'AK Mods' SC Class A 15W Amplifier

[Deleted]

Mar 14, 2013 10:22:35 GMT @davek said:

Hi Guys,
I know you're all waiting with bated breath for a progress report on my amp so I just thought I'd mention that Sean expects to complete one amp any day now and it is on target for mid April completion. I'm looking forward to it .

Hi Dave
I am looking forward to seeing what a pro can do with this build.
Make sure you take some internal photos too.

Kind Regards
Alex

[Deleted]

Hi Alex,
I will of course take as many pics as anyone might want but Sean also posted that he will take pics as he builds the amps so I suspect that there will be no shortage.
Dave.

[sean]

I've got one monoblock finished in a mechanical sense - all bolted together and looks the part, now to finish off the wiring between modules and turn it on (gulp) - the PSU board tests OK so far, so i'm going to delve into this thread and the other, and check all the info before I start trying to power up the amp board itself. As promised, here's a photo of the story so far...

[Deleted]

‘’so I’m going to delve into this thread and the other, and check all the info before I start trying to power up the amp board itself’’

Yup a really good idea just to have a skim through the threads and a good look at wills set up instructions before lift-off.

Hi Sean (curious spelling )

That’s great work and quick fire on the Speaker pro boards. Where did you order them from?

Those HIFI2000 cases are really nice units and give the whole thing a solid professional look and feel.

Looking forward to hearing your thoughts on the SQ.

Take care

[Deleted]

Looking good Sean - don't know whether I'm looking forward more to my week in St. Ives or the receipt of the amps on my return .
Regarding the spelling of your name, I used to work with a guy called Sean who absolutely insisted on the use of an accent on the 'e' when anyone wrote his name. I have no idea of the background to the accent but he was most insistent. Apart from that he was a really nice guy!! .
Dave.

[Deleted]

Hi Dave

No worries just a standing joke between myself and a good friend I have with the same name but different spelling.

A lot of us around

Take care

[Deleted]

I was told the reasoning a while back so from memory ( not guaranteed by any means! )...

Sean, with an accent over the e or a is the original Irish spelling of the name, the accent moves depending on whether the pronunciation is lower Eire or Northern Ireland. Without the accent the meaning of the name/word is changed.

Other spellings have evolved along the way just like many other names.


Ok, you can wake up now, I've finished!

[sean]

CJ's right - mine is the Irish spelling of Sean (well, the Anglicised version without the accents anyway). Not that i've any Irish blood in me, parents must've just liked the name. Anyway, ah yes the amp - got it all up and running with no problems whatsoever, the wiring is all finished now and it looks nice and neat. Got the amp playing into a stunt speaker for now, once i get the other one built i'll get them on the main system. Had a chance to play with my new toy too - an IR temperature sensor, the output transistors are happy enough at about 50C and the heatsink is a reasonable 40-ish C for now - I expect it'll get a bit warmer when I get them onto the main speakers and crank it up a bit

Can't comment on SQ yet as the stunt speakers are oh-so-poor, but by chance i've got a good lineup to try them out against at the minute - my Naim NAP300, a Gainclone (LM3875) amp, a pair of Avondale NCC200 monoblocks and a Pioneer A-400 that i've modified. Should be a good day of testing them all out I reckon!

[sean]

Mar 16, 2013 13:43:56 GMT @shaun said:

That’s great work and quick fire on the Speaker pro boards. Where did you order them from?

Those HIFI2000 cases are really nice units and give the whole thing a solid professional look and feel.

The speaker pro boards are actually from Jaycar - you can see the logo in the picture. I only built up one side of them because it's a monoblock amp. The underside has the LED mod and I also added a link to connect ground to the AC sense input as per instructions. The HiFi2000/Modushop cases really are excellent, very reasonably priced for what you get I think too. I use their Galaxy range of cases in my own lineup of PSUs for Naim equipment, as well as numerous amp projects and custom builds. Now that i've seen this Dissipante range, i'm quite taken by the idea of building up my own power amp design in a 2U case, based around the Naim design with some extra mods here and there.

[Deleted]

Had a chance to play with my new toy too - an IR temperature sensor, the output transistors are happy enough at about 50C and the heatsink is a reasonable 40-ish C for now - I expect it'll get a bit warmer when I get them onto the main speakers and crank it up a bit


Read more: rockgrotto.proboards.com/posts/recent#ixzz2NklQpruF

Hi Sean
Unless your speakers are 4 ohms, it shouldn't make any real difference, as it should all be in pure Class A up to 15W in 8 ohms.

The underside has the LED mod and I also added a link to connect ground to the AC sense input as per instructions.

No, not ground , but +20V to act as a substitute for the rectified A.C.
However, turn off won't be as quick as when using A.C. which can be readily done here as the transformer is in the same case.

Kind Regards
Alex

P.S.
Now I see why you wanted to use 2 LS Protectors.
Nice work !

Just a reminder to others that Jaycar also has a U.K. direct order facility, and prices can be seen in GBP.

[sean]

Yes, my main speakers are 4 Ohm (a pair of Dynaudios) - I forgot to mention that. I also meant to say +20VDC to the AC sense input and not ground... a few tests of powering the amp up and down and the LSPRO board works perfectly, there's not the slightest sign of a snap, crackle or pop, or indeed any thud, hum or hiss for that matter. If it weren't for the front panel LED I wouldn't know if it was on at all! I'll pop another photo up once i've got the other monoblock finished off...

That's the first time I have used Jaycar, it was a good service and considering the parcel came all the way from Oz the postage was ridiculously cheap (£5, and it came by courier!). I'll definitely add them to my list of useful suppliers, they've got a few things that can be hard to find in other places.

[Deleted]

All sounds really good - I'm salivating .
Dave.

[Deleted]

Mar 17, 2013 9:58:45 GMT @davek said:

All sounds really good - I'm salivating .
Dave.

Dave
Because of the dual mono construction, even down to 2 Loudspeaker Protectors, it has the potential to be close to, if not the best sounding one made.
That will also depend on the actual components used too. What size toroidals (VA rating) are you using ?
Let's hope for your sake that Sean doesn't decide to keep it for himself !
Regards
Alex

[Deleted]

''If it weren't for the front panel LED I wouldn't know if it was on at all''

Hi Sean

Yes that’s my experience with the Class A

Dead quiet.

‘’That's the first time I have used Jaycar, it was a good service and considering the parcel came all the way from Oz the postage was ridiculously cheap (£5, and it came by courier!). I'll definitely add them to my list of useful suppliers, they've got a few things that can be hard to find in other places.’’

Also great service from Jaycar and cheaper than the Altronics version.

‘’I use their Galaxy range of cases in my own lineup of PSUs for Naim equipment, as well as numerous amp projects and custom builds. Now that i've seen this Dissipante range, i'm quite taken by the idea of building up my own power amp design in a 2U case’’

I’ve been using the galaxy range for my DAC and DC1B projects and have a 4U dissapante for my build of Alex’s class A PA. Really nice cases which all match which is a nice little bonus. The service from Modushop is also first rate as is the courier delivery.

I’m waiting on a 2U Dissipante to build my Audiosector chip amp into.

Just as an aside

It may be fun to try various pre’s to drive the PA with.

We can compare notes maybe.

Take care

[Will]

Some very, very nice builds going on here, with some different approaches!

[Deleted]

Hi Alex,
I think we took your advice and went for 1200va toroidals but Sean will confirm.
I asked Sean not to spoil the ship for a happ'orth o' tar, subject to it not costing me any limbs so I'm sure he will have chosen good components. I have had Sean build me a few items now and I have never been less than totally satisfied with his products or his service.
Will, this is all your fault - you were kind enough to welcome my participation in this GB knowing full well that I knew nothing about what I was getting involved with, so I hope we can all share notes on this and learn from each other.
Dave.

[sean]

*Dave means 120VA transformers of course, not 1200VA transformers (now THAT would be an impressive amp!), based on Alex's recommendation. I would have gone for something like 300VA if I were left to my own devices, but I do tend to over-engineer things on occasion.

A few notes of my own on the build - class A isn't my speciality, but the amp board looks completely spot-on. I did find it a bit fiddly to get more than one wire into the terminal blocks, but that was down to my own choice of terminal blocks rather than PCB design. The PSU PCB does the job fine - don't take this as a criticism, but if I were doing it from scratch i'd be using 2 or 3 caps per rail with intermediate inductors around 10uH, in a CLC(LC) configuration. The 317/337 would be replaced by a set of tracking pre-regulators (which is 2 regs set up with a constant voltage drop between them - 7 or 8 times less rail noise with only a few extra bits), with a few extra tweaks of my own.

One simple thing to do is use a tantalum capacitor across the trim pot on the PSU board instead of a small electrolytic (C3 and C8) - tants work really well here. There is loads of good info on 317-based PSUs here (the tracking pre-reg is mentioned in part 4) www.acoustica.org.uk/t/3pin_reg_notes1.html

[Deleted]

Mar 17, 2013 19:39:55 GMT sean said:

*Dave means 120VA transformers of course, not 1200VA transformers (now THAT would be an impressive amp!), based on Alex's recommendation. I would have gone for something like 300VA if I were left to my own devices, but I do tend to over-engineer things on occasion.

A few notes of my own on the build - class A isn't my speciality, but the amp board looks completely spot-on. I did find it a bit fiddly to get more than one wire into the terminal blocks, but that was down to my own choice of terminal blocks rather than PCB design. The PSU PCB does the job fine - don't take this as a criticism, but if I were doing it from scratch i'd be using 2 or 3 caps per rail with intermediate inductors around 10uH, in a CLC(LC) configuration. The 317/337 would be replaced by a set of tracking pre-regulators (which is 2 regs set up with a constant voltage drop between them - 7 or 8 times less rail noise with only a few extra bits), with a few extra tweaks of my own.

One simple thing to do is use a tantalum capacitor across the trim pot on the PSU board instead of a small electrolytic (C3 and C8) - tants work really well here. There is loads of good info on 317-based PSUs here (the tracking pre-reg is mentioned in part 4) www.acoustica.org.uk/t/3pin_reg_notes1.html

Hi Sean
As we are using the JLHs for the front ends of the amplifiers , we don't need to go to all that trouble with the basic PSU.
It also enables us to use commercially available PSUs if need be, to cut down cost without degrading performance.
To use your method, we would also need to use higher voltage toroidals with lower current capabilities for the same VA size.
I am actually using a Harbuch screened transformer of 160VA rating, with 2 sets of 21-0-21 secondary windings that are wound on a 300VA core.
Will and myself have also tried to keep the cost down to the builder, using readily available components from as few suppliers as possible.
The choice there is left to the builder, as the JLH is the determining factor here of the ultimate SQ, due to it's simulated capacitance of around .5 Farad,
and it's improved performance over a simple capacitance multiplier.
As you have already noted, the amplifier is dead quiet, and I have never heard any breakthrough from mains noise etc.
during many years of operation in different states of modification. Personally, these days I steer clear of tantalum capacitors wherever possible,
as I have had too many, that were working well within their ratings, go short circuit.
In the past, I have also found that when they are used at that location they have a tendency to harden the sound a little.
In my SC DAC I use a type of tracking pre-regulator for the +5V rail, as it also helps to reduce the dissipation of the output regulator.
It is also easy to do to the original Silicon Chip designed PSU PCB as used in the preamp, which is available at a good price complete with components.
Kind Regards
Alex

P.S.
With the 120VA transformer in this PSU, we also have the opportunity to increase the supply rails to + and - 22V, as well as increase the bias a little further if desired.
Not that you will be able to hear much difference, but the extra bias may help a little with 4 ohm speakers.

Did you have any problems getting the front end balance adjustment to within a steady + or -1 mV ?
That adjustment is the key to markedly improved performance, especially in soundstage and natural warmth, over a typical Douglas Self type design,
and the reason why we are using those dual LS devices in the differential pair especially.

[Will]

Hi Sean,

Thanks for the kind comments on the pcbs, and no criticism taken on the PSU's.

I'd agree with your comments regarding the PSU's, if we weren't using the JLH ripple eater boards in-between the PSU and amp pcb. As you mention, better PSU's really do improve designs considerably. In this particular case, and as Alex mentions above, the JLH RE allows us to use simple supplies and still get superb results.

I've played with other types of supplies in other circumstances (Fleas, Salas Shunts, Paul Hynes) and they do make for an improvement over basic 78xx/317 type supplies. I've often wondered how a nice set of PH shunts would work with the HA version of this speaker amp, but I'd have to do a bit of saving first

By the way - are you really Leo? The green mat under Dave's amp looks just like that shown in some of Leo's pictures

[sean]

Alex, Will - all good points made by yourselves. I can appreciate the need to keep the costs down where it doesn't impinge on SQ too much, and the PSU is usually where a lot of the expense is. You're right Alex, the TPR would need a larger transformer - and with all the other bits I mentioned, the cost would go up a lot. I did actually make the suggestion to Dave of using a TPR-based PSU when he first mentioned the project to me, but the estimated costs were too high. The JLHs are certainly doing a good job on the front end, so there's no real need to improve on that; i'd love to try out one of my TPRs on the output stage, or a nice beefy shunt regulator, and see what difference (if any...) that makes. In fact, some amps seem to prefer an unregulated feed for their output stages, so that'd be something else interesting to try.

I'll have a play with tweaking the bias for my 4 Ohm speakers - what would you recommend for the bias current? And how about upping the voltage rails to +/-22V, would this be optimal for 8 Ohm speakers too?

[Deleted]

Mar 17, 2013 22:12:05 GMT sean said:

Alex, Will - all good points made by yourselves. I can appreciate the need to keep the costs down where it doesn't impinge on SQ too much, and the PSU is usually where a lot of the expense is. You're right Alex, the TPR would need a larger transformer - and with all the other bits I mentioned, the cost would go up a lot. I did actually make the suggestion to Dave of using a TPR-based PSU when he first mentioned the project to me, but the estimated costs were too high. The JLHs are certainly doing a good job on the front end, so there's no real need to improve on that; i'd love to try out one of my TPRs on the output stage, or a nice beefy shunt regulator, and see what difference (if any...) that makes. In fact, some amps seem to prefer an unregulated feed for their output stages, so that'd be something else interesting to try.

I'll have a play with tweaking the bias for my 4 Ohm speakers - what would you recommend for the bias current? And how about upping the voltage rails to +/-22V, would this be optimal for 8 Ohm speakers too?

Hi Sean
I tried the JLHs without the current limiter section, but it hardened the sound. I suspect that using shunt regulators may also do the same with this circuit.
I don't see any problems with going to + and -22V provided that the mains voltage isn't on the low side and doesn't droop with peak demand . When I fit Will's PSU PCBs to mine instead of the existing Silicon Chip designed PSU,I will increase the voltage to + and -22V as my transformer has plenty of volts to spare. The later SC 20W Class A actually uses an unregulated supply for the whole amplifier, but despite what measurements may say, I prefer the sound when using a well regulated supply for the front end at least.
I haven't tried going past 1A bias , but provided the heatsinking is adequate, and also remembering that you guys don't have summer temperatures hitting as high as 45c,
there may be further benefits for 4 ohm speaker use in going a little higher than 1A.
Regards
Alex

[Deleted]

Hi Sean

All good comments re the PSU and the need for high quality regs is an argument that most of us here need no convincing on.

I’ve had a play with Salas shunts, Tent shunts and 6080 regs for my tube efforts to name a few.

I’ve also tried the teddy reg but not the Super teddy or Avondale which sounds a little like what you have in mind so can’t comment on its goodness although Naim users seem to like it much.

I am using the JLH in my build of Alex’s HA/PRE and have swapped it out to the detriment of the sound IMHO so from what I’ve heard the JLH do the business in that spot.

Yup I’m game for some experimentation PSU wise and would love to try a shunt on the OP of the PA.

But that’s going to be one hot dog with the extra current needed to keep the shunt working as it should.

TBH the real appeal for me when building Alex’s PA was that it was possible to build with my limited Skills and get great results from a design that had been proven over time. I’ll be the first to admit that I found the build challenging but I learned plenty for a possible round two PSU build if something comes up that looks interesting.

IMHO keeping cost down is one factor but making the build possible to a wide range of DIYers is just as important and in some ways more important. But that’s just a personal take and others may have a different view.

I’ve had my birthday boy up and running for a year now and paired with my PMCs it’s been super good SQ wise, super quiet and super reliable. So much so that I’ve not had much of an urge to play with it mod wise.

That is soooo unusual for me.

I’m probably on my own on this but I’ve never really found that what goes on before the regulator tank cap quality wise has much of an impact on SQ.

Like Alex I’ve tried Tants with 317 regs with all sorts of kit and TBH they are not my cup of tea. Now I’m not saying that they sound bad just not what I’m looking for sound wise.

I can see an argument for using CLC before the reg but I’m (gut feeling) not so sure it’s going to improve much on what we have now. Maybe for higher power designs it could make a difference but for us the extra complications may not be worth the effort involved.

It’s really nice to have the discussion though and interesting to have another take on things.

Take care

[Deleted]

What's TPR mean?

[Deleted]

Mar 18, 2013 1:03:14 GMT @gregerskine said:

What's TPR mean?

Hi Greg

Tracking Pre Reg


take care

[sean]

Hi Alex, just realised I missed your last question out - setting the LTP offset was pretty easy, I got it to within 0.3mV or so, with the lid on after 30 minutes of being powered up to make sure it's thermally stable. I'll re-test it when I come to finishing the amp off for good. Re. tantalums in the PSU, i'm going to try out some regular electrolytics in this position as well and see how they affect the sound; i'll report back on here when I get round to it.