Help! Calling Unsleepable, Vladamir, Davedotco etc.

[Gazzip]

Happy New Year chaps. Hopefully you, or anybody else on the forum of a technical bent, can help me out here. I have been having issues with a pre-amp/power amp impedance mismatch. The technical aspects of this are covered elsewhere on the forum (see link below), but the long and the short of it is that I am going to have to replace either the pre or the power section of the chain.
http://www.whathifi.com/forum/hi-fi/bias-adjustments
I started off looking at replacing the pre-amp. This item was purchased second hand (grey import) and subsequently fully serviced by the UK importer, so I stand to lose little/nothing on selling this, hence looking at replacing this instead of my power amps which were purchased new and would haemorrhage cash. However replacing the Reference 5SE is proving difficult. I didn't realise just how much I liked the sound until I started to audition other equipment. I may therefore have to look at replacing the Bryston amps instead which should, in theory, have less impact on the overall sonic flavour of my system. So here is my question: PMC's recommended amplification for my loudspeakers is 500W to 1200W but I cannot understand why it needs to be so high. My listening distance is 4m from face of drivers and my listening room is 6m x 5.5m. Speaker specs below. Impedance: 4 Ohm NominalSensitivity: 91dB They are physically large speakers with 15" LF drivers but the specs to me suggest that a much, much smaller amp could drive them easily without any clipping. Listening levels are usually fairly low for me. Any help would be much appreciated as I really don't want to damage anything. There are a pair of Audio Research Reference 210's on eBay you see and if they are man enough for the job that could be my answer. Any help would be appreciated!

 

[Vladimir]

Why PMC recommends such high power is because transient peaks suck in high amounts of power. Most of the musical program needs no more than few watts, but when it gets going, it really goes. To add just 3dB gain, an amp needs to double its power output. To hear twice as loud requires 10 times the power. And to add insult to injury, 91dB is not high efficiency, they are deadly 4ohms nominal and go as low as 20Hz!

If you feed your PMCs with small power amp or an integrated amp, be asured there will be clipping and FR bending due to the low impedance of the PMCs. You praise the AR but those Brystons are the true Hercules in your system.

I would personally give Rothwell a ring before selling anything. Link them the thread we discuess before and ask them to make you a custom attenuator that addresses both the gain and impedance mismatch. They may even weigh in with their own more accurate explanation what is the issue you are having and an adequate solution for it.

 

[Electro]

I am probably sounding like a broken record *smile* but ----

Buy this

http://www.audio-cinema.co.uk/electrocompaniet-ec48-mono-preamplifier-2104-p.asp

And two of these ex demo

http://www.audio-cinema.co.uk/electrocompaniet-nemo-aw600-mono-block-power-amplifier-6099-p.asp

And I can give you my personal assurance that you will never worry about amplification again because you will be too busy listening to music to care about what matches what , they will probably last you for the rest of you life ( or at the very least 30 years ) *biggrin* .

If you buy them and I am wrong I will eat any style of headware you choose dipped in any sauce of your choice .*bad* *biggrin*

 

[Gazzip]

You may be right Vlad so will give Rothwell a buzz on Monday. I have no burning desire to sell/buy any of my kit if a tweak such as attenuators will fix it. However, back to the original question in case Rothwell cannot help me out, do you really think that a minimum of 500W is really the correct power rating for these speakers? I take your points about peak load, but getting anywhere near the supply capacity of a pair of 7BSST2's the momentary peak would need to be minbendingly demanding no?

Thanks Electro. If I can get one on home demo then I will give it a go. Although having just finished demo-ing a Musical Fidelity M8PRE I may have been put off solid state amplification for life. "Clever" amp the M8. Remove all of the lower frequency and then artificially boost the HF and MR. Voila!, "high fidelity" is born. Not. My hearing may be permenantly damaged after this afternoon in my listening room with that steaming pile. Looking forward to seeing the bench test results on that one. Good soundstage though!

 

[davedotco]

I followed the other thread and the one thought that came to me is that your system has a phenominal amount of gain.

Given that your dac outputs in excess of 4volts and your pre-power has a gain in excess of 40dB I find myself wondering what it is all for.

I can't really fault any of your equipment but as a system, it looks ungainly, electronically speaking, and as you have surmised, somewhat poorly matched.

Have you considered a high quality passive pre-amp?

Maybe something like this?

 

[Vladimir]

However, back to the original question in case Rothwell cannot help me out, do you really think that a minimum of 500W is really the correct power rating for these speakers? I take your points about peak load, but getting anywhere near the supply capacity of a pair of 7BSST2's the momentary peak would need to be minbendingly demanding no?

The Celestion NTI-1550 15" woofers in those PMCs handle 600W. The front driver chassis looks like a wheel on a submarine hatch because they designed it for cooling the 4 inch voice coils that is bombarded with magnetic flux by a large neodymium magnet. This is to get them to play clean with low power compression at very high SPL.

Oh you can play those with SET flea watt amp and be happy. But if you want high fidelity concert SPL in your room, well you already got it.

 

[Gazzip]

I can't really fault any of your equipment but as a system, it looks ungainly, electronically speaking, and as you have surmised, somewhat poorly matched.

Have you considered a high quality passive pre-amp?

Maybe something like this?

Hi Dave, I agree with all of your comments. I had a really well balanced system until only a few months ago. Bryston BP26, 7BSST2's and PMC IB2's. Unfortunately a bout of upgradeitis which flew out of control, plus a free upgrade that I should never have accepted, has left me with a bit of a mess and trying to sort it out is proving problematic.

Regarding the passive pre-amp route I have never really considered it before. Have you heard it? Also my pre and powers are approx 6m apart so balanced is how I interconnect. I am guessing however that this product is not a "balanced" design inspire of the xlr inputs? Finally those upgrades. Worth it or just throwing money away.

Any further advice would be great. Thanks.

 

[Gazzip]

Sorry just read that it is balanced. Surprised that can be done passively?

 

[Gazzip]

Crikey, also which resistance? Out of my depth here!

Resistance: 10, 20, 50, 100, 200 kohm or custom values

 

[Electro]

You may be right Vlad so will give Rothwell a buzz on Monday. I have no burning desire to sell/buy any of my kit if a tweak such as attenuators will fix it. However, back to the original question in case Rothwell cannot help me out, do you really think that a minimum of 500W is really the correct power rating for these speakers? I take your points about peak load, but getting anywhere near the supply capacity of a pair of 7BSST2's the momentary peak would need to be minbendingly demanding no?

Thanks Electro. If I can get one on home demo then I will give it a go. Although having just finished demo-ing a Musical Fidelity M8PRE I may have been put off solid state amplification for life. "Clever" amp the M8. Remove all of the lower frequency and then artificially boost the HF and MR. Voila!, "high fidelity" is born. Not. My hearing may be permenantly damaged after this afternoon in my listening room with that steaming pile. Looking forward to seeing the bench test results on that one. Good soundstage though!

It sounds like the MF did not work that well then !

In my experience mixing and matching pre and power amps from different manufacturers is a bit of a lottery you can get lucky but most of the time it is just a compromise that never seems to sound quite right .

This is why I was surprised that you don't use a BP26 pre with the 7b's , is there something you don't like about the sound of this combo ?

One thing I will add about the Electro pre/ power I recommended is that they don't sound like a solid state amp or indeed a valve amp , they do not sound like anything at all they just reproduce music nothing added or taken away .

I was playing a Cd earlier this afternoon by Robben Ford called Soul on Ten and I am not joking when I say it seemed like the wall behind the speakers was taken away and a stage was built in it's place , the sense of real people playing live in a real space with all the scale,power and dynamics of live music or a least a convincing large scale model of it , so I can't even begin to imagine what your massive BB5SE's would be with like with the Electro's powering them , but it would probably be very close to the real thing indeed !

 

[davedotco]

Crikey, also which resistance? Out of my depth here!

Resistance: 10, 20, 50, 100, 200 kohm or custom values

Firstly, the 'sound' should be effectively non-existent, there really is nothing to give the pre-amp any character. I have a lot of time for ARC product, but their pre-amps always sound more real than 'real'. Difficult to come to terms with as they sound so 'insightful' and 'revealing', I have no idea how they do that but they can be pretty persuasive, I have owned a few in my time and used several others and they all seem to do that.

In reality the only real issue with a passive is impedence matching and given the 'pro' pedigree of the rest of your gear, I would expect the problems to be minimal. Tell the maunufacturer the spec of your dac and power amp and ask them to build the unit to match. If you can shorten the interconnects I would do that too, if not, tell them exactly how you have things set-up.

 

[unsleepable]

I guess what you need to change in your setup depends on what you are really trying to solve.

If it's still the gain issue, before changing anything else I would actually try a different DAC with lower output voltage than the Chord QBD76 DAC you have. Can you borrow a DAC from your dealer or a friend? Or try the Rothwell attenuators between the DAC and the preamp, if you still keep them.

Also, do you also balanced or single-ended interconnects between the preamp and the power amp? On single-ended, the preamp will naturally produce a 6dB lower signal at a given volume position. But the power amp gain may be fixed regardless of input, and therefore the final volume may actually be lower on single-ended. If you are using balanced interconnects, this may also be worth a try—although there is the issue of the long cable runs between the preamp and the mono-blocks.

If you are using balanced interconnects between the DAC and the preamp, the same applies.

If you like how your setup sounds, I wouldn't be concerned about the impedance. But if you are, matching preamp and power amp from the same vendor is the obvious solution. A passive preamp could also work, but the long cable runs may be a problem.

 

[drummerman]

Sad really. I guess the only thing this thread proves is that no matter how much cash you throw at it, a system can still end up sounding like crxxp.

I don't mean to rub it in or sound extra clever but why not revert to your set-up previous to all the 'upgradeitis'?

According to you it sounded well balanced and enjoyable.

 

[Vladimir]

I got the impression Gazzip's system sounds amazing but it has the input sensitivity issue that makes it go too loud too soon. I doubt it sounds like crxxp. *unknw*

 

[Gazzip]

Sad really. I guess the only thing this thread proves is that no matter how much cash you throw at it, a system can still end up sounding like crxxp.

I don't mean to rub it in or sound extra clever but why not revert to your set-up previous to all the 'upgradeitis'?

According to you it sounded well balanced and enjoyable.

It doesn't sound bad it sounds absolutely great. The problem is that I have very little rotation on the volume pot for the reasons stated by Vladamir, making it difficult to adjust the volume in small increments. Trying to solve this and talking it through on this forum has left me with a few avenues to explore, ranging from custom built attenuators to passive pre-amps and maybe even a full replacement of my amplification section if it comes to it. I am not a man to "throw cash" at anything so will be trying these solutions in order of least cost, only replacing components as a last resort.

Each of my components, with the exception of the pre-amp, were tested for compatibility at home and in my system before making each purchase. The pre-amp I got from a Germany audio website, based on review only, and for a third the price it retails at. As a result it could not be tested but was a bargain I knew I could easily sell on for no loss if it didn't fit my system. From a sonic perspective it does fit perfectly but from an electronics perspective it does not, so fixing the problem will bring me the biggest reward, not reverting to my old system which has now been sonically surpassed.

I completely agree with the premise that buying the most expensive of everything will not necessarily get you the best of everything, nor will it guarantee a synergy between those elements. However I am not sure that this thread proves that theory and I feel you may have missed the point.

 

[drummerman]

Uhh Ahh Ohh ... my bad. Apologies.

 

[unsleepable]

The problem is that I have very little rotation on the volume pot for the reasons stated by Vladamir, making it difficult to adjust the volume in small increments. Trying to solve this and talking it through on this forum has left me with a few avenues to explore, ranging from custom built attenuators to passive pre-amps and maybe even a full replacement of my amplification section if it comes to it.

Gazzip, replacing your mono-blocks with the Audio Research Reference 210 you mentioned, will not help with your gain issue—even being less powerful, the Audio Research Reference 210 has more gain than your current amp. As for a passive preamp, I think it's a bit tricky.

 

[Gazzip]

Had some email chitchat with Andrew Rothwell today regarding his attenuators. He reckons that their standard balanced -10dB units will do the job, so I guess that is my starting point. Will report back once I have received them but in the meantime thanks for all of your help.

 

[Vladimir]

I'd smack a -20dB on it. If it felt too much you can flip the 29dB switch on the back of the Bryston for added +6dB.

Report back if the -10dB was sufficient.

Try it also before the preamp, not just after.

Cheers