I have a TEAC A-H500 amp which has some slight hum. Suspected a power supply problem; scoped it and found approximately 50 mV 120 Hz ripple under the load.
The 4700 uF filtering caps looked bloated so I replaced them with the new 5600 uF; however, both ripple and hum didn't go away. The attached picture shows this ripple for positive and negative rails going into power amp PCB after capacitors replacement; it looked the same way before.
The A-H500 amp is sort of high-end-ish; however, it was made in late 1990s and few components inside look cheap so it's possible they saved on a power supply.
Is it normal for amp's power supply to have such 50 mV ripples? If not what could be wrong, or perhaps it's some easy way to improve this PS?
Thank you.
The 4700 uF filtering caps looked bloated so I replaced them with the new 5600 uF; however, both ripple and hum didn't go away. The attached picture shows this ripple for positive and negative rails going into power amp PCB after capacitors replacement; it looked the same way before.
The A-H500 amp is sort of high-end-ish; however, it was made in late 1990s and few components inside look cheap so it's possible they saved on a power supply.
Is it normal for amp's power supply to have such 50 mV ripples? If not what could be wrong, or perhaps it's some easy way to improve this PS?
Thank you.
Attachments
The height of the ripple depends on the DC current drawn, as per: I = C x dV/dt
If the ripple is 50mV peak, and the capacitance is 5600uF, then the idle current
would be expected to be: 0.0056F x 0.05V/0.0083S = 0.0337A.
Seems reasonable as the idle current per channel.
If the rectifiers can handle the peak currents, you could further increase C further to decrease the ripple.
If the ripple is 50mV peak, and the capacitance is 5600uF, then the idle current
would be expected to be: 0.0056F x 0.05V/0.0083S = 0.0337A.
Seems reasonable as the idle current per channel.
If the rectifiers can handle the peak currents, you could further increase C further to decrease the ripple.
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50mV ripple is nothing for HIGH-level stages.
I bet it did not have audible hum when new.
But there's a lot more in the box. Including low-level stages fed from R-C filters. It could be some little 220uFd filter for a single chip which has gone bad.
If ANY "mods" have been done, layout is suspect.
I bet it did not have audible hum when new.
But there's a lot more in the box. Including low-level stages fed from R-C filters. It could be some little 220uFd filter for a single chip which has gone bad.
If ANY "mods" have been done, layout is suspect.
A good amp shouldn't notice even a volt of ripple on the rails, this is very likely signal path related.
But one thing to check is if the output hum is 60 or 120Hz, that's going to say whether its
mains interference in the front end (ie due to ground layout) or rail ripple related.
But one thing to check is if the output hum is 60 or 120Hz, that's going to say whether its
mains interference in the front end (ie due to ground layout) or rail ripple related.
@kotofei Did you solve this issue? I've observed something similar on mine, and you're one of only a couple of search results on the internet and the most recent by a long way.
I don't think TEAC skimped on the power supply, it's a very well made and shielded toroidal unit. I'd be very interested to hear any more that you found out...
I don't think TEAC skimped on the power supply, it's a very well made and shielded toroidal unit. I'd be very interested to hear any more that you found out...
@yeahmaybe No I didn't. First, It didn't bother me much since it didn't give audible hum at normal or slightly higher than normal listening levels.
Then I sold this thing.
It's my opinion some capacitors in the preamp section should be replaced since they are of unknown (to me) brands and ~20 yrears old. However, it's not that easy. In order to do this one should re-assemble the whole H500.
Then I sold this thing.
It's my opinion some capacitors in the preamp section should be replaced since they are of unknown (to me) brands and ~20 yrears old. However, it's not that easy. In order to do this one should re-assemble the whole H500.