Is anything wrong with my Anthem MCA-525?

[TLS Guy]

On and off thumps due to DC offset turning on and off should not occur. That is bad design period.

There are two approaches to prevention. One is to design an amp that does not send DC offset as the power transistors charge and discharge. That is the optimal approach. My Quads do not send speaker damaging thumps out at turn on and turn off. There are no relays in the speaker circuit.

The other solution is to use relays to connect and disconnect the speakers during the time of turn on and turn off. The relays are driven by LM 500 series timer ICs. This is common. The downside is relay contacts in the speaker leads.

The cap in the speaker lead is a bad solution. Once you do that the amp is no longer a direct coupled one, and the bass response will be limited.

 

[PENG]

Can i ask you while all input devices off to measure DC voltage on front speaker output. During switching amp on and off and after off for some time. With speaker connected and without. In auto on an manual. Sorry probably asking a lot. I need to decide what to do with this amp.

Input devices on and off made very little difference, basically with no speakers connected:

Power amp "ON" output voltage at binding posts: 24 to 26 mV dc right channel, -34 to 37 mV LCH
Power amp "OFF" output voltage at binding posts: 11 mV dc right channel, near 0 mV dc RCH

The outage drop slowly upon power off eventually settled at around 11 mV (Left) and almost 0 mV (Right).

With speakers connected, basically same as above except as soon as power amp is turned "OFF", voltage at binding post went to 0 quickly, that should be expected because of the low resistance (to dc) of the speakers.

So I can now conclude that the voltages you are getting are most likely "normal" though a little high for my taste. They are still just phantom voltages due to capacitive coupling effects easily picked up by a good quality digital multimeter that has very high input impedance. My more expensive amps registered much lower phantom voltages but being more expensive it is reasonable to expect they have better shielding, grounding schemes and isolation where needed.

By the way the MCA does have relay isolation for power on.

 

[PENG]

OK, may be then.

Dunno, I never really jacked with any of this, never had any problems, on commercial gear.

Of course, for DIY gear you need to check that you don't have some serious design flaw or something mis-connected, BEFORE you hook up your speakers.

Actually I am sure you are right, that the MCA does not use capacitor coupled output like one of my vintage Marantz does. The 20-40 mV dc are most likely just capacitive coupling effect caused not by real physical capacitors but by inherent capacitive effects due to imperfect shielding, wiring and components layout, and insulation/isolation etc.. I am sure guys like you and TLSG know what I am referring to.

 

[Andrein]

On and off thumps due to DC offset turning on and off should not occur. That is bad design period.

There are two approaches to prevention. One is to design an amp that does not send DC offset as the power transistors charge and discharge. That is the optimal approach. My Quads do not send speaker damaging thumps out at turn on and turn off. There are no relays in the speaker circuit.

The other solution is to use relays to connect and disconnect the speakers during the time of turn on and turn off. The relays are driven by LM 500 series timer ICs. This is common. The downside is relay contacts in the speaker leads.

The cap in the speaker lead is a bad solution. Once you do that the amp is no longer a direct coupled one, and the bass response will be limited.

Thank you for response. Could you give me a link to devices like you mentioned in p.2 please. This amp sounds great. So would like to try that solution

 

[PENG]

Thank you for response. Could you give me a link to devices like you mentioned in p.2 please. This amp sounds great. So would like to try that solution

My older MCA20 does have relay isolation, your MCA525 is a newer version of the same basic design so I am quite sure it has relay isolation build in already. When you turn the amp power off, it should continue to make sound because of the large power supply filter capacitors, but after a little delay you should hear the relay clicks, to isolate the speakers.

 

[Andrein]

Input devices on and off made very little difference, basically with no speakers connected:

Power amp "ON" output voltage at binding posts: 24 to 26 mV dc right channel, -34 to 37 mV LCH
Power amp "OFF" output voltage at binding posts: 11 mV dc right channel, near 0 mV dc RCH

The outage drop slowly upon power off eventually settled at around 11 mV (Left) and almost 0 mV (Right).

With speakers connected, basically same as above except as soon as power amp is turned "OFF", voltage at binding post went to 0 quickly, that should be expected because of the low resistance (to dc) of the speakers.

So I can now conclude that the voltages you are getting are most likely "normal" though a little high for my taste. They are still just phantom voltages due to capacitive coupling effects easily picked up by a good quality digital multimeter that has very high input impedance. My more expensive amps registered much lower phantom voltages but being more expensive it is reasonable to expect they have better shielding, grounding schemes and isolation where needed.

By the way the MCA does have relay isolation for power on.

Thank you for checking. Yeah my amp shows more dc than yours. Despite that relay you mentioned. And being a newer model))) will try to contact Anthem tomorrow. But guess they will say it is normal. In this case i would like to try that timer relay.

 

[PENG]

What is the sensitivity of your speakers and do they pop loud, or just barely audible?

 

[PENG]

Thank you for checking. Yeah my amp shows more dc than yours. Despite that relay you mentioned. And being a newer model))) will try to contact Anthem tomorrow. But guess they will say it is normal. In this case i would like to try that timer relay.

The relay in the amp should take care of the turning on issue but maybe in your case the time delay was not long enough. Turning off is a different story, and I am not sure if it is a better idea (or worse) to open the speaker before turning off the power amp. I also don't think it is a good idea to introduce another relay down stream, that's another source of trouble. The device could be subject to a lot of switching under load if you forget to turn the volume down first every time. You can program things to turn the preamp power off first, but that is not recommended best practice either. Common practice is to always turn the preamp on first, power amp last and reverse the order on powering down.

 

[Andrein]

I

The relay in the amp should take care of the turning on issue but maybe in your case the time delay was not long enough. Turning off is a different story, and I am not sure if it is a better idea (or worse) to open the speaker before turning off the power amp. I also don't think it is a good idea to introduce another relay down stream, that's another source of trouble. The device could be subject to a lot of switching under load if you forget to turn the volume down first every time. You can program things to turn the preamp power off first, but that is not recommended best practice either. Common practice is to always turn the preamp on first, power amp last and reverse the order on powering down.

In my case the is a pop even without pre connected. My front speakers have sensitivity of 91db. The pop is not too loud but noticeble.

 

[Andrein]

Maybe manual switch which connects or disconnects all speakers at once?

 

[PENG]

Maybe manual switch which connects or disconnects all speakers at once?

Not really, the relay works the same way in manual or Auto.

 

[PENG]

Can you try it with a different speaker?

 

[highfigh]

Hi,

I bought MCA 525 recently and the first thing i noticed is a noticable pop in speakers when switching amp on and off. This happens even if nothing is connected to the amp. After that i measured dc voltage on speaker output and noticed that when i switch amp on, dc voltage goes up to about 0.5-0.6v dc and then goes down to 10-20mv. When I switch the amp off, there is another pop and this time speaker cones go forward and stay in that position for about 2 seconds, then go back. But even after switching amp off i can see about 0.5v DC in speaker outputs for quite a long time (at least some minutes).

Anthem dealer says there is nothing to worry about. But I don't see the same with my Yamaha a860 and Monolith 5 while doing the same test.

My question is is that normal and safe for speakers? I got ProAc 148s front and 118s surround.

By 'the amp', do you mean 'the Anthem', or do you have an external amp? If the latter, don't turn the power amp on until the Anthem is on.

 

[highfigh]

btw those pops can be heard in bass drivers only. So i suspect speaker crossover caps doing exactly this job here.

They aren't there to block DC.

 

[Andrein]

Can you try it with a different speaker?

Pop is less loud in my surround speakers which have sensitivity 2.5 db less

 

[Andrein]

Not really, the relay works the same way in manual or Auto.

But it looks the Anthem relay is not enough because it allows the pop to happen.

 

[PENG]

What is the sensitivity of your speakers and do they pop loud, or just barely audible?

As I said, in you case maybe the time delay is not long enough in our case so the relay clicks in a little too soon. There is one design change in the MCA525 from the previous MCA50. They now share the two power supplies for all 5 channels, that means the cap bank is now much larger and it will take a little longer for them to settle down when first powered on.

Please do an experiment as follow:

1. Select auto (MCA525).
2. Turn on your system normally, i.e. source, pre-amp, power amp and listen to something at moderate volume to trigger it on so you can see the blue light (MCA525).
3. After 10 seconds or longer, turn down the volume so you can hear any pops easily.
4. Now turn off the power amp and listen for "pop".
5. Repeat steps 2 and 3.
6. Wait 1 to 2 seconds maximum and turn it back on and listen carefully for pop, at that point you won't have the blue light but the amp output is still there and if the pre-amp volume is turned up it will still be playing sound.

In steps 4 and 6 you should not hear that "pop", or at least the "pop" should be much quieter.
The idea is to try and get the amp to the point where is is more or less, though not totally in stable state when you turn it on and off.

If you use the time delayed relay previously suggested, you get to control the time delay so you can make sure that by the time the relay contact connects/disconnects the speakers the amp would be in steady state condition for sure. This experiment is not going to match that exactly but at least get close to it. I timed my MCA20 and found the "ON" delay was about 2 seconds and "OFF" delay was about 5 seconds. So even without the blue light, the amp output will not ramp down to 0 for about 5 seconds. So at the 1 second mark, as far as the speaker is concerned, the output is still close to being maintained, or "ON" and if you turn it back on now, it should be almost like having that time delay relay to connect the speakers after there is enough time for the amp to reach steady state.

If you can still hear the same "pop" in step 4 and 6, then the time delay device TLSGuy suggested is probably not going to work for you either. Then you can either live with that quiet pop, or return it and get another amp.

 

[Andrein]

As I said, in you case maybe the time delay is not long enough in our case so the relay clicks in a little too soon. There is one design change in the MCA525 from the previous MCA50. They now share the two power supplies for all 5 channels, that means the cap bank is now much larger and it will take a little longer for them to settle down when first powered on.

Please do an experiment as follow:

1. Select auto (MCA525).
2. Turn on your system normally, i.e. source, preamp, power amp and listen to something to trigger it on so you can see the blue light (MCA525).
3. Turn down the volume so you can hear any pops easily.
4. Now turn off the power amp and listen for "pop".
5. Wait a few seconds but make sure the blue light is still on.
6. Turn on the source, preamp and the MCA525 and listen carefully for any "pop".

In steps 4 and 6 you should not hear that "pop", or at least the "pop" should be much quieter.

If you can still hear the same "pop", then the time delay device TLSGuy suggested is not going to work and if you are concerned, then you may consider getting a refund but before that you really should also try it with a different speaker just in case.

Steps 4 and 5 seem to be conflicting. If I turn amp off, then there will be no blue light.

 

[PENG]

Maybe manual switch which connects or disconnects all speakers at once?

Sorry you are right. I was in a hurry. I have think of another way.

 

[slipperybidness]

As I said, in you case maybe the time delay is not long enough in our case so the relay clicks in a little too soon. There is one design change in the MCA525 from the previous MCA50. They now share the two power supplies for all 5 channels, that means the cap bank is now much larger and it will take a little longer for them to settle down when first powered on.

Please do an experiment as follow:

1. Select auto (MCA525).
2. Turn on your system normally, i.e. source, preamp, power amp and listen to something to trigger it on so you can see the blue light (MCA525).
3. Turn down the volume so you can hear any pops easily.
4. Now turn off the power amp and listen for "pop".
5. Wait a few seconds but make sure the blue light is still on.
6. Turn on the source, preamp and the MCA525 and listen carefully for any "pop".

In steps 4 and 6 you should not hear that "pop", or at least the "pop" should be much quieter.

If you can still hear the same "pop", then the time delay device TLSGuy suggested is not going to work and if you are concerned, then you may consider getting a refund but before that you really should also try it with a different speaker just in case.

These time delays that TLS mentioned seem to be a timer IC. Those timer ICs typically have the time set by an external RC circuit.....so if the timing is off, that would suggest to me that the R or C is off on the external control circuit. Obviously, the cap would be much more likely to be out of spec.

But, again, if this were me, my amp, my $, the Anthem website clearly states "30 DAY MONEY BACK GUARANTEE" and I would personally be using that offer to get myself out of a possible bad situation. Basically "this amp does not meet my expectations at this price point".