im using this circuit for my preamps. when i pull the preamp tubes all hum goes away, meaning the cause is indeed, the pre? stranger part is the 12at7 drivers for my 807's don't seem to hum at all even tho they have a much higher gain?
using a smps dc supply on my heaters.
its somewhat bearable if i dont pay attention to it but i would like to try and get it silent if i can.
using a smps dc supply on my heaters.
An externally hosted image should be here but it was not working when we last tested it.
its somewhat bearable if i dont pay attention to it but i would like to try and get it silent if i can.
Last edited:
ryuji,
Just a thought!
It could be:
The cathode on tube 2 on the circuit is at 165V.
The heater supply is SMPS. So the SMPS output needs to be isolated from Gnd and lifted as in the Aikido circuit.
To prove this if you put a two pole switch in the connection from the heater supply then after its all working and up to temp switch the heaters off for a second and see if the hum stops.
This will show if its the heater supply problem.
Regards
M. Gregg
Hi!
As the previous poster said, the cause could be the missing reference to ground of the heaters. The heaters should be elevated so that the heater-cathode voltage is maintained within limits. This is best done with a voltage divider from B+. Also out a cap from heater to ground, sa 47uF.
Another cause could be too much ripple on the B+ or a grounding issue
Best regards
Thomas
As the previous poster said, the cause could be the missing reference to ground of the heaters. The heaters should be elevated so that the heater-cathode voltage is maintained within limits. This is best done with a voltage divider from B+. Also out a cap from heater to ground, sa 47uF.
Another cause could be too much ripple on the B+ or a grounding issue
Best regards
Thomas
ryuji
Are you sure that none of the cables to the tube heaters are connected to the mains earth inside the SMPS?
The output from the SMPS is completely isolated?
Regards
M. Gregg
there is a mains earth connection on the smps. i could disconnect it. i could also use some insulating material on the metal on the smps chassis and the amp chassis for further isolation.
when i initially build my amp i continuity checked my heaters with b+ and ground, there was no connection at least when powered down.
i would think that my higher gain 12at7 stage would hum too if there was b+ ripple. psud2 shows there being almost none.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
this is the rest of my tube amp, just im running one output tube instead of two.
An externally hosted image should be here but it was not working when we last tested it.
due to my higher b+ the preamp stages run at 160-170v on the anode and ~211v on the cathode but its still well within datasheet limits
total consumption after warmup is 260 mA on b+
Last edited:
ryuji
Just try switching the heaters off on the pre amp for a second and see if the hum stops. It has to be both + & - of the SMPS.
You must not remove the safety Earth on the SMPS. Just check that the output is isolated from Gnd if you try to lift the heaters.
What is the Plot like on volts C1, C2?
Do you remember the plot on some PSUs I tried! C1 ripple is interesting. What is the largest cap you can use after the rectifier without damage? (Just to try it).
The charge pulses may be an issue.
Just a few thoughts!
The ony other thing is a Gnd loop!
Regards
M. Gregg
Just try switching the heaters off on the pre amp for a second and see if the hum stops. It has to be both + & - of the SMPS.
You must not remove the safety Earth on the SMPS. Just check that the output is isolated from Gnd if you try to lift the heaters.
What is the Plot like on volts C1, C2?
Do you remember the plot on some PSUs I tried! C1 ripple is interesting. What is the largest cap you can use after the rectifier without damage? (Just to try it).
The charge pulses may be an issue.
Just a few thoughts!
The ony other thing is a Gnd loop!
Regards
M. Gregg
Last edited:
i just continuity tested with it unplugged again. both sides of the filament outputs have no continuity with the chassis, earth, or AC hot/neutral
testing disconnecting the pre's heaters will be difficult. my heater circuit would allow me to disconnect all of the 12a[x,t]7 tubes as a unit. much easier to pull up my whole amps 12v supply at once from the smps, but i imagine output tubes would react much more rapidly to loss of heater emissions?
If you turn the filaments off with the B+ On, on the pre while power amp is on does it stop huming? The filaments will stay hot for a few seconds. Just to try it.
I think you need to split the circuit at least so you know if its filament supply or B+.
Regards
M. Gregg
Last edited:
ill try it out. give me a little bit ill see how long i get just turning the smps entirely off for listening time. maybe it will get me usable results. the smps uses screw on wire terminals so it wouldnt be so hard to pull a wire out(my whole amp powers up as a unit, no individual switching)
ok ill have to disconnect it inside the amp, which will take me more then a minute or two as all my heaters are parallel connected, all of the 12a series tubes are paralell connected. fairly unreasonable to focus on the pre alone. drivers will have to suffer to loss of heater too?
might be helpful to know that there are 5 channels to this amplifier so wiring while simple is made complex by quantity of channels
An externally hosted image should be here but it was not working when we last tested it.
as you see i used star grounding, so ground loops should be i think reduced to a minimum?
Last edited:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
I found that increase in C1 improved the hum and supply. YMMV.
I think that the 10uF is low. You could try an increase and see if the hum reduces! This will give some indication of reducing the ripple linked to hum if you increase and nothing happens then it could be heaters. Is it possible to work on one channel? The reason I ask is because if you pull all the tubes except one channel the ripple will reduce with the reduced current!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.