Sugden A21/A51 diy pcb: anybody? - diyAudio
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Old 26th April 2011, 10:51 AM   #1
rmgvs is offline rmgvs  Netherlands
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Default Sugden A21/A51 diy pcb: anybody?

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.
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Old 26th April 2011, 12:06 PM   #2
rmgvs is offline rmgvs  Netherlands
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Default 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.
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Old 26th April 2011, 03:59 PM   #3
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I also want to get PCB for this amp too.
What is your Power transistor for this project?

Last edited by mindengine; 26th April 2011 at 04:02 PM.
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Old 26th April 2011, 04:48 PM   #4
rmgvs is offline rmgvs  Netherlands
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Default power transistor

I used the golden oldie 2N3055 Motorola to keep in line with the tube sound of this design. But quite a number of transistors can be used here, I don't think it's very critical.
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Old 26th April 2011, 06:35 PM   #5
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I think sugden's circuit shows some hint hint about CCS modulation , like Aleph CCS .
This seems to me very interesting and want to make and test this amplifier.
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Old 26th April 2011, 06:48 PM   #6
lineup is offline lineup  Sweden
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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.
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Old 28th April 2011, 12:35 PM   #7
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bc109 could be replaced with bc550?
bfy52 with bd139?
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Old 2nd November 2011, 07:00 PM   #8
rmgvs is offline rmgvs  Netherlands
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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.
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Old 2nd November 2011, 09:23 PM   #9
seebert is offline seebert  United States
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Quote:
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
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Old 3rd November 2011, 12:59 AM   #10
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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?
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