'AK Mods' SC Class A 15W Amplifier

[jeffc]

Hi Shaun/Alan,

Thanks for your concern guys, my plumbing was given the "ALL CLEAR" on Thu , well as much as a doctor will ever state.
Now no worries on that front, if I can only complete this amp plumbing, which unfortunately won't be this weekend as I'm away to catch up with friends.

cheers.. jeffc

[Deleted]

Hi Jeff
They tell me that drinking too much beer when away with the boys on weekends bumps up your PSA !
Regards
Alex

[Deleted]

Good to hear that Jeff.................. Yeah! amp plumbing is a whole heap better than what the U/T plumbers get up to.

Sounds like Alex has a thing going with PSA


Regards,

Alan 

[jeffc]

Hi Alex/Alan,

After being a pin cushion for a second time in 4 years I'm at the point now where I'm doing nothing unless my PSA levels shoot through the roof . Just need to get symptoms under control.

OK.. wiring almost completed and have just now sucked up the courage to power one amp PCB and its JLHs . And............................................ wait for it...................................NO SMOKE
Voltages +/-20.2V and +/-20.1V in from the JLHs. Voltages on opamp pins 4/7 are -/+14.8V. Amp PCB heat sink warming up nicely in preparation for winter. Other amp PCB and the Speaker Protector PCB still to check BUT.... hopefully all will be well with these too. Right ....... will finish off wiring now to test with junk speakers.... and then fingers crossed... for sound

cheers.. jeffc

[Deleted]

Hi Jeff
Looking good. How much DC out do you have ?
I presume that you have the speaker protector in line ready to protect the speakers ?
There isn't a great deal to go wrong with that for someone with your experience.
Kind Regards
Alex

P.S.
Did you remember to fit the 2.2nF across the 1 megohm resistors of the offset correctors ?

[Deleted]

''fingers crossed... for sound''

looking good Jeff.

use stunt speakers if you have them. my stunts where cheap as chips from the local boot sale.

but

worth every penny in stress reduction.

take care

[Deleted]

Hi Jeff,

Sorry to hear about the plumbing, I assume all tests thus far have revealed nothing too nasty, best of luck with that and coping.

The same goes for the amp, hoping for a room full of sound and not smoke

[Deleted]

Feb 13, 2013 14:20:16 GMT @cjarchez said:

Hi Jeff,

Sorry to hear about the plumbing, I assume all tests thus far have revealed nothing too nasty, best of luck with that and coping.

The same goes for the amp, hoping for a room full of sound and not smoke

Chris
Many of us as we age will have plumbing problems and the need to get up during the night.
I recommend the supplements Saw Palmetto and Pygeum in combination.
Saw Palmetto saved me from a surgeon's knife many years ago.
Pygeum is reported to magnify the effects of Saw Palmetto.
Kind Regards
Alex

[Deleted]

Alex,

Yes I'm aware of this problem that we can all, potentially, look forward to

I was just a little more concerned with the regular PSA checks, although it's good Jeff is is being watched closely.

I'm off to google your "little helpers" in a mo.

[Deleted]

Feb 13, 2013 23:13:08 GMT @cjarchez said:

Alex,

Yes I'm aware of this problem that we can all, potentially, look forward to

I was just a little more concerned with the regular PSA checks, although it's good Jeff is is being watched closely.

I'm off to google your "little helpers" in a mo.

Hi Chris
The right combination of supplements can actually reduce PSA, and even beat Prostate Cancer.
I started using Saw Palmetto,Zinc and Selenium MANY years ago, before it became well known,
after reading the book by Australian Naturopath Ron Gellately, who fought Prostate Cancer and won.


Kind Regards
Alex

health-e-books.com/html/ron_gellatley.html

[jeffc]

Shaun/Chris/Alex,

Thanks for the well-wishes and all the prostate and amp tips. Need to start a "Beating prostate problems" thread . Seriously though, Alex's tips are very good ones and I must get on to these ASAP. Apparently the chances of having problems increases proportionally with each decade, so at 50 you have a 1 in 2 chance of having enlargement and symptoms due to whatever cause, hopefully benign, at 60 a 3 in 5 chance and if you make it to 100 , you won't be missed out on the all the 'sleep-depriving' hassles....

On the amp, no smoke and voltages being OK to the various stages have given me confidence to continue with wiring up.... so I should be good to test for sound in a day or 2.

Alex, yes 2.2nf MKPs have been fitted across the 1 meg resistor in the offset correctors
Shaun, yes I have few speaker pulls lying about from my old car and TVs etc to smoke and not care about, so good there

On with the business, and if successful I’ll post a few happy snaps.

Cheers.. jeffc

[Deleted]

Hi Jeff

looking forward to lift off.

hope it goes well

take care

[jeffc]

looking forward to lift off. hope it goes well

Thanks Shaun,

That's what I was really hoping for too, but having this amp work OK........ well that would be like my chances of winning the lotto, ZERO.....

So where to start with problems - sorry Alex.... but I'm sure you've been "waiting in anticipation" for a long list...
1. R17 500R bias trimmer resistor not touched yet
2. DC offset on either channel L = 1.6mV, R = 19.8mV
3. green LED in the relay of the SPKPRO stays on......, refitted 22K resistors instead of link and 47K, why, beacuse the circuit diagram is really confusing (well to me) here about which or any of the 2 x 22K can be replaced by the 47K, the other by the link, so I removed that problem, but still no go...
4. Resistances measured across 2 x 22K 0.5W resistors on SPKPRO L channel = increases gradually from ~15K to close to 22K, R channel = each reads about 13K and stays there
5. Tp1/Tp2 voltages, each started at ~ 500mV and triming these down, 500R trimmer bottoms out at ~65mV, lid off but amp left on for a while, stays about there. Will the lid on fix this, guessing not
6. L channel heat sink somewhat warmer than the R channel heat sink.

Problem is I'm exhausted mentally from building this and really don't feel inclined right now to be removing boads or changing parts to fix whatever I've Funked up.

cheers.. jeffc

[Deleted]

Hi Jeff
I think I had better get that coffee about now!
Let's get a channel at a time right, without the other one powered up.
A quick answer to one question. If you can adjust the balance down to 65mV, then it should go much closer with the lid on. or even a newspaper over the top to warm up the interior.
I use a nice pair of leads from Altronics with I.C. clips on one end , and banana plugs on the other to go into my DMM.
I then sit the cover on top.
I WILL get back to you with the rest after a bit of research and the help of some morning tea.
Kind Regards
Alex
P.S.
I assume you are using SF11 or SF12 diodes ?

[jeffc]

Thanks Alex,

I'll go buy the Sunday Mail and use the travel section.... or just place the lid on.... for 1/2 h and check again after this.
Yes I have SF12 diodes fitted, K positioned toward the circle marking.

cheers.. jeffc

[Deleted]

Hi Jeff
With the Loudspeaker Protector, just remove both of the bipolar electros closest to the 22k resistors either side of the relay itself.
Looking at the front, with the main large terminals on the LHS , they are the left caps of the 2 pairs.
You should be able to turn off the green LED by connecting a 1.5V battery across the input terminals.
The protection threshold is around + and - 600mV which is more than adequate to protect speakers from damage.
A small improvement in sensitivity can be gained by replacing the 22K resistor from base to earth with a 47K
These are near Q7 and Q10 and connect to the big outside (top and bottom) main earth tracks.
Kind Regards
Alex

P.S.
Let's just concentrate on getting the L channel and the LS Protector 100 % first.
As we both know, no matter how tempting it is, pushing ahead when you are mentally exhausted invariably let's the magic smoke out.

With regards to the other channel, IIRC you have links instead of the NFB cap.
If you have a 100uF or even up to 470uF electro laying around, then with your side cutters, snip through the centre of the link and lift up the ends to tack on the electro.
( don't use much heat. Later on you can remove the electro , push the leads together again and solder across them without having to remove the PCB again.
When you get the chance, and have a had a relatively stress free day at the orifice, fit those nice 8 pin i.c. sockets.
You should be able to safely remove the I.C.s without damage if you use that nice little heated solder sucker you recommended to me.

[Deleted]

Hi Jeff/Alex

As Alex has said one board at a time so power down one side (that’s how I worked when Alex helped me out)

Those DC offset figures look too high by quite a bit so I’m guessing that a good place to start looking would be the DC servo. Did you fit the links for the DC servo? And the link in the FB loop

If so you could remove the links to isolate the servo and pop a 100uf cap in the FB loop and have another look at the offset. If it’s unchanged then we need to look elsewhere.

Luckily enough Will provide links to disconnect the DC servo and also a link for a cap in the feedback loop so that should speed things along a little...
The led staying on could just be the speaker protection telling you that you have to high DC offset so the problem may not be that board at all.

Warmer one side than the other could just be Different bias settings and if you’ve not twiddled the bias trim pots then that’s likely.

I’d not worry about the front end balance until the end when you do a final setup.

Jeff it’s no worries when you are ready we can get started but believe me when I say that you are in good shape if you’ve had no magic smoke.

Luckily enough I found that the front end function of the board can be tested with a regular + and – 20v supply (like the jaycar ones). That was useful in the elimination process.

It’s all fixable so don’t worry and it’s going to be something small. I’ve been building for years and still managed a gaff or two.

A nice photo when you have time would be helpful.

Getting there Jeff

lets see what the Gaffer has to say

Take care

[jeffc]

Hi Alex/Shaun,

Thanks guys for the encouragement and suggestions.. I’ll get to looking into these to try and fix whatever problems there are later, I’m too dejected right now to problem solve and need to attend to home duties I’m getting behind in anyway. Will get back when I’m over sulking and in a more positive mood ……

cheers.. jeffc

[Deleted]

Feb 17, 2013 0:53:38 GMT jeffc said:

Hi Alex/Shaun,

Thanks guys for the encouragement and suggestions.. I’ll get to looking into these to try and fix whatever problems there are later, I’m too dejected right now to problem solve and need to attend to home duties I’m getting behind in anyway. Will get back when I’m over sulking and in a more positive mood ……

cheers.. jeffc

Hi Jeff
How is your little canine friend ? Is she now at peace ?
Kind Regards
Alex

[Deleted]

Feb 17, 2013 0:53:38 GMT jeffc said:

Hi Alex/Shaun,

Thanks guys for the encouragement and suggestions.. I’ll get to looking into these to try and fix whatever problems there are later, I’m too dejected right now to problem solve and need to attend to home duties I’m getting behind in anyway. Will get back when I’m over sulking and in a more positive mood ……

cheers.. jeffc

Hi Jeff

good idea

when you are ready well get started.

luckily enough i've already made most of the mistakes so be cool

take care

[jeffc]

Hi Alex,

Yes she's no longer with us, except for now resting peacefully in our garden, so all up, its not been the best of weeks.
Thanks Shaun, I'm sure you guys can walk me through these problems... appreciated....

cheers.. jeffc

[jeffc]

Hi again Alex,

OK.... first stuff-up identified.......

SPKPRO
1. no link inserted between CON1 +ve and CON2 "AC sense" input, this now fitted to power Q1
2. Checking voltages on transitor pins as suggested in "Troubleshooting", I noted these were wrong for some, and close inspection identified that for Q1 (BC546) and Q4 (BC556), I had these swapped around. So best I get new ones ? for inserting these the correct way about. Any idea whether this error might have affected others?, particularly thinking Q2 and Q3 here. If so, I'll get a few extras just in case.
3. Also for the addition green LED mod, I had fitted a 2.2K between relay + inductor side the now-isolated land of the overtemp input. Seeing I'll need to lift the SPKPRO PCB, is this value OK for a green LED? Might as well try and get this right too.

cheers.. jeffc

[Deleted]

Hi Jeff
Q4 is almost certainly damaged.Q1 should be O.K. Q3 likely to have survived.
I would get all those you listed to perhaps save another trip later , as they should only cost around $2 at Jaycar.
If the front panel green LED is too bright, just increase the value of the 2.2K. 4.7K may be more appropiate unless the green LED is not very bright
Kind Regards
Alex

[Deleted]

Loudspeaker Protection PCB - Suggested changes.

As most will not be using the A.C. Sense Input, a link is needed between CON1+ and CON 2. Either terminal can be used.
The capacitors to be removed are the 2 x 47uF next to the 22K resistors either side of the relay.

URL=http://imageshack.us/photo/my-images/51/part3p2upgraded.jpg/][/URL]

[Will]

Thanks for posting this Alex, it really helps!

What values do you use for R1 & R2, the ones for the 20W Class A?