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Group order of non-inverted LM3875 pc boards? Anyone interested?

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BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
Sandy H. said:
Brian,

You (and wifey to be) have been kicking 'B' on the GC kit. I also think a group order on the attenuator is a good idea, but these things must be made of gold! Even with a group buy, I'm guessing you'll get the cost to $50-60 + the resistors yielding an $80+ kit cost, as you mentioned. Is there any way to combine 2x 6-way switches to yield a similar result, with the obvious compromise in user friendliness? I like the idea of an attenuator vs. a pot, but I really am too cheap to pay more for an attenuator than the amp.

What are the other options for those of us who just bug out at paying the bucks for a mechanical switch?

No offense is intended and in the end, I'll probably be interested in an attenuator, just since it is being offered. . . :(

Sandy.
Click to expand...

The cost of the switch alone will be around $70 (for 100 units), unless we get an amazing huge quantity, but resistor prices will go down quite a bit.

As for cheaper options, I used a $3 radioshack dual 100k pot for my first gainclone... The main consideration for a stepped attenuator is to get a shorting switch, so that you don't have an open connection, when changing volume settings. My current attenuator doesn't seem to be shorting, and makes popping sounds when I change the settings. It sounds like a machine gun if I change the volume fast. (This is one of the preassembled ones like jrsun is selling for $50.)

$90 is a lot, but is half the price of the DACT switch:
http://www.diycable.com/main/product_info.php?products_id=274
which uses the same Elma hardware, but different pcbs. I think that it will be better also, since you have a vast selection of resistors that you can use, rather then the SMD ones that the DACT uses.

This seems to be the volume control that I have been searching for, and a perfect match for the gainclone.

Looks like these are sold for $130 each from Percy Audio, $171.50 with holco resistors.

--
Brian
 
V

vsr123

Member
Joined 2003
Transformer secondary Voltage?

Going through the thread I assume the choice of the transformer is a 320VA, 2x24 VAC. If I design to a 6 ohm speaker can I go higher with the supply voltage - say to 30VAC?
Looking at the datasheet at http://www.national.com/ds/LM/LM3875.pdf
it seems that the chip should be capable of handling this without any issues.
My Question is whether anyone has done this and noticed any degradation in sound quality? Some people seem to have used a 2x18VAC with good results but could not find anyone using higher than 25VAC.

thanks
vsr
 
M

MereGT

Member
Joined 2004
Update

Here is a brief shipping update. Today I only got out 18 orders, a few less than the 24 I sent yesterday. I hope to get out another 20 to 30 orders out tomorrow. Hopefully all the orders will be done by next thursday at the lastest. Brian is trying for next tuesday, but he tends to be overly optimistic!
-meredith
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
Peter Daniel said:
I thought it was Grand Touring;)
Click to expand...

Yeah, I have gotten this question several times... I tried to think of an alternate name, and considered changing to "Brian Bell" for a while. In the end, I decided to stick with it.

GT does stand for Georgia Tech, and I graduated in December with an EE degree.

I actually just registered BrianGT.com yesterday, for $12 a year, so I guess I am stuck with this name for a while.

--
Brian
 

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BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
Da5id4Vz said:
Inexplicably our friend has some spare time for experimenting:

http://www.diyaudio.com/forums/showthread.php?postid=352209#post352209

Very interesting.
Click to expand...

Not too much time invested in this yet.. I had the idea at lunchtime at work today, and when I got home, I had the heatsinks sitting across the room, and Meredith's assembled boards on the coffee table, so I decided to take a picture, and see what other's thought about this idea for a project. I even have a transformer sitting in my office room that would work in this thing... It is just asking to be built in a few weeks. I can't help it, or even find a reason that I need a higher powered amplifier. I spoke to National, and they said that the LM3875 would work just fine in this setup, but not as much power of heat dissipation as the LM3886 in the same setup.

Kits are still being put together right now, and more will be mailed out tommorrow.

--
Brian
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
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