Pop Sound in my speakers when driven loud from studio recorded CD sources.

Hi Mike,

Thanks for providing the link. I had previously found the service manual, including the schematic, at hifiengine.com, but the block diagram provided at your link is also helpful.

But after looking at these documents I’m still at a loss to explain the mystery. The circuitry between the line-level inputs (Aux, Tape In 1, Tape In 2) and the volume control looks pretty straightforward and conventional. With nothing I can see that would explain why the problem is apparently introduced in circuitry that is "ahead" of the volume control while also manifesting itself or not depending on the setting of the volume control, when the DAC’s preamp function is not used. As you said in one of your earlier posts:

Playing the same CD passages at lower volume does not produce any of the "pop" "fart" sounds. It only happens at higher volumes.

And as I indicated previously, signal levels in the circuitry that is "after" the volume control are presumably about the same for a given perceived volume regardless of whether you are using the DAC’s preamp function or not.

Best regards,
-- Al

Glad that the problem is finally solved.

It seems that what I had said in a post which I subsequently deleted (because it seemed inconsistent with the sensitivity of the problem to the setting of the volume control), but which I quoted in a subsequent post after you asked what I had said, was in fact applicable:

Given the 180 mv sensitivity of the Marantz receiver and the 2.1 volt maximum output level of the DacMagic+ unbalanced outputs, it seems very conceivable to me that the problem may be due to overdriving whatever circuitry in the Marantz precedes (i.e., is "upstream" of) its volume control.

As an experiment, and conceivably as a permanent solution, try enabling the DacMagic’s digital preamp function, reduce its volume control setting significantly, and increase the volume control setting of the Marantz to provide preferred volume levels. See if the problem still occurs.

I can’t explain, though, why putting a smaller signal level into the Marantz has helped, given that the problem had only occurred at higher settings of the volume control. Detailed knowledge of the Marantz' circuit design might be required to explain that.  As I indicated earlier sensitivity of the problem to volume control settings would seem to signify that the "pop" is being introduced "after" the volume control in the Marantz’ internal signal path, where signal levels are presumably about the same for a given perceived volume regardless of whether you are using the DAC’s preamp function or not.

Regards,
-- Al

... the effect is more pronounced with recordings on CD that are more compressed, which generally you want to listen to louder to give the sound more ’presence’ in the room. As you also pointed out, the more ’spacious’ recordings, within my system can definitely be played louder without the clipping effect emerging... no question about that.

I’m not sure that we’re using the term "compressed" in the same way. I use the term to refer to a recording that has been engineered such that there is a relatively small difference in volume between the loudest notes and the softest notes. The opposite of that would be a recording having wide "dynamic range," meaning a large difference in volume between the loudest notes and the softest notes.

The majority of pop and rock recordings are dynamically compressed to a considerable degree, and consequently have a relatively small difference in volume between the various notes. Less than 10 db in many cases, which corresponds to the loudest note requiring less than 10 times as much power to be reproduced as the softest note.

**Some** well engineered classical symphonic recordings, on the other hand, can have dynamic ranges of 30, 40, or even 50 db. Those numbers correspond respectively to requiring 1000 times, 10000 times and 100000 times as much power to reproduce the loudest notes as the softest notes, the loudest notes usually being very brief, and the softest notes usually being far softer than on most pop and rock recordings.

Therefore it is the latter recordings, having wide dynamic range, that will usually result in the user turning up the volume control higher than for the highly compressed recordings. And consequently much more power will usually be required to reproduce the (usually brief) high volume dynamic peaks on recordings having wide dynamic range than on recordings on which the volume of the notes doesn’t vary a great deal.

But if in fact you are finding that recordings having wide dynamic range do not cause the problem, while some recordings having narrow dynamic range do, it would lead me to suspect that the problem is not inadequate amplifier power. Rather it would suggest the possibility that either the amplifier section of the receiver is not able to handle the thermal (heating) effects of having to supply high power levels fairly constantly, or the speakers are not able to handle the thermal (heating) effects of receiving high power levels fairly constantly. And perhaps the recordings with the strong drum beats that you referred to are putting that over the edge.


But the situation I described in the previous paragraph would be unusual, compared to problems involving clipping of an underpowered amplifier on brief high volume dynamic peaks, or problems involving defective equipment. Which leads me to suspect, as I said at the beginning of this post, that we may be using the term "compressed" to mean different things.


Regards,
-- Al

Al, Thanks for reviewing your original response. Most here seem to think that the amp is clipping. Is that what you are describing by saying....

No. What I was referring to in the post I deleted was clipping of the "small signal" circuitry in the receiver that precedes the volume control in the signal path, that is in the receiver’s preamp section. The others are referring to clipping of the power amp section of the receiver, that would result if the amp is asked to provide more power to the speakers than it is capable of providing. As I indicated in my previous post I deleted my earlier post when I noticed your statements that the problem only occurs at high volumes. If my hypothesis had been applicable the problem would manifest itself at any perceivable volume.

In any event, after looking further at the specs on the 2275 and doing some calculations, it’s hard for me to say whether the problem is inadequate amplifier power, resulting in clipping, or a defect of some sort in the receiver or the speakers.

On the one hand my understanding is that as a rough approximation rotary volume controls tend to provide attenuation at the 12 o’clock position (which is where you stated the problem tends to begin to appear, for those recordings which cause it to appear) that is roughly in the area of 20 db or so. 20 db of attenuation would reduce the 2.1 volt maximum output of the DAC to slightly more than the 180 mv that would cause the amp to reach its maximum power capability. Which in turn points in the direction of not having enough amplifier power.

On the other hand, according to the specs I’ve looked at the amp is rated to provide 75 watts into the speaker’s 8 ohm nominal impedance, and you indicated it was recently bench tested as providing 85 watts. In a medium sized room at typical listening distances (say 10 or 12 feet) 75 or 85 watts into two 86 db 8 ohm speakers should be able to produce sound pressure levels of around 100 db or so at the listening position, assuming the speaker specs are accurate (although that is certainly not always a good assumption, particularly when it comes to speaker specs). SPLs of 100 db or so are more than most listeners would require on most or all of their recordings, the most likely exceptions being recordings having exceptionally wide dynamic range (i.e., very large differences in volume between the loudest notes and the softest notes, such as some well engineered minimally compressed classical symphonic recordings). But in most cases the ability to produce that much volume at the listening position would suggest that amplifier power is adequate.

So I’m not sure what to point to as the likely cause of the issue, aside from the probability that it is being introduced downstream of ("after") the volume control in the signal path.

Regards,
-- Al

Almarg, if you are out there I would like to know your full response. Not sure why it didn’t get posted here.

I deleted my post a couple of minutes after I submitted it, because when I composed it I hadn’t noticed your statements to the effect that the problem only occurs when the volume is turned up to loud levels. That fact makes what I had said in my post inapplicable, since it indicates that the cause of the problem is "downstream" of the volume control. FWIW, though, what I had said is as follows:

Given the 180 mv sensitivity of the Marantz receiver and the 2.1 volt maximum output level of the DacMagic+ unbalanced outputs, it seems very conceivable to me that the problem may be due to overdriving whatever circuitry in the Marantz precedes (i.e., is "upstream" of) its volume control.

As an experiment, and conceivably as a permanent solution, try enabling the DacMagic’s digital preamp function, reduce its volume control setting significantly, and increase the volume control setting of the Marantz to provide preferred volume levels. See if the problem still occurs.

Alternatively, you could try enabling the DacMagic’s digital preamp function and connecting it to the input jacks of the power amp section of the Marantz (initially with the DacMagic’s volume control set low!), while disconnecting the Marantz’ pre-outs from those jacks.

If one or both of those experiments confirms this diagnosis, an alternative solution would be to insert a pair of Rothwell attenuators between the DacMagic and the Marantz.

Again, none of this appears to be applicable, given the sensitivity of the problem to the setting of the volume control. Not sure what to suggest at this point, beyond what the others have said.

Good luck. Regards,
-- Al