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DIY-project with LM3886 - Page 2

post #16 of 27
Thread Starter 
Hello again!
Another question just came in to my mind:
I started discussion bout the cmoy-amp on a PCB.
Would you construct a PCB or solder the pins more or less directly anyway ? I actually would like to do it with a PCB but not sure about noises and oscillations with the PCB.(I know that there exist a hansen PCB but don´t want to buy that)
I want to use a OPA604AP.Is that thing enough for a 32Ohms headphone?
If you like building headphoneamps : I got a circuit from a magazine which looks interesting and is supposed to be from high quality.Can send it off if you´re interested.
post #17 of 27
I put all projects i intend to use on PC boards. I only Do bred boards when Exparamenting and latly it seems i am making boards for my Evaluation projects. I think bread Boards belong only in the lab not in the Field or your home. But Bread boards work verry well for most folks hear and you can design a working circuit while thinking about it. BTW my first bread board was in the classic sence a lenght of plywood with Nails for Solder Lugs. and this was using tubes. Nice smell.
post #18 of 27
Thread Starter 
The amp is finished.
I wished I would have invested money in a case.Man this was a struggle.(Don´t like metal work)
Well, the amp sounds cool.
My only concern is that even with full volume it doesn´t blast really (and I´m not extreme).I used a 10K stereopot and there is a 22k resistor in the feedback paralleled by another 22k and a 47p cap in series.As I mentioned before this is a finished design and it said you should use 24V secondary trannies,maybe that´s the point that I have to change the feedback loop.
I used a 2*18V transformer and have about 27V at low volume.
I can´t trace it at the moment.Maybe something dumb I´d overseen.Maybe just my ****ty speakers which will obviously be my next project.
If you´re interested I can send you the design.
Ramble on!
post #19 of 27
Is the Amp Clipping at these levels or is the gain just to low? If the amp is Clipping Measure the Powersupply Both at full power and no signal if the voltage drops dramaticy a larger Transformer it should be rated for about 3 Amps@24VCT. Otherwise measure the output voltage of the amp into a resistor and calculate the Power whitch should be at least 28 watts typicaly 32 watts.
post #20 of 27
Thread Starter 
The amp isn´t clipping at all.It sounds cool.
Just that I can turn up the pot and still can sit next to the speakers.My marantz amp has got 2*50W and I can´t turn it up even half way in my room.So actually it can´t be the speakers either (simple magnats rated at 120W,4-8Ohm it says on the back)
The trannie I used is a 220VA,18V secondary which should be enough as well.About 27VDC that fall only a little with full volume.
I think it must be the gain and so the feedback loop I have to maybe change a little to make it more effective.
I just can´t understand the equations really in the datasheet and am not sure bout the pot on the input.
I started discussions on specialized IC-amp site posted in this forum and try out a few things.
Thanks for suggestions and I get back if I know more.
post #21 of 27
You can get more gain by reducing the value of the Feedback Resistor from the (-) input of the opamp to Ground. Try a value about half of what you are now using, This will raise the gain if thats not enough then decrece the Resistors value again untill it is where you want.
post #22 of 27
Thread Starter 
Hi ppl!
I was away for a few days and didn´t try.
But what you write really confuses me.
Somebody else told me to take a bigger Rfeedback to rise gain
which sounds logical to me cause isn´t it calculated like a normal operational non-inverting amplifier:
Vu=Rfeedback/Rtoground+1 ???
I think I´ll just try that and get back to you.
thanks and greetings
post #23 of 27
You could do it eather way, But since Changing the resistor around the Opamp will Change the values of the Compensation Network I like to Keep things simple and just change one Part not several. Also regarding yoyr Power supply you should have +24 and -24 Volts to get 30 Watts into 8 ohms with this chip. this will also give 60 Watts into 4 ohms if your supply has the Current.
post #24 of 27
Thread Starter 
i mean i got +-27v so this is OK?
it falls anyway and the peak protection should be okay

(by the way,where can i find the ultraregulator you used,
maybe i go for a bigger case and add that too)

the amp sounds so good that i even thinking about using this for my hifi setup; any proposals for toggle-switch for the input (at least 5*IN) i can get here in germany?for example sony,panasonic,pioneer..
(i work in a tv-shop here so i got connections to most of the tv-companys but not stuff like radioshack)
post #25 of 27
Decades ago i to Did TV/ Audio Service Then moved up to otherthings. Boy you are in a gold mine for parts just look through the service manuals of Different HI-Fi Components and order through your shop whatever Kinda switch you want. No radio Shack in your Area I thought thay were World Wide? Maby just on the Web. Good Luck
post #26 of 27


They should have anything you need (although their prices are kinda high)


post #27 of 27
Thread Starter 
yeah, you´re right it´s kinda lot parts flying around here
and what my boss doesn´t know won´t make him hot.lol
i always wanted to try those specific tv-transistors(bu508 etc)
for a hifi and check out if they sound ok but i´m just too lazy
and woffling about electronics studies as well so.
sad that we do 95% tv stuff
so not so much hifi"rubbish" around
and i haven´t thought about looking in the service manuals
which is a good idea
thanks for the real cool support
stay cool and keep the forum "delivered"
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