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Old 26th May 2013, 06:48 PM   #201
dvv is offline dvv  Serbia
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Let's hope so, Aniket.

But, we cannot know it's all right until you connect the specified power source. Only then can we be sure.

So, let's not open the champagne bottle just yet, a little more patience will not go amiss.
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Old 26th May 2013, 06:59 PM   #202
Mooly is offline Mooly  United Kingdom
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Originally Posted by dvv View Post
Let's hope so, Aniket.

But, we cannot know it's all right until you connect the specified power source. Only then can we be sure.

So, let's not open the champagne bottle just yet, a little more patience will not go amiss.
Indeed.

And you really need to revise that input filter too. Increasing C3 is really "fiddling" the issue. You don't need alter the PCB. Just replace the input cap with a cap plus series resistor and change the input filter cap value.
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Old 27th May 2013, 03:25 AM   #203
Aniket is online now Aniket  India
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Hello dvv,

i sent you a mail on your id: dvv@beograd.com, but it bounced back.
better you can mail me at aniket.ani_sharma@yahoo.co.in

Regards,
Aniket
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Old 27th May 2013, 04:45 AM   #204
alex mm is offline alex mm  Europe
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Hi,
I'm pleased to hear it's working your amplifier , but I can't see the output coil ...... or it's a link somewhere on bottom PCB , with wire ?
Regards ,Alex
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Old 27th May 2013, 07:59 AM   #205
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Hi Aniket . Here is an idea I have tried . Run it through the simulator . The values should be OK to get an idea . The purple node might be best ? I suspect the purple also can have a more even split of values . On the purple version I was able to use 100 R ( 56 + 270 pF on mine ) . The idea is to win back some HF performance whilst maintaining stability .

Here is a Darlington VAS ( etc ) that seems almost too good to be true !

Single darlington line preamp.

Last edited by nigel pearson; 27th May 2013 at 08:03 AM.
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Old 27th May 2013, 09:02 AM   #206
dvv is offline dvv  Serbia
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Hello dvv,

i sent you a mail on your id: dvv@beograd.com, but it bounced back.
better you can mail me at aniket.ani_sharma@yahoo.co.in

Regards,
Aniket
I may as well say it here and now.

You have all read my whining and moaning about how incomplete DIY projects are, lacking even the most basic protection and amenities. Well, anyone can whine and moan, but the real thing to do is to sit down and do it the way you think it should be done, hopefully achieving excellent results. Even knowing that excellence is most often the result of a long development process.

So that's what I did. Then, when I had a working model in my simulator I was sastisfied with, I asked Alex mm to work his magic. This morning, he came back to me with the first of TWO piggybacked boards, I suspect the big one. It looks like a million dollars.

So, Alex, since I am experiencing unexplained problems with uploading pictures from my PC to this forum, you do the honors. Please post first my PDF schematic, then your current board and when you complete it, the second board as well.

A few points you should know, as you will when you see the schematic.

Quite by chance, my take on this is almost the exact opposite of Aniket's. He opted for what I feel is an atiquated design, from the early 70ies, when it was felt that NFB could solve all problems. My design logic is much more recent, I believe in high local NFB (correct the problem where it begins) and relatively low global NFB. In other words, make it so that it might just work with no global NFB at all, and then use global NFB to polish it up, as an icing on the cake. Off hand, Aniket's global NFB was around 80 dB (10,000:1), mine is just 20 dB (10:1).

This is the result of my understanding that THD, as an absolute value, has NO BEARING WHATSOEVER on the sound, assuming it stays below say 0.3% in the very worst of cases, by which time the amp is dumping over 500W into 2 Ohms.

In other words, the topology which Aniket used was developed to promote specifications at a time of specs wars among manufacturers, while my topology was developed with good sound in mind. Of course, this is certainly not to say Aniket's topology cannot produce a good amp, of course it can, it's just much harder, the odds of achieving that are in my favor (oods, not a guarantee).

Last note: many, if not most, of you will be frightened by the parts count, around 200 bits and pieces. However, understand that as you add this or that subcircuit, the components tend to add up very quickly. And it has regulated power supplies for the input and VAS, protection from overheating and excessive DC, overvoltage and overcurrent, DC offset adujstment taken as much out of the signal path as possible (a completely separate circuit), and full signal status indication, for showing power on, signal present, nominal 0 dB VA (nominal output) point and clipping, all supported by LEDs.

However, you can always leave out any and all of it, except the DC offset circuit, which is simply too useful to be skipped no matter what anyone says, including Nigel.
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Last edited by dvv; 27th May 2013 at 09:05 AM.
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Old 27th May 2013, 10:55 AM   #207
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Hi Dvv , Aniket . DC offset < 100 mV is OK . To be frank I never had it above 40 mV if working correctly . A Rotel RA 931 I fixed recent was an identical 75 mV left and right . I am told some designers do that to reduce crossover distortion ( no idea if true or why ) . A device to detect and protect is great .

My two pole VAS EQ . I suspect 56 + 270 will work for you . The output stage is not the same as the rail or ground . I would imagine it would require more work . I did get very good results especially after 20 kHz when I tried it . I include the rail as I think it was easier to drive in an amp I built ?

For fun I have added a DC offset control to a 741 mic preamp ( it looks like a power amp ) . These days a NE5534 will exceed it in all ways and cost less ( BC560 might have lower noise ) . The BC 560's and current source almost makes a 741 into hi fi . Many recordings that are well respected used this ( 2N4403 's ) . The values in purple are for +/- 40 to 60 V approximately . A friend says some mixing desks still in use have this !
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Old 27th May 2013, 11:27 AM   #208
Aniket is online now Aniket  India
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Thanks all,

i would take some time to simulate your mod Nigel.

@dvv, i strongly suggest you to upgrade your simulator to a newer version, the version 12 i use has all the necessary models from ON semiconductor, Texas instruments etc. if not version 12 then upgrade to version 11 atleast. I have used 10.3 version you are using and there's a lot of difference in simulation results of both version for the same schematic. that is why you are getting odd simulation results.

i have one more update, i bought new 2n5551/5401(philips) transistors, and replaced bc546/556 with them. also connected a 1.8K resistor in series after the input cap(2.2uF). did some testing and DC offset now is +8mV and exactly 0mV for channel 1 and 2 respectively. sounds all good.

Regards,
Aniket
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Old 27th May 2013, 11:54 AM   #209
dvv is offline dvv  Serbia
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@Nigel Pearson

Nige, 100 mV of DC is NOT all right simply because it's so easy to make that number much smaller.

If it does 100 mV of DC with no signal, what might it be doing when dispensing 200 Watts into 4 Ohms?

@Aniket

Many thanks for the tip, Aniket. My version also has some Motorola devices, but is otherwise not too well supplied with models of semiconductors.

I will look into it ASAP.
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Old 27th May 2013, 12:34 PM   #210
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When I square-wave tested the idea it worked OK . I think it does produce a mild overshoot which I think is acceptable . Sounds good ( more open ) .

I have no experience of amps with DC oftest at 100 mV doing any harm . I will ask around my PA friends to see what they have to say .
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