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PostPosted: 24 Jul 2009, 18:35 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
Hi all,

in the last weeks, i had the chance to build up a gainclone with the LM3886 IC on protoboards. The amp uses a circuit without the muting switch (shorted by resistor) and some little added / changed stuff, but not really new stuff. (Only my often used "tuning"). If someone has interests for this - please do a short post.

At saturday i'm away for the next 2 weeks. (without i-net). After then, i could release the plan / circuit.

Have fun ;-)

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 25 Jul 2009, 16:38 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Tom, have a nice vacation. We will want to see some details when you return.
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 10 Aug 2009, 06:08 
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Hi Gio, Hi all!

Now i'm back @ home and lucky to be here again. OK - i'll put the details on the site asap. First i have to do the schematics. It should be ready on tuesday. Maybe earlier (tonight).

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 10 Aug 2009, 08:58 
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Welcome back Tom. How was the vacation? Looking forward to your GC.
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 10 Aug 2009, 21:17 
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Hi!

Thanks Gio, very very nice! After some weeks with a lot of trouble and work at my house, this 2 weeks were like in heaven. But - also 2 weeks without the hot iron and more weeks filled with work to come... I'm looking forward to the next holidays ;-)

OK - here it is. Done in a few weeks, hour by hour, piece by piece - the GC - built with the LM3886 ICs. First i wanted to build an GC with the LM3875 chips, but they are hard to get here. So - why not use the 3886?! The enclosure is an 19' rack type and the circuit is built on protos. The PS is powered by one 2*30VAC / 160VA / 2,6A (per channel) toroidal tranny using the CarlosFM supply circuit (what else?!). The complete supply is 84VDC +/- filtered with 10KuF per channel and buffered with 220uF at the chips.
Attachment:
gc_ins.jpg
I'm very happy with the sound! The bass is a bit decreased by adding an 4,7uF cap (6,8uF in total) to cut off the lower frequencies. Otherwise there was too much bass... The mids and heights are very fine! The muting circuit is bridged. There was no need for an mute switch. Mute is set to =/> 0,5mA for max. output.
Attachment:
LM3886_GC_pers_used.JPG
It wasn't very easy to get the ICs on the protos. The ICs had to be mounted with an 45 degree angle on the boards.
Attachment:
boards_r1.JPG

Have fun ;-)


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 11 Aug 2009, 12:20 
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Hi Tom, very neat protoboard work. :up: It is remarkable how good this little amps can sound. I'm sure you will enjoy it.

At 84V you are right at the upper limit of the chip. I imagine the chips must get pretty hot when you start to push it. Have you had any thermal problems? Also, how much DC offset are you measuring?
Cheers

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PostPosted: 11 Aug 2009, 13:58 
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Hey Gio, thanks!

There were no thermal problems until now. But - I must say, that i hadn't any chance, to drive the amp to the limits. The power is enormous and with the selected values it runs slightly at the limit. The muting circuit is completely turned off and the 84VDC (V+ |+| V-) are nearly the max allowed. The 3886 can handle up to 94VDC (V+ |+| V-) spike with no signal. When the amp is connected to the speakers in the living room i can turn the pot only to about 30% - then it's really very loud... The sound is great!

I can't say something to the DC Offset now. First i have to measure it, but I think that the signal output is very clean (free of DC). Same as the TDA2050. My speakers are very unhappy with low ammounts of DC. Imho - with low DC ammounts they sound very - hmm - "washed" or distorted or somewhat else. I'll measure it and post the results later. If there is DC-Offset is at the output i'll surely add some blocking caps at the output. Thanks for the hint!

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 12 Aug 2009, 09:51 
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Have never even considered running the rails that high. I wonder what the quality in sound is vs maybe 24V. Something to try someday I suppose.
The protoboard work is really nice Tom. As good as any pcb for sure. The amps layout in your case is nice and clean. Congrats!
So.. the real question... Does it glow in anyway? Someone once said "doesnt glow, doesnt sound". :)
Uriah

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PostPosted: 12 Aug 2009, 12:33 
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Just a couple of extra quick "checks" that I always do with a new chipamp prior to powering up for the first time. If you are using a metal tabbed chip, make sure that there is no continuity between the tab of the chip and ground. If there is, you will blow chip on application of power.
tombethe wrote:
I can't say something to the DC Offset now. First i have to measure it,
Another check I always do before attaching a speaker is to measure the DC offset. It does not take much DC at the output to cook a speaker.

So Tom, have you done a comparison with your TDA2050 chip amp?
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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PostPosted: 12 Aug 2009, 14:10 
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Hey Uriah - lol - yes, it doesn't glow, but it does sound - and not soo bad ;-)
I have no idea how the amp sounds at lower voltages. I didn't test it with other PSUs because it was planed to run it at the max. available power.
The amp must drive a pair of HK PAs (HK AUDIO RS 153 POWERWORKS) in a party room. Thanks that you like the boards. I can tell that it wasn't very easy to solder the connections / rails on the backside because there always was the 45 deg. angle from point to point... The backside looks loke a snake's nest. But - i was very happy that i could get the ground to 1 single line / lead...

Yep Gio, the chips packages are not isolated. I checked out the tabs to the chassis and to ground. The silipads i used work great and they also have good thermal properties. OK - surely, i compared the 3886 to the TDA2050. I was that curious that i couldn't wait to hear both in a session... Now, the differences between both amps are not easy to describe. I have really(!) good ears but it was hard to find the right opinion. Now - both amps have an very deep and crispy bass. The 3886 imho is able to reproduce lower frequencies (for this, i built in a higher cut off). Tha bass sounds very hard or punchy (don't know better how to say it). The 2050 is a bit softer but even very deep. Both amps are able to reproduce clear and detailed mids. The 3886 is slightly more detailed and has a wider stage. It seems that the room gets a bit larger while listening to it. On the other side it could have more and finer weighted heights. At this point the TDA sounds more sharp and still very clear - but, i miss the stage a bit.. It sounds more compressed. Not dull, but i missed something... At the end - i like them both.
I couldn't compare the 3886 at headphones. I can say that the TDA is nearly as good as the Szekeres when it's connected to the phones. As said, the TDA is a bit sharp.

I still didn't measure the DC-offset... Meeen - i really should do that in time... (my opinion is, that it is clean, but who knows)

The next amp surely glows ;-)

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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