I use the same tubes. I cant comment yet, the high freq. tone makes the whole tone harsh at the moment so will have to find the problem first....
Annoying noise....
I have isolated the annoying noise I get from the phono the input is shorted to ground so I have no idea where is it coming from...WIFI???
I have added the sound file in ZIP....
View attachment noise-EO-phono.zip
I have isolated the annoying noise I get from the phono the input is shorted to ground so I have no idea where is it coming from...WIFI???
I have added the sound file in ZIP....
View attachment noise-EO-phono.zip
I don't know either. Looking at it quick and dirty in foobar2000, the high frequency noise appears about 3kHz with some additional near 5kHz. The level is equal in both left and right and runs -30 to -35 dB.
The fact that it is in both channels suggests it is not a single tube or single component in the signal path. Could you measure the power supplies to see if the noise is in them?
If it is airborne RF noise, you might take your cell phone and wave it near to the circuit. I have often had cell phone generate a noise similar to that on other circuits, especially when the cover is off the enclosure.
Anyone else have suggestions for tracing this?
The fact that it is in both channels suggests it is not a single tube or single component in the signal path. Could you measure the power supplies to see if the noise is in them?
If it is airborne RF noise, you might take your cell phone and wave it near to the circuit. I have often had cell phone generate a noise similar to that on other circuits, especially when the cover is off the enclosure.
Anyone else have suggestions for tracing this?
Guys, I think I found the problem in B- power supply so I changed the RAW filter but after power up R54 this is the 8.2K resitor on the B+ regulator began to cook....so I turned it down and cant find the problem! The B- supply work I get -13.5V. The heater is working just the B+ is collepsing! I hope the JFETs arent dead! Any idea?
Not sure what to recommend.
When you say that you changed the output cap from 220 uF to 470 uF with no effect, are you referring to C24 in the schematic below? If so, you might try the same change at C23 instead. From my experience, the cap at the adjust terminal is important for controlling ripple.
Also, not a likely thing, but check that the polarity of these electrolytics is correct with the plus terminal to ground. It could form a leak current in the wrong polarity and the schematic isn't very specific about marking polarity.
Does the noise look like a sine, indicating ripple? It is possible that there is a faulty component that is breaking down or leaking somehow. D9, D19, and the LM337 would be the next things to try replacing.
Good luck with this. Hunting down noises is never much fun.
Jac
When you say that you changed the output cap from 220 uF to 470 uF with no effect, are you referring to C24 in the schematic below? If so, you might try the same change at C23 instead. From my experience, the cap at the adjust terminal is important for controlling ripple.
Also, not a likely thing, but check that the polarity of these electrolytics is correct with the plus terminal to ground. It could form a leak current in the wrong polarity and the schematic isn't very specific about marking polarity.
Does the noise look like a sine, indicating ripple? It is possible that there is a faulty component that is breaking down or leaking somehow. D9, D19, and the LM337 would be the next things to try replacing.
Good luck with this. Hunting down noises is never much fun.
Jac
Yes Its sine wave 2-3mV...When connected to speakers there is hum on both channels on the LEFT a little more than on RIGHT. The hum is not constant it depends on volume control.On scope it is coming from B- supply. hmmmm
I disconnected the B+ and the hum is coming from B-. Its 2-3mV mixed freq. humming on speakers when the volume control is turned more 1/2 turns I can hear it near the speakers.
I must correct myself after I tested the new installed C22 I replaced the 1nF caps with 220uF as my raw psu is 1 meter apart from the amp stage the regulator has no ringing but the Hum I get from the speakers is constant in both speakers just slightly more on left! A ground loop? I am using the graounding shematic SY proppsed.
The 220 uF replacement of C22 might be part of your problem. The datasheet for the LM337 recommends a 1 uF tantalum cap for distances longer than about 100mm from the RAW supply filter cap. But a jump to a 220 uF electrolytic is pretty big and may not be better. The internal LM337 circuit is somewhat complex, so it isn't easy to estimate what might happen, but perhaps something in the 1 to 2.2 uF range might be worth a try. I would also consider a parallel 1 nF cap to address higher frequencies.
For what it is worth, my RAW supply is almost 1 meter from the regulator and I am using only the 1 nF recommended by SY. If yours is ringing with the 1 nF, there might be something else going on.
For what it is worth, my RAW supply is almost 1 meter from the regulator and I am using only the 1 nF recommended by SY. If yours is ringing with the 1 nF, there might be something else going on.
Think. If it varies with the volume control, what does that tell you about is origin?
If you put your scope directly across the last elco on the B- supply, directly at the elco, what do you see?
Jan
Was looking for a phono pre for my MM an i stumbled onto Sy's HMN MC pre and after messaging him on a MM version of HMN he suggested the Equal Opportunity pre.
I really like the design and would build it in a heart beat.
The only problem is the availability of the LSJ74 jfets wich are out of stock everywhere. Does anyone know of any substitutes? Any recommendations would be very welcome.
I really like the design and would build it in a heart beat.
The only problem is the availability of the LSJ74 jfets wich are out of stock everywhere. Does anyone know of any substitutes? Any recommendations would be very welcome.
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