It's very weird that the Audio Note engineers have not paid any attention to that critical part of their preamp kit, the power supply!!! The 20Hy choke for the 6X5 tube is a little more than the double according to the tube characteristics ( 8Hy ).
So what do you think would be the risk of using a 10Hy choke instead of 50Hy?? My choke is a military-made one from the early 60's ( it has been taken by an old radar).
According to the formula, the AN 20Hy choke will draw 52mA. This is too much for a preamp.
So what do you think would be the risk of using a 10Hy choke instead of 50Hy?? My choke is a military-made one from the early 60's ( it has been taken by an old radar).
According to the formula, the AN 20Hy choke will draw 52mA. This is too much for a preamp.
Once again: the choke value doesn't depend on rectifier characteristics.
You can use any choke. If the equation in my previous pic isn't satisfied by the values of current and inductance, the circuit still will work. But it will behave as an intermediate between choke and capacitor input filter. In such case, large variations on output voltage may occur. Choke input is just characterzed by output constance of voltage with load variations, that's why is used in class AB1, AB2 & B final stages.
Are you able to make your own choke?
You can use any choke. If the equation in my previous pic isn't satisfied by the values of current and inductance, the circuit still will work. But it will behave as an intermediate between choke and capacitor input filter. In such case, large variations on output voltage may occur. Choke input is just characterzed by output constance of voltage with load variations, that's why is used in class AB1, AB2 & B final stages.
Are you able to make your own choke?
I completely understood what you wrote and what I read in the article as my knowledge of electronics is quite good. According to the given formula, you are 100% right.
My question is why the AN designers have skipped that formula if a wrong value inductor would be fatal or problematic for their preamplifier kit. It's really weird!! Don't you think so?? When I first checked the schematic, I thought that the choke was placed first to get rid of the first small capacitor taking advantage of the choke resistance.
Thank you very much for your concern and the deep analysis.
Best regards from sunny Greece.
My question is why the AN designers have skipped that formula if a wrong value inductor would be fatal or problematic for their preamplifier kit. It's really weird!! Don't you think so?? When I first checked the schematic, I thought that the choke was placed first to get rid of the first small capacitor taking advantage of the choke resistance.
Thank you very much for your concern and the deep analysis.
Best regards from sunny Greece.
OK. Really I can't tell you why. I am a lover of old text books: Terman, Seely, Gray, Wallman and the like. And all theory was wrotten in those era. Nowadays it has been re-writed using Hfe in plase of mu, but all reminds the same.
I almost always find errors in circuits published. Ignoring by the moment if its a naif error or deliverate. Actually I am following an old discussion between authors about 1950 regarding high stability oscillators for HF: Klapp, Vackar, Llewellyn and many others. Fortunatelly its easy thanks to worldradiohistory.com that has all this papers scanned and published. And were discussions of high quality with proofs at hand. Now, any fool thinks that pasting a circuit in a web become or believes he/she is Edison.
Those are some of my self designed chokes.
I almost always find errors in circuits published. Ignoring by the moment if its a naif error or deliverate. Actually I am following an old discussion between authors about 1950 regarding high stability oscillators for HF: Klapp, Vackar, Llewellyn and many others. Fortunatelly its easy thanks to worldradiohistory.com that has all this papers scanned and published. And were discussions of high quality with proofs at hand. Now, any fool thinks that pasting a circuit in a web become or believes he/she is Edison.
Those are some of my self designed chokes.
Attachments
My local transformer distributor can make any choke on request. A 50Hy / 10mA choke costs 20- to 30 euros. I can't deal with choke construction because of the lack of space at my lab.
You are right about the mistakes of the schematics.
If you take a look at the AN power supply, you will see that the 12,6VDC circuit uses an 18-volt winding and after rectification, the capacitors are rated at 16 volts. (Boom) I don't know if all these mistakes are made on purpose or something else happens.
Anyway, I will give it a try with my existing configuration and see if there will be any problem.
You are right about the mistakes of the schematics.
If you take a look at the AN power supply, you will see that the 12,6VDC circuit uses an 18-volt winding and after rectification, the capacitors are rated at 16 volts. (Boom) I don't know if all these mistakes are made on purpose or something else happens.
Anyway, I will give it a try with my existing configuration and see if there will be any problem.
metanastis, can you elaborate on why this new build has 'no hum', when your earlier builds had noticeable hum? Was there some aspect of this new build that was different to your previous builds? In post #17 it seems you think your hum issue was related to valve heaters for your various preamps, and by elevating the heater and making it dc you have suppressed the hum? Did you try elevating the heater by itself, or just using dc by itself for a preamp heater, or did it require both methods, and was that the aspect that was different to your earlier builds?
You reference "Audio Note M7Kit11 preamplifier' in post #1. I can't identify that model on the AN website, or in their manuals download - can you provide a link to that preamplifier and the details of its power supply that you then copied ?
Did you measure the B+ rail current draw from your preamplifier? I see that you estimate it at 4.7mA in post #20. As Osvaldo goes to length to educate you about choke input power supplies, your B+ feed from the choke was likely providing a less than ideal current waveform to your pcb first cap filter, which would indicate that you had abnormal hum coming onto the pcb, but you didn't notice it with your pre-amp performance. You would also likely have a higher than normal B+ voltage from such an insufficient load current for choke regulation, and perhaps you didn't notice that either?
Imho, if you were to revisit your pcb then there may be benefit from including an RC snubber for each primary HT half-winding (as per quasimodo threads on this forum), and including a tuning RC across the choke to suppress mains 2nd harmonic ripple and lower the minimum choke inductance needed for regulation, and inserting an 1N4007 in series with each 6X4 anode to avoid future arcing, and include a 5x20 250Vac fuse in the CT link to avoid damage from faults, and making pcb trace connections to the lowest noise nodes such as direct to capacitor pads rather than along traces (especially to connect the 100uF elevation cap's pos terminal to the 12Vdc output terminal, rather than to the noisy end of that trace back at the bridge rectifier).
Ciao, Tim
You reference "Audio Note M7Kit11 preamplifier' in post #1. I can't identify that model on the AN website, or in their manuals download - can you provide a link to that preamplifier and the details of its power supply that you then copied ?
Did you measure the B+ rail current draw from your preamplifier? I see that you estimate it at 4.7mA in post #20. As Osvaldo goes to length to educate you about choke input power supplies, your B+ feed from the choke was likely providing a less than ideal current waveform to your pcb first cap filter, which would indicate that you had abnormal hum coming onto the pcb, but you didn't notice it with your pre-amp performance. You would also likely have a higher than normal B+ voltage from such an insufficient load current for choke regulation, and perhaps you didn't notice that either?
Imho, if you were to revisit your pcb then there may be benefit from including an RC snubber for each primary HT half-winding (as per quasimodo threads on this forum), and including a tuning RC across the choke to suppress mains 2nd harmonic ripple and lower the minimum choke inductance needed for regulation, and inserting an 1N4007 in series with each 6X4 anode to avoid future arcing, and include a 5x20 250Vac fuse in the CT link to avoid damage from faults, and making pcb trace connections to the lowest noise nodes such as direct to capacitor pads rather than along traces (especially to connect the 100uF elevation cap's pos terminal to the 12Vdc output terminal, rather than to the noisy end of that trace back at the bridge rectifier).
Ciao, Tim
hello Tim,
At first, if you take a close look at the schematic of the preamp, you will see both 12,6 and 300vdc power supplies.
As you can see on the schematic, there is a 15K and a 22nF between the secondary (snubber).
My mistake with the previous preamps is the floating heater DC voltage.
I have built that preamp and tested it with a signal generator at 1Khz/2v sine wave and an oscilloscope.
Perfect shapes (triangle and square) and X-10 amplification using 2 JAN5814 tubes. When testing an amp I always trust my ears. If there is no noise or hum, it will be a good build. The only problem that may occur is the one that Osvaldo described previously ( The choke value).
I know that the schematic is not among the AN official kits but it doesn't matter at all whether it sounds good. Besides, the preamp schematic itself, it is a classic and simple preamp.
I don't want to use any semiconductor ( except the heater DC circuit) in my designs as I want a true tube preamp or amp.
Take a look at the complete preamp design.
Cheers,
Spiros
At first, if you take a close look at the schematic of the preamp, you will see both 12,6 and 300vdc power supplies.
As you can see on the schematic, there is a 15K and a 22nF between the secondary (snubber).
My mistake with the previous preamps is the floating heater DC voltage.
I have built that preamp and tested it with a signal generator at 1Khz/2v sine wave and an oscilloscope.
Perfect shapes (triangle and square) and X-10 amplification using 2 JAN5814 tubes. When testing an amp I always trust my ears. If there is no noise or hum, it will be a good build. The only problem that may occur is the one that Osvaldo described previously ( The choke value).
I know that the schematic is not among the AN official kits but it doesn't matter at all whether it sounds good. Besides, the preamp schematic itself, it is a classic and simple preamp.
I don't want to use any semiconductor ( except the heater DC circuit) in my designs as I want a true tube preamp or amp.
Take a look at the complete preamp design.
Cheers,
Spiros
Hi Spiros - yes I saw the single AC snubber in the AN schematic in post #1, which is why I suggested using the better arrangement of separate snubbers for each half-winding, although the benefit of such snubbers is very low level for valve rectified secondaries - it could be more influential for the 6V winding as that is ss diode rectified with a huge filter cap.
The point of linking to Mk7 details is that there may be more information on the choke than what is shown by the schematic in post #1.
Ears are often deceived, and I'd recommend using more than just a scope to assess preamp/power supply performance. The forums are littered with people who initially state a particular hum is at a certain frequency, only to latter measure it at a different frequency. Also, your speakers/amp and setup may not be the same as others, and their setup may allow noise and distortion and hum to be detectable, which is why there is a benefit to using measurement techniques that go beyond the limits of audibility, as a way of better appreciating if there are remnant concerns.
The point of linking to Mk7 details is that there may be more information on the choke than what is shown by the schematic in post #1.
Ears are often deceived, and I'd recommend using more than just a scope to assess preamp/power supply performance. The forums are littered with people who initially state a particular hum is at a certain frequency, only to latter measure it at a different frequency. Also, your speakers/amp and setup may not be the same as others, and their setup may allow noise and distortion and hum to be detectable, which is why there is a benefit to using measurement techniques that go beyond the limits of audibility, as a way of better appreciating if there are remnant concerns.
Tim,
The 50/60 or 100/120Hz hum is audible in any hi-fi system. You need no special instrument to hear it. Ground noise is something different.
Yes, you are right that I have to use my HP frequency counter to identify precisely the hum. 90-something percent, the hum comes from the power supply. An RC or an NTC thermistor and star grounding can eliminate ground loops. There is always the matter of the RF interference.....
I am aware of the Quasimodo circuit but it demands many calculations and all the specific characteristics of the transformer. If it were just a standard circuit, I would add it.
I have dealt with tubes since 1988 as a professional but just 5 years ago I dealt with my hobby of constructing my systems of my own.
Besides, military radar is something very different from audio equipment.
If a hi-fi setup pleases my ears, I will enjoy and that is what matters to me.
I design my pcbs and cabinets of my own, using aluminum and wood.
I try to build only class-A designs as I believe it has the best sound.
Any suggestions are always welcome.
Best regards to OZ and my relatives in Clayton
Spiros
The 50/60 or 100/120Hz hum is audible in any hi-fi system. You need no special instrument to hear it. Ground noise is something different.
Yes, you are right that I have to use my HP frequency counter to identify precisely the hum. 90-something percent, the hum comes from the power supply. An RC or an NTC thermistor and star grounding can eliminate ground loops. There is always the matter of the RF interference.....
I am aware of the Quasimodo circuit but it demands many calculations and all the specific characteristics of the transformer. If it were just a standard circuit, I would add it.
I have dealt with tubes since 1988 as a professional but just 5 years ago I dealt with my hobby of constructing my systems of my own.
Besides, military radar is something very different from audio equipment.
If a hi-fi setup pleases my ears, I will enjoy and that is what matters to me.
I design my pcbs and cabinets of my own, using aluminum and wood.
I try to build only class-A designs as I believe it has the best sound.
Any suggestions are always welcome.
Best regards to OZ and my relatives in Clayton
Spiros
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