Hi Gents, I had an interesting occurrence I was curious if anyone had some insight to. I have a Classe DR-8, I've recapped it, new signal wire, generally left the power section alone. It's been great for weeks continually on - all of a sudden the transformer started humming fairly loudly. I shut the amp off, noticed the power fuse blown - replace the fuse with a 6A (from 8, it's what I had), turned it back on - all fine.
Very interesting, would this be a symptom of a Toroidal on it's way out? Or symptom indicative of something else?
Would enjoy the thoughts! Thanks..
Very interesting, would this be a symptom of a Toroidal on it's way out? Or symptom indicative of something else?
Would enjoy the thoughts! Thanks..
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That looks to me like there was some residual magnetization in the core, causing saturation. That could blow the fuse. A subsequent power-on transient may have degaussed it, depending on waveform polarity when power was applied.
Possible and very well could have been. Just never an occurrence I’ve never encountered before. Appreciate it.
Also a symptom of DC on your AC incoming from the wall. DC offset will make them buzz. You can easily make a dc blocker for a few dollars. It’s not a bad idea no matter what is going on.
I honestly don't see this as a possibility. The only time the core could have any N/S magnetization, is at the time of switch-off. Otherwise, the core is exposed to high frequency (from the core-material point of view, the 50/60Hz is high frequency...) current that keeps that core de-magnetised (if thinking from the permanent magnet angle/point of view).
Q. What has changed for that to become a problem??
A. You re-caped it....
A blown fuse means something is definitely not okay. Providing more details may help us further... like, what do you mean by: "generally left the power section alone"??
Which box did you re-cap?? The pre-amp, or the power supply as well?
If you played with the pre-amp only, did you replace the DC rails filtering caps as well?
Did you measure the voltage rails AND current consumption BEFORE and AFTER you re-caped it? The current consumption can usually be measured across high-power resistors, found in the DC rails' regulation section.
Judging by the blown fuse thingy... it seems to me your mods are not done correctly - there might be some extra load introduced there.... for example, the orientation of electrolytes might be back to front..?
I assume you had some sort of circuit diagram with you? if YES, post it here and circle the capacitors you replaced.
Also, take some photos and show us what you did, exactly.
A noisy transformer can be DC on the mains.
Requires a mains DC blocker. 4 diodes and a cap.
Or an overload on the output.
Might be an electrolytic cap on the way out ?
Requires a mains DC blocker. 4 diodes and a cap.
Or an overload on the output.
Might be an electrolytic cap on the way out ?
That is likely a capacitor soldered in backwards that started to protest. No pictures, not enough information so all guesswork. It very probably is a consequence of the recapping so check again if all caps are soldered in right.
The DR-6 outboard PSU was not touched? Please do check the caps in the PSU and the rectifier diodes. If all is OK then measuring current in the PSU rails to the preamp could tell something.
The DR-6 outboard PSU was not touched? Please do check the caps in the PSU and the rectifier diodes. If all is OK then measuring current in the PSU rails to the preamp could tell something.
Guys, I appreciate all of your responses. The work I did was really on the amp boards and signal - caps and wire. No change to anything power. I've attached some pics, if they show anything. I'm generally obsessed with cap polarity, so ensured that was of course in check. I did a little maneuver bypassing the signal film cap with a .1uF mundorf, great results.
I didn't touch the main filter caps, since they are $80+ each. The power board I was going to replace the electrolytics, but on the underside had all sorts of surprises I didn't feel like dealing with - resistors, transistors tacked to the main cap, so I just left it. Still have the replacement caps, maybe I'll get to it. Not thrilled about ripping it apart again, but will. Since yesterday all fine again - I can't say I've ever had an amp do that, only to just reset with a power cycle.
Appreciate your input Jean-Paul, I followed a lot of your guidance on another thread/amp.
I was thinking rectifier?
I didn't touch the main filter caps, since they are $80+ each. The power board I was going to replace the electrolytics, but on the underside had all sorts of surprises I didn't feel like dealing with - resistors, transistors tacked to the main cap, so I just left it. Still have the replacement caps, maybe I'll get to it. Not thrilled about ripping it apart again, but will. Since yesterday all fine again - I can't say I've ever had an amp do that, only to just reset with a power cycle.
Appreciate your input Jean-Paul, I followed a lot of your guidance on another thread/amp.
I was thinking rectifier?
That is not an DR-6 AFAIK and yes of all caps the main filter caps need replacement most, certainly in power amplifiers 😉
Please measure the rectifiers and replace them just in case (to exclude them). They did a good job for decades and better retire in time. Low cost so no drama and imagine the damage when one diode becomes a short circuit which is the usual error mode. The symptoms would be similar to what happened but normally the faulty diode does not recover. Same would apply to a faulty filter capacitor but those can recover. Transformer failure is more rare but still a possibility. Last possibility would be one of the circuits having an error that causes large currents.
Please note that the short but quite serious fault may return with then a possibly less good outcome. One just knows something is about to happen. BTW It is not the best practice leaving (vintage) electronics powered on 24/7 unattended.
Please measure the rectifiers and replace them just in case (to exclude them). They did a good job for decades and better retire in time. Low cost so no drama and imagine the damage when one diode becomes a short circuit which is the usual error mode. The symptoms would be similar to what happened but normally the faulty diode does not recover. Same would apply to a faulty filter capacitor but those can recover. Transformer failure is more rare but still a possibility. Last possibility would be one of the circuits having an error that causes large currents.
Please note that the short but quite serious fault may return with then a possibly less good outcome. One just knows something is about to happen. BTW It is not the best practice leaving (vintage) electronics powered on 24/7 unattended.
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Thanks Jean Paul, typo! DR-8, and yes, we're zoning in to some good possibilities - inexpensive too, beyond the caps. Really appreciate you jumping in to these discussions the way you do.
So this is an interesting development - amp started buzzing again, only this time I switched on the source. Played some music for a few seconds, then switched it off - buzz gone...
🙂 maybe the filter caps??
🙂 maybe the filter caps??
If you wait till the intermittent fault becomes a permanent one the damage may be more costly than the caps. Of course you can gamble (you already do) but it would be good to do some searching for good quality caps for normal prices. Replacing the rectifiers speaks for itself as explained.
When the question mark becomes an exclamation mark you will be too late. Just imagine what may happen and what the resulting damage will be.
Please put the power plug of the source the other way around in the wall socket. Just curious.
When the question mark becomes an exclamation mark you will be too late. Just imagine what may happen and what the resulting damage will be.
Please put the power plug of the source the other way around in the wall socket. Just curious.
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Hey Jean-Paul, oh for sure. You'd suspect the filter caps then? The correlation between the power draw with no active driving of power and then remedied by driving the amp seems indicative of capacitance. On the power plug, mine are polarized, so only one way..
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Let’s agree that replacing filter caps and rectifiers that have had a service life of several decades is not that strange. After all it are exactly these parts that do wear out contrary to the coupling and decoupling caps that rarely fail.
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Yes, what is this thing anyway, '91? 🙂 Whats a few more hundred in caps anyway... Thanks for your opinions..
Well it is not about opinions but about avoiding total, costly and frustrating failure that does not care about anyones opinions.
What value and voltage are the caps in the DR-8? Last time I bought large can electrolytic caps was before Covid I think and they were not that expensive then but things unfortunately have changed.
Maybe a fellow DIYer that reads this has that caps in stock...
What value and voltage are the caps in the DR-8? Last time I bought large can electrolytic caps was before Covid I think and they were not that expensive then but things unfortunately have changed.
Maybe a fellow DIYer that reads this has that caps in stock...
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