Question Amp under-power?? Marantz PM-47 amplifier (40w) + JPW P1 speakers (70w)

[mrlawrencelam]

This is my first post here.

I have an Marantz PM-47 amplifier from 1996. The label behind the case showing 8~16 ohm.

Online information shows:

Power output: 40 watts per channel into 8 ohm (stereo)
Frequency response: 10Hz to 50kHz
Total harmonic distortion: 0.008%
Damping factor: 60
Input sensitivity: 2.5mV (MM), 150mV (line)
Signal to noise ratio: 86dB (MM), 96dB (line)
Channel separation: 80dB (line)
Dimensions: 439 × 103 × 340mm
Weight: 5.4kg
Year: 1996

The two speakers are 2-way JPW P1:

Nominal impedance: 8 ohms
Power handling: 70 watts
Sensitivity at 1w/1m: 89dB

Is the Marantz amp (40w) too weak to handle the JPW speakers (70)? I see people recommending the power of amp should be 50%-100% more than the speakers. In my case, my amp should be 60~80w, right?

I find the sound quality of the speakers to be less satisfying although almost everybody from different online forums are praising the these speakers. I wonder if it is the undersizing of my amp?

 

[shadders]

Hi,
The amplifier has enough power. The speakers being 89dBW sensitivity, means that 10watts output from the amplifier the SPL will be 99dB, which is quite loud. Depending on the chart you use, it is a helicopter, inside a subway train, disco speaker at 1metre.

Maybe you do not like the overall tone of the speakers ?

What were you expecting, sound wise ?

They are a sealed box, so is it the slightly reduced bass that concerns you ?

Regards,
Shadders.

 

[mrlawrencelam]

Thanks for the reply.

One reason I think why I am not satisfied with the JPW's sound quality is due to the positioning. I am getting a technician to re-orientate the speakers so that they are facing the listeners.

My sister gave me an old Pioneer mini CD player. I detached the speakers (model: S-Q150, 8 ohm / 25w, same impedance as the JPW). I attached these cheap speakers in parallel to the amp.

Surprisingly now, working together with the JPW, the overall sound quality improves a lot and much more balance. I can feel a better bass and treble. Those Pioneer speakers are really cheapskate speakers. I wonder why.

 

[Gray]

Welcome to the forum.
Don't pay too much attention to power figures and recommendations.
They're a rough guide.
The 70 Watt figure is the nominal maximum amount JPW is quoting for your speakers.

 

[mrlawrencelam]

They are a sealed box, so is it the slightly reduced bass that concerns you ?

I find the bass to be less solid and treble also less sharp. My friend said the speakers might be more for vocal. I am less convinced with his point.

But as I said in my previous message, I am now very happy with the sound quality after adding in the cheap Pioneer speakers. I am sure the sound will greatly improve after I reposition the JPW speakers.

 

[mrlawrencelam]

Welcome to the forum.
Don't pay too much attention to power figures and recommendations.
They're a rough guide.
The 70 Watt figure is the nominal maximum amount JPW is quoting for your speakers.

Thanks. I am happy to know the amp is not under-sized.

 

[shadders]

I am getting a technician to re-orientate the speakers so that they are facing the listeners.

Hi,
That helps a lot.

My sister gave me an old Pioneer mini CD player. I detached the speakers (model: S-Q150, 8 ohm / 25w, same impedance as the JPW). I attached these cheap speakers in parallel to the amp.

Surprisingly now, working together with the JPW, the overall sound quality improves a lot and much more balance. I can feel a better bass and treble. Those Pioneer speakers are really cheapskate speakers. I wonder why.

I would not connect speakers in parallel. There are issues with too low impedance with this type of connection.

If it sounds better, then perhaps the tone of the JPW P1's are not for you. You could try another amplifier, but i think this will have minimal change compared to changing the speaker.

Regards,
Shadders.

 

[mrlawrencelam]

I would not connect speakers in parallel. There are issues with too low impedance with this type of connection.

1. The loudest I go is 1/3 of the volumn knob (or it will be too loud for my neighbor). I hope that will prevent amp/speakers burn?

2. JPW speakers 70w, 8 ohm. Pioneer speakers 25w, 8 ohm. Marantz amp 40w to each channel.

Based on this, what is the calculation I should know when I attach the 4 speakers together? I hope to learn some calculation.

Thanks for all the advice to this 53yo Hifi newbie. With all those precious advice, I am sure I will soon have a better retirement days : -)

 

[Gray]

I find the bass to be less solid and treble also less sharp. My friend said the speakers might be more for vocal. I am less convinced with his point.

Your friend may be basing that judgement on the fact that the midrange (where vocals hang out) is the only frequency band you haven't complained about 🙂

Wait to see what optimum positioning does for your JPW sound.
As Shadder's said, it's best not to connect speakers in parallel.
The 8 ohm is another nominal figure - once music is playing it can dip substantially.
With 2x 8 ohm in parallel you're already down to 4 ohm, before any dips (from one or both speakers).

 

[mrlawrencelam]

Or should I connect the speakers in series instead of parallel (currently)? My amp is rated 8~16 ohms. Each speaker is 8 ohms. So, in series, it will be 2 x 8 ohms = 16 ohms and well within the specs.

 

[Gray]

Or should I connect the speakers in series

You could do. Purists certainly wouldn't.
(You'd be compromising on the imaging that 2 channel stereo is all about)
Others might say that, if you think it improves your sound.....do what pleases you.
Best thing would be to listen to some of the current offerings - and choose a pair that give you even better performance.
Have you at least got the JPWs on stands?

 

[mrlawrencelam]

You could do. Purists certainly wouldn't. Others might say that, if you think it improves your sound.....do what pleases you.
Best thing would be to listen to some of the current offerings - and choose a pair that give you even better performance.
Have you at least got the JPWs on stands?

The JPWs are currently wall mounted and facing the wrong direction. Will re-position.

 

[Gray]

The JPWs are currently wall mounted and facing the wrong direction. Will re-position.

Close to wall can certainly compromise bass in particular, less so with sealed boxes but even so......try them on stands if you can.

 

[Edbostan]

This is my first post here.

I have an Marantz PM-47 amplifier from 1996. The label behind the case showing 8~16 ohm.

Online information shows:

Power output: 40 watts per channel into 8 ohm (stereo)
Frequency response: 10Hz to 50kHz
Total harmonic distortion: 0.008%
Damping factor: 60
Input sensitivity: 2.5mV (MM), 150mV (line)
Signal to noise ratio: 86dB (MM), 96dB (line)
Channel separation: 80dB (line)
Dimensions: 439 × 103 × 340mm
Weight: 5.4kg
Year: 1996

The two speakers are 2-way JPW P1:

Nominal impedance: 8 ohms
Power handling: 70 watts
Sensitivity at 1w/1m: 89dB

Is the Marantz amp (40w) too weak to handle the JPW speakers (70)? I see people recommending the power of amp should be 50%-100% more than the speakers. In my case, my amp should be 60~80w, right?

I find the sound quality of the speakers to be less satisfying although almost everybody from different online forums are praising the these speakers. I wonder if it is the undersizing of my amp?

I owned a pair of JPW AP2 which are similar to the P1s driven by a Cyrus One amp which was rated at 25W per channel. It had plenty of power to drive the AP2s.

 

[mrlawrencelam]

Thanks for all the valuable advice.

I have just re-wired the speakers. Now they are in SERIES (previously in parallel). That means from the amp, the current will flow through a Pioneer speaker (25w, 8 ohm) and then a JPW speaker (70w, 8 ohm). So total is 16 ohm. The Marantz amp is rated 8~16 ohm. Does that mean it is now safer to pump up the volume slightly compared to before in parallel? I don't see any difference in sound quality or volume before and after.

 

[shadders]

Thanks for all the valuable advice.

I have just re-wired the speakers. Now they are in SERIES (previously in parallel). That means from the amp, the current will flow through a Pioneer speaker (25w, 8 ohm) and then a JPW speaker (70w, 8 ohm). So total is 16 ohm. The Marantz amp is rated 8~16 ohm. Does that mean it is now safer to pump up the volume slightly compared to before in parallel? I don't see any difference in sound quality or volume before and after.

Hi,
Yes, you can safely turn the volume up. I am sure that when the JPW speakers are facing you as they should be, then the sound will be better.

Regards,
Shadders.

 

[plastic penguin]

Agree with the others. I used to own a 40 watt Arcam and they were powering Monitor Audio RS6, which measured 120 watts per channel into 6 ohms with a dip to 2.5 ohms. They were driven fine by the 40 watter

 

[mrlawrencelam]

Really good advice from this forum. Thank you for being patient with me. The next thing I need to do is to reorient the direction of the JPW speakers. Currently it is wall mounted too high and facing wrong direction.

Please see images below. Hope to get some advice. Both the JPW speakers are facing the RED WALL. I didn't think much about the drop of sound quality when I renovated the house 17 years ago.

 

[shadders]

Hi,
There should be an appreciable difference when the speakers are in front of you, either side of the television. You will probably need some speaker stands, and they can be in all different sizes and designs.

Regards,
Shadders.

 

[Gray]

Please see images below. Hope to get some advice.

Text books assume speakers are facing you 😉
Golden rules say tweeters at ear height. Speakers should be positioned well away from walls and especially clear of corners 😆....
Mind you, I've seen photos from 'experts', with their perfectly positioned speakers (wired with expensive cable).......but their sound completely blocked by stupidly positioned sofas 🤪

Not surprised the JPW sound is currently not to your liking.
Maybe the sound will still not be to your liking after repositioning, but at least you'll be giving them every chance 👍

 

[mrlawrencelam]

@Gray I am quite confident the sound will greatly improve after repositioning. Really looking forward to it.

 

[mrlawrencelam]

Not surprised the JPW sound is currently not to your liking.
Maybe the sound will still not be to your liking after repositioning, but at least you'll be giving them every chance 👍

I just realized that the wires connecting the JPW speakers and the Amp were oppositely connected. The black point was connected to the red point and vice versa. I earlier assumed it was OK since it was AC (alternate current) and I still heard the sound coming up from the speakers. Only these few days have I learned that it is not OK and will cause something called "out of phase bla bla bla".

Maybe that was why I wasn't happy with the sound quality and deserted the system for the past 17 years. I really can't believe (now blaming myself) I let it collect dust for almost 2 decades. Now I started falling in love with it.

 

[Gray]

I just realized that the wires connecting the JPW speakers and the Amp were oppositely connected. The black point was connected to the red point and vice versa. I earlier assumed it was OK since it was AC (alternate current) and I still heard the sound coming up from the speakers. Only these few days have I learned that it is not OK and will cause something called "out of phase bla bla bla".

....the speakers would have been out of phase with each other if just one of them (at speaker or amp end) was incorrectly wired.
If both speakers had black / red reversed, they would still have been in phase with each other.

 

[mrlawrencelam]

....the speakers would have been out of phase with each other if just one of them (at speaker or amp end) was incorrectly wired.
If both speakers had black / red reversed, they would still have been in phase with each other.

Looks like this is my case. BOTH speakers were oppositely connected. After correcting the connection, there is no difference of sound quality (it's already perfect).

 

[mrlawrencelam]

The new wires I ordered online just arrived.

One side is copper; the other side is tinned copper.

Question: Which side (copper or tinned) do I connect to the red plug, which to the black plug of the speakers/amplifier??