'AK Mods' SC Class A 15W Amplifier

[Deleted]

Will
TBH. at the moment I feel like chucking it all in. Shaun and Alan have working amplifiers now too.
I will contact you via an email.
Regards
Alex

[Deleted]

Feb 23, 2013 8:40:26 GMT jeffc said:

Hi again Alex,

Speakers connected....nothing else connected... amp case sitting directly on top of the PSU case, no Al lid on PSU case, put ear to speaker and there is hum, but I need to have my ear very close to the speaker before this is clear, touch the amp Al lid touching the heat sinks, and you hear this touching and if my finger is held there, hum gets a little louder. Connect crappy old test CDP, and hum is now very low, ear right on speaker cone needed to hear anything, nothing really, hit play and VERY VERY LOUD MUSIC.......... no preamp...

Feeling better....

It works......

Knowing this, I can rest easy and chip away for a little while longer to get everything optimized.

Sorry for getting a little OTT, as said last weekend, I’m close to exhaustion trying to build this amp amongst everything else expected of me at work and at home…..

cheers.. jeffc

way to go Jeff



Nothing much to worry about from what you have posted and yes I had a few of those moments also but sometimes it's just good to keep going.

You’ve got to the music stage and now it's all gravy.

‘’The change from 120 to 130 ohms was found necessary for a couple of U.K. members to achieve complete balance.’’

Yup Us Brits shivering our timbers off needed to experiment a little to get balance. As Alex mentioned it seems to be a heat thing so just a little bit of small work for you but hey it’s working.

Let’s make no mistake about it the class A is a challenging build in many ways but with a little perseverance and grit it’s possible.

Great work from the Sunshine State

Stubby holder out and VB’s on ice

Take care

[Deleted]

‘’Shaun and Alan have working amplifiers now too’’

Yup but only thanks to your patience.

I have the amp but lack the expertise so no chucking anything in Main Man

Take care

[Deleted]

Hi Guys,
Just thought I'd let you know that I have asked Sean, my builder, to go ahead with the build of my amp(s). I've gone for the dual mono, 2 PSU option and asked the builder not to spoil the ship for a ha'porth o' tar. My logic is that I only expect to do this once so I'm going to do it right. It is, on my part, pretty much an act of faith in Alex, his design and the glowing reports of others here of the SQ this amp produces.
I've been surprised, ney shocked, at the cost of everything, particularly the cases, but it should look as pretty as everyone says it sounds, on completion. I will of course post a few pics of Sean's build, on completion. We are currently aiming for a mid April date for collection.
Stand by for numptie requests for guidance in the next couple of months.
Cheers,
Dave.

[Deleted]

Keep them coming Dave, we all learn from them!

[Deleted]

Hi Guys (but principally Alex I guess ),
Sean has just mentioned the transformers for the build. He has focussed on: -
£48 for a 120VA pair or £60 for a 160VA pair. Given the price difference is there any benefit to be had from going for the larger ones?
For the record we have agreed on these as the cases: -

www.modushop.biz/ecommerce/cat079_l2.php?n=1

Cheers,
Dave.

[Deleted]

Feb 23, 2013 20:30:21 GMT @davek said:

Hi Guys (but principally Alex I guess ),
Sean has just mentioned the transformers for the build. He has focussed on: -
£48 for a 120VA pair or £60 for a 160VA pair. Given the price difference is there any benefit to be had from going for the larger ones?
For the record we have agreed on these as the cases: -

www.modushop.biz/ecommerce/cat079_l2.php?n=1

Cheers,
Dave.

Hi Dave
The 120VA will be fine, as we could just get by with 2 x 80VA.
Kind Regards
Alex,

[jeffc]

TBH. at the moment I feel like chucking it all in.

Hi Alex,

No don't do that.......

Apologies for the headaches I've caused over the past couple of weeks. A few very silly errors on my part with the SPKPRO PCB that was populated with parts so long ago now I can't remember, the crappy RCA socket problem, having the front-end balance WAY OFF initially, the confusion of what circuit is most up-to-date etc had me very frustrated..... and I have no right to point any of that frustration at you......

I'll leave the amp 'as is' ATM with balance as close as the trimmer will allow (13-16mV) and set it up for proper listening

Checking voltages again this morning, I noted a couple of interesting things....
Amp plugged in but turned off at the wall socket, there are a few (3-10) mV across Tp1-Tp2, touch the heat sink and this varies a couple of mV, ground the heat sink and this then goes to 00.0mV on the DMM 200mV scale. Not being grounded would have also been the reason for the increased hum when touched during testing with stunt speakers yesterday. Anyway, with a timber case except for top plate and heat sinks, I'll make sure that these are now connected to ground.

And BTW, when I said I thought I could here something (hum) after the CDP was connected directly yesterday, I checked this a couple of times after posting and wasn't convinced that I could hear anything whatsoever, ear touching the speaker cone, so this amp will be deathly quite in real-world operation I'm sure.

OK... you're free of me...

cheers.. jeffc

PS. Shaun, yes all working fine with just a couple of very minor things to attend to, just need to give Alex some TLC now to help him recover from putting up with my little tanties......

[Deleted]

Anyway, with a timber case except for top plate and heat sinks, I'll make sure that these are now connected to ground.

Hi Jeff
You have probably now realised that with a metal case that the heatsinks become automatically connected to 0 Volts/"earth".
I don't know if you have yet seen the email I sent you with another method to get the balance closer initially.
You are almost there now.
Kind Regards
Alex

P.S.
I hope your ears have now recovered after copping music at maximum level at such close range without a volume control ?

[Deleted]

PS. Shaun, yes all working fine with just a couple of very minor things to attend to, just need to give Alex some TLC now to help him recover from putting up with my little tanties......

Hi Jeff

Looking good with most of the work done.

Tantrums haaa don't worry on that. You look like a saint compared to my fits of frustration.

I’ve been building for 20 or so years and still find it amazing that the handful of components that I put together actually makes any sound at all.

I still find that magical.

I’ve enjoyed watching your progress.

Well done

Take care

[Deleted]

Shaun,
X2 on that one

I’ve been building for 20 or so years and still find it amazing that the handful of components that I put together actually makes any sound at all.

I still find that magical.

Hi Jeff,
nice one getting to the the loud music stage, well done.
How about lining the wooden case with the heaviest catering style cooking foil you can get like you'd do a turkey in.
Mark you I don't cook so don't know what a turkey's done in.
Just glue it to the wood with cheap white PVA, works well. 
I did that with my DIY built four channel mixer.
Regards,
Alan 

[jeffc]

Hi Alex,

Glad you're not too cranky with me still...
I'll check my email later for a read through your "front-end balancing for dummies" course.....
I'm really very happy now to know the Amp works just fine...
Hopefully it will be sitting 'pride-of-place' in my rack connected to my DML Panels by next weekend....

Hi Shaun/Alan,
Thanks guys.... some good tips through all this fun... and encouragement... and like you I'm just as amazed that nearly every DIY audio project I've attempted has worked..... in the end.... and sounded better than they had any right too....

As promised some pics... still a couple of things to finish off before I'm done...... but close enough for Show-And-Tell.......

PSU

PSU - lid on

Amp

Amp + JLH PCBs

Amp + PSU - Front - as they will sit on shelves of my rack

Amp + PSU - Back - all direct wiring, no plugs, no switches


cheers.. jeffc

[Deleted]

Hi Jeff
It all looks great !
It looks much less cluttered without the need for external Offset Correctors too.
Relocated power feed for Speaker Corrector next ?
Kind Regards
Alex.

[jeffc]

Thanks Alex....

The very wide cases helped my cause in keeping L/R channels well separated and wiring uncluttered...
Attempting to build cases was an additional challenge that helped stress me out, but as I've said to you personally, I respect all the improvements you've pioneered with this already terrific design and in honour of that, and you for your dedication to getting it into systems of friends like me, decided I could go a little anal on layout and parts..... I'm hoping that this amp will have me contented until I’m pushing up daisy's...

The SPKPRO is now connected to the 20.2 +V input side of a JLH, gnd connected at output... there something better I can do here?

Input wiring is cotton-sleeved 0.5mm silver...
Output wiring is cotton-sleeved 1mm enamelled wire, same used to wind the inductors....

cheers.. jeffc

[Deleted]

Hi Jeff
I see what you have done now. At first glance it looked like you may have been taking the Speaker protector power from wrong side of the JLH.
When you have it fully operational , you may also wish to try connecting the main earths of each side together to see if there is any audible difference.
You should have used something like multi strand wire, such as 7.5A or 10A rated mains wire for both the leads to the speaker protector, and from the speaker protector to keep the speaker damping factor very low.
In the SC 20W they used heavy duty 90/.18 speaker cable for both to and from the speaker protector.If you have an old disused 10A mains lead laying around, you could strip the outside and use the 3 wires inside. If it's a fairly long cable the stolen bit won't be noticed, and you can then refit the mains plug/ socket to it again.
Kind Regards
Alex

[Deleted]

hi Jeff,

Nice build. You are giving me some inspiration to get my finger out and finish a few of my amps. I think I have one of these amps that I started 5 or 6 years ago, after I first heard Alex's modded one.

Do you guys have to have a fuse on the main power in?

Also, when you run a power cable through the case you need a cable clamp (at least) on the inside, a cable gland is preferable. You have to allow for the cable to be pulled with some force and you have to ensure that the earth cable doesn't come lose.

If you run a cable through metal you should install a rubber grommet.

regards

[Deleted]

Feb 24, 2013 9:26:26 GMT @gregerskine said:

hi Jeff,

Nice build. You are giving me some inspiration to get my finger out and finish a few of my amps. I think I have one of these amps that I started 5 or 6 years ago, after I first heard Alex's modded one.

Do you guys have to have a fuse on the main power in?

Also, when you run a power cable through the case you need a cable clamp (at least) on the inside, a cable gland is preferable. You have to allow for the cable to be pulled with some force and you have to ensure that the earth cable doesn't come lose.

If you run a cable through metal you should install a rubber grommet.

regards

Hi Greg
All good points.
I presume that Jeff may intend using a rear mounted fused IEC socket with switch ,when he gets the electronics working.correctly , as I couldn't see what he had done there.
Ideally, there should be a separate fuse for the primary side of each toroidal, but you can get away with a single fuse of no more than double the transformer manufacturer's specified fuse.
The earth wire should also be a little longer than the active and neutral for the reasons you stated.
Most of the guys should have access to the original article though, and be able to implement things safely in that area.
Regards
Alex

[Deleted]

Hi Jeff,
that's a really nice clean build and one to be proud of.
Regards,
Alan

[Deleted]

Hi Jeff

another great build rolls off of the production line.

just great to see the end result looking a million dollars.

well done

take care

[jeffc]

Hi guys,

Thanks for the nice comments and suggestions on what I've done with the build.

A few points to clarify stuff maybe not so clear from the pictures.

On the internal speaker wire from PCB to SPKPRO to binding posts. I figured that with almost 1m of 1mm dia solid core copper wire in the 18.5 turns inductor, another ~30cm to connect to the binding posts would make little difference, particularly as the output traces on the PCB must have less copper area than this. In addition, I have 4 x 15" H-frame woofers for bass that will be driven by either my Class D Audio amp or my Yamaha receiver, so the Class A amp will be ultimately relieved of low bass duties.

On fuses, I decided to use 3.15A rated PCB mount types for each 160VA transformer, pins soldered directly inside power wires, no BS about mega $ audio fuses, gold plating etc to be bothered about.

AC and DC wiring through the Al angle brackets..agree Greg that this "could" be a hazard. However, what I've used is 1.3mm dia cable made to US spec, which uses much thicker PVC wire insulation than almost any wire I've come across locally, note this from the pictures. This will be restrained with cable ties or clamps or both once cases are in my rack, and these won't be moved once in place. To move will be lid off and unscrew wires from terminal blocks etc job, so something done ONLY if I really have too. Moreover, with 16mm wood outside the 1mm Al bracket on the inside, the cables will not be stressed against the Al through movement as they will be fixed in place by the wood.

Alex, I have no intention of using IEC sockets, sorry, thought about this and the cables I'm using had beautiful copper IEC plugs, but....... too hard to install sockets in a DIY wooden case.

Note that all exposed high-current wire has been covered with heat shrink, even the potentially exposed portions of the SBYV28 diodes on the PSU PCBs... I have tried to be extremely safety conscious, even if not strictly adhering to RULES....

cheers.. jeffc

[Deleted]

On the internal speaker wire from PCB to SPKPRO to binding posts. I figured that with almost 1m of 1mm dia solid core copper wire in the 18.5 turns inductor, another ~30cm to connect to the binding posts would make little difference, particularly as the output traces on the PCB must have less copper area than this.

Jeff
You still need the lower output impedance to properly drive the speaker cables with their high capacitance and inductance, whatever kind of speakers you are using.
You may wish to one day demonstrate your gear at a friend's place through very different speakers.
You may even want to have a shootout with Phil's build at a future date.

Regards
Alex

[jeffc]

You still need the lower output impedance to properly drive the speaker cables with their high capacitance and inductance, whatever kind of speakers you are using.

Hi Alex,

Point taken... maybe I should try and determine what the output imdedance actually is......
Found this calculator macro that might be useful for this.....
www.sengpielaudio.com/calculator-InputOutputImpedance.htm
but.... not exactly sure whether I need anything fancier than a 4R-8R power resistor and my DMM from measuring voltage change with/without load to populate the equation.....

cheers.. jeffc

PS.. see a 1kHz input signal is needed too....

[Deleted]

Feb 24, 2013 20:29:53 GMT jeffc said:

You still need the lower output impedance to properly drive the speaker cables with their high capacitance and inductance, whatever kind of speakers you are using.

Hi Alex,

Point taken... maybe I should try and determine what the output imdedance actually is......
Found this calculator macro that might be useful for this.....
www.sengpielaudio.com/calculator-InputOutputImpedance.htm
but.... not exactly sure whether I need anything fancier than a 4R-8R power resistor and my DMM from measuring voltage change with/without load to populate the equation.....

cheers.. jeffc

PS.. see a 1kHz input signal is needed too....

Hi Jeff
Why not just take the word of the guys with their Audio Precision test gear etc. that design these things.?
I honestly doubt that you will find any published designs, or for that matter, any major commercial products that don't use multi strand cables in that area.
That's also another reason why S.C. specified a relay with such heavy duty contacts in the Speaker Protector.

Kind Regards
Alex

[Deleted]

Hi Jeff/Alex

Gulp speaker cables

OK here's what I did

Initially
I used one twisted pair of 15A silver on copper PTFE hot and one of the same for cold between my amp board and binding posts pretty much because that was the speaker cable that I was using at the time.

So if you have solid core on the outside then maybe have it on the inside also and if you have stranded then do likewise.

However the cable that I’ve ended up using with Alex's Class A is about as far away from that as is possible to get.

I started by trying Tellurium Q blue and liked them some much I went for the Black soon after which seemed along with the matching black IC's to get the sort of presentation that I was looking for in my set up (in spades ).cool calm and very focused.

I’ve not changed out the internal cables as yet but I may do for the next build now that I have some spare blue to play with.

If it where me doing it from scratch again then I’d most likely start with some thick multistrand internally and experiment with external cable later.

But that’s IMHO

All fine tuning now though

Take care

[jeffc]

Hi Shaun,

Those Tellurium Q speaker cables look terrific, might be a bit tricky though, as by the pictures they look to be quite stiff, to use them for internal wiring.... But if you have space... and the patience.... why not. They look to use evenly spaced wires which reminds me of these musings into DIY interconnect cables, which the designer liked best when spaced evenly about 19 mm apart.

forum.audiogon.com/cgi-bin/frr.pl?rcabl&1150905409

Interestingly the Eichmann cable pods I decided to use are low mass and made of tellurium copper. When I replaced the binding posts on my Wharfdale Diamond 8.4s with some years ago I remember there being a quite significant change in presentation for the better, amazing that changing something as basic as a binding post can have such an effect.... anyway, had some so used them..

I also have some skinned Eichmann Express 6 speaker cables (freebees) that I might try with this amp. I haven't done anything in the way of testing different cables with my DML panels yet, so might be time to investigate.

Problem with this wide-band Class A amp compared to my Class D Audio amp with steep HF attenuation via its output filtering will be the naked piezo tweeter cones I have in parallel with exciters on my DMP panels..... I'm expecting a bit of fun with this.... and have a feeling the Class A might not be too enthusiastic about driving them... but there are easy fixes should this prove to be the case.

cheers.. Jeff