(AK) classA HA/Preamplifier.

[jonclancy]

Ah, you're being silly now!

Yes, it's got S&B (MF) TX-102 MkIII transformers in it. And Seiden switches, silver RCAs etc.

Currently in the main system, but will be head to head with the Class A. That's certainly not lacking in the attenuator department! We'll see what the overall effect it (apart from LOUD!!).

[Deleted]

Mar 6, 2013 22:23:52 GMT jonclancy said:

Ah, you're being silly now!

Yes, it's got S&B (MF) TX-102 MkIII transformers in it. And Seiden switches, silver RCAs etc.

Currently in the main system, but will be head to head with the Class A. That's certainly not lacking in the attenuator department! We'll see what the overall effect it (apart from LOUD!!).

Hi Jon

It may be a horses for courses thing with your unity gain TVC matching the higher than usual sensitivity of the REF C. I tried the same thing with my Audiosector chip amp and well with Alex's Class A the gain was a little toooo much so my Glass house also with seiden switches (nice quality units) pre is a better match.

That’s why I gave you the nudge about being careful with the VOLCO.

But with Alex's matching PA nope no comparison or contest in my system. the HA/PRE/ Power sounds loads better in every way.

As a combination Alex’s HA/PRE PA combo is the one I have in my main set up with the TVA/Audiosector relegated to the second system status. I’m tempted to try something a little more elaborate in the way of another chip amp build at some point just to see how far that can be pushed along.

Oh by the way you were lucky to get the earlier S&B transformers which apart from being hard to get for DIY use sound a little better than the Silks IMHO.

take care

[Deleted]

Well here I am back  in the SC Class A thread again...............this time I've just finished my rebuild of #1 AKMODS SC HA/PRE.....well not quite but  with the major part,
building a new slimmer neater case and  re-installing the modules done that's how I feel about it, especially since I've at last got that pesky low level high pitched whine fixed.

With regard to the whine, it was always there just below the audible threshold as soon as  the volco was turned up a little.

With volume at zero it was there at low level but did not increase with volume advanced.

It did not seem to affect the audio so I constantly put off attempting to fix it.

Now that it's gone I can say that it was affecting the quality, I'm listening to some of Alex's files just now through it and am delighted with the SQ 

it is definitely much improved. I can't say what was wrong with it to cause the whine, only that it seemed to go when I added the capacitance of

my body to it hence the lump of wire in past pics.
The last few days has seen me change all the caps' a few resistors and anything else I thought might 

be affecting it. I also changed the LS transistors..............I've a sneaky feeling that at least one of them was to blame as they were the last parts to go.
I'm waiting for a 50K Valabs to replace the Ebay cheepo that Jeff pointed us to a while back and possibly swap out the AD744 for Alex's recommended OP134 since I've stitched in the 2N2. 

Sound now is amazing, what more can I say just that it deserves an upgrade to my HPs.
So just a new faceplate to make, extenders for the switches and volco out to the front, some nice rubber feet and batten down the hatches and enjoy, all else is good.
Regards,
Alan

[Deleted]

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[Deleted]

And just to show what it looked like before the revamp and clean up.

[Deleted]

Hi Alan
Looks good!
Perhaps it was the improved layout that got rid of the low level whine ?
Kind Regards
Alex

[Deleted]

Hi Alex,

Perhaps it was the improved layout that got rid of the low level whine ?

no the whine was still there as before, that was my hope when I'd revamped the whole layout and fired it back up for the first time.

The better layout has improved the overall sound of the amp but certainly had no effect on the whine.
The whine only vanished when I had replaced the two LS transistors and that was the last thing I did.

TRC ........................problem......Low level high pitched whine on one amp module only.

Was associated with the circuitry between the 2SC5171 output and  the input specifically the base of the LS352...............that covers a whole lot of ground.
Whine could be negated by adding body capacitance to the 2SC heatsink and touching the blade of an insulated screwdriver to various points along the circuit.
Circuitry associated with the 2SA had no effect on whine.
Checked all joints re-flowed many, checked all resistors for value..............still got whine.
Touching screwdriver to top of the 100uf on the 2SC emitter whine gone so replaced it...........no change.
Replaced all capacitors between input and 2SC output................no change, but whilst doing this discovered that I'd a 100nf installed where I should have had a 1uf.
Replaced the 3v3 diode whine no longer associated with that diode, 2SC heatsink and 100uf cap. bad joint not sure but whine still with us.
Touching base of LS352 whine goes away so replaced it.......................no change.
Lastly replaced LS313 to find whine is gone and whole sound of amp much improved.

Offset with AD744 installed is -0.1mv , balance on the LTP 0.0mv  and bias set at 100mv (250mv across the 10R)
Regards,
Alan 

[Deleted]

Mar 15, 2013 10:09:13 GMT drymdrum said:

Hi Alex,

Perhaps it was the improved layout that got rid of the low level whine ?

no the whine was still there as before, that was my hope when I'd revamped the whole layout and fired it back up for the first time.

The better layout has improved the overall sound of the amp but certainly had no effect on the whine.
The whine only vanished when I had replaced the two LS transistors and that was the last thing I did.

TRC ........................problem......Low level high pitched whine on one amp module only.

Was associated with the circuitry between the 2SC5171 output and  the input specifically the base of the LS352...............that covers a whole lot of ground.
Whine could be negated by adding body capacitance to the 2SC heatsink and touching the blade of an insulated screwdriver to various points along the circuit.
Circuitry associated with the 2SA had no effect on whine.
Checked all joints re-flowed many, checked all resistors for value..............still got whine.
Touching screwdriver to top of the 100uf on the 2SC emitter whine gone so replaced it...........no change.
Replaced all capacitors between input and 2SC output................no change, but whilst doing this discovered that I'd a 100nf installed where I should have had a 1uf.
Replaced the 3v3 diode whine no longer associated with that diode, 2SC heatsink and 100uf cap. bad joint not sure but whine still with us.
Touching base of LS352 whine goes away so replaced it.......................no change.
Lastly replaced LS313 to find whine is gone and whole sound of amp much improved.

Offset with AD744 installed is -0.1mv , balance on the LTP 0.0mv  and bias set at 100mv (250mv across the 10R)
Regards,
Alan 

Hi Alan

Interesting stuff

I found that when I build up the first of Alex’s HA/PRE that I had the same low level HF noise (whine).

I did find after much head scratching that careful routing of the IP/OP connections to avoid getting toooo close to the DC servo circuit cured that.

The thing that i keep in mind is that we are talking pre amp (gain) as opposed to line stage (no gain) where wire routing issues are more important.

I try to keep IP/OP cables separate and well away from the servo which is connected from the OP to IP via the FB loop. Any noise in that spot is going to be injected straight back to the IP signal.

I’ve built 2 without issue with using the above method without whine (well perhaps just a glass or two.

I may be wrong and your more thorough noise finding exercise is an interesting read.

Thanks

Take care

[Deleted]

Hi Shaun,
thanks for your observations, have to say that I am a bit miffed at this point as I'd no whine present in the rebuild when I shut the door on it Thursday past.
Today I'm feeling pretty sore all over and am only fit to lay back and listen to that SandyK sound which I did for about an hour and a half up here.
Mhaler's 6th Tragic via Medici TV, enjoyed that and the laying back relaxed.
Came on to the Grotto read your post all's quiet music stopped............................all's quiet...........bugger where's that whine coming from?
Sounds like an incandescent light bulb about to snuff it, of course ear at the TL's mid soon tells me I've got the blasted whine back in the same module.
I  had it in mind to cut another board and Tuesday did that but made a mess of it, the tracks around the AD744 section are a bugger to cut,
so I ditched it and pulled the errant board to see if I could track the little bugger down, thought I had as it was certainly gone when I posted the results.

Ah! now I see it ninety minutes of Mahler's TRAGIC.................................bloody Tragic.
I've stuck on some Chris Barber...........The Berlin Concerts.................foot tapping stuff perhaps that'll fix the whining little bugger.

Okay just have to pull the board again and get back to poking around, I'll cut and build another  board just in case. Fortunately I've still got #2 build here so the music goes on.
Sorry son you'll just have to wait.
Regards,
Alan

Just had a thought...................what heats up that could be complaining?
 

[Deleted]

Hi Alan

Just a quick poke in of my long nosed pliers.

It may be worth trying to separate the DC offset board part of the PRE board (as in mini daughter board style) to see if changing locations will sort the problem.

I found that a little experimentation with cable location helped quite a bit.

Just out of interest

Is the HF noise evident with the PRE or HA use?

Does it increase as the amp warms up?

Have you tried gently moving ALL cables as that sometimes can make a difference? I used a small insulated screwdriver to tease the cables in one direction or another. It may not totally sort the noise but often if you move something and it gets louder or softer then it give a clue as to what needs changing.

Oh yes is it one channel or both? Louder on one or the same both sides?

Also have a look at those signal lines in relation to the power ones.

Maybe put the VOLCO on longer leads just to make sure that it’s not picking up any noise from the regs.

One thing at a time so you don’t get lost with the changes.

Just my noise busting routine and ones I’ve tried in the past with various builds.

Happy hunting

Take care

[jonclancy]

Ah, the sting of being thrashed by the Welsh!!

(They deserved it, mind you!!)

I'll be back to catch up, but in the meanwhile I have added a load of pics of the latest work on my Class A to my album.





Now all the mechanicals have been done. I'm looking at testing the LEDs with 3W 1K5 resistors. I want lots of light and little overheat!

I have decided I like working with Perspex. It's a joy on a slow drill.

Cheers...
for now.


Jon

[Crispy]

Mar 16, 2013 18:57:28 GMT jonclancy said:

Ah, the sting of being thrashed by the Welsh!!

(They deserved it, mind you!!)

Totally outclassed in my opinion Jon :'(but well worth watching.

[Deleted]

Now all the mechanicals have been done. I'm looking at testing the LEDs with 3W 1K5 resistors. I want lots of light and little overheat!

Jon
Why on earth would you want huge 3W resistors when even .6W metal films have more than 4 times the power rating needed ?
Kind Regards
Alex

[Will]

Hi Jon,

Are you going for a illuminated bottom - as in the leds illuminating the plexi on the base of the PSU?

That should look quite posh indeed?

Did you get the plexi precut or did you finish it yourself?

[pingu]

Mar 16, 2013 19:38:22 GMT Crispy said:

Mar 16, 2013 18:57:28 GMT jonclancy said:

Ah, the sting of being thrashed by the Welsh!!

(They deserved it, mind you!!)

Totally outclassed in my opinion Jon :'(but well worth watching.

In the Stadium with the roof on it was MAGIC boys. I think we realy lifted their spirits.
Reminded me what we have here, and as usual a very low police profile in near the stadium.....a very good day. Prices in all the bars/cafes/ Gregs all up at least 10%
Martin

[Deleted]

Hi Martin

Even though I can feel the words sticking

The best team most definitely won.

And Jon

I’m turning green

Great work

Take care

[pingu]

Mar 17, 2013 12:24:56 GMT @shaun said:

Hi Martin

Even though I can feel the words sticking

The best team most definitely won.

And Jon

I’m turning green

Great work

Take care

Well I can remember when we got the wooden spoon more than once.
Thanks for the generosity.
martin

[jonclancy]

Yup, definitely the better team won. For sure.

My mate was in the Stadium too - it must have been an epic atmosphere!! I almost wish I was there (with a big hanky to cry into!!).

Catching up on the Class A:

The reason I have got a selection of 1, 2 & 3W resistors is that I need a range in stock and that the LED calc tool I used specified at least 1W rating for the dissipation. Will's regs have the LED feed just after the diodes. This makes sense to me to keep any noise before the regs. But, with a Vf of around 2.8V, and my trafos putting out around 22V unloaded, this gives around 33VDC. I just wanted to make sure that the resistors stayed well within limits. Happy to take advice on this, though.

The idea behind the Perspex is twofold. Firstly, the bolt length and thickness of the nyloc versus the chassis feet. The stainless bolt and nyloc are actually ground down a little and polished (for my own aesthetic reasons). Secondly, the polished blind holes into the Perspex are designed (hopefully) to light the edge of the plastic sheet. This has been lightly sanded to match the frosted surface finish. The chassis base was used as a template for drilling the 4mm fixing holes (to allows a little positional leeway) and also meant I could easily set the step-drill (which has a 4mm start) to drill the 6mm diameter for the stainless socket cap screws to the perfect depth. The pillar-drill was reset to the lowest speed and it seemed to work out OK.

Finally, the two, over-specced, trafos weigh a bit. The case is only 1mm steel, so the plastic base also provides mechanical stiffness. I think it'll all work out OK, and the extra cost was about a tenner and around an hour or two of work.

I found a plastics supplier on eBay who offered custom size cutting. A quick call to confirm size and cost and the order was placed. They were absolutely spot on with the size, and I am delighted with the quality of the frosted finish - it's very satisfying peeling off the protective plastic layers.

I'm currently sat while my motor's being serviced - all done now catch up later!

[jonclancy]

BTW, my Class A psu is running. It's a very subtle effect with the white LEDs and I like it!! Just need to order some 18 or 20mm stand offs and I'll be bolting it together for the final assembly.

[jonclancy]

BTW BTW, (is that like PPS?)

Martin, welcome to the GB runner's club.

It's like getting flogged with a tree in the snow before the hot sauna (so I'm told). Or is it the other way round??!!

Painful while it's happening, but you'd do it again (when the sting wears off!).

[jonclancy]

And Alan, your new chassis looks just like the awesome copper-coated one in the CD960. Ace!

[Deleted]

Will's regs have the LED feed just after the diodes. This makes sense to me to keep any noise before the regs. But, with a Vf of around 2.8V, and my trafos putting out around 22V unloaded, this gives around 33VDC. I just wanted to make sure that the resistors stayed well within limits. Happy to take advice on this, though.

Hi Jon
If your PSU PCBs are in the same case (?) as the rest of it, why are you worried about unloaded DC voltage ?
Modern LEDs are very quiet and often used as voltage references.If you are concerned about them radiating noise due to using long leads
and the higher ripple voltage before the voltage regulators, you would be better off powering them from the output of the voltage regulator.
Kind Regards
Alex

P.S.
I even used a couple of selected Blue LEDs in place of the 3.3V zeners in a previous version of the 15W.