I have a Cyrus 3 that sounds great, but every time I turn it on, it makes an almighty thump. I think it is supposed to be a 'soft switch on'. Can anyone suggest what might need servicing?
I thought I might replace the power caps, but beyond that I don't know what it will need. anyone know how to check the bias and adjust DC offset on this?
Thanks!
I thought I might replace the power caps, but beyond that I don't know what it will need. anyone know how to check the bias and adjust DC offset on this?
Thanks!
On start up a soft start circuit typically loads the transformer via a resistor to limit the inrush current. Then half a second later or similar, it is switched out of the circuit and the transformer is then connected directly to the mains supply.
Usually the in rush current and the current the resistor is exposed to will be many many times the rated power of said resistor. This is usually not a problem, as power resistors generally have a very large surge current capacity. But, over time it could have burnt out. If this is the case then the soft start section of the power on sequence would fail to operate and instead, when the relay that switches the resistor out of the circuit switches, the transformer will be connected directly to the mains, causing the thump.
Of course if it is relay controlled its reasonable to assume that a relay could have failed too.
One thing to mention is that the Cyrus three isn't a particularly powerful amplifier and as a result the required transformer wouldn't be that large. Say 200-300 VA, typically you don't need a soft start circuit in these cases, as the inrush current demanded by the transformer, to establish it's magnetic field, isn't high enough to be a concern, or trip circuit breakers.
Usually one prevents start on thumps by having the amplifier output disconnected from the loudspeakers, via a relay on turn on. Then a couple of seconds after the amplifier has stabilised, providing there isn't a fault condition, the relay would close and connect the amplifier to the loudspeakers.
It looks like you need to pop the lid off and see what's going on
Usually the in rush current and the current the resistor is exposed to will be many many times the rated power of said resistor. This is usually not a problem, as power resistors generally have a very large surge current capacity. But, over time it could have burnt out. If this is the case then the soft start section of the power on sequence would fail to operate and instead, when the relay that switches the resistor out of the circuit switches, the transformer will be connected directly to the mains, causing the thump.
Of course if it is relay controlled its reasonable to assume that a relay could have failed too.
One thing to mention is that the Cyrus three isn't a particularly powerful amplifier and as a result the required transformer wouldn't be that large. Say 200-300 VA, typically you don't need a soft start circuit in these cases, as the inrush current demanded by the transformer, to establish it's magnetic field, isn't high enough to be a concern, or trip circuit breakers.
Usually one prevents start on thumps by having the amplifier output disconnected from the loudspeakers, via a relay on turn on. Then a couple of seconds after the amplifier has stabilised, providing there isn't a fault condition, the relay would close and connect the amplifier to the loudspeakers.
It looks like you need to pop the lid off and see what's going on
Here are some pictures from inside the amp. I don't see any relays at all! There is about 8mV of DC on the outputs.
Any tips on what those little pots do? Adjust bias a guess, in which case how do I go about making sure that is correct?
I wonder if the non-polar caps in the pre-amp section just need replacing? The pre-amp PSU just seems to run on 3-pin regs so I guess that should be okay.
Any tips?
Big pictures here:
Any tips on what those little pots do? Adjust bias a guess, in which case how do I go about making sure that is correct?
I wonder if the non-polar caps in the pre-amp section just need replacing? The pre-amp PSU just seems to run on 3-pin regs so I guess that should be okay.
Any tips?
Big pictures here:
It seems those pics were resized.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
What richieboy said. Has the amp always done this? Or is it a recent problem?
I can't see any relays from those pictures either.
Usually turn on thump is nothing to be worried about, unless it's large enough to damage the loudspeakers. Both the Musical Fidelity A1 (old version) and the Quad 77 integrated we've got here both have turn on thump.
I can't see any relays from those pictures either.
Usually turn on thump is nothing to be worried about, unless it's large enough to damage the loudspeakers. Both the Musical Fidelity A1 (old version) and the Quad 77 integrated we've got here both have turn on thump.
Hi,
I don't really remember if it always did it. On fully passive speakers it's not too annoying, although still more than I expect. Recently though, I have semi-active speakers. The bass section has it's own amps that take a feed from the main speaker level signal, knock it down by resistors and then does it's stuff. Like this, the thump is massive and I worry about the speakers.
I just checked my Mum's Cyrus 7 and that also has a small thump at switch on with her passive speakers. Maybe it is normal, but I wonder why it is stronger with the semi-active ones?
I don't really remember if it always did it. On fully passive speakers it's not too annoying, although still more than I expect. Recently though, I have semi-active speakers. The bass section has it's own amps that take a feed from the main speaker level signal, knock it down by resistors and then does it's stuff. Like this, the thump is massive and I worry about the speakers.
I just checked my Mum's Cyrus 7 and that also has a small thump at switch on with her passive speakers. Maybe it is normal, but I wonder why it is stronger with the semi-active ones?
The turn on thump shouldn't change depending on the loudspeaker configuration, unless of course you're driving a tweeter directly.
Normally in a passive crossover a cap would prevent any thumps from reaching the tweeter, but nothing should attenuate anything to a mid/bass. If the turn on thump is significantly worse when going to a mid/bass unit, in the active configuration then, to me, it would hint at something else being wrong.
You say you take the high level signal, then reduce it by a combination of resistors and then feed that into the amplifier. I don't suppose you're amplifying a turn on thump in some way?
Normally in a passive crossover a cap would prevent any thumps from reaching the tweeter, but nothing should attenuate anything to a mid/bass. If the turn on thump is significantly worse when going to a mid/bass unit, in the active configuration then, to me, it would hint at something else being wrong.
You say you take the high level signal, then reduce it by a combination of resistors and then feed that into the amplifier. I don't suppose you're amplifying a turn on thump in some way?
Indeed, or whatever order the chain needs to be turned on to prevent any accidental amplification of turn on thumps.
In my system if I turn the power amps on, then turn on the active xover/preamp I'll get a real nasty noise being sent to the speakers. Then if I turn the DAC on after the power amp and after the pre amp, I'll get another thump! Naturally I can attenuate the turn on thump from the DAC by turning the volume down on the preamp.
Either way I leave the preamp and DAC on all the time, only the power amps get turned on and off.
But it is certainly necessary to observe the power on sequence in a chain of audio products, if they don't have relays to mute the outputs, until after the unit has settled down.
Rather then attenuating the high level output of the first power amp I'd be looking at DIYing in a set of preouts to drive the second amplifier.
There are 100u tantalum capacitors in the amp feedback. This is a bit nasty: they are polaire, while there is no DC voltage. It might be that these break down. But then, it is unlikely that both break down at the same time: So if you have the thumb on 1 output only, then, this might be your problem.
This is a long shot - I'm trying to find answers around the internet..
Has anyone had an experience of the 3i taking a while to "warm up" before it will switch on?
I've just aquired one and it goes through the self-test and then takes a good while before a button press will take it out of standby.. 12 minutes (I was waiting whilst I typed this).
Then it sounds fine (other than some zipper noise from the volume control).
I am guessing that this isn't normal! What could it be, old caps?
Has anyone had an experience of the 3i taking a while to "warm up" before it will switch on?
I've just aquired one and it goes through the self-test and then takes a good while before a button press will take it out of standby.. 12 minutes (I was waiting whilst I typed this).
Then it sounds fine (other than some zipper noise from the volume control).
I am guessing that this isn't normal! What could it be, old caps?
Just a hunch but I would check the voltage regulators for dry joints.
If similar to my (same period) 'Power' and 'Pre', they stay active even in standby mode, so get pretty hot and can be a failure point with charred PCB in some cases. Hence they have those heatsinks on them.
I did have a Cyrus 7 that refused to come out of standby. I sold it as broken, but the chap told me he baked the PCB in the oven and it came back to life. Must have been a bad joint somewhere, even though I had looked and didn't find any.
If similar to my (same period) 'Power' and 'Pre', they stay active even in standby mode, so get pretty hot and can be a failure point with charred PCB in some cases. Hence they have those heatsinks on them.
I did have a Cyrus 7 that refused to come out of standby. I sold it as broken, but the chap told me he baked the PCB in the oven and it came back to life. Must have been a bad joint somewhere, even though I had looked and didn't find any.
Last edited:
When kept near the balcony sliding door in this colder weather, that's when it took about 10 mins to switch on from being plugged in. When in the middle of the flat, a warmer spot, it was only about a minute to wait.. When plugged-in on standby, no trouble at all.
It must be fairly slight. I wonder if there actually is a temperature control in there rather than a dry joint.
It must be fairly slight. I wonder if there actually is a temperature control in there rather than a dry joint.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.