My first shot at an IGC

[Aunkst]

Well I have been collecting parts, and reading everything I can find on building a Gainclone. Last weekend I built the power supply. yesterday and today I built the amps. I am very satisfied. I ran into NO problems, I used the schematic from Decible Dungeon, I built EXACTLY as the plans show and the worked perfect on the first try. I plan to build a case around them later as time allows, Maybe using more acrilic as the tom or front, we'll see. What do you think about my layout? I tried to stay as symetrical as possible.

Thanks for all the info, DD especially.

[Aunkst]

I attempted to post a picture with my post, Do I just use the attach file function?

[nemestra]

Originally posted by Aunkst
What do you think about my layout?

Well done. Hope this encourages you to do more DIY. Did you mean to include a drawing or photo?

James

[Aunkst]

Yes, I tried to include a picture. Is there some trick that I am missing to get a picture to show?

I have been DIY ing everythig I can for a while now. this was just my first stab at electronics. Very encouraging.

[Nuuk]

Yes, an excellent first attempt. Well done!

When I see successes like yours, it makes all the work of creating those Gainclone pages more than worthwhile!

[Albo]

Hi Everyone.

First time on this forum. Just built this.

http://server6.uploadit.org/files/alnewall-DSCF0002.JPG

It's a fairly basic interpretation of the Decibel Dungeon one.
Been running in for around 6 hours now and sounding quite impressive. Not so far removed from the valve sound that I am used to.

This is the first thing I've ever built, apart from speaker crossovers. So a big thankyou to NUUK for his superb plain english website.

This was a great way of learning the basics and gaining a bit of confidence.

Bye for now.
AL

[Nuuk]

Congratulations to you too Albo - another nice neat layout and I see, like me you use your local hardware shop!

Building on a piece of wood is an excellent way to build a Gainclone before putting it into a case. My OPA buffered IGC is still on its plank after more than seven months though!

Seems that we are doing well in 'spreading the word'; what next? world peace?

[Aunkst]

I just checked the DC offset at the speaker terminals,

I got 21mV.

Is this too much?
I asked my electronics professor and he says that ANY DC is too much and he recomended putting a 100uf cap in series with the output.

what do you think?

[Albo]

Aunkst.

Did you put the 216k resistor in, between pin 7 and signal ground?

This dropped the offset on mine to less than 1mV. Although it wasn't very high to start with. This addition was mentioned after the build instructions, but not on the schematic.

Albo

[Joe Rasmussen]

Originally posted by Aunkst
I just checked the DC offset at the speaker terminals,

I got 21mV.

Is this too much?
I asked my electronics professor and he says that ANY DC is too much and he recomended putting a 100uf cap in series with the output.

what do you think?

What? #&@&%#&*@%*!... Oops, forgot that I don't swear.

It will kill the DC all-right, it will probably also kill the sound. It will most definitely kill the bass as 100uF just isn't enough. Even 1000uF will get you -6dB at around 20 Hertz.

No, 21mV is not too bad a result, I have a friend's NAD 317 amp here and it had a bit more than that, so in a commercial product this was deemed OK. Personally, when possible I'd trim it down below 10mV. In direct coupled power amps there is always a small DC offset, it's just a matter of it being acceptibly low. To get zero is unlikely, nay near impossible! Unless you put a dirty (and likely sounding that way) big electrolytic cap there and no DC... oh the leak at bit, don't they? The whole idea of direct coupling circuits was getting rid of that cap in the first place, because from early on it was considered undesirable.

So what is the effect of the 21mV?

Assuming, in your case, near worse case scenario, low 4 Ohm speakers, DCR of voice coil 3 Ohm, then 21mV:

(0.021/3)*0.021 = 0.000147W

So 147 microWatts dissipation in the voice coil, and even much less than 100uW with 8 Ohm speakers. I would'nt loose much sleep over that and neither should the good professor.

Happy listening.

Joe R.

PS: Would you be game enough to print this out and show it to your professor. It could be interesting to know his reaction?