Last edited:
Need to do some tests:
Short the input of J1 to ground. Is the noise present? If not, the cause is external.
Are you using a pre-preamp, or directly connecting the cartridge to the input?
Is the pre-preamp power being switched also?
If the noise is still present, short the grid of U2 to ground. Is the noise still present?
if not, the cause is the warm-up behavior of the U1 stage.
If the noise is still present, the cause is the warm-up behavior of the U2 stage.
Short the input of J1 to ground. Is the noise present? If not, the cause is external.
Are you using a pre-preamp, or directly connecting the cartridge to the input?
Is the pre-preamp power being switched also?
If the noise is still present, short the grid of U2 to ground. Is the noise still present?
if not, the cause is the warm-up behavior of the U1 stage.
If the noise is still present, the cause is the warm-up behavior of the U2 stage.
Last edited:
Thank you all for replying.
I did some measurements as suggested and found following:
After 30min:
High Voltage / AC=210V / DC=261V / REG=248V
Low Voltage (heaters) / AC=8.75V / DC=9.3V / REG=6.97V
I will try to either replace LM317 with LT1084 or other regulator with lower drop voltage. Change the transformer for higher power rating.
I know pretty much what is causing this.
First of all, is because I know how to read a data sheet.
Secondly, "data sheets lie".......
1. Data sheet "suggests" at least 3-4 volts margin for stable regulation. BS.
I suggest you use at least 2X input voltage for stable output regulation.
2. LM317 can generate finger burning heat. I tell most folks use Artic Ice, or some other really good thermal paste with the heatsink that matches your LM footprint.
3. Having worked with LM317(s) in the past, I did devise a scheme which mitigates all thermal waste generated by said device. Perhaps if Lounge Lizard swears to me he won't rip me off on this one, perhaps I'd might post the fix .
Sorry Rayma, you`ve lost me. Which noise are you referring to?
The 40V pulse.
Last edited:
Guys, read post #12. The noise from the output was solved. Transformer replaced. The regulators are working properly and there is no more noise.
The other issue was the 40V DC voltage spike at the output, when I power OFF the unit. This was fixed by adding a input capacitor. I`m trying to understand the cause of the voltage spike and if there is another fix. I have a mute circuit but the relay does not switch off fast enough to block the voltage spike.
The other issue was the 40V DC voltage spike at the output, when I power OFF the unit. This was fixed by adding a input capacitor. I`m trying to understand the cause of the voltage spike and if there is another fix. I have a mute circuit but the relay does not switch off fast enough to block the voltage spike.
Since your simulating replace the B+ supply (250v) with a pulse source. You can then see the effect of turning on and off the supply.
That's a good plan. Also vary the B+ supply's impedance. You have three stages fed from the same (common) supply, which is one too many. Instability is possible with non-zero supply impedance.
YOS,
Chris
YOS,
Chris
Pulse source plus series diode plus reservoir cap to mimic a simple supply. I had a simple problem with PA design and this showed it up nicely.
Thanks for suggestion. I wish I was that good in LT Spice and understand how to do it. I can put bits and pieces together, but my knowledge is limited.
I`m attaching the simulation file. Maybe someone can have a look. Thanks.
View attachment Phono MM-MC-CCS.asc
I`m attaching the simulation file. Maybe someone can have a look. Thanks.
View attachment Phono MM-MC-CCS.asc
Since your simulating replace the B+ supply (250v) with a pulse source. You can then see the effect of turning on and off the supply.
The problem seems to stem from that when you turn off the supply U1 is taking a constant current. Thus any supply changes appear on the plate of U1. This drives U2 out of conduction causing the big spike. This is bad too as any hum on the supply will get directly into U1 plate and to the output. Maybe split U1 plate resistor and decouple. Actaully seemed to oscillate when supply turned off. Did not find a good solution. Making C4 smaller may help a bit.
Last edited:
- Home
- Amplifiers
- Tubes / Valves
- Need help troubleshooting the output noise