Is my Roksan Oxygene Amp powerful enough for my PMC speakers.....

Pete Shields

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Sep 23, 2008
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I have a Roksan Oxygene 75 watt @ 8 OHM amplifier which I use to power a pair of 8 OHM PMC 20/24 speakers.

They sound great but I sometimes feel that the amp is not powerful enough for the speakers.

I need to have the amp volume running at 60/100 plus for the speakers to really sing.

Are the Roksan / PMC a good match and are they compatible size and sound wise......
 

Al ears

Moderator
Must be a very large room......
The speakers are quite efficient so amp should have no problems driving them.
I find it odd that you are asking about compatibility when you actually own them.
Can we assume you didn't audition before you got them?
 
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Pete Shields

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Sep 23, 2008
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Al Ears, I took a punt on them as I saw them on Ebay for £1400, boxed in immaculate condition and only 2 years old with I think 18 years warranty still left.
I'm not used to big floor standers having moved from my old Mission 731 stand mounts so a major change!

The room is big 16 feet deep (as you face them) and 14 wide with high ceilings. I have them too close to the wall, but not much choice as the photo below shows.

Might just be a case of me not being used to firing the amp up to 60% plus to get them sounding at their best. I think I get the best output from them at this volume, so I usually have to wait until everybody is out to listen......maybe I'm just going a bit deaf as well at low volumes....

shows.IMG_20200630_224412.jpg
 

jonathanRD

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Jan 27, 2011
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The room is big 16 feet deep (as you face them) and 14 wide with high ceilings. I have them too close to the wall, but not much choice as the photo below shows.


shows.View attachment 1403
My room is 15ft long by 12ft wide with a lower ceiling. My speakers have about 2.5ft behind them, and my seating position is over 2ft in from the back wall so the actual straight line distance between my ears and the front of each speaker is about 10ft.
Can you experiment by temporarily moving the speakers out from the wall, giving them some room, and effectively getting a bit closer to them?
 

millennia_one

Well-known member
Sep 1, 2014
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I have a Roksan Oxygene 75 watt @ 8 OHM amplifier which I use to power a pair of 8 OHM PMC 20/24 speakers.

They sound great but I sometimes feel that the amp is not powerful enough for the speakers.

I need to have the amp volume running at 60/100 plus for the speakers to really sing.

Are the Roksan / PMC a good match and are they compatible size and sound wise......
PMCs are a picky speaker I find, the room has to be just so in my experience, with the right dimensions for the transmission line to be really effective and to give the performance many write about. I had some 20/23's on the end of a 70watt Naim nap 200dr (not that means much) and found them to be very lacklustre in my room. And the naim, in theory, has plenty on tap.

I think there DB rating is a little optimistic. In my experience, the 23's where more like 83db and the same is probably true of the 24's (lower than they sate ). The 20 series seem to require a good healthy turn of the volume knob to get them going and plenty of current on tap to get their driver moving. Which is important as that little driver has to push air through a 3+meter (effective) Transmission line.

The PMC's like to be played loud in my experience, they're certainly not low volume listening speakers. Well you can but they don't sound full you get a lot tweeter action when played low and not much else.

The 20 series where/are some of the most hyped speakers, but you see a great deal of them going second hand probably for the reasons your stating. Kef ls50 suffering the same fate.

Everything you have described basically boils down to speaker sensitivity/the preception of sensitivity. To counteract this you need POWER and lots of it. I hate to say it 75 watts just isn't enough weather it doubles into 4ohms or not. They need more like 2-300w aside to really wake them up. Much the same as ATC. and it was the same for me with my nap 200 it just wasn't powerful enough.

Having said all that and putting my own experiences to one side!

Before spending money maybe try optimising room/ speaker placement a few CM's here and there can make a massive difference or maybe if you can move your listening spot even if you're just sitting on a stool for a couple of secs to see if the sound improves as you move around the room. Where you have them if anything they should be really boomy.

If it requires you spending money and you like the sound of PMC try out the Revel performer 3 series very hard to find second hand though but for good reason. Revels just have more of everything.
 

Gray

Well-known member
Nov 27, 2015
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The 20 series where/are some of the most hyped speakers
I bought my twenty21s before most of the reviews were done, fed them with 70W and loved them (but then I would say that :) ).
Halfway on the volume control is way too loud for me (never mind the neighbours).

Then I started reading the reviews.....
Now I take reviews with a pinch of salt. On and off I've read every title of hi-fi mag since the 70's.....never seen a more unanimously favourable verdict on any model (of anything).......from magazines that often go out of their way to disagree with each other.
I've owned plenty of speakers (and worked for a couple of companies that make them), call it hype if you like, but I have to say that, to my ears at least, the favourable reviews are justified.
 

Al ears

Moderator
PMCs are a picky speaker I find, the room has to be just so in my experience, with the right dimensions for the transmission line to be really effective and to give the performance many write about. I had some 20/23's on the end of a 70watt Naim nap 200dr (not that means much) and found them to be very lacklustre in my room. And the naim, in theory, has plenty on tap.

I think there DB rating is a little optimistic. In my experience, the 23's where more like 83db and the same is probably true of the 24's (lower than they sate ). The 20 series seem to require a good healthy turn of the volume knob to get them going and plenty of current on tap to get their driver moving. Which is important as that little driver has to push air through a 3+meter (effective) Transmission line.

The PMC's like to be played loud in my experience, they're certainly not low volume listening speakers. Well you can but they don't sound full you get a lot tweeter action when played low and not much else.

The 20 series where/are some of the most hyped speakers, but you see a great deal of them going second hand probably for the reasons your stating. Kef ls50 suffering the same fate.

Everything you have described basically boils down to speaker sensitivity/the preception of sensitivity. To counteract this you need POWER and lots of it. I hate to say it 75 watts just isn't enough weather it doubles into 4ohms or not. They need more like 2-300w aside to really wake them up. Much the same as ATC. and it was the same for me with my nap 200 it just wasn't powerful enough.

Having said all that and putting my own experiences to one side!

Before spending money maybe try optimising room/ speaker placement a few CM's here and there can make a massive difference or maybe if you can move your listening spot even if you're just sitting on a stool for a couple of secs to see if the sound improves as you move around the room. Where you have them if anything they should be really boomy.

If it requires you spending money and you like the sound of PMC try out the Revel performer 3 series very hard to find second hand though but for good reason. Revels just have more of everything.
Excellent to hear from someone with first-hand experience.
Now you mention it I rechecked a HiFi News review of the twenty-five 24 speakers and they were quoted as 89dBm but actually measured 86, so perhaps this is similar across the range.
This would account for the lack of output with 75 watt amp.
Regards the Revels the F206 should have similar traits and are available for £1800
 
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Jez l

Active member
May 1, 2020
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My pmc 21 need a bit of volume to come alive, I wonder if this is what you are experiencing.

As stated above they are fussy speakers. It looks as if yours are positioned quite close to the rear walls? My pmc 21 are about 25cm from the rear wall and this is ok.

Wonder if its worth playing about with positioning as stated above, fully optimising what you have before looking at upgrading.
 

millennia_one

Well-known member
Sep 1, 2014
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I bought my twenty21s before most of the reviews were done, fed them with 70W and loved them (but then I would say that :) ).
Halfway on the volume control is way too loud for me (never mind the neighbours).

Then I started reading the reviews.....
Now I take reviews with a pinch of salt. On and off I've read every title of hi-fi mag since the 70's.....never seen a more unanimously favourable verdict on any model (of anything).......from magazines that often go out of their way to disagree with each other.
I've owned plenty of speakers (and worked for a couple of companies that make them), call it hype if you like, but I have to say that, to my ears at least, the favourable reviews are justified.
I didn't mean any disrespect by that, poor wording on my part! maybe what I should have said is "talked about" and I couldn't disagree with the reviews once up and running and at there stride they have a wonderful sound. I never said they didn't.

But you are comparing 2 different speaker designs the port on the 21's is at ear level 23 24 26 all effectively on the floor, And if you have have thick carpet/foating floor the already delicate bass from them at low levels will be robbed from you. Mix that with low sensitivity the only way you're going to get round it, is with power and headroom

As we know not all watts are made equal! and neither are volume readouts.

I, for instance, have a Sugden a21 with Klipsch heresy 3's My volume never even reaches a quarter before it's rocking my world (heck it bearly comes off 7-8 o'clock on the dial), its all relative, 20 watts and a 100Db (claimed) speakers I'm never using more than 1 watt maybe 2, but it sounds like 200-watt monoblocks and i have plenty of headroom for dynamics.
 
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daytona600

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Oct 5, 2012
168
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Speakers that sound good at low volumes are very rare , most speakers need volume to compensate for lack of dynamic range
Hardest trick for speakers to play at very low & very high volumes they either sound flat & lifeless or fall apart

back in the 1920/30 western electric could fill a vast cinema of 4000+ people from 8wpc from one mono speaker & can still shame most expensive modern speakers
 

millennia_one

Well-known member
Sep 1, 2014
230
78
10,870
Speakers that sound good at low volumes are very rare , most speakers need volume to compensate for lack of dynamic range
Hardest trick for speakers to play at very low & very high volumes they either sound flat & lifeless or fall apart

back in the 1920/30 western electric could fill a vast cinema of 4000+ people from 8wpc from one mono speaker & can still shame most expensive modern speakers
They are now, back in the day they where everywhere.
 

Pete Shields

Well-known member
Sep 23, 2008
130
0
18,590
Thanks for the advice guys.
I need to find a quiet time when I'm in the house without others and move the speakers out a foot into the room and give them a blast. Might have to do this then every time I have a music night if there is a great difference.
Little steps buts the other half has agreed to me moving them out a couple of inches off the wall on a permanent basis. A couple of inches usually makes a difference. Just have to be resigned that they need to be played loud or for a good solo listen when the house is full that I have to use headphones. The system sounds great through the M-Dac and Sennheiser 650's anyway so pretty happy....
 

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