'AK Mods' SC Class A 15W Amplifier

[jeffc]

The secondary windings are of course those with heavier gauge wire because of the much higher current (and lower voltage)in the secondary

Hi Alex,

You'd think so, BUT...... I'm not so sure, usually these are 240V mains rated and thus correspondingly thick, but these are ~0.4-0.5 mm dia at best and single solid strands (which would be very unusual for mains rated wires) plus they have loose double insulation like often seen on secondaries, hence my reasoning for them being the secondaries. Questions to be asked at TorTech

And nothing on the transformer sides except brand name and model no.

cheers.. jeffc

[Deleted]

Nov 24, 2011 18:12:00 GMT Will said:

Nov 24, 2011 3:46:15 GMT Spirit said:

Finally
This is what I've been waiting for! Glad to hear you're almost there
Good work.

If any group buys go ahead before early February, could you shoot me an email directly Will?
I'm buggering off to India for 9 weeks on Saturday
I should be able to check email at least once a week, and can organise paypal or whatever payment from there (will have a netbook with me).

Hi Phil, thought you might be pleased!

I'll keep you in the loop on any GB's for parts. I've found a good cheap supplier for the output devices, although you can buy them over the counter at Altronics. LS devices are easy to get now, as Mintech sell them online, so all good their as well.

You have a great time in India, sounds fab!

Hi Syd

i was just waiting to see when we needed to think about them.

I've checked out Mintech's web site but cant find a listing for the LS devices.

so if someone would give me a clue on how to order we can get the ball rolling.


take care

[Deleted]

Hi Jeff
Check the resistance with your DMM.Each primary winding is likely to be somewhere in the vicinity of 30 ohms. The primary windings are likely to be around 1/10 th of that resistance ( perhaps even less ?) Have you emailed them about the missing mounting bits ?
With the individual primary windings once identified,it is a simple matter of connecting them in series across the mains and checking for >20 VAC on each secondary winding. If there isn't, just reverse one primary winding.Then you will also be able to check the phasing of the secondary widings by a similar method. With the correct way, you will have >40V AC between 2 of the wires, and the 2 joined together becomes the centre tap.We can worry about that later ?
Alex

[jeffc]

Hi Alex,

Resistances

Thick Green-Red and Black-White approx 9-10 ohm
Thin Brown-Orange and Blue-Yellow approx 15.5 ohm

This seems to have confirmed that the thin wires are indeed the primaries, correct?

If YES, I'll check voltages when it cools down.

I have sent TorTech an email.

cheers.. jeffc

[Deleted]

Dec 3, 2011 2:06:22 GMT jeffc said:

Hi Alex,

Resistances

Thick Green-Red and Black-White approx 9-10 ohm
Thin Brown-Orange and Blue-Yellow approx 15.5 ohm

This seems to have confirmed that the thin wires are indeed the primaries, correct?

If YES, I'll check voltages when it cools down.

I have sent TorTech an email.

cheers.. jeffc

Hi Jeff
The thinner wires, often multistrand, are usually the primary, although I did expect the secondary resistances to be much lower than you read.Let's see what Tortech says first?
Alex

P.S. Are you sure you don't mean 0.9 and 1 ohm for the secondary windings ?
I just checked a 20VA 15-0-15 and the resistance was 1.3 ohms for each winding.
As your transformer has a higher current capability, I would expect even lower than mine, perhaps 0.9 or 1 ohm as suggested ?

[Will]

I've checked out Mintech's web site but cant find a listing for the LS devices.so if someone would give me a clue on how to order we can get the ball rolling.

Hi Shaun,

The online purchase bit is here: www.micross.com/packaged-parts-plastic-discretes.aspx type ls31 or ls35 into the search, and the slection will pop up. Prices seem to have gone up overnight (by 40p) with the to71 (what we had last time) now over £4 each. The prices are ex. VAT, a minimum £25 order and there is a £10 delivery charge. All this can be spread across the buyers of course.

I'll email you a suggestion on GB parts, as I have a suggestion

Thanks for taking the LS's on. I'm happy to do the PCB's, and some of the components, but spreading the load make my life much easier. Thanks Shaun

It's worth a look around the micross site, if we are ordering, as they have some nice, not easy to get stuff. The whole range of J5** CRD's, LSK389's and other stuff.

[jeffc]

Alex,

I just checked again at a 2K ohm setting and then at a 200m ohm setting, which is the lowest on my DMM, and readings on the secondaries are now in the 1-2 ohm range. My DMM is a bit dicky at the best of times, and maybe its time to change the battery.

cheers.. jeffc

[Deleted]

Hi Jeff
You know what to do now, so have fun , but take care, as Shaun says.
Regards
Alex

[Will]

Here is the circuit diagram that the manufactured pcb is based upon.



Nothing new, really, but the diodes are to220 types (used the model for mur810), capability for a noise cap on the input AC, space for a film cap after the output cap, and the layout useable with 317/337 or lt devices.

I should have the layout finished in rough this weekend (much the same as the original class A, with both regs at the end of the pcb, making it easier to 'sink). I'll get Dad to OK it, and then post.

[Deleted]

HiWill
I would still be inclined to go with vertically mounted "Fast Recovery,Ultra Soft,SBYV28-150" Not just because they are very cheap.either .
Alex

[Will]

Dec 3, 2011 9:44:41 GMT @sandyk said:

HiWill
I would still be inclined to go with vertically mounted "Fast Recovery,Ultra Soft,SBYV28-150" Not just because they are very cheap.either .
Alex

Hi Alex,

They'll fit fine, no problem. The mur marking is not a recommendation, and leaves that area wide open. That 4700uF cap will drop in fine, too

[Deleted]

Dec 3, 2011 8:55:16 GMT Will said:

I've checked out Mintech's web site but cant find a listing for the LS devices.so if someone would give me a clue on how to order we can get the ball rolling.

Hi Shaun,

The online purchase bit is here: www.micross.com/packaged-parts-plastic-discretes.aspx type ls31 or ls35 into the search, and the slection will pop up. Prices seem to have gone up overnight (by 40p) with the to71 (what we had last time) now over £4 each. The prices are ex. VAT, a minimum £25 order and there is a £10 delivery charge. All this can be spread across the buyers of course.

I'll email you a suggestion on GB parts, as I have a suggestion

Thanks for taking the LS's on. I'm happy to do the PCB's, and some of the components, but spreading the load make my life much easier. Thanks Shaun

It's worth a look around the micross site, if we are ordering, as they have some nice, not easy to get stuff. The whole range of J5** CRD's, LSK389's and other stuff.

Hi Will

No worries on the GB front as I'm more than happy to take some of the workload.

what I'm going to suggest is that we do the GB's in a few lots,

so first LS devices of which we will need

2x LS352

2X LS313

so i think I'll start taking orders now so if people let me know what they require we will go from there.

any extra requirements from Micross I'll see what can be done.

then later we can have a look at other things that we will need like OP devices and the like.

for matched pairs of transistors it may also be useful for us to pool resources. i have a full set and have some spare pairs and I'm sure that others may have some pairs but not others.

just a quick word on matching those 327/337transistors for matched quads.

so far I've ordered two lots of 50 of each 327/337. both batches of 327 where high and the 327 low with a Hfe (measured with Atlas tester) range that seemed to meet in the middle around 300. i think that Will also found this with the ClassA build.

so just to say order mucho of these as i only managed 3 matched Quads from 100 of each.

so any needs to be posted so we can see if we can help each other out a little.

so let's be having some requests.

so that we can get this part nicely tucked up.

take care

[Deleted]

I should have the layout finished in rough this weekend (much the same as the original class A, with both regs at the end of the pcb, making it easier to 'sink). I'll get Dad to OK it, and then post.

Hi Will

just on that

looking at the original PSU layout it seems to have a nice star ground layout .

mmmm nice and is one of the things i really like about the original design.

take care

[Will]

looking at the original PSU layout it seems to have a nice star ground layout .mmmm nice and is one of the things i really like about the original design.

[Will]

OK Chaps, a show of hands please.

Who is interested in a parts kit GB?

All electrical components included, with the following detail:

• Power supply decoupling caps not included (everyone has their own ideas here)
  
• Resistors not included.
  
• The LTP emitter resistors will be included, as these are the 0.1% ones we used last time, and help ensure good operation of the LTP mod.
  
• All transistors matched, except the LS devices. This includes the output devices.
  

I've been chatting with Shaun, and the daft bugger good man has volunteered to do this, if there are enough numbers. Once we get numbers, we'll get some costs figured out.

So numbers please (I have Phil down already)

To help out, if you know of cheap suppliers of the components we used in the AK Class A (like Chris's find of Banzai for the 3u3 film cap in the offset corrector) then let me know. Also sources for on semi and philips transistors would be nice.

[Deleted]

Hi All

for the LS device GB so far i have

Will 2x LS352 and 2X LS313
Phil 2x LS352 and 2X LS313 (provisional)
Me 2x LS352 and 2X LS313
Syd 2x LS352 and 2X LS313
Alan 2X LS352 and 2X LS313
Alex 2X LS352 and 2X LS313
Mark 2X LS352 and 2X LS313 (cyteen)
Jeff 2X LS352 and 2X LS313
Jon C 2X LS352 and 2X LS313

Kits GB

Chris
Syd
Phil
Will
mark (cyteen)
Jon C

Boards only GB

Alex
me

anyone else?

take care

[Deleted]

Hi Shaun,

Just for clarification, I won't need the LS devices as I have a set left over from the headphone amp build. Which, of course, will become my preamp as well when someone is kind enough to produce an idiots how-to guide!

While on the subject, I also have a spare pair of the headpone/preamp boards, unmolested! If anyone would like to play catch up they are up for grabs at whatever they cost back then. I also have some of the terminal blocks with the extra long pins to go with them.

[Deleted]

OK Chaps, a show of hands please.Who is interested in a parts kit GB?

[Deleted]

So numbers please (I have Phil down already)

Shaun/Will

I'm in for whatever is going.

This is very much appreciated.

Syd

[Deleted]

Dec 3, 2011 16:11:33 GMT @cjarchez said:

Hi Shaun,

Just for clarification, I won't need the LS devices as I have a set left over from the headphone amp build. Which, of course, will become my preamp as well when someone is kind enough to produce an idiots how-to guide!

While on the subject, I also have a spare pair of the headpone/preamp boards, unmolested! If anyone would like to play catch up they are up for grabs at whatever they cost back then. I also have some of the terminal blocks with the extra long pins to go with them.

Hi Chris

i think that we are starting this discussion on the Class A HA/PRE thread.

you'll find Alex's lucid explanation above my incomprehensible ramble.

take care

[Deleted]

Hi Shaun,
I'm in for 2X LS352 and 2X LS313
and possibly the Kit,
but have to rake through what I've got first.
Regards,
Alan

[Will]

Chris's mention of a spare ha/pre pcb gave me an idea.

As I'll be ordering pcb's up I'll offer up previous pcb's that I've had done.

These are:


JLH (single stackable version)
AK Cricket (op amp low current power supply)
Pocket Knife Dac
Single Rail PSU
Dual Rail PSU
AK Class A HA/Pre pcb (normal thickness, but Chris's would be cheaper if the numbers for this are enough)

PM me if you are interested.

[Deleted]

All transistors matched, except the LS devices. This includes the output devices.

A good idea, BUT SWMBO is going to be VERY pissed off with the amount of time you spend doing this !

I would be interested in a set of the 4 PCBs and LS devices though.
Kind Regards
Alex

[Deleted]

so far I've ordered two lots of 50 of each 327/337. both batches of 327 where high and the 327 low with a Hfe (measured with Atlas tester) range that seemed to meet in the middle around 300. i think that Will also found this with the ClassA build.

I had a similar problem to everyone else.
Chances of a match may be better with the BC3x7-25 versions which are specified for an HFE of 160 - 400 with 100mA collector current? (The HFE will be higher at the currents we use/test them at).
If using the ordinary BC327 and BC337, then replacing the type with the lower average HFE with the -25 (or even-40) version may give more to choose pairs from.

Attachments:

[Deleted]

I would still be inclined to go with vertically mounted "Fast Recovery,Ultra Soft,SBYV28-150" Not just because they are very cheap.either .
Alex

Alex,
as I intend to use the SBYV28-150 would you care to expand on why you would mount them vertically.
RS have them on back order due in about three weeks time.........
think they were around 24p each
Interested,
Alan