I have plans to make myself a power amp according to the schematics of the original Sugden A51 class A amp. The circuit can be found easily on the internet (for example, see the class a amplier site http://www.tcaas.btinternet.co.uk/sugden10w.gif). The circuit is in essence the same as the A21 Mk II. Does anybody have the skills to design a nice and compact / flexible (catering for different sorts of components) pcb for the circuit less the power supply? Maybe others are interested too and we can do a group buy of the pcb's.
picture of veroboard
An earlier attempt of mine to construct this amp using veroboard and hard-wiring. The result is a very smooth and musical sounding power amp. On the board you see 3 capacitors of 10.000 mF, one is for the output coupling to the speaker, the other two are for a C-R-C power supply per channel. I used a number of 2N1711's (metal can). You see two pots, one for setting the idling current (I choose mine at 1 Amp) and one for setting the mid point of the power supply voltage (around 18 V in my case). The same can be done easier and cleaner using well laid-out pcb's I guess.
An earlier attempt of mine to construct this amp using veroboard and hard-wiring. The result is a very smooth and musical sounding power amp. On the board you see 3 capacitors of 10.000 mF, one is for the output coupling to the speaker, the other two are for a C-R-C power supply per channel. I used a number of 2N1711's (metal can). You see two pots, one for setting the idling current (I choose mine at 1 Amp) and one for setting the mid point of the power supply voltage (around 18 V in my case). The same can be done easier and cleaner using well laid-out pcb's I guess.
Attachments
TR2, BC109, is the heart of the sugden.
I tested only that voltage amplifier with its local feedback R8, 470k in SPICE
It is a very simple one transistor volt amp.
It shows a bit distortion. Like 0.3%-0.7% THD.
Now, there is a feedback from the output to this TR2.
I would guess this is a Class A with quite a bit distortion, as a whole.
Especially at higher output levels, of course.
It is nothing I would long to build. When there are alternatives with lower THD.
I tested only that voltage amplifier with its local feedback R8, 470k in SPICE
It is a very simple one transistor volt amp.
It shows a bit distortion. Like 0.3%-0.7% THD.
Now, there is a feedback from the output to this TR2.
I would guess this is a Class A with quite a bit distortion, as a whole.
Especially at higher output levels, of course.
It is nothing I would long to build. When there are alternatives with lower THD.
pity
Nobody seems interested in the design/pcb. I don't know about measured distortion, can be true, must be pleasant distortion, it's not the latest and the greatest. The only thing I have experienced (I'm not talking from Spice analysis experience) is that this is as far as you can go with transistors sounding close to good tube-designs. This is an amplifier you can fit and forget. Soundwise in the same league as Hiraga, Linsley-Hood and Pass. Many owners of the original A51 (40 years old) have discoverd that newer is not better most of the time.
Nobody seems interested in the design/pcb. I don't know about measured distortion, can be true, must be pleasant distortion, it's not the latest and the greatest. The only thing I have experienced (I'm not talking from Spice analysis experience) is that this is as far as you can go with transistors sounding close to good tube-designs. This is an amplifier you can fit and forget. Soundwise in the same league as Hiraga, Linsley-Hood and Pass. Many owners of the original A51 (40 years old) have discoverd that newer is not better most of the time.
Totally agree.
If you're lucky enough to have been able to save the money - i.e. not on a fixed income, never needed high co-pay medical treatment and so on - then I guess the later top end audio gear can be better than vintage audio gear but it sure costs a lot more in pro-rata-year dollars. Unfortunately I fall into the group above (sorry guys but I couldn't have done or given more than I did) so it's vintage gear for me plus repairs plus any building that I can do.
The Sugdens were good sounding amps despite their 'distortion' and design limitations - once again isn't it all down to system component matching and aiming for component synergy.
Snake oil and snobbery be gone ... it's hearing what your own ears like that counts
If you are just looking for a PCB to make your DIY more attractive, consider that this design is based, like many old UK amplifiers, on a Mullard circuit from around 1970. Even the NAD 3020 and its many descendents have their roots there. The BC109s and BFY51,2 are a clue since they were not ideal for the job but obviously generated lots of sweet distortion. It may be possible to adapt other PCBs of this basic design, if available.
Sure, you can substitute parts with modern, better types, but losing some distortion or gaining something else in the process. I don't believe there would be much interest in cloning a particular low power design for the world market when it still seems available at reasonable cost. The popular JLH design covers most DIY interest in the genre.
Take care that high current power supplies, as class A requires, are separated from the amplifiers to minimise hum. Other than heat issues, there is not much wrong with using stripboard, as many famous amps used awful PCB layouts on similar "phenolic" material.
I would not be ashamed of an amplifier built carefully like yours on stripboard etc. When the cover is on, what is the difference, except for bragging rights?
Sure, you can substitute parts with modern, better types, but losing some distortion or gaining something else in the process. I don't believe there would be much interest in cloning a particular low power design for the world market when it still seems available at reasonable cost. The popular JLH design covers most DIY interest in the genre.
Take care that high current power supplies, as class A requires, are separated from the amplifiers to minimise hum. Other than heat issues, there is not much wrong with using stripboard, as many famous amps used awful PCB layouts on similar "phenolic" material.
I would not be ashamed of an amplifier built carefully like yours on stripboard etc. When the cover is on, what is the difference, except for bragging rights?
Sugden 21 Mk 3 or later
Dear All,
I have a Sugden A28 Mk 3 which according to the schematic I have is much the same as a A48 Mk 3 but with 71 V rather than 73.6V power supply, and uses 120 VA transformers rather than 140 VA.
Unlike Sugden DIY design but like the Sugden A21 Mk2/A51, in the A28 mk3 the feedback goes to Tr1's Emitter.
The with the exception of the circuit driving the output transistors it is in essence the same topology but with a constant current phase splitter as this amp is a class AB bias heavily into class A.
To my ears at least ( no distortion measurements or equipment suitable for doing this) this is the nicest amplifier I have by some margin. Followed by the Quad 303, the Quad 306 and then many other amps I have had. The old JLH design I made years ago (without enough spent on the transformers) has never been compared as they are in different countries.
I would be very interested in a Sugden A21 Mk3 or later schematic, as I would not be surprised if it is essentially a scaled up A51 with modern components (probably lower distortion) and optimized for 4-6 Ohm speakers. Such a clone (with a PCB) would probably tempt me to build it as the A28 Sugden box is not so much better than that of a DIY design.
Some one with more knowledge than I, would I expect clone the Sugden A51 with a few more constant current sources. My uneducated guess is that (Referring to the A51 schematic) R13/R14 and R18 should be replaced with a constant current supply. I imaging the bias of Tr1 could be made more conventional. I personally don't understand what X2 is for.
How would the experts on the forum improve upon a Sugden A51?
Regards
Owen
Dear All,
I have a Sugden A28 Mk 3 which according to the schematic I have is much the same as a A48 Mk 3 but with 71 V rather than 73.6V power supply, and uses 120 VA transformers rather than 140 VA.
Unlike Sugden DIY design but like the Sugden A21 Mk2/A51, in the A28 mk3 the feedback goes to Tr1's Emitter.
The with the exception of the circuit driving the output transistors it is in essence the same topology but with a constant current phase splitter as this amp is a class AB bias heavily into class A.
To my ears at least ( no distortion measurements or equipment suitable for doing this) this is the nicest amplifier I have by some margin. Followed by the Quad 303, the Quad 306 and then many other amps I have had. The old JLH design I made years ago (without enough spent on the transformers) has never been compared as they are in different countries.
I would be very interested in a Sugden A21 Mk3 or later schematic, as I would not be surprised if it is essentially a scaled up A51 with modern components (probably lower distortion) and optimized for 4-6 Ohm speakers. Such a clone (with a PCB) would probably tempt me to build it as the A28 Sugden box is not so much better than that of a DIY design.
Some one with more knowledge than I, would I expect clone the Sugden A51 with a few more constant current sources. My uneducated guess is that (Referring to the A51 schematic) R13/R14 and R18 should be replaced with a constant current supply. I imaging the bias of Tr1 could be made more conventional. I personally don't understand what X2 is for.
How would the experts on the forum improve upon a Sugden A51?
Regards
Owen
Hallo Owen,
I had several A28/A48 in the past (original ones, not diy), and though good they are not in the class of the old A21 and A51. It remains to be seen why this is so (use of parts, power supply, circuit diagram, distortion spectrum etc), but for me this is the starting point.
The design is kept rather constant during time, mostly newer parts and some circuit revisions. But it's open secret that the old design still is the best in terms of subjective quality like mellowness (new design sounds more hifi).
So the A51 with common available parts and a good power supply on a well laid out pcb can be the answer. Must be on the same level as JLH and Hiraga, and (having all of them on a diy basis) personally I like to listen to the Sugden the most.
Well, this is all words. Now the waiting is on somebody who has the time and wisdom to design a suitable pcb.
I had several A28/A48 in the past (original ones, not diy), and though good they are not in the class of the old A21 and A51. It remains to be seen why this is so (use of parts, power supply, circuit diagram, distortion spectrum etc), but for me this is the starting point.
The design is kept rather constant during time, mostly newer parts and some circuit revisions. But it's open secret that the old design still is the best in terms of subjective quality like mellowness (new design sounds more hifi).
So the A51 with common available parts and a good power supply on a well laid out pcb can be the answer. Must be on the same level as JLH and Hiraga, and (having all of them on a diy basis) personally I like to listen to the Sugden the most.
Well, this is all words. Now the waiting is on somebody who has the time and wisdom to design a suitable pcb.
I have an A21 and although it's good in terms of "warmth" etc I wouldn't personally rate it all that highly overall..... It does indeed sound very similar to 60's valve amps but that includes the soft bass, slightly rounded top end etc.
I am re-opening a catering pack of worms here but to me an amp should be accurate not "Nice". And by accurate I mean just that... NOT harsh, grainy, rounded or anything else.
BTW Be wary of later versions of these amps as when they reached I think MKIII they became a different amp in the same case and no longer class A !
I am re-opening a catering pack of worms here but to me an amp should be accurate not "Nice". And by accurate I mean just that... NOT harsh, grainy, rounded or anything else.
BTW Be wary of later versions of these amps as when they reached I think MKIII they became a different amp in the same case and no longer class A !
Jez, you are right of course. It's an old discussion. I think that all good amps that have become classics have less or more euphony in the sound. Hiraga, JLH, some Pass amps, Sugden, the A1/A100/A1000: they all do not sound clinical but err on the side of warmth.
BTW: all these class-A classics do sound slightly different in some respects (and of course one piece can sound different on its own depending on how you build it).
An amp that gives it all would be the preferred option: warmth, details etc. Most of the amps that give a lot of details and are considered neutral or accurate, don't give me much pleasure at the end of the day. And let's be honest, that's what it is all about.
BTW: all these class-A classics do sound slightly different in some respects (and of course one piece can sound different on its own depending on how you build it).
An amp that gives it all would be the preferred option: warmth, details etc. Most of the amps that give a lot of details and are considered neutral or accurate, don't give me much pleasure at the end of the day. And let's be honest, that's what it is all about.
Dear Jez,
I think some of it has to do with what speakers your driving. Accurate low bass is not essential in an amplifier if your driving electrostatics and Quad ESL 63's roll off their treble around the same place as my hearing, since they don't go down so low.
The Quad 306 is defiantly a lot better in low bass than my other amps but is some times grating (harsh in the higher frequency regions) but then maybe thats the source material being accurately reproduced. Although some of the other power amps under the bed sound nice in the bass department, for me its all about how they sound in the human voice region. Some how the Sugden A28 Mk3 is more reach out and touch it, closely followed by the Quad 303's. Though it must be said I will test the Net audio power supply module soon (its coming hopefully before Christmas) to see how it compares with original Quad 303's and if it can match my Sugden A28 then.
I am not yet sure what for me makes a great amp, but would be very tempted build a Sugden clone as I can always convert it to a JLH Class A/Hiraga if it fails to beat my current champion.
Regards
Owen
I think some of it has to do with what speakers your driving. Accurate low bass is not essential in an amplifier if your driving electrostatics and Quad ESL 63's roll off their treble around the same place as my hearing, since they don't go down so low.
The Quad 306 is defiantly a lot better in low bass than my other amps but is some times grating (harsh in the higher frequency regions) but then maybe thats the source material being accurately reproduced. Although some of the other power amps under the bed sound nice in the bass department, for me its all about how they sound in the human voice region. Some how the Sugden A28 Mk3 is more reach out and touch it, closely followed by the Quad 303's. Though it must be said I will test the Net audio power supply module soon (its coming hopefully before Christmas) to see how it compares with original Quad 303's and if it can match my Sugden A28 then.
I am not yet sure what for me makes a great amp, but would be very tempted build a Sugden clone as I can always convert it to a JLH Class A/Hiraga if it fails to beat my current champion.
Regards
Owen
I think it very unlikely that tag board would result in any substantial difference to the sound. Parasitics can be just as low (lower in fact) with pcb's....
I've nothing against tagboard and I'm familiar with it's reputation but I reckon it's all more snake oil to justify certain highly priced "boutique" amps both in hifi and guitar amps. YMMV.
Fair dinkum Hugh! My bro (Simon) done one and left the sinking ship... Married one of you colonials and now has a restaurant in your area... It gets very good reviews Chester White | Home Page Ask him how the pre-amp I made him is doing if you go and tell him his brother sent you....
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