Upgrading a Croft 7 Power Amp to a 7R - How does this help?

[loonytunes]

I am currently enjoying listening to a pair of Magnepan MG-1 loudspeakers - within their limitations in my sitting room. I say within their limitations because I understand that 'Maggies' really need a lot of power and control (similar to Electrostatics) to really make Maggie sing. So I am intrigued at the potential left in this design.

I really like my current Croft 7 pre/power combo - so my dilemma is that I like the panel sound I am getting from these Magneplanars - but I don't want to ditch the Croft in favour of a more powerful amp with greater drive.

However, it would seem that by upgrading Croft's power amp to an R - which adds a (valve?) Regulated power supply - this will greatly improve the Croft's ability to deal with the varying impedance fluctuations of panel speakers like these (and Electrostatics if I choose to try those later too).

If 'R' only adds Regulation and not more power (so 45 Watts now and 45 Watts after upgrading to the 7R) how is this so? And how does that work electrically speaking where Regulation help control difficult loads despite not altering the Wattage of the amp?

Thanks.

[Firebottle]

Unfortunately it is not the output stage that benefits from the regulation.

As I understand it the regulation is only to the driver (valve) stage.

[loonytunes]

Unfortunately it is not the output stage that benefits from the regulation.

As I understand it the regulation is only to the driver (valve) stage.

Damn - I either give up panels or give up Croft - and I don't want to give up either right now! If keeping the panels I will be in search of a very powerful and stable SS amp that drive low impedances well (powerful SS amps usually sound flat and lifeless and are over complicated designs - but hopefully there are exceptions).

Perhaps the Cambridge Audio 851W. That's valve designs going up in smoke. I would rather have a minimum of 200 Watts plus if I am going the SS route. For example a Roger Sanders amplifier is 500 Watts - but a tad expensive and not from the UK.

[Firebottle]

Well I make Croft inspired monoblocks that include driver regulation and are rated at 55W.

They drive Maggies very well, I used to have some 1.6QRs.

[hifi_dave]

If you are enjoying the sound of your Maggies with the Croft, then there is nothing wrong with the combination and a 7R will just improve on what you have.

[JohnJo]

I'm pretty sure there were 100w Croft 7 monoblocks for sale here a while ago. So a "special" could probably be ordered from Mr. C.

[Macca]

Damn - I either give up panels or give up Croft - and I don't want to give up either right now! If keeping the panels I will be in search of a very powerful and stable SS amp that drive low impedances well (powerful SS amps usually sound flat and lifeless and are over complicated designs - but hopefully there are exceptions).

Perhaps the Cambridge Audio 851W. That's valve designs going up in smoke. I would rather have a minimum of 200 Watts plus if I am going the SS route. For example a Roger Sanders amplifier is 500 Watts - but a tad expensive and not from the UK.

The Cambridge certainly has wattage. But is that what you need? If volume is not the issue then you don't. You need power into a low impedance load. Both Rotel and Cyrus do power amps that will double output as impedance halves, Can't recall the models but I think about a grand new. Or consider a second hand Krell. This one I am using right now just cannot be faulted in any respect. Makes a nonsense of all the valve vs solid state business.

[Jimbo]

If you email Glenn C and tell him what speakers you are using he will upgrade your Series 7 power amp accordingly. The whole point of the 7R was its ability to drive difficult speaker loads but if you tell Glenn exactly what speakers your are using he will also up the wattage if needs be or as in Josie ( Blackadders) speakers he actually reduced the output power.

[Sherwood]

Maggies need high current designs. Very few amps work well with Maggies.

[Yomanze]

Well I make Croft inspired monoblocks that include driver regulation and are rated at 55W.

They drive Maggies very well, I used to have some 1.6QRs.

They might drive them 'well', but they won't drive them optimally. Is that 55W into 8 Ohms or 4 Ohms?

As has been mentioned, what Maggies want (and what Magnepan recommend themselves) is solid state with high current capability (amps that double wattage from 8 Ohms to 4 Ohms as a general identifier). Instantaneous current delivery is also important i.e. the ability for the amplifier to 'dump' huge amounts of current during musical peaks, think 20 amps plus.

[Wakefield Turntables]

You really need to speak to Glenn Croft. I asked for a list of mods for my Croft Epoch and suffice to say they completely changed the amp into a stellar performer. It still has the classic Croft sound and it's the only piece of kit in my valve setup that will not be sold/swapped or replaced.

[Firebottle]

They might drive them 'well', but they won't drive them optimally. Is that 55W into 8 Ohms or 4 Ohms?

That's 55W into 8 ohms and 90W into 4 ohms. There was no problem with driving the maggies :)

[loonytunes]

Sorry I didn't say this but - I'm not using the Croft's with the Maggies right now "just in case" I may cause an issues with old panels like this causing damage to the Croft. I am playing safe and using an integrated Musical Fidelity M3si (specified to deliver 25A but is only 85 Watts p/c).

There are no specs online showing what both the Croft's can do when presented with a 4 or 2 ohms load, or what the MF can do over 4/2 ohms either - so - it's the best I can do for now.

[Firebottle]

I found that the maggies had a fixed 4.5 ohm load, so maybe not such a difficulty after all.

[Sherwood]

I tried many power amps with my Maggies before finding something that really drove them well. That included powerful amps from Exposure, Parasound, Audiolabs, Musical Fidelity, and QUAD, none of which really gelled. Yes they can sound fine with lesser amps, but they seem to soak up power (current) like a sponge. I even tried them with my Art Audio Quintet valve power amp in pentode mode. They sounded very nice with spectacular imaging and a very sweet midrange but only at low volumes. Dynamics were constricted and bass very soft.

Once you get the amplification right, the difference is startling! At that point I think they are really one of the audiophile bargains (even with the outrageous UK mark-ups). I agree, it is not just about brute force power and low impedance stability, but matching is a challenge.

Geoff

[Yomanze]

It's not that they are a 'difficult' load, it's a non-reactive resistive load, but they eat watts for breakfast & thrive on high current delivery amps.

[loonytunes]

I wonder if you techies could read the following article from top to bottom by a chap in the States that designs and sells Elecrostatic loudspeakers, who has also designed an amplifier that can control his speakers and the Maggies (and possibly every speaker on the Planet for that matter) - it should do being 500 Watts per channel - but if you read his white paper it would seem that everyone and his dog should have a powerful amplifier, even for convential loudspeaker design...

http://sanderssoundsystems.com/technical-white-papers/172-tubes-vs-transistors

Those with the necessary instruments (Firebottle for example) can you run the 'Scope' test as explained in the article and tell me your results?

[JohnJo]

I wonder if you techies could read the following article from top to bottom by a chap in the States that designs and sells Elecrostatic loudspeakers, who has also designed an amplifier that can control his speakers and the Maggies (and possibly every speaker on the Planet for that matter) - it should do being 500 Watts per channel - but if you read his white paper it would seem that everyone and his dog should have a powerful amplifier, even for convential loudspeaker design...

http://sanderssoundsystems.com/technical-white-papers/172-tubes-vs-transistors

Those with the necessary instruments (Firebottle for example) can you run the 'Scope' test as explained in the article and tell me your results?

Just had a quick flick through this white paper and found this
"Resistance is measured in ohms. The term "resistance" is used in DC (direct current) circuits. "Impedance" is the same thing as resistance. But it is used when discussing AC (alternating current) circuits because the impedance often varies with the frequency of the AC"

I'll be first to admit I know very little about audio engineering but in my opinion, from a simple electrical point of view, this is wrong. Impedance refers to the out of phase relationship of current and voltage due to reactive components i.e. capacitance and inductance in AC circuits. The only guy I ever heard referring to this on AoS is Alan (Firebottle) with regard to the capacitive nature of Quad ESLs. I suspect Tannoy HPDs are similarly awkward at the other end of the spectrum, a highly inductive load but I've never seen any graphs other than simple resistive plots. An amp's ability to drive lowish resistances at awkward phase angles may be the key to getting the most out of these speakers.

If Maggies are a reasonably constant >4 ohm load and not reactive I can't understand how they need high current unless they are just massively inefficient. What's the typical efficiency of a pair of these?

[JohnJo]

Here's a bit more info: http://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase/page-2

As can be seen from the table at a 60 degree phase angle 1/6th of the current being drawn from the amplifier's power supply is actually going to the speaker. If I remember correctly Alan's graphs for Quad 57s showed a phase angle of something like 55 degrees at the same time as a pretty low impedance at certain frequencies. This is a massive ask of an amplifier and is probably why electrostatics are sometimes accused of sounding undynamic when actually it's the amp that's incapable of keeping up. I imagine Maggie's to be similar in this respect to the Quads.
I also suspect that valve amplifier's are much less susceptible sagging under difficult phase angles than most solid state amps hence the development of the term "valve watts" or "it's only a 20W valve amp but it sounds louder than my 50W SS amp.

[Yomanze]

86db at 2.83v, but the speaker is 4 Ohms, so this is 2W not 1W power, so at the more common 1W / 1M sensitivity measurement they are 83db, and below...

[Macca]

Maggies all seem to be around 83dB sensitivity, so pretty low. Watts will be needed if you want high SPL in a big room.

Don't know about maggies in particular but so many speakers are difficult loads, even if it is just over part of the frequency spectrum, I'm sure this, combined with taste in music, is why people have such differing opinions over whether a particular amp is a 'good un' or not.

In an ideal world all amps would have a very stiff power supply and be able to increase power as impedance drops. But this is the most expensive part of an amplifier to implement so corners get cut. From the manufacturer's point of view what will sell more amps? Good technical spec or a 5mm brushed aluminium fascia? Fact is: it is the fancy fascia.

Even if a given amp drives the speakers and it sounds fine it isn't necessarily driving them optimally, but you won't notice until you replace it with one that does.

[Sherwood]

Maggies all seem to be around 83dB sensitivity, so pretty low. Watts will be needed if you want high SPL in a big room.

Don't know about maggies in particular but so many speakers are difficult loads, even if it is just over part of the frequency spectrum, I'm sure this, combined with taste in music, is why people have such differing opinions over whether a particular amp is a 'good un' or not.

In an ideal world all amps would have a very stiff power supply and be able to increase power as impedance drops. But this is the most expensive part of an amplifier to implement so corners get cut. From the manufacturer's point of view what will sell more amps? Good technical spec or a 5mm brushed aluminium fascia? Fact is: it is the fancy fascia.

Even if a given amp drives the speakers and it sounds fine it isn't necessarily driving them optimally, but you won't notice until you replace it with one that does.

Exactly! Maggies are current "leeches". I can't explain why this is so as although they are relatively inefficient, they are not off the scale.

They are capable of so much more than many people realise because they hear them with decent amplification not ideal amplification.

Geoff

[Yomanze]

Exactly! Maggies are current "leeches". I can't explain why this is so as although they are relatively inefficient, they are not off the scale.

They are capable of so much more than many people realise because they hear them with decent amplification not ideal amplification.

Geoff

Consider that musical peaks can be over 10db from average SPLs, so that 20W or whatever you need for 90db average with Maggies quickly turns into 150W at 100db peaks.

[OD1]

I recall reading somewhere that Glenn Croft uses stacked Quad electrostatics to test his amplifiers, so would assume the Maggies would not pose a problem ?

[Yomanze]

I recall reading somewhere that Glenn Croft uses stacked Quad electrostatics to test his amplifiers, so would assume the Maggies would not pose a problem ?

Despite both having panels, electrostatics are very different to planar magnetic speakers. Quads don't need a lot of watts, but what they do need is an amp that can handle very high capacitance and a reactive load.

[loonytunes]

As mentioned earlier - I didn't hook up the Croft to these old Maggies knowing that the Croft produces about 45 Watts p/c, so instead tethered the most powerful amp I have at my disposal, a Musical Fidelity MS3i. And from the MF I got some nice sounds so I at least felt that the MF was able to drive some music successfully through these panels whilst I left the Croft sitting disconnected in the corner of a room.

But it bugged me - shall I try the Croft anyway despite the lowly 45 Watts - and I did! Well by complete surprise it sounded far better than the MF. I was playing music over and over again marveling at the ability of the Crofts having only half the power of the MF, and in turn much lower power than recommended for panels like these! Croft amplification is superb - there's no doubt about it! If you've never owned a Croft - it's about time you did :) (sorry getting carried away here)...

This prompted me to email Glenn asking specifics about both driving difficult loudspeakers and what the R upgrade would bring to the party- this is how Glenn replied ...

The 7 produces 45W into 8 ohms, 50W into 4 ohms and 50W into 2 ohms. It is stable into any load – I have used them into triple stacked Quad 57s which drop to 0.5 ohms at high frequencies.

The regulation in the 7R is for the driver stage – it does have better output mosfets and a bigger transformer so produces 55W into 8 ohms, 75W into 4 ohms and 90W into 2 ohms.