Hi,
I am building tube preamplifier with ECC82 valves. It is SRPP desing with 350V power suply voltage. Well, my problem is that I have buzz mixed with sound and I don't know how to solve that problem. Buzz is louder with more opened volume pot. I did everything to solve it: remove input selector(I left only one input without any relays and output directly connected to power amp), stabilized voltage using TL 783, star ground scheme(left and right channels are separated completly-I am using one power suply so it is only point of connection). All of this didn't help. Is it possible that my suply voltage is too high? or it can't deliver enough current? Transformer is toroid with 300V 50mA secondar.
I am building tube preamplifier with ECC82 valves. It is SRPP desing with 350V power suply voltage. Well, my problem is that I have buzz mixed with sound and I don't know how to solve that problem. Buzz is louder with more opened volume pot. I did everything to solve it: remove input selector(I left only one input without any relays and output directly connected to power amp), stabilized voltage using TL 783, star ground scheme(left and right channels are separated completly-I am using one power suply so it is only point of connection). All of this didn't help. Is it possible that my suply voltage is too high? or it can't deliver enough current? Transformer is toroid with 300V 50mA secondar.
Have you scoped the power supply rail to see what's going on there?
And I wouldn't discount a ground loop- there are star grounds and star grounds.
It's often useful to have someone else go through your wiring to see if you've made an obvious error; they're the ones that will drive you crazy because you're soclose to the problem, you can't see them.
And I wouldn't discount a ground loop- there are star grounds and star grounds.
It's often useful to have someone else go through your wiring to see if you've made an obvious error; they're the ones that will drive you crazy because you're soclose to the problem, you can't see them.
Hi,
With a B+ of 350V on the top triodes you're very close to exceeding the max. design ratings for the heater/cathode insulation of the ECC82/12AU7.
As you're using two ECC82s you should use one for the top triodes and the other for the bottom ones.
The heater supplies should be independent of each other so the top triodes heaters can be bias upwards by injecting a portion of the B+ into the heater circuit.
If you must use a single heater supply or have to use a single valve per channel you can average the voltage you inject into the heater supply so that you still stay within limits for both valves.
Cheers,
With a B+ of 350V on the top triodes you're very close to exceeding the max. design ratings for the heater/cathode insulation of the ECC82/12AU7.
As you're using two ECC82s you should use one for the top triodes and the other for the bottom ones.
The heater supplies should be independent of each other so the top triodes heaters can be bias upwards by injecting a portion of the B+ into the heater circuit.
If you must use a single heater supply or have to use a single valve per channel you can average the voltage you inject into the heater supply so that you still stay within limits for both valves.
Cheers,
Perhaps it is a question of layout? Depending on what type of preamp you could consider it as a high gain device and more susceptable to field induced hum. Can you move any power supply components or wiring away from the signal wiring, or visa-versa? Have you neatly ordered all you wiring and kept heater wires spaced out into the case corners? Sometimes the buzz comes from a choke or transformer mounted a little too close to the signal path. It sounds like you are moving closer to the end so don't give up.
EMI/RFI
mot,
If you are shure that you have EMI induced voltages through PS or signal wires, than the best way is to try,first,to move tx as away as possible from the low level circuitry,than try next step to turn tx for 90 degrees or 45 degrees(try both axes) and finally shield the tx with magnetic iron sheet,about 1-2 mm. or thicker(better), not alumunium or copper.They are good for RFI unduced voltages(have a look inside tuner input circuits and it will became you clearer).
Regards,
Yugovitz
mot,
If you are shure that you have EMI induced voltages through PS or signal wires, than the best way is to try,first,to move tx as away as possible from the low level circuitry,than try next step to turn tx for 90 degrees or 45 degrees(try both axes) and finally shield the tx with magnetic iron sheet,about 1-2 mm. or thicker(better), not alumunium or copper.They are good for RFI unduced voltages(have a look inside tuner input circuits and it will became you clearer).
Regards,
Yugovitz
Yugo,
After all I did with my preamp I am sure this is only possibility. I belive that wiring is OK. When I disconect input board- there is only shielded cable to volume and balance pots and from that point to preamp circuitry there is no buzz and hum at all. I also checked my input board, compared my design with some others and I am sure that is not problem. Also all high voltages wires are placed as far as possible and verticaly to signal wires. Only my heater wires are parallel with input board for about 5-6 cm. I didn't try to change that(my heater voltage is stabilized). All power supply stuff is max on left side of preamp and other boards, input RCA connectors and pots are on right side.
After all I did with my preamp I am sure this is only possibility. I belive that wiring is OK. When I disconect input board- there is only shielded cable to volume and balance pots and from that point to preamp circuitry there is no buzz and hum at all. I also checked my input board, compared my design with some others and I am sure that is not problem. Also all high voltages wires are placed as far as possible and verticaly to signal wires. Only my heater wires are parallel with input board for about 5-6 cm. I didn't try to change that(my heater voltage is stabilized). All power supply stuff is max on left side of preamp and other boards, input RCA connectors and pots are on right side.
Buzz/hum
mot,
in the past i have met the same problems and believe me grounding and "all that jazz" can be PITA!So you are not the only one who buzz and hum problems drove you crazy!Tell me have you grounded heater supply properly?It should be tied to the first B+ cap in a star ground configuration.And how much capacitance do you have in the B+?Sometimes all things settle down with experience so you have to be patient.And by the way ,do you have buzz or hum or both?If it is buzz it can be more oscilation somewhere or induced interference.If it is hum it can be motorboating,less filtering capacitance or a ground loop.
Regards,
Yugovitz
mot,
in the past i have met the same problems and believe me grounding and "all that jazz" can be PITA!So you are not the only one who buzz and hum problems drove you crazy!Tell me have you grounded heater supply properly?It should be tied to the first B+ cap in a star ground configuration.And how much capacitance do you have in the B+?Sometimes all things settle down with experience so you have to be patient.And by the way ,do you have buzz or hum or both?If it is buzz it can be more oscilation somewhere or induced interference.If it is hum it can be motorboating,less filtering capacitance or a ground loop.
Regards,
Yugovitz
My heater suply is connected via voltage divider to B+ cap placed after stabilization circuit with TL783. Lower resistor bypass 100uF cap.
B+ cap is 150uF / 400V BCcomponents. I tryed with bigger one(220uF) with no success.
Yesterday I decided to power it up and played some music and noticed that after 10-15 min buzz dispappear on other inputs but was present when amp was cool. This is really confusing me
Before this preamp I built few of them(all solid state) and I never had such problems...
B+ cap is 150uF / 400V BCcomponents. I tryed with bigger one(220uF) with no success.
Yesterday I decided to power it up and played some music and noticed that after 10-15 min buzz dispappear on other inputs but was present when amp was cool. This is really confusing me
Before this preamp I built few of them(all solid state) and I never had such problems...
@mot said:My heater suply is connected via voltage divider to B+ cap placed after stabilization circuit with TL783. Lower resistor bypass 100uF cap.
B+ cap is 150uF / 400V BCcomponents. I tryed with bigger one(220uF) with no success.
Yesterday I decided to power it up and played some music and noticed that after 10-15 min buzz dispappear on other inputs but was present when amp was cool. This is really confusing me
Before this preamp I built few of them(all solid state) and I never had such problems...
It looks to me like two of your inputs are acting as antennas, and at turn on, some component in your system is putting out RFI until, for some reason, it stops.
Have you tried putting 100R to 1k carbon comp gridstoppers right against your grid pins? If this buzz is from oscillation, this might stop it.
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