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SM7UYJ

SM7UYJ

Member
Joined 2004
rcdesign.se
Gain Clone with LM1875

Inputs selectable via push button on front panel - switching + memory function using 16F629 PIC.

An externally hosted image should be here but it was not working when we last tested it.



An externally hosted image should be here but it was not working when we last tested it.



An externally hosted image should be here but it was not working when we last tested it.



/R
 
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Dielkius

Member
Joined 2005
sukyone

sukyone

Member
Joined 2006
bestrunning-shoes.com
sorry for non picture:D
 

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markiemrboo

Member
Joined 2006
My latest and best so far. Three LM3886s in parallel per channel with PSU on the same board. Board size is 100mm by 100mm for the lot (mono). Just connect a transformer, input and output and you're off :)

I am really proud of it because it works with minimal grounding effort, no hum or buzz to be heard and only a very faint hiss from less than 1cm away.

No case yet. That's the next thing. It's going to be made out of real wood though. I'm getting help with it, because I am useless with power tools :rolleyes: I've also got a PIC controlled push button (made to switch a relay on and off) to go with it, with a fading power LED (ring around the power button).

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.



Yay or Nay? :)
 
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markiemrboo

Member
Joined 2006
wim said:
Very, very nice work markiemrboo !!

How does it sound?
Click to expand...

Thanks wim!

I'm just testing it at the moment to make sure nothing bad happens. They are my old speakers, 4 ohm nominal Eltax Monitor IIIs. It seems to drive them very well indeed though. The rectifiers stay stone cold, the heatsink gets fairly hot, but I can keep my hand on it for 10 seconds+ pretty easy.

I seem to remember that using these speakers with my current amp (regulated single LM3886) and old Cambridge Audio A5 on particularly bassy tracks the woofer would give up and start making clunky noises. With this amp it seems to behave much better with the same tracks. Obviously the poor little woofer still has it's limits though.


dudaindc said:
Great stuff Markiemrboo - surely a YAY for construction. :up:

Please provide your impression after listening tests.

Do you plan to publish/share the board construction files? Please? :tilt:

Cheers,

LS
Click to expand...

Thanks dudaindc!

I will try. I am really not good at describing sound though. I probably also need to calm down a bit. I am so excited that it's working so amazingly well, and is so neat compared to previous attempts :angel: I can't turn it off. I set out to test it for an hour and it's been on all day!

I will post the layout soon. I've got a fair bit on my plate at the moment so it won't be instantly! It's oriented towards home made PCB construction though, with blobs of trace around smaller holes (i.e small resistors) so that drilling doesn't lift the traces as easily. I'm not sure how well the layout will work when sent off to a pro place either. Maybe someone can give hints when I eventually post it :)
 
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markiemrboo

Member
Joined 2006
Dennis5587 said:
markiemrboo, how much power does that amp put out?
Click to expand...

I don't have the means to actually test it, but I think (probably quite wrong?) given an adequate heatsink and power supply... it's capable of something like, per channel:

8 ohms - 50W RMS continuous average, 100W peak
4 ohms - 100W RMS continuous average, 200W peak


I'm not sure about 2 ohms. If it was a 2 ohm resistive load then could it manage something like 28Vpk = 14Apk? 14A / 3 (chips) = 4.6A per chip, which is well below the 7-11A limit of the LM3886. That equates to 400W peak / 200W "RMS" in to 2 ohms though, which just seems a bit unrealistic :hot: I can't help but feel that I am missing something with power ratings as large as that from a chip amp....

Power ratings still do confuse me a bit :) I'm fairly sure the first two (8/4R) are realistic though. AndrewT did some calculations for me a while back and concluded that it should be able to cope with the most evil of 4 ohm speakers, but wouldn't recommend trying a 2 ohm speaker.
 
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markiemrboo

Member
Joined 2006
With regards to how mine sounds....

Today I have ripped my old amp, LM338 / snubbered / single LM3886 per channel, out of it's case and placed the new one in to test with my usual speakers, a pair of lowly Celestion 7's.

I shall start by saying that I am not a big believer in amplifiers and such making differences to the sound, so this is purely subjective and may well just be because I am happy it works etc etc etc.

Initial impressions are that bass lines seem very easy to follow, possibly what some might refer to as tight and well controlled. Midrange and treble seem to be sounding really quite lovely. There does seem to be detail that I haven't heard before. Airy echoes and midrange stuff. There is a certain delicateness about it that is just magic. I haven't noticed much of a change in imaging / sound stage etc.

I've just got the house free to myself for a bit and have had a chance to test briefly (I do like my hearing, so I dont tend to listen loud for long) how well it copes "under load". It is also an improvement, much to my surprise! I can turn the volume all the way and it still sounds very clean! The bass seems to have way, way more punch to it, very noticeable. I can actually feel it now...

Very cool! I know it's not much to go on, but subjectively I have to say it does sound nice. Hope that satisfies some curiosity for now :)
 
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