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PostPosted: 22 Oct 2012, 07:57 
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Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
guicam,

what is the value (resistance) of the potentiometer?? Do you have any other informations about it?

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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: 22 Oct 2012, 08:31 
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Joined: 24 Dec 2011, 12:43
Posts: 6
There's written "25k 728m piher" on it so i guess it's 25 kohm, even though i can't remember that from when i buyed it.


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PostPosted: 24 Oct 2012, 10:30 
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Joined: 24 Dec 2011, 12:43
Posts: 6
It seems that the pot isn't actually logarithmic. I guess i'll just get an Alps.


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PostPosted: 25 Oct 2012, 13:31 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
giucam wrote:
It seems that the pot isn't actually logarithmic

That's what i thought too. Linear pots turn loud very fast while logs are very smooth to adjust.

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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: 03 Nov 2012, 07:12 
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Joined: 31 Aug 2012, 11:35
Posts: 13
Location: Erlangen, Germany
Hi everyone,

just wanted to post some pics of the finished project.

The amp sounds pretty good. Not sure but the bass seemed to be
lacking the first time i tried it out but it was probably due to the input impedance of my
preamp, which has a 500 ohm output and a 2k ohm RCA output. Orig. i used the 500
ohm one, so this was prob. the reason. I will experiment some more here. Input
coupling cap is 2.5 uF.

The "only" remaining problem is some hum. No matter how loud i turn it up, its there
and has a constant level. It's not super loud but def. noticeable when no input signal
is present. It's probably due to the transformer being so close to the boards but i
wanted this project to be as small as possible. Or maybe there is some ground loop
present somewhere. Psu and amp boards are not grounded to the chassis but only
to one another.


Regards,
Chris


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PostPosted: 11 Nov 2012, 07:34 
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Joined: 31 Aug 2012, 11:35
Posts: 13
Location: Erlangen, Germany
Hi everyone,

after experimenting a bit with the position of the transformer, I determined
that the hum is mainly due to the transformers position/orientation.
When i moved it outside of the enclosure almost all of the noise was gone.
If i put it in vertically near the rear panel, i was also able to get rid of most
of the noise.

Other possibilities might be to cover it with aluminum sheeting in the horizontal
position but i don't really have enough space for that.

So i will probably modify the enclosure, since i still have some left over aluminum.
But in order to secure the transformer vertically, i will have to cut a rectangular hole
in the bottom of the chassis. So the trany will hang out of the bottom of the chassis
a bit. This should be fine, since the enclosure has rubber feet that are about 12mm
high.

The other problem is that i won't be able to use the fused power socket anymore due
to insufficient space. Which is a bit unfortunate, since it allowed for easy transporting.

Regards,
Chris


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PostPosted: 29 Nov 2012, 21:51 
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Joined: 05 Nov 2012, 06:04
Posts: 1
Hi Tom!
Can i make PSU with 2 10000uf cap ?
if i use them then you can suggest me the new schematic or reduce any cap ?
my english so poor :blush: i wish you can understand
i'm beginner :|


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PostPosted: 24 Dec 2012, 14:36 
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Joined: 24 Dec 2012, 14:28
Posts: 1
ixcoatl wrote:
I built your TDA amplifier and worked pretty well at my first try (which is great because it's the first time I try something like this). I was really excited when the first channel was finished and started throwing out perfect un-distortioned sound.

But now that the 2 channels are done I find the sound somehow 'boxy'. What I try to say is that it is not crisp, I sounds like if its behind an obstacle or something like that. No distortion, the sound is 'whole', all the details are there, but no shinning as I would expect.

I used standard cheap components that I found in my local electronic store and changed the power supply to use two 18V 2 Amp transformers instead of the one in your diagram that I couldn't find. I also changed the potentiometers to a 50k one (the 25k were sold out).

Could the standard quality components be reducing the sound quality? Or the 2 amp transformers maybe? The potentiometers?

What is value of the pot which you are using? If it is 100K then try 10K as there might be a high frequency roll off cuased by the high resistance of the pot.


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PostPosted: 08 Jan 2013, 21:43 
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Joined: 17 Nov 2012, 21:32
Posts: 3
Hi, would it make any sense that attaching both TDA's to the same (conductive) heatsink would cause a decrease in bass response? When I first briefly tested the amplifier without a heatsink, I am sure that the bass response was absolutely fine (quite warm and musical, in fact). However, I have now installed an aluminum heatsink to which both TDA's are attached. There is a conductive path between both of the metal wings on top of the chip, as verified by my multimeter. I would have thought this shouldn't make a difference, but I don't know if the "fin" of the chip actually becomes a part of the TDA's internal circuit... like some kind of grounding perhaps.

Anyway, it's really hard for me to remove the heatsink to retest, so I wanted to know what you guys thought about this before I do anything.

Sam


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PostPosted: 08 Jan 2013, 23:13 
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Joined: 17 Nov 2012, 21:32
Posts: 3
Hello again, after a bit more investigation the conductive path provided by the heat sink seems to be a non-issue. I slipped a piece of paper in between one of the TDAs and the heatsink, and the bass was still not present.

What I notice is that it seems that after giving the amp a long rest period, the bass is present for a period of time, before slipping back away. I can't verify this 100%, but I have noticed it twice, in both channels at separate times. Does this indicate an issue with the power supply? What do you think?

This has been a fantastic few months of planning, learning, and building this fine amplifier. I feel that I am so close, and I can't wait to have a solid hand crafted amplifier unit for years of enjoyment down the road. Thank you for your advice in helping me accomplish that goal.

Sam


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