast. His Morse Code transmissions are audible on my basement H.T. system but not often enough or predictable to test the phono yet.
P.s. Glad I used a volume control with enough steps.
I would like to further explore it’s imunity to r.f. interference, I have a neighbour with a tall antenna mast. His Morse Code transmissions are audible on my basement H.T. system but not often enough or predictable to test the phono yet.
P.s. Glad I used a volume control with enough steps.
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I’ve discovered that warm and comfortable sounding amps are nice to listen to, relaxing in a retro kind if way. Not much bass punch, quickly fall apart when they go loud, can struggle with complex music. Clean amps can grate on you, fatigue sets in early. But the best amps / preamps are hard for me to describe, not sure if musical is the term. This Ashizawa-Kondo inspired preamp sounds clean without fatigue, has bass without being mushy, it gets out of the way of the music yet you are glad it’s there. Really nice, but hard to pin labels on it. Could it be an X factor thing?
My diy TGM8 solid state class ABC power amp has some unusual qualities too, clean, relaxed, crushing bass impact, all at the same time. Different from this preamp but also a challenge to put labels on it.
Yes thanks, you made my question clearer. I can agree your point about the circuit design parameters (large enough anode resistor and the grid cap size) should keep the grid leak bias 'under control' e.g. without it causing noticeable noise. Grid bias control is in itself an interesting topic though where i don't see a clear design guide for now. But never mind, I am looking forward to follow your listening experiences from your build. It might be the best way to grow wiser 🙂
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You will note of course, that the GE-10 phono that I’ve used here has a filtered bias supply for the upper cascode, not the same high value resistor grid leak from the original M7.
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I'll look into it. Asked because i was interested what You really have done, don't remember schematics, only pictures of sub-moduls.
On the other hand web is full of AN / K false schematics and chinese sell M7 phono+line kit with one tube less than in original ( at least regarding the first versions when UK & Japan worked together under the same name ).
I would very much like to see schematic of exactly what You did, if possible.
Regards and thanks, Krca
Hi All, first of all - thanks to al of you for valuable contribution. I have two questions as I am starting this build.
Question 1
I have spoted over internet some inconsistencies in schematic diagrams. Wast majority of them is showing 250kohm in anodes and 2nd cathode and 8k2/5k1 in 1st cathode. HOWEVER I seen one schematic that claims to be also genuine where I see 240kohm and 6k8/5k1. This is only one though, additionaly schematic claims 12AU7 that is wrong tube here in my opinion. So I guess it can be wrong (chinese fake or so). Would like to make sure correct values are 250k and 8k2/5k1 assuming tube 12AY7. Are they?
Question 2
What is correct HV pover supply value in the point I've marked on the schematic? Aain - some information noise over web. Some says 250V another 260V, I seen 225V or 248V as well. I am using quite "hi-tech" 😉 , complex, regulated and very good in therms of ripple rejection, MOSFET based power supply, so I can set voltage up to 0,1V as I want. Just need to know what is correct value, please?
I have seen over the threat that @Bigun was deeply on the topic. @Bigun - may I ask your assistance here, please?
Question 1
I have spoted over internet some inconsistencies in schematic diagrams. Wast majority of them is showing 250kohm in anodes and 2nd cathode and 8k2/5k1 in 1st cathode. HOWEVER I seen one schematic that claims to be also genuine where I see 240kohm and 6k8/5k1. This is only one though, additionaly schematic claims 12AU7 that is wrong tube here in my opinion. So I guess it can be wrong (chinese fake or so). Would like to make sure correct values are 250k and 8k2/5k1 assuming tube 12AY7. Are they?
Question 2
What is correct HV pover supply value in the point I've marked on the schematic? Aain - some information noise over web. Some says 250V another 260V, I seen 225V or 248V as well. I am using quite "hi-tech" 😉 , complex, regulated and very good in therms of ripple rejection, MOSFET based power supply, so I can set voltage up to 0,1V as I want. Just need to know what is correct value, please?
I have seen over the threat that @Bigun was deeply on the topic. @Bigun - may I ask your assistance here, please?
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Hi. I see you are from Poland. Write to me at rhatalo@gmail.com I recently built this preamplifier so we can share experiences
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Howdy,
Well, right now I'm away on travel and my 'notes' are back home. My memory is that I was aiming for ~260V for the HT at the input to the circuit (see post #100). I will need to check my notes if it's not in the thread already. Nevertheless, I don't think +/-10V is going to be material to the results and you might shed some light on this yourself by reporting on any possible changes in sound with your adjustable supply. A complex (your description) regulated supply though is a departure from my clone and that alone means you are impacting the circuit behaviour in ways that go beyond the choice of HT voltage.
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@Bigun thanks for your reply. Are you implying, that power supply (let's leave voltage topic aside now, say it will be 260V) can impact preamp performance? If so, what would be a potential reasons for that? Different regulated power supply I am using output impedance? Current efficiency? Something else?
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The amplifier circuits do not have infinite PSRR, meaning that the power supply behaviour has some impact on the signal. And the power supply does not have zero output impedance, meaning that it can be affected by the current drawn and any signals on that current. It stands to reason that there can be an interaction between them - the power supply and the amplifier circult and it all works in unison.
Different power supply designs will have some impact, it maybe inaudible of course.
Almost all practical voltage regulators work with negative feedback and the output impedance is a function of frequency. Stability of the feedback loop is a function of the regulator circuit, its implementation and load etc. Much has been said on this topic by people with more experience and knowledge than I have so I won't try to say too much here.
The point I want to make is that you have modified the circuit, taking your own path. That's perfectly fine, it just isn't the circuit that this thread was created for and so I can't guide those aspects. I studied the choices made by Kondo and Ashizawa because they had their own idea about what the power supply should be. The design, choice of parts, brands, construction - all maybe important. I have taken the path of trusting their decisions and hence I have been careful in these details of the implementation of the power supply in my project.
Different power supply designs will have some impact, it maybe inaudible of course.
Almost all practical voltage regulators work with negative feedback and the output impedance is a function of frequency. Stability of the feedback loop is a function of the regulator circuit, its implementation and load etc. Much has been said on this topic by people with more experience and knowledge than I have so I won't try to say too much here.
The point I want to make is that you have modified the circuit, taking your own path. That's perfectly fine, it just isn't the circuit that this thread was created for and so I can't guide those aspects. I studied the choices made by Kondo and Ashizawa because they had their own idea about what the power supply should be. The design, choice of parts, brands, construction - all maybe important. I have taken the path of trusting their decisions and hence I have been careful in these details of the implementation of the power supply in my project.