'LGT' Construction Diary

[ShinOBIWAN]

Worked on an amp on this evening. It makes a nice change from the all consuming speaker work which does get both tiring and a little boring.

[imjatse]

As usual, your work looks like junk.

Seriously, very nice! Was there a link further back in the thread to the amp kits / housing?

And they even look to match the speakers!

[edit] 4 channels right? That might be exactly the project I was looking for.

[wigginjs]

Soft start circuit?

[wigginjs]

Oh, also, transformer specs?

[Bratislav]

Very nice.
As far as soft start, inrush supressors a-ka thermistors are widely used by Nelson Pass in his designs, so it can't be that bad. Put one CL-60 or similar in primary of each toroid and forget.
There seem to be enough room for a mains DC blocker too. They can be useful if your mains is "dirty". Even best toroids can buzz under load if even small amount of DC is present. Though, at low bias Greg uses in his SKA's it may not be as critical as in hungry A class monsters. Still, planning one from the start saves you redesigning later (who, me, never )

[ShinOBIWAN]

Originally posted by imjatse
As usual, your work looks like junk.

Seriously, very nice! Was there a link further back in the thread to the amp kits / housing?

And they even look to match the speakers!

[edit] 4 channels right? That might be exactly the project I was looking for.

Thanks. As for the bits, they came from these places:

GB300D amp modules and GB300S PSU's are kitsets designed by Greg Ball and available here:

http://www.ska-audio.com/diy/

Chassis is the ATI 639M from ATI Research:

http://www.atiresearch-anodized.com/products.html

[ShinOBIWAN]

Originally posted by m0tion
Soft start circuit?

I'm still debating where to put them and will have to experiment with positioning to ensure a hum free amp. Most likely spot will be vertical squeezed down the side of the transformers.

The soft starts are a pair of Hypex types:

http://www.hypex.nl/docs/softstart.pdf

Transformer specs are four 500VA with 240v primary and 45v secondaries.

[ShinOBIWAN]

Originally posted by Bratislav
Very nice.
As far as soft start, inrush supressors a-ka thermistors are widely used by Nelson Pass in his designs, so it can't be that bad. Put one CL-60 or similar in primary of each toroid and forget.
There seem to be enough room for a mains DC blocker too. They can be useful if your mains is "dirty". Even best toroids can buzz under load if even small amount of DC is present. Though, at low bias Greg uses in his SKA's it may not be as critical as in hungry A class monsters. Still, planning one from the start saves you redesigning later (who, me, never )

Hi

I have a few of the thermistors and they work well but the Hypex soft starts allow the amps to be turned on via a relay meaning I can run a wire using a 2 pin connection between the amps and preamp. The preamp is then able to power up or down all 10 channels channels of amplification spread across three cases when it itself is powered on or off.

[Bratislav]

Originally posted by ShinOBIWAN

The preamp is then able to power up or down all 10 channels channels of amplification spread across three cases when it itself is powered on or off.

Now, that is useful ...

[ShinOBIWAN]

Can anyone help me correctly identify where baffle step is occurring please. I'm not sure whether its 800hz or 1.2Khz or maybe something completely different.

This is an unsmoothed plot of a single 5" AT mid running fullrange and with some basic correction:


This is a smoothed(24dB/oct) overlay of raw response, corrected response and corrected with XO in place. Ignore the data below 300hz as it isn't accurate.


Here is a comparison of Audiotechnology's measurement of the 5" driver I use on an IEC baffle vs. my driver mounted in the enclosure.




Thanks
Ant