Looking over the Harman Kardon power amplifier circuits with their wide bandwidth and low feedback, I see the output devices are 30 MHz types which are feed by a stopper arrangement using a resistor and parallel inductor.
The apparent aim of this approach is to enable the high instantaneous currents where required but to act as a buffer at HF.
Using 30 MHz devices is to maximize output devices slew rate since this is proportional to fT and current available from the driver stage - source Cordell's articles in Audio Magazine accessible from his website.
If a design is made as linear as possible in terms of distortion and phase, the compensation measures to reduce the gain to less than unity arise at higher frequencies than possible with 4 MHz devices in the same layout. I believe this is the HK approach.
I noticed that HK have avoided use of Cdom around the Vas stage. It appears the small capacitors used for lead and lag in combination the base series inductor have a complementary role to achieve the same end.
The output devices used in the Otala amplifier have fT of 3MHz - slew output device slew rate is less of a problem for the power specified. The slew rate can be maximized by running the drivers hot and in this design the emitters are returned through resistors to the opposite voltage rails. It may be less efficient in terms of power consumption but again it is less of a problem than it would be in a high power amplifier.
I am not arguing against MJ15 or MJL 21XXX which I think of as more safe and user friendly for DIY - If one were to run more current through the driver stage it would be helpful to use more robust devices. I will be interested in your progress with your Otala amplifier build.
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Sanken modern MT-200 (2sa1295/2sc3264) are both 35mhz Ft and can
blow a MJL21193/4 away (SOA).
Using the Harmon kardon OPS (with the sankens) ,
me and "co-conspirators" blew a single pair at 200W using a oscillating amplifier -
to test a solid state relay.
These Sankens can also do 1mhz from of my CFA designs with
no "latch up".
PS - the "oscillating amp" was at 2mhz - outputs lasted over 10 minutes
@ 200W ... zobel resistor "glowed".
3 pair of these sankens can take a full power short and easily survive.
OS
blow a MJL21193/4 away (SOA).
Using the Harmon kardon OPS (with the sankens) ,
me and "co-conspirators" blew a single pair at 200W using a oscillating amplifier -
to test a solid state relay.
These Sankens can also do 1mhz from of my CFA designs with
no "latch up".
PS - the "oscillating amp" was at 2mhz - outputs lasted over 10 minutes
@ 200W ... zobel resistor "glowed".
3 pair of these sankens can take a full power short and easily survive.
OS
MJona, the Otala/Lohstroh amp has nothing to do with me, it's a straightforward implementation of the original project, changed insofar only that some of the transistors used then either no longer exist, or are VERY hard to find. For example, the output devices, BD 203/204 will be replaced by BD 8xx equivalents, newer versions of those old types, in all things practically the same.
All I added was what the authers clearly stated that they left out for simplicity's sake, the I/V protection circuit, and I daresay the one I am using is very likeyl much better than the one they used (e.g. it has a 100 mS lag before activating, to allow transients to pass through, and that's 5 tims longer than IEC standards call for).
All I added was what the authers clearly stated that they left out for simplicity's sake, the I/V protection circuit, and I daresay the one I am using is very likeyl much better than the one they used (e.g. it has a 100 mS lag before activating, to allow transients to pass through, and that's 5 tims longer than IEC standards call for).
Ostripper, what does "blow away" mean?
Frankly, I find that the old MJ 21195/21196 are excelent sounding devices. True, their nominal performance in switching times and Ft cannot compete with modern devices, but their SOAR can, and does. In addition wot what they can dissipate more given that they are rated as 250W than transistors rated at 200W can. Either that, or somebody is doing some heavy lying in ther data sheets.
I have seen way more burnt out Sanken powere output stages than those with burnt out MJ stages. While it's true that statistically many more output stages are made with Sanken devices than with MJ stages, that should be correcetd by the fact that the Sanken devices are palstic packed and thus easie and chepaer for the industry to install, and the fact that amps using the MJ devices are mostly pro orientated amps, expected to work at extreme power levels under extreme conditions.
A personal note here - my experinecs with Sanken devices is that with them stability is more of an issue than with for example Motorola/ON Semi MJL 4328/4302, which are, BTW, rated at 230W rather than 200W.
Frankly, I find that the old MJ 21195/21196 are excelent sounding devices. True, their nominal performance in switching times and Ft cannot compete with modern devices, but their SOAR can, and does. In addition wot what they can dissipate more given that they are rated as 250W than transistors rated at 200W can. Either that, or somebody is doing some heavy lying in ther data sheets.
I have seen way more burnt out Sanken powere output stages than those with burnt out MJ stages. While it's true that statistically many more output stages are made with Sanken devices than with MJ stages, that should be correcetd by the fact that the Sanken devices are palstic packed and thus easie and chepaer for the industry to install, and the fact that amps using the MJ devices are mostly pro orientated amps, expected to work at extreme power levels under extreme conditions.
A personal note here - my experinecs with Sanken devices is that with them stability is more of an issue than with for example Motorola/ON Semi MJL 4328/4302, which are, BTW, rated at 230W rather than 200W.
A point of clarification - at the start of your post you disconnected yourself from the Otala/Lohstroh amplifier, continuing to mention "the original project" and the " authors clearly stated that they left out for safety's sake.. et cetera." Did you mean "their original project" or that of some other parties?
I am aware that other's such as "Electocompaniet" were on the scene in the 70's and the possibility of projects in European Electronics magazines which were not known about "down under" in Australia and New Zealand before the days of the internet.
If that is the case can you give the project title and name the authors.
I refer to the project as initially published in IEEE 1973, signed by Matti Otala and Jan Lohstroh. The text includes the amp schematic and BOM. That is the the one and only original.
Two years later, a then new company called Electrocompaniet, founded by one Per Abrahamsen, produced an amplifier based on that same project, but with some proprietary mods. I heard it and was able to compare it to my execution of the original, and in my view, the original sounded better.
Visit Jan Lohstroh's site to pick up the scanned original text and by all means, do read his excellent interview with Jan Lohstroh (lineraudio, something).
My aim now is to make a newer version of the original project, however this time round using what I have learnt about PCB design since then, and after 42 years, it's quite a bit. Once I am done and have made sure it works as it should, I will be quite happy to pass on the files required for anyone to make his own boards locally. I firmly believe the project quality deserves to be passed around.
Ask John Curl, he still has his from them yore days. He swears by it.
As for look-alikes, the world was chock full of them. For example, Pioneer used exactly the same topology for their top of the line products as late as the late 80ies. kenwood also used it ad nauseum, as did Sansui.
One of my most succesful projects uses the same rough idea, but with a different implementation. Loosly put, I suppose I could call it "Otala Reloaded" or some such, though I hate such names. That's the one I managed to wreak a 140 kHz full power bandwidth at rated 40 V peak and "beat" the original on literally every point, item by item. It's waiting for me to complete a second, different version of my own Centurion topology and it's off to Alex for PCB design (Alex is a friend from Romania, and quite an artist I must say, he does that for a living, and the only problem I have with him is making him take the money, because I think it's unfair to misuse him and his considerable talent for free, it's just not right).
Sanken modern MT-200 (2sa1295/2sc3264) are both 35mhz Ft and can
blow a MJL21193/4 away (SOA).
Using the Harmon kardon OPS (with the sankens) ,
me and "co-conspirators" blew a single pair at 200W using a oscillating amplifier -
to test a solid state relay.
These Sankens can also do 1mhz from of my CFA designs with
no "latch up".
PS - the "oscillating amp" was at 2mhz - outputs lasted over 10 minutes
@ 200W ... zobel resistor "glowed".
3 pair of these sankens can take a full power short and easily survive.
OS
That could be a spectacle worthy of Jeremy Clarkson and the Top Gear Roadshow.
The shape and size of the Sanken Packages appears to be less conducive to a compact arrangement on a given size of heat sink than power devices in conventional packages.
Would it not be possible to stack more of the latter in the space occupied by 3 pairs of Sanken Flat Packages and improve conduction from more devices into the heat sink. I am thinking of Amcron and TO-3 packages arranged closely and at an angle - and perhaps there is more to the issue than would appear at first glance - mindful of the bulk and appearance of equipment and, above all, the "you are not bringing that thing in here" wife non approval factor.
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You know Mjona, that may not have been the ebst amp ever made but it pulled off quite a feat, to make a 25/50W into 8/4 Ohms amp sound BIG. If you didn't know what it was, you'd probably be tempted to venture a guess that it was like a 150W amp or some such. You know, Mjona, that mayever made, but it mamaged to push all the right buttons and manages It simply didn't play by the the commercial ommercial rules, it gave you everything straight off.
Obviously, because of its relatively low power output, it assumed you have relatively efficient speakers, say from 92 dB/2,83V/1m and upwards, and indeed, when driving JBL 4312 speakers (95 dB/2,83V/1m) that was a marriage made in heaven, for regular home listening you needed some good source material and that was it. Most High End amps of the day, from the likes of SAE and Phase Linear, had a tough time catching up.
Actually, there was a small integrated amp made 10 or 12 years later, from Toshiba, the SB-420 model, which was built in a similar way and declared at 40WPC78 Ohms, which reiterated the point that power output was NOT the key point, but the design was. I bought one for funny money (€40) locally, refreshed it with new caps and I think it's a phenomenal deal even at its nominal price, which was low. However, it was sabotaged by its small power supply transformer, which can feed it for loads down to 6 Ohms or so, but no lower. There's no space in the original case for anything bigger, or I would have changed it.
The first next best thing I am aware of is my own H/K 6550, which has a whopping big transformer, but uses only a single pair of output devices (Toshiba 2SC3281/2SA1302, H/K's favorite devices, my PA 2400 also uses them, but with 4 pairs per side), and that only with swappeing the volume pot for an Alps Blue. And that one uses 17 dB of GNFB, less than the Otala, and has an insignificantly smaller slew rate of 80 V/uS (Otala 100 V/uS).
My Marantz 170 DC power amp is alse called a low feedback design by its makers, but I don't know its specifics.
All of this is what leads me to believe that a truly low GNFB amp has a better chance of sounding great than the traditional way of using lost of GNFB, all maths, theories and ideas notwithstanding. I admit to having heard a few big NFB amps which did sound excellent, but overall, these were more expensive and up market devices.
Obviously, because of its relatively low power output, it assumed you have relatively efficient speakers, say from 92 dB/2,83V/1m and upwards, and indeed, when driving JBL 4312 speakers (95 dB/2,83V/1m) that was a marriage made in heaven, for regular home listening you needed some good source material and that was it. Most High End amps of the day, from the likes of SAE and Phase Linear, had a tough time catching up.
Actually, there was a small integrated amp made 10 or 12 years later, from Toshiba, the SB-420 model, which was built in a similar way and declared at 40WPC78 Ohms, which reiterated the point that power output was NOT the key point, but the design was. I bought one for funny money (€40) locally, refreshed it with new caps and I think it's a phenomenal deal even at its nominal price, which was low. However, it was sabotaged by its small power supply transformer, which can feed it for loads down to 6 Ohms or so, but no lower. There's no space in the original case for anything bigger, or I would have changed it.
The first next best thing I am aware of is my own H/K 6550, which has a whopping big transformer, but uses only a single pair of output devices (Toshiba 2SC3281/2SA1302, H/K's favorite devices, my PA 2400 also uses them, but with 4 pairs per side), and that only with swappeing the volume pot for an Alps Blue. And that one uses 17 dB of GNFB, less than the Otala, and has an insignificantly smaller slew rate of 80 V/uS (Otala 100 V/uS).
My Marantz 170 DC power amp is alse called a low feedback design by its makers, but I don't know its specifics.
All of this is what leads me to believe that a truly low GNFB amp has a better chance of sounding great than the traditional way of using lost of GNFB, all maths, theories and ideas notwithstanding. I admit to having heard a few big NFB amps which did sound excellent, but overall, these were more expensive and up market devices.
Dejan. We all should build zero loop feedback SE valve amps. If anyone wants to I can make sure you stay on track. The sad thing as far as I can tell is that 5 watts is when the idea goes wrong. I think I know how to solve that. You must not use 300B if so or anything like that. You must not use push pull. Something in the middle.
There is great value in this if you are one of the few who gets it right. The Quad ESL 63 will be fine. Surprisingly 5 watts is OK. Some get the idea that 20 watts would be better. No way. If you do get it right you will hear layers you never thought existed. Mostly any distortion will be your speaker. The Quad 63's will hold distortion down to about 1% or far less with such an amp if the design is as good as it can be. The PYE Mozart is good. You don't need a special transformer as the feedback if used is by including the speaker side in series with the cathode of the EL 34. The output transformer makes that easy to do as phase is how it is hooked up. You won't get as much feedback as the PYE and you wouldn't want that.
I took my little valve amp to my friends house. He has hearing problems ( tinitus ). He insisted we use some very cheap Mission speakers or similar. To me it blew away his Naim system that includes NAP 250 and more PSU's than is possible. I thought it right for him to have something like this. Alas his problems stop him being able to hear the positive changes. I was so sure he would find it easier to listen to.
My valve amp has zero loop feedback and has full bootstrapping for maximum gain. And yet it is of very low distortion. This came from reading a non David Hafler account of how Ultra Linear feedback works for the first years of it's use. It showed how a pentode curve and triode curve were in fact two nasty curves with a nice one between them. I have always strongly disliked amps with Ultra Linear feedback. Actually that is not true. I like Dynaco and Leak. Thus I did a test and found I very much like UL. I don't like UL and global feedback with off the shelf transformers. So I built my amp with what I call East-West Ultra Linear.
Having got this far I tried to relate this to transistor amps. If you build a op-amp driven class A it is possible to try many things. The really big deal is slewing. This can not be true as the amps need nothing special regardless of how you see slewing. Nor can it be crossover distortion as there is none. All the same all the usual nasties are heard. All it can be is amplifers don't like speakers. Valve amps as described don't really know the speaker is there is my best guess. They are run as a constant current device so do not really care what is outside of their simplest world. The valve looks mostly like a resistor.
My Quad 303 seems to have been designed by someone desperate to move to transistors who unfortunately had made one of the better valve designs. It turns out Quad were a bit cunning and used null tests. MP3 seems to prove most of the things we feel sure we hear we don't. I think this goes for the 303. To give it any chance of sounding like the Quad 2/22 they had to just get it to do the simple things right. One of these seems to be although class AB it seems not to realise a speaker is there. If my guess is right feedback is the slewing issue.
My OB speakers seem to be working OK. Elvis was very good last night. The tweeters are exactly as they show on the graphs. In the ideal world I would get 5 kHz more. That needs an active setup, then 50 kHz is possible with a tweeter I have. I played Kate Bush Army Dreamers. The OB without them was not very good on that. Her and Peter G singing Don't Give Up was great as was Phil Collins Something in the air Tonight. The latter was stunning, it is one I usually get bored with. Real bight. The slight problem is the tweeters work so well it is easy to think they are not there. The music form last night proves they are. I really must sort out the 15 inch drivers, taking them out of the packing would be a start. An Aperiodic speaker foot is needed I feel. Qts measured is 1.2 so I might get lucky. OB with the 15 inch might be a waste of the driver. If I can scale up my Dynacos 25's I will be pleased. Fo is 30 Hz and about 5R6.
There is great value in this if you are one of the few who gets it right. The Quad ESL 63 will be fine. Surprisingly 5 watts is OK. Some get the idea that 20 watts would be better. No way. If you do get it right you will hear layers you never thought existed. Mostly any distortion will be your speaker. The Quad 63's will hold distortion down to about 1% or far less with such an amp if the design is as good as it can be. The PYE Mozart is good. You don't need a special transformer as the feedback if used is by including the speaker side in series with the cathode of the EL 34. The output transformer makes that easy to do as phase is how it is hooked up. You won't get as much feedback as the PYE and you wouldn't want that.
I took my little valve amp to my friends house. He has hearing problems ( tinitus ). He insisted we use some very cheap Mission speakers or similar. To me it blew away his Naim system that includes NAP 250 and more PSU's than is possible. I thought it right for him to have something like this. Alas his problems stop him being able to hear the positive changes. I was so sure he would find it easier to listen to.
My valve amp has zero loop feedback and has full bootstrapping for maximum gain. And yet it is of very low distortion. This came from reading a non David Hafler account of how Ultra Linear feedback works for the first years of it's use. It showed how a pentode curve and triode curve were in fact two nasty curves with a nice one between them. I have always strongly disliked amps with Ultra Linear feedback. Actually that is not true. I like Dynaco and Leak. Thus I did a test and found I very much like UL. I don't like UL and global feedback with off the shelf transformers. So I built my amp with what I call East-West Ultra Linear.
Having got this far I tried to relate this to transistor amps. If you build a op-amp driven class A it is possible to try many things. The really big deal is slewing. This can not be true as the amps need nothing special regardless of how you see slewing. Nor can it be crossover distortion as there is none. All the same all the usual nasties are heard. All it can be is amplifers don't like speakers. Valve amps as described don't really know the speaker is there is my best guess. They are run as a constant current device so do not really care what is outside of their simplest world. The valve looks mostly like a resistor.
My Quad 303 seems to have been designed by someone desperate to move to transistors who unfortunately had made one of the better valve designs. It turns out Quad were a bit cunning and used null tests. MP3 seems to prove most of the things we feel sure we hear we don't. I think this goes for the 303. To give it any chance of sounding like the Quad 2/22 they had to just get it to do the simple things right. One of these seems to be although class AB it seems not to realise a speaker is there. If my guess is right feedback is the slewing issue.
My OB speakers seem to be working OK. Elvis was very good last night. The tweeters are exactly as they show on the graphs. In the ideal world I would get 5 kHz more. That needs an active setup, then 50 kHz is possible with a tweeter I have. I played Kate Bush Army Dreamers. The OB without them was not very good on that. Her and Peter G singing Don't Give Up was great as was Phil Collins Something in the air Tonight. The latter was stunning, it is one I usually get bored with. Real bight. The slight problem is the tweeters work so well it is easy to think they are not there. The music form last night proves they are. I really must sort out the 15 inch drivers, taking them out of the packing would be a start. An Aperiodic speaker foot is needed I feel. Qts measured is 1.2 so I might get lucky. OB with the 15 inch might be a waste of the driver. If I can scale up my Dynacos 25's I will be pleased. Fo is 30 Hz and about 5R6.
Nige, I think I told you this, but I could be wrong. I have heard only a handful of zero GNFB amps in my life, and surprisingly, didn't like any of them. They sounded to me as if they were not finished yet, in poor control of the speakers, and not quite in focus, so to speak. This despite a quite reasonable measured performance. Pushed well into class A. It just didn't sound right to me.
This includes both tube and SS gear, although I might add that it seemed to me that the SS gear did have a somewhat better grip over the speakers.
Sorry. tube just doesn't do it for me.
This includes both tube and SS gear, although I might add that it seemed to me that the SS gear did have a somewhat better grip over the speakers.
Sorry. tube just doesn't do it for me.
Strangely my visit to my friend who deals in second hand Hi-Fi, hearing a Harman Kardon amplifier, a 655 model and some other passing comment he made triggered my interest in low feedback designs. We were discussing local affairs in New Zealand and a runaway housing market in Auckland and Christchurch and the fact Auckland has become a magnet for immigrants for whom the money is no problem. Elsewhere house prices, such as in the region where we live, near the capital city are trailing. Anyway, my friend has an acquaintance who has money and had outlaid over $200,000 to buy the latest Naim "Statement" amplifier.
I was interested in what one got for that sort of money and so I looked up the Naim website to see what they are up to. Apparently "Statement" still remains an all NPN output amplifier, but that stage is not part of the feedback loop. I think there is some theatre about the output rating of 746 watts into 8 ohms as that equates to one horsepower. They claim 9000 watts instantaneous into 1 Ohm.
There is a non-dramatic description of the beast on another site Naim makes a Statement at CES | SECRETS Press Releases . The part of the Naim website I found most interesting was the video of Steve Sells describing his design philosophy.
I could be wrong but I cannot see many interested enough to emulate that either in the industry or the DIY fraternity.
Dejan, Years ago Art Audio lent me a SE amp that surprised me. When I built my own I was asking the question does it need to cost big money. Art lent me a Sowter transformer which was well above my price limit. I found the very low cost Danbury transfomers can give Sowter a run for their money. Danbury mains transformers were less impressive.
The speakers most people own need a conventional amplifier. These speakers are acceptable to non hi fi people. My OB speaker are not acceptable even to me! The Quad is a well respected speaker that almost is OK with wives. Ones who understand the love of music etc. These speakers do not need high damping factor. Recent trends suggest a very high impedance output amplifer might be the correct way to go. These people even suggest conventional amps cause more problems than they solve. Whatever the truth of all of this we can sometimes find that what we accept as correct practice is just normal practice. Seen from that angle all a jet engine is, is getting rid of the pistons and using the exhaust pipe to blow the aircraft along. What a daft idea, it will never catch on. Frank Whittle was told that from 1927 until 1942. Wittgenstein was a pioneer of Pulse Jets circa 1915. Yes that is the same Wittgenstein as one would think of.
Wittgenstein's aeronautical investigation | Notes and Records of the Royal Society
The speakers most people own need a conventional amplifier. These speakers are acceptable to non hi fi people. My OB speaker are not acceptable even to me! The Quad is a well respected speaker that almost is OK with wives. Ones who understand the love of music etc. These speakers do not need high damping factor. Recent trends suggest a very high impedance output amplifer might be the correct way to go. These people even suggest conventional amps cause more problems than they solve. Whatever the truth of all of this we can sometimes find that what we accept as correct practice is just normal practice. Seen from that angle all a jet engine is, is getting rid of the pistons and using the exhaust pipe to blow the aircraft along. What a daft idea, it will never catch on. Frank Whittle was told that from 1927 until 1942. Wittgenstein was a pioneer of Pulse Jets circa 1915. Yes that is the same Wittgenstein as one would think of.
Wittgenstein's aeronautical investigation | Notes and Records of the Royal Society
Mjona, odd you should say that. I also noticed something, truly low GNFB amps have a tenency to claim bigger impulse output powers than traditional designs, especially into low impedance loads. Not always so, but most often.
H/K for example make some bold claims for High Instantaneous Current Capacity (HCC). While the figures look great (my PA 2400 is rated at 150 Amps!), it doesn't really tell me much. Into what load, for how long? Missing data, as if they were reading it off the output transistor Data Sheet. Electrocompaniet also makes some wild claims, but they do say in very small print that's their 1 mS power output, which is in my view uselessly short.
H/K for example make some bold claims for High Instantaneous Current Capacity (HCC). While the figures look great (my PA 2400 is rated at 150 Amps!), it doesn't really tell me much. Into what load, for how long? Missing data, as if they were reading it off the output transistor Data Sheet. Electrocompaniet also makes some wild claims, but they do say in very small print that's their 1 mS power output, which is in my view uselessly short.
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My understanding is negative feedback improves the inherent ability of a circuit in rejecting extraneous signals on a given power supply, and better results come with a higher feedback factor.
If the same result is required with a reduced feedback factor then the power supply will to be beefed up with more capacitance and a larger transformer. You would than have on your hands a low impedance power supply within a amplifier that would have been more expensive at the time low feedback designs arrived on the market.
It would have been hard to sell a 50 watt rated amplifier against a product rated at say 75-100 watts for the same sort of money and to offset that paper disadvantage, instantaneous current delivery became a new buzzword in the market. Hi-Fi magazines soon got on board with this notion and in due course quite a few respected manufacturers followed suit.
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I should add that the ability to drive low impedance loads was a further advantage of specifying a low impedance power supply assuming robust output transistors.
I have six sets of speakers other than the Quad 63's. Those in our lounge are Rogers LS6 a two way reflex cabinet with a 6.5 inch poly bass unit and a 1 inch metal dome high frequency unit. I have not had them apart so to inspect what is inside but they are rated at 200 watts, sensitivity 89 dB, response at 2 metres +/- 2 dB from 50 Hz to 20 kHz. I have a two pair of home built speakers, both reflex two way systems. The drive units and crossover are from a Madisound project using Vifa drivers, bass 5.5 inches, and 1 inch soft dome high frequency unit. The volume 9 litres however the bass holds up to 60 Hz due to a slight hump in the reflex tuning. The sensitivity is roughly the same. I also have a set of mini-monitors I designed myself using a 4 inch bass mid-range from the SEAS range and a 3/4 inch soft dome high frequency unit. It has taken a lot of effort to get these to sound right as the box is only 5 litres and quite narrow across the front baffle. These are a little low in sensitivity due to lost efficiency of a large coil in the bass feed.
The other speakers are at a holiday property, and old pair of three way sealed box ones with paired 8 inch drivers a soft dome midrange and tweeter - I built these about 30 years ago.
There is a set of PSB similar in size and design concept to the Madisound. project ones. The main ones in the lounge at the holiday property are EPOS model 11 which have a six inch polycone base with phase correcting dust cover and metal dome high frequency unit 1 inch. The driver characteristics are devised to be such that the only crossover component is a capacitor in the feed to the latter unit.
I believe a low power amp around 25 or so watts will be sufficient to drive any of these to limits to reach volumes where I would have to turn it down or leave the room. The PSB has the lowest nominal impedance at 4 ohms - the others are between 6 and 8 ohms.
I have three commercial amplifiers with 8 ohm power ratings of around 50 watts and retained a couple of DIY ones from a number of builds with lesser output than this.
I would quite like to add a HK to my collection however owners seem to want to hold onto them and they don't come up for sale that often in this country. Having compared the 655 model I saw last week to the 6550 you own I feel yours is a better circuit. That presents a dilemma over whether to chance waiting or do something about a build.
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Mjona, agreed, the original Otalal/Lohstroh amp should be able to drive any of the speakers you mentioned to reasonable room listening levels. All the more so because it operates in pure class A up to 2.9/5.8W into 4/8 Ohms, where we live 98% of the time anyway.
By the same token, twice the power (50W/8Ohms) should add some headroom resreve, just in case. That said, I also feel a much more powerful amp would still sound just that little bit better, everything else being the same.
As for H/K availability, that's out of out hands. H/K was highly regarded and did good business in Germany in particular, but in Europe in general as well, with the exception of the UK (it seems the Brits don't like them much). Locally, lost of them are for sale at more than reasonable prices. For example, a 6550 in resonable condition goes for €100 or so. I purchased my PA 2400 (2*170W/8 Ohms) for just €330, which is cheap, and it's in a very good condition too. I haven't refreshed it yet, but I can tell you straight off that those 4 12,000 uF caps (2 per channel) will become 15,000 or 18,000 uF. It has a massive toroidal transformer with separate windings for each channel.
Also, the 6550 may have what was already an option, the phono RIAA eq amp board, which is very good as well. Not as good as the ne in the Luxman, but then the said Luxman preamp (C-03) did cost a bit more than the whole integrated amp.
FYI, the 6550 will drive my AR94 speakers (not the easiset of loads) with ease to very high SPL levels.
All told, if I were you, I'd wait it out, as I did with my PA 2400, I waited 4 years for it to appear, but I nabbed it in the end.
On the other hand, if you want something special, making one may be a better option, because you can do what you like with it, like adding another ouput pair, and/or make a very low impedance PSU, etc.
By the same token, twice the power (50W/8Ohms) should add some headroom resreve, just in case. That said, I also feel a much more powerful amp would still sound just that little bit better, everything else being the same.
As for H/K availability, that's out of out hands. H/K was highly regarded and did good business in Germany in particular, but in Europe in general as well, with the exception of the UK (it seems the Brits don't like them much). Locally, lost of them are for sale at more than reasonable prices. For example, a 6550 in resonable condition goes for €100 or so. I purchased my PA 2400 (2*170W/8 Ohms) for just €330, which is cheap, and it's in a very good condition too. I haven't refreshed it yet, but I can tell you straight off that those 4 12,000 uF caps (2 per channel) will become 15,000 or 18,000 uF. It has a massive toroidal transformer with separate windings for each channel.
Also, the 6550 may have what was already an option, the phono RIAA eq amp board, which is very good as well. Not as good as the ne in the Luxman, but then the said Luxman preamp (C-03) did cost a bit more than the whole integrated amp.
FYI, the 6550 will drive my AR94 speakers (not the easiset of loads) with ease to very high SPL levels.
All told, if I were you, I'd wait it out, as I did with my PA 2400, I waited 4 years for it to appear, but I nabbed it in the end.
On the other hand, if you want something special, making one may be a better option, because you can do what you like with it, like adding another ouput pair, and/or make a very low impedance PSU, etc.
Offcourse iT can be measured, and THE factories which say iT can't and sell powercords for 4000dollars , only are too cheap let it tested ; they sell an illegal cable. Those companies are hypocrites; They do show how low their wow/flutter, tone arm-damping etc is. But why do 90% with a high education, when it comes to in my case micro-electronics and off course chemistry etc. say that it's a rip off two buy expensive leads, connectors. Mr. Placebo plays a big part and since salesmen don't have a clue what they sell often: then you are plane stupid to buy it. And cables that need to run in........
But the charistics of a new cable can just be that tiny better for your system and then it overall sounds better, only is it trying. And I don't know a proffessor which gives you those companies right, besides that they often use the same cables with another brand.
Greats richard
But the charistics of a new cable can just be that tiny better for your system and then it overall sounds better, only is it trying. And I don't know a proffessor which gives you those companies right, besides that they often use the same cables with another brand.
Greats richard
I agree that cables CAN play SOME part in the overall sound, but I suspect not too much, except perhaps for the speaker cables, and even they more by their size in relation to length.
In his book on audio amplifiers, Ben Duncan has offered some advice on this matter. Since the room architecture forces me to use 2*6 m of speaker cables, I do use van den Hul's 352 Hybrid cables, 5.5 mm square, 2*256 strands. I bought it after trying out as many cables as I could borrow from frineds, and in my view, the 352 did everything much more expensive cables did for less money.
My wife's system needs only 2*2.5 m lengths, so it is wired with the same cable, CS 122, which differes from mine only in size, it's 2*3.5 mm squared. Size does matter if you want to let the amp actually pass lots of current on to the speaker.
I also like to use pure silver Neotech cable for internal wiring of everything, includig speakers. I feel they do sound better than the usual OFC opper cables, the difference is not very big but is big enough to be just heard. So, I didn't expect and didn't get any miracles and)or revelations, but I did get some very clean and tonally balanced sound. That said, I will admit that Neotech does have an OFC cable which is almost indistingushable from pure silver, and rememebr, that's just one manufacturer whose cables are reold with different badges at 3 or 4 TIMES the price.
In his book on audio amplifiers, Ben Duncan has offered some advice on this matter. Since the room architecture forces me to use 2*6 m of speaker cables, I do use van den Hul's 352 Hybrid cables, 5.5 mm square, 2*256 strands. I bought it after trying out as many cables as I could borrow from frineds, and in my view, the 352 did everything much more expensive cables did for less money.
My wife's system needs only 2*2.5 m lengths, so it is wired with the same cable, CS 122, which differes from mine only in size, it's 2*3.5 mm squared. Size does matter if you want to let the amp actually pass lots of current on to the speaker.
I also like to use pure silver Neotech cable for internal wiring of everything, includig speakers. I feel they do sound better than the usual OFC opper cables, the difference is not very big but is big enough to be just heard. So, I didn't expect and didn't get any miracles and)or revelations, but I did get some very clean and tonally balanced sound. That said, I will admit that Neotech does have an OFC cable which is almost indistingushable from pure silver, and rememebr, that's just one manufacturer whose cables are reold with different badges at 3 or 4 TIMES the price.
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