Yes, I think I can say with high confidence that noise is generated on amp board. I used the old equipment from Portugal a "tube-guru" sold to me for "nothing" and told me it could be very useful for tracing "errors". I used the setting where an small amp amplifies the signal and outputs it to the built-in speaker. It has a 9V battery inside and I could hear the noise very clearly when I "measure" at -O at amp board but not at -D which is the input/output from FE-board. I also did a similar comparation with other channel where there is only a faint "ssshhhyyyy" sound at -O.
I have not tried to "work" with pot to check if a bad connection could cause this strange noise.
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Yes, ear has to be that close to hear it. But I was surprised that it was also audible in midrange speaker and in some periods of time it is almost gone so it can also change in amplitude. Can such kind of noise almost disappear and then come back again?
I will write down these steps.
Now amp is in a good period......dead silent as other channel.
I worked the pot a little bit (first placed a dot on pot so I could re-position). Now when top is off I will check bias and if problem comes back and I can't live with it I will re-flow and change zeners.
So zeners can create this kind of noise.....ok....they are connected directly to the gates....
Now amp is in a good period......dead silent as other channel.
I worked the pot a little bit (first placed a dot on pot so I could re-position). Now when top is off I will check bias and if problem comes back and I can't live with it I will re-flow and change zeners.
So zeners can create this kind of noise.....ok....they are connected directly to the gates....
My amp made a slight "hissing" noise as well as a faint hum at the tweeters(both) when I first powered up the amp after building it.My ear had to be within the 20cm range.I ignored it and now it is dead silent (its been a couple of weeks).I'm not sure when it went away but I initially checked for noises because I read other people say their amps were dead silent and so I wanted to check mine.Maybe something (p.s.) or amp has to "break in".
Still spitballing TA 4650 chassis. One heatsink per VFET card if necessary. Will try one heatsink first for both cards and measure Temperature. looks like room for cards and even internal SMPS power supply.
I guess I have a few months to conceptualize while auction feeding frenzies going on and before alternate cards become available.
I ordered small SMPS 20v PS to see if the preamp section will work with it.
Anyone have measurements on the actual size of the cards and VFET aluminum mounting bracket?
I guess I have a few months to conceptualize while auction feeding frenzies going on and before alternate cards become available.
I ordered small SMPS 20v PS to see if the preamp section will work with it.
Anyone have measurements on the actual size of the cards and VFET aluminum mounting bracket?
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Maybe there are some thermal mechanical stress inside the components that has to be "released"/"relaxed". Could this can of mechanical stress created by heat create noise inside the semiconductors?
Now amp has been silent in both channels for a couple of hours (as when it was just built some weeks ago). I wonder if it was the "work" with bias pot that has "cured" the noise?
So now I can give a small review how it works using a passive pre (10k Goldpoint pot in a metal box). It works very well. Sound is fantastic. Passive pre works much better with this amp than with e.g. ACA. So from DAC 75cm RCA cable to pre and then 75cm RCA cable to VFET amp. Only the JFET PP pair + VFET from DAC to speakers.
Now with dead silent speakers with no signal background is very "dark" and fade out of instruments just continues so room information and details are "extreme".
Normal listening level with passive pre is with pot from 1 to 5 o'clock depending of recording level. A while ago I contacted DAC manufacture and asked if DAC could drive a 10k pot and answer was "no problem". I could even go with 5k pot.
So now I can give a small review how it works using a passive pre (10k Goldpoint pot in a metal box). It works very well. Sound is fantastic. Passive pre works much better with this amp than with e.g. ACA. So from DAC 75cm RCA cable to pre and then 75cm RCA cable to VFET amp. Only the JFET PP pair + VFET from DAC to speakers.
Now with dead silent speakers with no signal background is very "dark" and fade out of instruments just continues so room information and details are "extreme".
Normal listening level with passive pre is with pot from 1 to 5 o'clock depending of recording level. A while ago I contacted DAC manufacture and asked if DAC could drive a 10k pot and answer was "no problem". I could even go with 5k pot.
From memory great Mr. Rothacher article about gate leakage current
and adjustement solutions. Extract is from this source: Fun With PASS-SIT-1 | AudioMaker
Thanks to Audiomaker.tech
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Ok....so I could measure the DC voltage over R9 (100k) to check the gate leakage current on both channels?
This current will create some noise on output?
Now amp has been dead silent until I switched it off for tonight. I am in doubt what caused the bit of noise.
With passive pre I need high input impedance of amp.......
I can hope it was just the bias pot that needed to be "worked" a bit to create a solid stable connection......
This current will create some noise on output?
Now amp has been dead silent until I switched it off for tonight. I am in doubt what caused the bit of noise.
With passive pre I need high input impedance of amp.......
I can hope it was just the bias pot that needed to be "worked" a bit to create a solid stable connection......
Meper, just chill for now
if trimpot fiddle cured noise, think first of replacing it, if issue persist (again)
that's just nature of the beast ...... I have exactly same experience with "brand name" and "clones" ( say Bourns and say Baoxxxx) - result is that I'm putting each one in multitester, at least checking them to test as 2 resistors
same (small) number of Duds , whatever written on them
if trimpot fiddle cured noise, think first of replacing it, if issue persist (again)
that's just nature of the beast ...... I have exactly same experience with "brand name" and "clones" ( say Bourns and say Baoxxxx) - result is that I'm putting each one in multitester, at least checking them to test as 2 resistors
same (small) number of Duds , whatever written on them
I think Sony TA 4650 chassis for this amp will work. I am going to commit myself to the concept over the next couple of months and strategize. I think the single heat sink will be OK dissipation for two channels, 20W class A, since heat sink was designed for 80-120 watt class AB, but will measure with T gun and alter strategy as necessary and add a heat sink/fan as necessary.
It also looks like there will be room for dual SMPS, one for each channel, a small smps for the preamp, volume knob and input section, and reasonable room for additional smoothing card and input cards. It already has an on/off input harness and switch selectors if necessary.
It also looks like there will be room for dual SMPS, one for each channel, a small smps for the preamp, volume knob and input section, and reasonable room for additional smoothing card and input cards. It already has an on/off input harness and switch selectors if necessary.
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MEPER mentioned hearing the noise from the midrange and tweeter.
My speaker's midrange driver runs full range with no crossover at all. The tweeter has only a capacitor in series. As I mentioned previously, the very high gate leakage current is not audible in my system.
The gate leakage current in my devices is constant DC so I do not know how that may be audible.
@ Ben Mah
Thanks for the answer to my question.
Transistors current leakage in audio circuit is an interesting topic..
not many articles & informations in my Ebooks library..
I do want learn more about..
I noise gets back I will work the Bourns and if this cures it again I will do something about it.
Yesterday I checked that all solder joints had tin flowing all the way from back to front of PCB holes but I could re-solder anyway if problem comes again.
The approach that pretending it is a tube is probably good. They make funny metallic sounds in the speaker during warm up.....but this is expected.