I have built a hybrid class D Hypex poweramp with an Aikido Cathode Follower tube preamp in one case.
It combines the good things of tubesound and clean power of class D. I like the sound a lot and so o others.
The only problem is the HUM. It is low level but annoying and of low frequency. Ik have tried almost everything but it stays and stays. Ofcourse I have stargrounding and so on.
But let me sort out how it is configured:
I built double mono UCD 400 and SMPS400 from Hypex. One of the 65 Volt +/- and GND of the SPMS going to the poweramp UCD400 are shared with my Aikido Cathode Follower with 6N6P. See example
Heaters of tubes are fed by the DC Aux of the SPMS and regulated to 6,3 Volts DC.
The way I see it, everything into the ACF is DC, even the heaters. So how come it can generate HUM??
Is there someone who has the answer of recommendations, I'll be very happy.
Peter Monjet
It combines the good things of tubesound and clean power of class D. I like the sound a lot and so o others.
The only problem is the HUM. It is low level but annoying and of low frequency. Ik have tried almost everything but it stays and stays. Ofcourse I have stargrounding and so on.
But let me sort out how it is configured:
I built double mono UCD 400 and SMPS400 from Hypex. One of the 65 Volt +/- and GND of the SPMS going to the poweramp UCD400 are shared with my Aikido Cathode Follower with 6N6P. See example
Heaters of tubes are fed by the DC Aux of the SPMS and regulated to 6,3 Volts DC.
The way I see it, everything into the ACF is DC, even the heaters. So how come it can generate HUM??
Is there someone who has the answer of recommendations, I'll be very happy.
Peter Monjet
Are you floating the filament of the lower tube to at least -50VDC? It may need at least that much to reduce the hum.
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Hi Rayma,
The top and lower tube half are actually one 6N6P tube. And the heaters are fed by 6,3 Volts DC with one heater pin 4 connected to common GND.
Grid and Cathode of bottom half tube are with a resistor of 120 Ohm connected to -65VDC
Peter
I built double mono UCD 400 and SMPS400 from Hypex. One of the 65 Volt +/- and GND of the SPMS going to the poweramp UCD400 are shared with my Aikido Cathode Follower with 6N6P....
from my little experience building two analog metric balanced tube pre, is to put those 6.3 volts heaters (1200 mA per channel) on their own supply and ground. and since you're building one unit you can go overkill...
as in Power Supply Ripple Rejection of -132 db.
this is what i use: a ULN-PS2 Ultra Low Noise Dual Positive Power Supply
you specify 6.3 volts when you order.
i have too put my ear on the horn too listen to the noise floor that way
when you start using those supply you will want to replace every other supply that sits in your house.
my 2 cents
Martin Gagnon
from my little experience building two analog metric balanced tube pre, is to put those 6.3 volts heaters (1200 mA per channel) on their own supply and ground. and since you're building one unit you can go overkill...
as in Power Supply Ripple Rejection of -132 db.
this is what i use: a ULN-PS2 Ultra Low Noise Dual Positive Power Supply
you specify 6.3 volts when you order.
i have too put my ear on the horn too listen to the noise floor that way
when you start using those supply you will want to replace every other supply that sits in your house.
my 2 cents
Martin Gagnon
Use a resistive divider with a total resistance of a few 100k between the B- and ground.
The center of the divider should be at around half the B- voltage.
Decouple this point to ground with a capacitor, 1-10uF. Connect the filament supply to this node, instead of to ground.
I can't locate the H-K voltage rating for the 6N6P tube. Hopefully it is more than +/- 60V.
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Hi Rayman,
As 2 valves are involved for stereo, the heaters are fed by 12,6VDC and i divide voltage by applying the voltage in series from pin from 4-pin5 of valve 1 to pin 4 of valve 2 en from pin 5 of V2 to heater supply both valves on pin 4-5 have 1kOhm resisters to divide the voltage exactly to 6,3VDC.
I have to think about how to arrange things in the proper way. Thanks anyway, its very helpful
Peter
You may be able to float the entire filament circuit downward by half the B- voltage and get some hum reduction.
Hello Martin, I think it's not the underpowering of the heater supply, both tubes together needs 0,75 amperes at 12,6 Volts. I have used a 5 ampere 12 Volt DC notebook supply without any audible changes. The hum stays. I thinks it has got something to do with with Rayma says the kathode heater voltage and how to elevate the heater voltage to operate within max ratings of the 6N6P.
Nevertheless I am sure the ULN-PS2 Ultra Low Noise Dual Positive Power Supply are marvellous, but I really want to know the cause of the HUM. I think it is not just a matter of ripple rejection. My Paul Hynes heater supply is surely good enough.
Thank Peter
I've just found out that the H-K maximum voltage on this tube is 100V. So, set the tap at -50VDC
and float the entire filament circuit at that level, decoupled to ground.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CC0QFjAC&url=http%3A%2F%2Fforum.zelfbouwaudio.nl%2Fdownload%2Ffile.php%3Fid%3D9980&ei=5KEZVdyUC8bhoASup4DgBA&usg=AFQjCNFM3nfZbRvuwqFWKdFC0Tek-SX00A&bvm=bv.89381419,d.cGU
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You can try 2 capacitors in serie with the balanced outputs to your class D module.
If the balance is off in the cathode follower a 100K pot can balance the DC.
I find it strange that filament could hum in a cathode follower. Try to disconnect the cathode follower and drive directly the hypex module to see if the hum is caused by the module.
If the balance is off in the cathode follower a 100K pot can balance the DC.
I find it strange that filament could hum in a cathode follower. Try to disconnect the cathode follower and drive directly the hypex module to see if the hum is caused by the module.
Thanks very much Rayma, for the investigation. I'll try it tomorrow and will keep you posted. I hope it helps.
But strange anyway that all voltages are DC , nevertheless it can cause hum (AC!) if A-K voltage is exceeded? Weird electrons?
Thanks, Peter
This is a long-familiar effect known to those growing up with the devices. The giveaway is that the noise is 60Hz, not 120Hz.
This almost certainly means heater-cathode leakage.
ACF hum
Hi GABDX,
The output has 4uF in series to input UCD 400 with a 100k resister to GND. I use the single ended ACF, not the balanced ACF fyi.
The hum is caused by the ACF module, I have tested and tried it before. The problem lies in the ACF.
Where do i put the 100 k pot to balance the ACF?
Thanks for your help.
Peter
Hi GABDX,
The output has 4uF in series to input UCD 400 with a 100k resister to GND. I use the single ended ACF, not the balanced ACF fyi.
The hum is caused by the ACF module, I have tested and tried it before. The problem lies in the ACF.
Where do i put the 100 k pot to balance the ACF?
Thanks for your help.
Peter
i just pull out my Variable Tube Voltage Regulator PS200 like this picture:
with something much more simple
Martin Gagnon
I just finished ACF last weekend, using glassware PCB(not the all-in-one),6922 tube, and AC heater, hook to my class D AMS1000-2600 AMP, dead silent. The key is to twist the wire, and lift the heater. Use 2X510 resister to divide AC heater, and 47k/200K resisters on B+. Here show you how to do it, take a look a PS part
Yes, this is the right circuit, except the bias voltage should be negative in this case.
Just use a DC voltage of about -50V, half the H-K rating.
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Hi Peter,
(serie 50k to middle of 50k trimpot to ground ) // (6.8 K* should not be + something)
Turn the trimpot to cancel 2nd harmonics or lower noise.
you remove the 150uf, can put a 100R after the main caps in + and - supplies, then another cap in each supplies, then the voltage drop 6.8k* in each supplies.
Try an input capacitors after the volume, just before the 1M this could be another spot.
Finally just get rid of the tubes
is our source bad enough that sound deteriorates if going directly to uc modules ???
*** cathode follower are almost noise proof due to cancellation, so your noise must come at the grid input, some input wire interference.
(serie 50k to middle of 50k trimpot to ground ) // (6.8 K* should not be + something)
Turn the trimpot to cancel 2nd harmonics or lower noise.
you remove the 150uf, can put a 100R after the main caps in + and - supplies, then another cap in each supplies, then the voltage drop 6.8k* in each supplies.
Try an input capacitors after the volume, just before the 1M this could be another spot.
Finally just get rid of the tubes
is our source bad enough that sound deteriorates if going directly to uc modules ???*** cathode follower are almost noise proof due to cancellation, so your noise must come at the grid input, some input wire interference.
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