Volume changed to 2v
To follow VAR’s instructions, you would need to also set GEN1 (QA403 output signal) to +6 DBV, and then adjust the Volume control to get 2.0vRMS, so that the Gain should read approximately 0.0 dB (i.e. “Unity Gain”).
That does appear to show that your 60 Hz spike is about 20 dB quieter with your preamp turned off, indicating there is a significant contribution from the power supply in the preamp.
Ideas on how to reduce?
I have a ground connection on an old Heathkit sig generator, that is tied to ground in my wall outlet. I have a 16gauge wire, probably about 5’ long that I will connect to the phono ground on a preamp and sometimes it will reduce that 60hz noise spike quite a bit. Also, if you are using a powered usb adapter instead of the one from your PC, it may not be clean. As far as replacing things- power supply caps may cause a problem but replacing them does not guarantee a reduction in them. Sometimes there are some small caps, say 1-10uf typically around the collectors of the output transistors than go bad that may lead to extra hum…
Cute diagram. Are you suggesting an torroidal choke?
I am just shooting in the dark, but I wonder if this would be of any help to insert at the DC Out of the PS.
Just curious - what are you working with? A preamp, integrated amp, receiver? Do you have audible hum or buzzing? Are you just going for lower THD or S/N ratio numbers for the sake of lower numbers? Or maybe seeing those 60 Hz + harmonic spikes on the analyzer graph is keeping you up at night? (I can relate!) So audible hum/buzz is one thing and of course you’d want to correct it if at all possible. If it’s more the desire for lower numbers and/or a cleaner graph, you may be up against a case of diminishing returns.
What I mean is that maybe you are just seeing the results inherent in the design and the original engineers rolled with what they deemed acceptable performance given the cost and other constraints they had to work within. So you might be able to reduce the 60/120/180 Hz noise if you can find deficient parts (i.e. electrolytic caps) and replace them with better/newer parts. You may find that grounding schemes can be improved. You may be able to add shielding. You may be able to use some type of “line conditioner”. Etc, etc. Some guys try to switch to torroidal transformers, some guys move the power supply entirely out to a separate chassis, etc. You can really go to town if money, time and/or space are not constraints!
Anyway, I’m sorry if I’m getting carried away, I’m just curious what your goal is and if it’s reasonably attainable. I do wish you best of luck with it!
Cheers - Steve
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GlasgowGrip makes a lot of the points I would ask. I would not try to add anything extra into the circuits like what you are showing. Your preamp should not be that noisy as your amp will make it worse. What is the loop through of just your QA403?
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Am I missing something here, shouldn’t this circuit be attenuating the signal below 70hz if so selected? Spec defines 12db attenuation
I am measuring the Yamaha CA-1000 Integrated Amp. I am not sure what you know about the history of this unit, it was the major landmark for Yamaha defining the best of Natural Sound.
YES. I want to squeeze the best possible performance out of this unit that can be realized. I have changed out a great deal of parts and maybe have I have not made entirely correct choices.
Hi YamahaCA. Restorer-John here from ASR and AK.
Do you have the Class A switch on or off on the CA-1000? In Class A mode, the current draw on the PSU increases, the supply voltage is dropped and the mains spikes will become much more elevated. Not only that, you should consider testing the preamp stage separated (the rear switch) and the power stage separately.
Check for residual noise/mains spikes with both the selected input on the preamp shorted and with the power stage, short the inputs and look at residual too.
It’s a pity you have thrown bags of components at the amplifier before quantifying the problem/s (if any), but it is what it is.
The 70Hz HPF you ask about is 12dB per octave, so it will hardly affect mains and its harmonics.
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Do you have the Class A switch on or off on the CA-1000? I have tested in both, see post 42 & 43
In Class A mode, the current draw on the PSU increases, the supply voltage is dropped and the mains spikes will become much more elevated.
Not only that, you should consider testing the preamp stage separated (the rear switch) and the power stage separately. That is what I have shown
Check for residual noise/mains spikes with both the selected input on the preamp shorted and with the power stage, short the inputs and look at residual too. I will do that and post the results, see post 41
It’s* a pity you have thrown bags of components at the amplifier before quantifying the problem/s (if any), but it is what it is. I am not sure how you have come to that conclusion. The QA403 is a new piece of equipment for me, thus I am learning how this can assist in providing a better product. The consensus I receive from one of the forums you listed, the vast majority do not have testing abilities beyond connecting a set of very low end speakers to the amp and conduct a listen test. I have the desire to go far beyond that
The 70Hz HPF you ask about is 12dB per octave, so it will hardly affect mains and its harmonics. Thank you, I saw that in the spec and was not sure of the total effect.
This test result is only the Preamp, I have turned the coupler switch off’
Since this thread was for the “Preamp Testing” I have only shown and discussed the Preamp.
I am not sure if I understand exactly what you are asking me to do, please explain further.
I have not tested or listened to the CA-1000. Not sure what the best of natural sound means, other than Yamaha described their units as having that quality. I think what restorer-john (he knows his shit!) is suggesting that you do is to short say the AUX input with that input selected, as well as the inputs to the power amp stage and look at just the power amp noise, but I think you only care about the preamp section. THe shorts could be 50/75ohm terminations as well. I am assuming that you have the “-” inputs for both left and right channels on your QA40x terminated or shorted when measuring the preamp- I made that mistake in the beginning of my time with my QA402.
short say the AUX input with that input selected, as well as the inputs to the power amp stage and look at just the power amp noise,
So where is the QA403 connected to? You are saying to only connect the QA403 to the Main Amp Out?
but I think you only care about the preamp section.
I care very much about both. I am simply trying to divide and conquer.
THe shorts could be 50/75ohm terminations as well. I am assuming that you have the “-” inputs for both left and right channels on your QA40x terminated or shorted when measuring the preamp- I made that mistake in the beginning of my time with my QA402.
Yes the “-” inputs are shorted.
