(AK) Class A HA PCB and parts Group Buy

[XTRProf]

Feb 18, 2013 3:59:06 GMT @sandyk said:

Feb 18, 2013 3:35:42 GMT XTRProf said:

Sorry, what have the new parts done to the amp as I don't have the old layout to compare.

Chong
A few people had problems with the 78L15 blowing up. This is a known problem with this VReg , and S.C. even reported about it.
Some brands of the more bullet proof 7815 and 7915 , need a minimum load current to properly regulate. That is the function of the additional 3.3K resistors.
Replacing the originally specified AD744 or TL072 of the Offset Corrector with an OPA134 will reduce the noise component from the Offset Corrector I.C. itself,
that appears at a reduced level into the feedback network.The 2.2nF to 4.7nF across the 1 Megohm in the offset corrector,
helps to further reduce wideband noise generated by , and amplified due to the high gain of the offset corrector I.C.
This further improves the S/N ratio of the amplifier and makes low level detail sound a little cleaner and more obvious.
Also helps to further improve the 3D sensation when used as a preamp and high quality power amplifier.
Do the same to both preamp and Class A power amp and you gain even more..
Regards
Alex

Thanks ..............

[gommer]

Nice work Will and many thanks to Alex for elaborating the improvements.

I wonder. When noise floor on the DC servo determines auditive resolution to some extend, wouldn't it be better to use other linear regs than the archaic 7x15's? LM317 would already be leaps and bound better, but these days many optimized linear regs do exist.

Cheers, Marc

[Deleted]

Feb 18, 2013 8:35:46 GMT gommer said:

Nice work Will and many thanks to Alex for elaborating the improvements.

I wonder. When noise floor on the DC servo determines auditive resolution to some extend, wouldn't it be better to use other linear regs than the archaic 7x15's? LM317 would already be leaps and bound better, but these days many optimized linear regs do exist.

Cheers, Marc

Hi Marc
The 7815 and 7915 are both powered via the JLHs in the ClassA HA/preamp and the 15W Class A.
Although not ideal, it has been my experience with the X-DAC V3, that as the 7815 and 7915 have SFA to do other than drop voltages,
that they do a much better job than normal .Some modern 7815/7915 versions even have measured noise as low as 30uV.
In the David Tilbrook designed AEM6000 and 6005 Mosftet power amplifiers,that were built in the 10s of 1,000s ,
lowly zener diodes were used to provide the regulated voltage to a much noisier TL071, without any additional filtering across the 1Meg resistor,
or any additional filtering at the output ,with he simple 100K output resistor from the I.C. going directly to the gate of the FET input pair on the feedback side of the pair.
I honestly doubt that any further audible improvements will be obtained, as the effects of both changing to the OPA134, and the additional 2n2 cap were quite subtle, as Shaun will verify.
I think that Shaun has already mentioned that this combo is dead quiet right at the speakers.
Kind Regards
Alex

[gommer]

All right, no worries then, it was just a thought.

Marc
The output noise from the preamp was so low that I had to make a special preamp in a diecast aluminium case ahead of my CRO ( just over 10 x gain IIRC) to see anything more than a slightly thicker straight horizontal trace. What I did see was then identified as SMPS crap of < 1/3 of a division that appeared to be coming from my Samsung LED TV via input cables.
Kind Regards
Alex
P.S.
Marc, sorry about editing your post.

[Deleted]

I think that Shaun has already mentioned that this combo is dead quiet right at the speakers.

X2................I thought at one point that my second build of the AK Mods SC 15 Watt driven by my first build AK SC Class A HA/Pre was not working,
as the noise floor at ear to speaker point was so low.
I thought it was dead till I managed to get some audio through it having forgotten to switch on the DAC. 
You wont be disappointed with this amp.

Regards,
Alan

[gommer]

Guys, I wouldn't doubt a minute that this amp is anything less than the best. After all, that's why I started this thread I was just asking from a theoretical technical POV. Fact is, there are better things out there than 7815 and 7915, but I understand everything else makes the quality of the linear regs irrelevant.


Something else...
Forgive my ignorance, but has there ever been designed a power supply board?

Cheers,
Marc

[Deleted]

Feb 18, 2013 10:55:07 GMT gommer said:

Guys, I wouldn't doubt a minute that this amp is anything less than the best. After all, that's why I started this thread I was just asking from a theoretical technical POV. Fact is, there are better things out there than 7815 and 7915, but I understand everything else makes the quality of the linear regs irrelevant.


Something else...
Forgive my ignorance, but has there ever been designed a power supply board?

Cheers,
Marc

Hi Marc
Will designed the PCB in the .jpg.


However, I used the same as in the SC (Jaycar) HA as they came as inexpensive kits from Jaycar. I had to do a little surgery with a PCB drill
to take the fatter and shorter electros needed to give me clearance inside a 1U rack case.IIRC they were more compact than Will's PCBs for my purpose.
Regards
Alex



Uploaded with ImageShack.us

[gommer]

I see, nice to know. Do the Class A takers also want the PS PCB? I know I do.

[Deleted]

Hi Marc

''I think that Shaun has already mentioned that this combo is dead quiet right at the speakers''.

yes this HA/PRE is Ghostly quiet as is the PA so no worries on that front. Ears right up to the speakers and just a slight Class A whisper is what I have. Much better than the commercial stuff I’ve heard in that regard.

OK on the PSU front

I’m guessing that most of us old hacks have some of Will’s lovely dual REG PSU boards and I know that I have two spare sets.

So PM me your Address and I’ll send you a set which leaves one set SPARE.

OK an offer open to new builders only.

First PM to me will get the other spare set of dual reg boards.

If we need more then maybe a Jaycar GB (I’m still using them in my HA/PRE) is the way to go as it’s a full kit and not just boards. Also those nice Suntan 4700 caps can be had at the same time for those that need them.

Take care

[pingu]

Shaun you have a PM
Martin

[gommer]

That's a mighty nice offer Shaun. Much appreciated.

OTOH, before you continue playing Santa, does the Jaycar/Silicon Chip dual reg resemble anything like this:
www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k8042.pdf

The Velleman kit can be had everywhere in Europe for about €10.

[Deleted]

Feb 18, 2013 14:26:33 GMT gommer said:

That's a mighty nice offer Shaun. Much appreciated.

OTOH, before you continue playing Santa, does the Jaycar/Silicon Chip dual reg resemble anything like this:
www.vellemanprojects.eu/downloads/0/illustrated/illustrated_assembly_manual_k8042.pdf

The Velleman kit can be had everywhere in Europe for about €10.

Hi Marc

No just plain Will’s boards this end

The Jaycar kit comes with everything needed but a few changes will need to be made. From memory some board drilling is needed for higher voltage Caps to be fitted. Also we used SF12 diodes for the bridge.

Looking at the velleman kit yup it looks ok but if it where me I’d swap out the bridge diodes for something faster (SF,UF or whatever). also put some slightly nicer PSU tank caps in and also change the 10uf OP cap for 100uf and maybe not have those noisy LED 's on the OP. I’d just use one and move it back and have it supplied by the tank cap. i'd also make the tank caps 2200uf for better performance.

I’ve use the vellerman single positive reg for a few projects and yes they are OK but the Jaycar and Will's boards are better IMHO.

To my mind the PSU quality is critical and by the time you make the above changes then how much of the original kit is left. Cost wise not much in it.

OK that's my take but others will think differently which is fine.

Other opinions welcome.

take care

[XTRProf]

Hi Marc,

If somebody can buy for you the Jaycar PS kit in UK, it's much cheaper than when you buy it from Aussie. Will's PS PCB will be superior as it can go until 5A, if I'm correct, and take bigger E-Caps. You didn't buy any to keep again?

Anyway, you can go unregulated and I can bet that any amp will go more dynamic. Many poweramps are unregulated, fyi. I may try a variation with a choke as regulation. Any suggestion for a choke size and circuit diagram from anyone?

[gommer]

Hi Chong, I wasn't even aware Will ever made one. In which thread are the details buried? I'd like a look at the schematic.

[XTRProf]

Feb 18, 2013 16:06:52 GMT gommer said:

Hi Chong, I wasn't even aware Will ever made one. In which thread are the details buried? I'd like a look at the schematic.

Around here, Marc.



rockgrotto.proboards.com/thread/7461/ak-mods-class-15w-amplifier?page=4#page=23

[Deleted]

Feb 18, 2013 15:59:35 GMT XTRProf said:

Hi Marc,

If somebody can buy for you the Jaycar PS kit in UK, it's much cheaper than when you buy it from Aussie. Will's PS PCB will be superior as it can go until 5A, if I'm correct, and take bigger E-Caps. You didn't buy any to keep again?

Anyway, you can go unregulated and I can bet that any amp will go more dynamic. Many poweramps are unregulated, fyi. I may try a variation with a choke as regulation. Any suggestion for a choke size and circuit diagram from anyone?

Hi Chong

Errrr marc that’s a link to the 15W class A PSU so not needed for this build.

the schematic is pretty much the same as the Jaycar unit but with more room for bigger caps, a more optimised board layout and better quality heavy copper PCB.

OH unregulated.

Chong. Can we have a schematic of what you have in mind? Did you try it out on your working AK Class A HA :-*if so can you give us an insight as to how you found that it improved the sound?

Anyhow Marc

Here is a link to the Jaycar PSU.

rockgrotto.proboards.com/thread/3622/silicon-chip-headphone-amp-tweaks?page=1#

Without some of the component changes I mentioned in my previous reply but it should give you some idea.

I’ll post a picture of the boards in question which IMHO are top rate.

Hope that helps

Take care

[Will]

These are the PSU pcb files that I have available:



Single rail, +ve psu - just a simpled lm317(or pin compatible) reg psu, with led bit and space for a VR to set the OP voltage



Dual rail version of the above. Same features.



Another dual rail, designed to be mounted on a heatsink, and supply the AK mods class A. Will do 3A with the right vregs, and most likely 5A.

No reason not to use it with the AK Class A HA, but perhaps a bit overkill.

More than happy to pass these over to the GB for buying, as I am the PK dac and AK Crickets.

[Will]

Feb 18, 2013 5:34:11 GMT jonclancy said:

Morning Alex!

Will,

We NEED a list of these mods as a separate MkII (locked) thread linked in your sig - pretty please!!

Some, at least, can be retro-fitted to current boards.

Cheers

Jon

Hiya Jon,

The main mod is the tuning that Alex has done to the offset corrector link
Alex emailed and posted about it, and thought it a good idea to provide for the 2n2.

Replacing the 78/79 regs on the dc servo will be a bit hard, and was to overcome a problem with the regs, as they died on a few people.

The feedback cap is only needed in the early stages of powering up the pcbs. If you have yours up and running, then you've no need for them. If someone has problem on power up, with a faulty pcb, installing a 100-470uF in the Cfb posisiton, and removing the op-amp allows for isolation of parts of the circuit. It's just a nice to have, and hopefully the Cfb position will normally have a nice bit of cryo'd rhodium plated teflon sleeved wire in it

[Spirit]

gommer x4
shaun x4
will x4
juke x2
cj x2
pingu x4
Spirit x4
total 24

Updated my order - in case I ever want to use one as a preamp.

I'm very keen for a set or two of Will's PSU boards to match if another GB goes ahead.
Also keen for any GBs on the other parts.

[XTRProf]

Hi Will and Marc,

May I request this new PCB be with a separate front and back end PS feed. If request accepted, I will add in my order for 4 (1 PCB = Mono?) 4 for balance version and not another pair as a pre-amp. I like the idea of more PSs to bring up the performance of the HA.

Thanks for considering the OCD idea.

[jonclancy]

Thanks Will!

[Will]

Feb 19, 2013 12:44:34 GMT XTRProf said:

May I request this new PCB be with a separate front and back end PS feed.

Hi Chong,

Do you mean separate supply connections for the front end and the 'power' stage, like in the power amp pcb?

You don't know how tempting that is, or how long I've been thinking of it

[XTRProf]

Feb 19, 2013 18:22:31 GMT Will said:

Feb 19, 2013 12:44:34 GMT XTRProf said:

May I request this new PCB be with a separate front and back end PS feed.

Hi Chong,

Do you mean separate supply connections for the front end and the 'power' stage, like in the power amp pcb?

You don't know how tempting that is, or how long I've been thinking of it

I don't know what the class A power connection is but I think you have struck the bullseye in what I mean. Yup, one separate ps connection for the pre stage and one separate connection for the power stage. So 2 ps for each pcb. So those preferring only 1 ps just paralleled the 2 ps connection terminals

[Deleted]

Feb 19, 2013 19:50:37 GMT XTRProf said:

Feb 19, 2013 18:22:31 GMT Will said:

Hi Chong,

Do you mean separate supply connections for the front end and the 'power' stage, like in the power amp pcb?

You don't know how tempting that is, or how long I've been thinking of it

I don't know what the class A power connection is but I think you have struck the bullseye in what I mean. Yup, one separate ps connection for the pre stage and one separate connection for the power stage. So 2 ps for each pcb. So those preferring only 1 ps just paralleled the 2 ps connection terminals

You could try it, but personally I do not believe there is anything to gain due to only 100mA bias current.
You risk interaction between JLHs if you use another JLH without the CL to supply just the output side.
If you used just the regulated PSU to supply the output stage, then the performance is almost certainly likely to be degraded.
As an exercise, try bypassing the CLs in the JHLs with an existing HA/preamp and see how you find it
Regards
Alex,

[Will]

Feb 19, 2013 20:32:15 GMT @sandyk said:

Feb 19, 2013 19:50:37 GMT XTRProf said:

I don't know what the class A power connection is but I think you have struck the bullseye in what I mean. Yup, one separate ps connection for the pre stage and one separate connection for the power stage. So 2 ps for each pcb. So those preferring only 1 ps just paralleled the 2 ps connection terminals

You could try it, but personally I do not believe there is anything to gain due to only 100mA bias current.
You risk interaction between JLHs if you use another JLH without the CL to supply just the output side.
If you used just the regulated PSU to supply the output stage, then the performance is almost certainly likely to be degraded.
As an exercise, try bypassing the CLs in the JHLs with an existing HA/preamp and see how you find it
Regards
Alex,

I think you said something similar about going to dual PSU/JLH's once

I like the idea, but there's not enough room to do it tidily on the existing pcb, without a whole bunch of rework.

Once I get the nod form Marc, I'll send over the revised pcb (and anything else wanted) and the pcb's can be on the way

It's very heartening that another couple of AK Class A's are going to be made