'AK Mods' SC Class A 15W Amplifier

[Will]

Dec 15, 2011 0:52:31 GMT @cjarchez said:

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

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?

Hi Chris,

Sorry, I should have been a bit clearer. My comment for needing a beefy reg was for those who do not want to buy this psu pcb.

The PSU PCB that I'm doing will cope with doing 3A, if you use LT10xx regs, so no worries there. It will also work with LM3xx regs, allowing for use up to 1.5A. This should give the following options:

• 1 PSU pcb with LT regs running two amp pcbs set at normal 1A bias (15W output)
  
• 2 PSU pcb with LM regs running two amp pcbs set at normal 1A bias (15W output) - only do this if you believe in the dual mono fairy
  
• 2 PSU pcb with LT regs running two amp pcbs set at normal 1A bias (15W output), giving lots of spare current capability for the future, and less stress on the regs.
  
• 2 PSU pcb with LT regs running two amp pcbs set at a higher bias (?W output), allowing Chris to entertain people in the next valley over with his music choice
  

I was mindful that not everyone will want to go dual mono, use the more expensive LT regs, or they may want to try for higher class A output levels, so thought along the above lines. I think the LT regs are also available in 5A to220 cases, if anybody fancied that?

Myself, I like the idea of the LT reg having an easy time running the normal 1A bias, in dual mono, so will head down that route.

One question:- is it too early in the day for Shaun's recommended brandy and orange?

[Deleted]

Dec 15, 2011 0:14:41 GMT drymdrum said:

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

Hi Alan

what do you take me for ;D

I'd never put any animal at risk like that.

so he's not going anywhere near my work without full health and safety being observed.

yup it's safety hat and goggles time for him.

take care

[Will]

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!

Hi Jon,

Alex did raise the issue of the transistors being in the same place, so if there are going to be a few of you who are going the kit case route, then I'd be happy to do this.

What I do need though, is the original pcb hole centres from an amp pcb, and also hole centre distance for the output transistors. If I could have these (Alex?) then I'll shift things about.

[Will]

A quick question: do you think that having wire links connecting the input and output of the dc offset corrector to the main amp circuitry would be useful?

[Deleted]

One question:- is it too early in the day for Shaun's recommended brandy and orange?

Hi Will

we have two distinct and totally different strains of flue here.

1) the really bad an totally debilitating variety that my wife has.

2) the mild and manageable ''Man flue'' which means that it's totally possible to go on as normal variety that i have.

Never toooo early for medicine and Dr Shaun recommends a double shot into warmed orange juice.

hope you feel better soon.

take care

[Will]

Dec 15, 2011 9:05:10 GMT @shaun said:

One question:- is it too early in the day for Shaun's recommended brandy and orange?

Hi Will

we have two distinct and totally different strains of flue here.

1) the really bad an totally debilitating variety that my wife has.

2) the mild and manageable ''Man flue'' which means that it's totally possible to go on as normal variety that i have.

Never toooo early for medicine and Dr Shaun recommends a double shot into warmed orange juice.

hope you feel better soon.

take care

Indeed. I had proper 'flu once (over my 18th birthday ) and it totally knocks you of your feet.

I've got a bad cold, but just really fancy a brandy

Hope Mrs Shaun is better soon.

[Deleted]

Will and Shaun,

Thanks for the clarification, I'll rest easy now

My plans were to go the full mono blocks route and of course I need mine to go up to 11!

As for the lurgy, I reckon we all get the same one for our area, it's just how your immune system handles it. My daughter and I both have good strong I.S. and have kicked our infestations into touch quite quickly with just the dregs left over. Wifey and son have weaker systems and suffer more and for longer. (strong cold not, flue, in our case)

I still have some dark coloured "medicine" before I hit the pit though

[Deleted]

Having read the SC article properly for the first time another question arises...

For the resistors on the amp boards the arcticle has the majority rated at 0.25w. On the pre/headphone amp we used 0.5w in place of all the 0.25w.

Is there an actual benefit/requirement for this or another reason?

Cheers.

[Will]

Hi Chris,

I think that 0.5W metal film resistors are the same physical size as 0.25W resistor from days of yore, and as most of us have them, it makes sense to use them.

I used some MF12 resistors (125mW) when building some mini3 amps, and they are silly small compared to other 125mW types.

[Deleted]

HI Will, Shaun,
just bought 2 lots of 4 LT1085CT from westfloridacomponents USA on Ebay...................

Subtotal: US $19.98....Postage & packaging:...US $4.55.......Total:US $24.53
@ today's exchange rate works out @ £15.67 for 8.............£1.96 each
Lets see what Paypal actually charge me first and what I get before you progress.
Alan

www.ebay.co.uk/itm/120637324370?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_1754wt_776

Above LT1085s arrived today
markings are stamped on....LT1085.....9540... with LT logo but no Linear


LT1085....1198078...e3....Linear..... I got a while back from RS is printed in white
same as the LT1033CT which came from Farnell today
also these have Linear on them.
Hope the USA ones are okay. £1.96 is a far cry from RS price.
Alan

[jeffc]

Hi Alan,

The 2 I have left from my lot of 4 from WestFlorida Components are both marker differently with different sized LT logo's, have slightly different sized TO220 cases , and one has Philippines printed on the back.. obviouusly they source these from different factories and genuine, who would know

BTW I came across this PSU variant, maybe Alex might comment.

www.diyaudio.com/forums/blogs/nazar_lv/200-psu-high-end-audio-without-electrolytic-capacitors.html

cheers.. jeffc

[Deleted]

BTW I came across this PSU variant, maybe Alex might comment.

Hi Jeff
He is right that electros do cause colouration, which is why I am using the Suntan CD268 where possible, as along with several U.K. members previously , they have found to be more neutral sounding than many other low ESR types. In the preamp/HA and 15W Class A, I use a parallel normal type for this reason in the JLH.What this guy has come up with is really only suitable for low current preamps etc, due to it's relatively high output impedance.Those shunt transistors are small signal types and IMO can't help much in that area. The original JLH had a measured output impedance of .02 ohms from 500HZ to 30kHz , and our version is likely to be even lower over a wider bandwidth. I think you can gauge it's perceived effectiveness by the lack of replies in a forum with >100,000 members.
Alex

[Deleted]

Hi All

initial testing of the first reg PSU this morning with 100ma load on each side.

I'll be working it up to full load when both are built.

it worked and i now have +20.2 and -20.2

so just one more to go.

pictures to follow.

take care

[Deleted]

Dec 15, 2011 19:11:34 GMT Will said:

I think that 0.5W metal film resistors are the same physical size as 0.25W resistor from days of yore, and as most of us have them, it makes sense to use them.

Aha! OK.

In my case I have loads of 0.25w resistors to hand so, except for critical areas as specified, I can use them.

[Deleted]

and the second board tested fine with a light 100ma load.

+20.2V -20.2V @100ma

so i just need to ramp the current up for the full load test.

GULP

take care

[Deleted]

Good one Shaun,
another board builder takes the stage.............I'm sure you'll have fairy lights for Christmas.
What are you sticking on the end for a full load?
might have cut a board today but we had snow overnight and spent the morning with the grandson building snowmen............after lunch we took both grandkids to a winter fair and that scuppered the milling plans.
Alan


Alan

[Deleted]

Hi All

Here are some pictures of my etched PSU boards
My first go at etching so not perfect but functional.
I managed to create two pretty much identical boards and the etching process from transferring the artwork to having a finished etch took around 1 hour to create two boards.
Above



And below



And a group shot with two of Gregg’s lovely dual JLH. thanks for the great boards Gregg.



So I’m pretty chuffed for a first effort but my having a go was totally down to Alan's inspirational work with boards.

thanks Alan

HIFI Superman

Take care

[Deleted]

Hi Shaun,
well worth the effort, maybe I should have a bash at the etching too.
So what's the next step.......a dual +/- board plus JLH plus Cricket.
Well done young Sir the etching world's now your Oyster........go forth and multiply.
Regards,
Alan

[Deleted]

Dec 18, 2011 14:06:19 GMT drymdrum said:

Hi Shaun,
well worth the effort, maybe I should have a bash at the etching too.
So what's the next step.......a dual +/- board plus JLH plus Cricket.
Well done young Sir the etching world's now your Oyster........go forth and multiply.
Regards,
Alan

Hi Alan

I'm pretty sure that either carving or etching methods work well.

for me i struggled to keep the star ground without etching so i went with that way.

that FR4 you sent was top draw stuff with a nice thick copper side.

mmmmm lovely.

having a go at making some boards has been real fun and i don't think I've had quite the same sense of pride and satisfaction for years. I'd probably not have bothered if you had not shown the way and I'm grateful for that kick up the BH.

any help you need with etching just ask.

IMHO single sided boards have limitations in terms of keeping the power and signal lines short. I'm sure that Will's boards are going to take full advantage of double sided for compact hi quality units.

I'm planing to use them for the final build.

but

for prototyping etching has definite merit as it allows me to try something quickly and evaluate.

which is cool

take care

[Will]

Shaun,

Excellent result with your first foray into etching!

There'll be no stopping you now you got this sorted out.

[Will]

Latest update, and hopefully close to final for the PSU.

I've tried to reduce the size to help keep cost down, whilst retaining the best bits of the original design. Need to check it for faults (crossed traces and the like), but not this side of a festive sized glass of Brandy (Torres 10 year old, lovely)

PCB is 71mm x 79mm

[Deleted]

Hi Will
Looking good .

For those who are wondering about the reasons for some of the changes to the original, here are the main reasons.
The length of the original PCB may have caused difficulties with positioning the toroidals in some of the smaller cases used.
A single larger value electrolytic may even sometimes sound better than 2 or more parallel types of the same value, and 4,700uF or even 10,000uF 35V Panasonic electros can be obtained for as low as $6 each from the major suppliers.
We are now able to use 2 x heavy duty 3 core mains cable for connecting power to the amplifier instead of 2 custom 4 wire cables.
Regards
Alex

[Deleted]

Dec 19, 2011 22:11:06 GMT Will said:

Latest update, and hopefully close to final for the PSU.

I've tried to reduce the size to help keep cost down, whilst retaining the best bits of the original design. Need to check it for faults (crossed traces and the like), but not this side of a festive sized glass of Brandy (Torres 10 year old, lovely)

PCB is 71mm x 79mm

Hi Will

thanks for your nice comments on my first etch

great work on the PSU front a really nice compact layout which keeps the best of the original.

outstanding.

take care

Hi Alex

''For those who are wondering about the reasons for some of the changes to the original, here are the main reasons.
The length of the original PCB may have caused difficulties with positioning the toroidals in some of the smaller cases used.
A single larger value electrolytic may even sometimes sound better than 2 or more parallel types of the same value, and 4,700uF or even 10,000uF 35V Panasonic electros can be obtained for as low as $6 each from the major suppliers.
We are now able to use 2 x heavy duty 3 core mains cable for connecting power to the amplifier instead of 2 custom 4 wire cables.
Regards
Alex''

yes all good points and as you say keeping the board size down when using two transformers certainly makes sense.

i have a 2u dissipante for my PSU case (yes overkill heat sink wise but i wanted it to match the 4u i have for the amp) so size not so much of a problem.

yup agreed on the one cap being better than two in this set up and again may save some space on the board. i used 1x rubycon 4700UF 63V per rail which is what i had to hand. the higher voltage rating may even help lower the ESR a little.

for the 10uf I've used 50V suntans and in the 100uf position I've gone for panasonic AM as they seem to have slightly higher ESR compared to the FM/FC.

take care

[Will]

Hi Chaps,

With my PSU pcb, does anybody want want a wirepad adding to where all the 0v meet (nestled between the tank caps), and does anybody want provision for an LED 'on' indicator?

Finished work for Christmas now - what a feeling!!!

[Deleted]

An amp conceived over the Christmas period without fairy lights

What could you be thinking Will

Yes please, power LED.