'AK Mods' SC Class A 15W Amplifier

[Will]

Dec 13, 2011 23:11:53 GMT @shaun said:

*snip*

Hi Will

hows it going?

nice work on the PSU and looking good on the star front.

just one question.

looks like you have the OP caps bypassed but after reading the 1033 data sheet it seems a little sensitive too low ESR in that position and also distance (impedance to the load from the reg.

also the data sheet for the LT1085 has built in protection so those diodes are maybe not needed but do seem to be for the 1033.

that circuit looks like a chip off of the old block of the original but soooo much more elegant.

well done on that.

i may have things wrong but would like to learn.

did my first etch today based on the original artwork minus the UN needed stuff component wise. came out better than expected and was great fun almost like developing a picture.

take care

Hi Shaun,

Going good here thanks, apart from the mundane interfering and having a head full of green gunge *sniff* *cough*

On the bypass cap, it's there as an option for those that wish to use it. I gather it's lower esr types that can cause instability/problems. Dropping a film across a normal gp capacitor can lower esr a bit, but not make it ultra low. Can possibly also make a difference to how things sound, but that's up to individual ears.

It also ties in with the pcb also being usable with the lm317/337 so really needing the diodes across the regs. The LT1033 needs them if you are using caps above certain sizes, and the 1084 in certain cases, so for the cost of the 1n4004 (pennies) it's worth fitting them in any case (either LM or LT regs) as insurance.

I've still got a bit of tidying up to do, so would like to bring the OP caps closer to the reg itself (currently 1" away), but it seems that the 'R1' resistor from the 1084/1033 datasheets (that sets Vo) is important.

Also meant to say that the PCB is 74mmx92mm is size, but I hope to shrink it a bit. The tank caps at the front are 35mm max, with 10mm pitch lead holes, just so people can idle a few hours on selecting that part (yes, I know what some of you are like )

Nice one on etching, i'd love to see how it's come out. If you've not etched the kitchen sink a little bit as well, by the way, then you done it wrong

[Deleted]

Hi Shaun,
count me in for the boards I'll take the PSU boards also, just incase mine blow up
Good news on the etching I'll have some questions for you on that when I get round to attempting that USB to I2S thinngy

Alex,
you'd just love this fresh air blowing in from the Atlantic it wafts across Northern Ireland first before clearing out all our cobwebs.
In fact I'm sure Syd had sausages for his evening meal I could smell 'em burning around six pm.

Will,
your PSU boards have that quality look again.
I'm afraid I've muddied the waters in this thread with my DIY posting I hope the rest of the lads who are going with the build realise that you are producing the required goods for a GB.
Regards,
Alan

[Will]

Dec 13, 2011 23:53:06 GMT drymdrum said:

Will,
your PSU boards have that quality look again.
I'm afraid I've muddied the waters in this thread with my DIY posting I hope the rest of the lads who are going with the build realise that you are producing the required goods for a GB.
Regards,
Alan

Alan,

Seriously, it's not muddying the waters at all, it's all good diy fun Your posts and thoughts have been very interesting, and I've learnt stuff in the process, so all good from that point of view. The pcb's I'm doing are for those who are not able or don't want to go the etching route/home pcb manufacture (myself included these days)
The only problem for them that want these pcbs is that they have to rely on me to finish the pcb ( ) and get them delivered by sea turtle from China, with a good chance that you'll have finished your amp and enjoying it's sonic delights

You carry on with what you are doing, and keep us informed.

[Deleted]

Dec 13, 2011 23:46:22 GMT Will said:

Dec 13, 2011 23:11:53 GMT @shaun said:

*snip*

Hi Will

hows it going?

nice work on the PSU and looking good on the star front.

just one question.

looks like you have the OP caps bypassed but after reading the 1033 data sheet it seems a little sensitive too low ESR in that position and also distance (impedance to the load from the reg.

also the data sheet for the LT1085 has built in protection so those diodes are maybe not needed but do seem to be for the 1033.

that circuit looks like a chip off of the old block of the original but soooo much more elegant.

well done on that.

i may have things wrong but would like to learn.

did my first etch today based on the original artwork minus the UN needed stuff component wise. came out better than expected and was great fun almost like developing a picture.

take care

Hi Shaun,

Going good here thanks, apart from the mundane interfering and having a head full of green gunge *sniff* *cough*

On the bypass cap, it's there as an option for those that wish to use it. I gather it's lower esr types that can cause instability/problems. Dropping a film across a normal gp capacitor can lower esr a bit, but not make it ultra low. Can possibly also make a difference to how things sound, but that's up to individual ears.

It also ties in with the pcb also being usable with the lm317/337 so really needing the diodes across the regs. The LT1033 needs them if you are using caps above certain sizes, and the 1084 in certain cases, so for the cost of the 1n4004 (pennies) it's worth fitting them in any case (either LM or LT regs) as insurance.

I've still got a bit of tidying up to do, so would like to bring the OP caps closer to the reg itself (currently 1" away), but it seems that the 'R1' resistor from the 1084/1033 datasheets (that sets Vo) is important.

Also meant to say that the PCB is 74mmx92mm is size, but I hope to shrink it a bit. The tank caps at the front are 35mm max, with 10mm pitch lead holes, just so people can idle a few hours on selecting that part (yes, I know what some of you are like )

Nice one on etching, i'd love to see how it's come out. If you've not etched the kitchen sink a little bit as well, by the way, then you done it wrong

Hi Will

yup I've joined the ministry of sad F***rs reading data sheets but it did lead me to believe that a one size fits all could be a problem.

seems like the only two things that the LT1085/1033 seem to have two things in common

are

1 they are 3A
2 they are adjustable

the 1033 looks much more like the older 317/337 family protection needs wise.

so for me I'm going to fit the diodes to the 1033 only but that's because it may get a little cosy under the board otherwise.

let me say it again

your board looks outstanding and just the job and I'll be taking some what ever happens with my errr lame efforts back here.
very much in the spirit of the original which IMHO is no slouch design wise and if it ain't broke why(well you know).

some designs just seem to ignore the grounding arrangements and just do it as an after thought. grounding pretty important to get right and just as important as every other part of the circuit.

so full marks to SC on that front.

I'll post pictures once I'm sure that i have a working PSU.

looks good but could be a smoker in which case he's going to have to stand outside in the cold.

i used some of that press and peel transfer stuff and even Mr butter fingers managed that OK.

plenty of brandy and orange is my sure fire cold cure (makes me feel much better every time).

steady on with shrinking the board mines 8cm x 10cm without rectifier diodes. i did do one with diodes but with single sided it started to look like a surf board. ;D ;D

take good care

[Deleted]

but it seems that the 'R1' resistor from the 1084/1033 datasheets (that sets Vo) is important.

Hi Will

yes agreed but that value only seems to be important if the reg is unloaded.

the 1033 seems to need between 3 and 5ma on it's OP to prevent it passing full B+ (30 ish V in this case) but thats why its important to rate the caps @35v or more.

that should not be a problem in and of it's self as Long as it's loaded for testing.

what is even more interesting is that performance is reduced a little according to OP impedance.

a bleed resistor may improve both of the above by keeping the reg loaded and keeping the load close to the reg.

the 1033 does seem to need a little more work to get the best out of it though.

just thinking out loud so i may be wrong on that.

take care

[Deleted]

the 1033 seems to need between 3 and 5ma on it's OP to prevent it passing full B (30 ish V in this case) but thats why its important to rate the caps @35v or more.

Shaun
If "R1" (between Adjust and Output terminals) is the typical 100 or 120 ohm resistor this will not be a problem.
Alex

[Deleted]

HI Shaun,
keep on thinking out loud it certainly makes for interesting reading and gets me to reassess my own position. With regard to R1 on the 1033 I've got it hard up against the output leg pin 2........
the protection diodes I'll certainly fit although they'r probably a belt and braces job as Will said for the coppers cost it's a no-brain'r.
Alan

[jonclancy]

Wotcha Chaps,

It's just started snowing here in Wilts!!

I was wondering if there may be any mileage in using the original Class A boards as a mounting template for Will's new AK version? The Altronics kit might be an option and to have a drop-in upgrade could be the way to go.

BTW, anyone else having a nightmare trying to solder in natural light at the moment? i.e. there isn't any!!

[dicky]

Hi Jo,

it's really belting down in Amesbury right now. I can see about 20 feet outside my office window. Too warm to settle though.

[dicky]

Sorry Jon. My keyboard is a bit sticky.

[Deleted]

Dec 14, 2011 9:33:21 GMT drymdrum said:

HI Shaun,
keep on thinking out loud it certainly makes for interesting reading and gets me to reassess my own position. With regard to R1 on the 1033 I've got it hard up against the output leg pin 2........
the protection diodes I'll certainly fit although they'r probably a belt and braces job as Will said for the coppers cost it's a no-brain'r.
Alan

Hi Alan

Just to get the ball rolling here’s the prep work that I did
Here is the original psu for the 15W class A



Copied from Silicon Chip Magazine July/August 1998 edition.

So then it was just a matter of taking out the UN needed parts



Which pretty much left our old faithful reg circuit?

Then I reworked the overlay provided in the Silicon Chip Magazine August 1998



And ended up with this



I hope that it’s not going to be a copy right problem to post the original SC material but I wanted to show how I arrived at my overlay.
Feel free to remove

Take care

[Deleted]

forgot to mention

just rain here in Worcestershire

take care

[Deleted]

Hi Shaun,
press........yes.......peel........NO.
Did I say press and peel?
press as in press your trousers.......yes borrow the flat iron and press your artwork onto the copper, but if you then straight off peel the paper up off the copper you will likely lose some of the circuit artwork.
So to recap just in-case.................................
1).....print by laser onto good and cheap......Tesco's own brand "Value Photo Paper....glossy for inkjet.....yes inkjet printers 150g/m..........other glossy photo paper probably just as good.
2)....Tray of water.......pop board with ironed on paper into water let it sit for a bit then finger rub the top layer of paper off whilst still in the water..........continue rubbing till the paper is all gone.......... don't try to peel the whole layer off dry you will cry.

Your layout looks good to me but I find it hard to understand layouts which I've not done myself, that's why I prefer to start from scratch with the schematic.
One point I'd make.........you have no holes for component legs showing............do you intend to etch then decide where to drill?
My way would be to mark precisely the position of each hole you wish to drill onto the artwork before you print.
The etchant then cuts the copper and you have a precise point to drill into, I've never etched a circuit myself but I'd try to have the hole diameter as close to the drill bit size you are going to use, you don't want to over etch the holes.

Since we are giving weather reports today..............I'll just say it's fresh up here in the hills of Lanarkshire.........was out this morning sweeping up leaves and drilling drainage holes..........we got loads of water.
Regards,
Alan

[Deleted]

you'd just love this fresh air blowing in from the Atlantic it wafts across Northern Ireland first before clearing out all our cobwebs.In fact I'm sure Syd had sausages for his evening meal I could smell 'em burning around six pm.

That was my solder flux you smelt

Syd

[Deleted]

There is some some seriously nifty work going on with the various incarnations of the PSU

As I'm far too lazy and not tooled up for creating my own boards I'm very grateful that all this work and GBs are done by you guys. Double

As regards Wills PCB PSU, is this going to be handled separately as its own GB or lumped in with the main boards etc?

Just in case you haven't guessed I'll be hanging on for Wills boards when ready.

The weather? Bright sunshine, 20 Celcius but set to break on Sunday.

[Deleted]

Dec 14, 2011 14:09:58 GMT drymdrum said:

Hi Shaun,
press........yes.......peel........NO.
Did I say press and peel?
press as in press your trousers.......yes borrow the flat iron and press your artwork onto the copper, but if you then straight off peel the paper up off the copper you will likely lose some of the circuit artwork.
So to recap just in-case.................................
1).....print by laser onto good and cheap......Tesco's own brand "Value Photo Paper....glossy for inkjet.....yes inkjet printers 150g/m..........other glossy photo paper probably just as good.
2)....Tray of water.......pop board with ironed on paper into water let it sit for a bit then finger rub the top layer of paper off whilst still in the water..........continue rubbing till the paper is all gone.......... don't try to peel the whole layer off dry you will cry.

Your layout looks good to me but I find it hard to understand layouts which I've not done myself, that's why I prefer to start from scratch with the schematic.
One point I'd make.........you have no holes for component legs showing............do you intend to etch then decide where to drill?
My way would be to mark precisely the position of each hole you wish to drill onto the artwork before you print.
The etchant then cuts the copper and you have a precise point to drill into, I've never etched a circuit myself but I'd try to have the hole diameter as close to the drill bit size you are going to use, you don't want to over etch the holes.

Since we are giving weather reports today..............I'll just say it's fresh up here in the hills of Lanarkshire.........was out this morning sweeping up leaves and drilling drainage holes..........we got loads of water.
Regards,
Alan

Hi Alan

Press and Peel is a design transfer sheet available from Maplins. just laser print or copy onto the sheet and then iron it onto the board. quench in cold water and peel the sheet of. the transfer acts as an etch resist layer.

www.techniks.com/how_to.htm

this stuff really does work.

when i first spotted it i thought how many time have i read ''oh it's so easy with'' and found the opposite.

yup i found that out about etching the drill pilots after I'd etched both boards and started to drill.

rats

still managed to drill the holes but used a scribe for making a pilot before drilling. i won't be doing that again but for me this is a learning exercise and I'm learning.

so one board built and ready to test fire suit ready dogs at a safe distance except the one that's ''volunteered'' to throw the switch. ;D ;D

found a pretty cool way of cutting the boards.

use a scribe and ruler to score the board

keep going until through the copper and a little way through the board.

put it in a plastic jawed vice with the score line ''lined'' up with the jaws.

push the board in the opposite direction to the copper side.

snap a dead straight line.

a quick dust with some fine paper and jobs a good un.

on the layout

it gives all of the components dedicated ground returns back to ground.

this way can help to minimize noise which can be cased by high current and low current devices sharing a ground return. for tubes i mostly used a grounding bus and earthed from the amp input but star is good with this sort of thing. i did use partial stars but with tubes it's a little different i guess.

from looking at the original amp board layout they have used the same star grounding method. so star ground and then grounded back to the supply ground point.

if that makes sense

nice

looks like a star.

Hi Chris

yes Will's boards look like they are going to be the usual high quality units. I'm sure that Will is going to lavish the usual amount of care and attention to detail that he seems to apply to everything he does.

the etching thing for me is just a way of learning something useful and that has been the case.

I'll be grabbing some of Will's boards but I've wanted to try my own boards for quite some time.

take care

[Will]

Dec 14, 2011 10:01:57 GMT jonclancy said:

Wotcha Chaps,

It's just started snowing here in Wilts!!

I was wondering if there may be any mileage in using the original Class A boards as a mounting template for Will's new AK version? The Altronics kit might be an option and to have a drop-in upgrade could be the way to go.

BTW, anyone else having a nightmare trying to solder in natural light at the moment? i.e. there isn't any!!

Hi Jon,

It's looking like the amp pcb will be wider than original, due to incorporating the offset corrector on board.

I really need to get those inductors down to you, as well

[Will]

Dec 14, 2011 15:00:34 GMT @cjarchez said:

There is some some seriously nifty work going on with the various incarnations of the PSU

As I'm far too lazy and not tooled up for creating my own boards I'm very grateful that all this work and GBs are done by you guys. Double

As regards Wills PCB PSU, is this going to be handled separately as its own GB or lumped in with the main boards etc?

Just in case you haven't guessed I'll be hanging on for Wills boards when ready.

The weather? Bright sunshine, 20 Celcius but set to break on Sunday.

Hi Chris,

The psu pcb is optional, but you'd need to find another pcb that can do 1A continuous, or more if you wish to run the amp at a higher bias. The GB will most likely run for the amp pcb and psu pcb separately, so people can buy what they want.

[Will]

on the layout it gives all of the components dedicated ground returns back to ground. this way can help to minimize noise which can be cased by high current and low current devices sharing a ground return. for tubes i mostly used a grounding bus and earthed from the amp input but star is good with this sort of thing. i did use partial stars but with tubes it's a little different i guess.from looking at the original amp board layout they have used the same star grounding method. so star ground and then grounded back to the supply ground point.if that makes sense

Hi Shaun,

That make perfect sense, and is well explained.

I like you psu plan as well. As you say, it's a well proven layout, and the star (in the amp especially) is needed for the good performance.

As for testing the PSU, I use an extension cable, and switch on from the other side of the room

[Deleted]

but you'd need to find another pcb that can do 1A continuous, or more if you wish to run the amp at a higher bias

Oh bugger! That leaves me a tad clueless
Would a simple components swap out do the trick? I am keen to extract more power if poss...

[jonclancy]

Dec 14, 2011 22:01:48 GMT Will said:

Dec 14, 2011 10:01:57 GMT jonclancy said:

Wotcha Chaps,

It's just started snowing here in Wilts!!

I was wondering if there may be any mileage in using the original Class A boards as a mounting template for Will's new AK version? The Altronics kit might be an option and to have a drop-in upgrade could be the way to go.

BTW, anyone else having a nightmare trying to solder in natural light at the moment? i.e. there isn't any!!

Hi Jon,

It's looking like the amp pcb will be wider than original, due to incorporating the offset corrector on board.

I really need to get those inductors down to you, as well

Just wondering if the mounting holes and transistor positioning could be the same - I don't think a wider board would be a prob.

I'm currently trying to get an amp off my bench (repaired) and chasing obsolete sized fasteners. Please send me the inductors before I go maaaaaaaad!

[Deleted]

Dec 14, 2011 22:16:05 GMT Will said:

on the layout it gives all of the components dedicated ground returns back to ground. this way can help to minimize noise which can be cased by high current and low current devices sharing a ground return. for tubes i mostly used a grounding bus and earthed from the amp input but star is good with this sort of thing. i did use partial stars but with tubes it's a little different i guess.from looking at the original amp board layout they have used the same star grounding method. so star ground and then grounded back to the supply ground point.if that makes sense

Hi Shaun,

That make perfect sense, and is well explained.

I like you psu plan as well. As you say, it's a well proven layout, and the star (in the amp especially) is needed for the good performance.

As for testing the PSU, I use an extension cable, and switch on from the other side of the room

Hi Will

i started to think i was saying ground too often but yes when i looked at the way SC had set things out there seemed to be a certain ''rightness'' about the grounding arrangements. it's even more of an achievement when you think they only had a single sided board to work with.

it's easy to miss how clever the original is at first glance.

nope

dog biscuit taped to the power switch usually does it and then just let mans best friend do the rest ;D ;D ;D

so I'm errr itching to lash the built one to a rectifier and TX.

for my part I'm ecstatic to have made a board that looks like it might work.

i was expecting to end up with a board with no copper left on it whatsoever.

so all good

so far

take care

[Deleted]

Dec 14, 2011 22:53:21 GMT @cjarchez said:

but you'd need to find another pcb that can do 1A continuous, or more if you wish to run the amp at a higher bias

Oh bugger! That leaves me a tad clueless
Would a simple components swap out do the trick? I am keen to extract more power if poss...

Hi Chris

i think Will published an initial idea for the PSU on the previous page.

I'm kind of hoping that the plan will turn into boards.

take care

[Deleted]

Nice one Shaun,
lets have some pics of the dog..................only if he's got more than his bollocks left after the big switch on.
No seriously a close up of your etch and what you used would be useful.
Alan

[Deleted]

Dec 14, 2011 23:42:08 GMT @shaun said:

Dec 14, 2011 22:53:21 GMT @cjarchez said:

Oh bugger! That leaves me a tad clueless
Would a simple components swap out do the trick? I am keen to extract more power if poss...

Hi Chris

i think Will published an initial idea for the PSU on the previous page.

I'm kind of hoping that the plan will turn into boards.

take care

Shaun,

I thought Will was referring to same posted boards when he said I'd need something beefier?

Maybe I misunderstood?