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Colin Wonfor's SECA amp build

Nice suggestion.

I'm the one using the open plan design ATM (children long gone) and have a dedicated listening room so no pets allowed.

No real issue with air circulation due to lack of case but it may be nice to get the fan up and running now.

Not really looking for the Max out bias wise (yet)just a little more room to breath heat dissipation wise.

or I may have a play with that now just for fun.

I'm a bit of a PC dunce so any suggestions on a nice quite fan would be helpful.:)
 
PigletsDad said:
To be honest, beyond about 200W dissipation, you really have to use a fan; there are some very quiet ones available now, intended for PCs.

The way of using it that I like best is to put the fan in the middle of the back panel, blowing past the PSU, and arrange a gap between the bottom of the case and the heatsinks, using spacers of some sort. The bottom panel extends out to the tips of the heatsink fins, and turns up by say 5mm. This directs the flow of air up the heatsink fins, reinforcing the natural convection. Even a small fan greatly improves heat transfer. For example, 40 cfm used well is equivalent to about 0.045C/W, which would need a natural convection sink the size of a wheelbarrow.
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Hi Dad,

My original TOCA at 300W Mono took 1800W to run here is a photo without fans. But it was a big heatsink and it got to 50C at a 20C ambient.

11102903_1406623836322643_4173622224759900736_n.jpg




The caption does say 200W but he who wrote it did not read the 300W on the baby mono amp.

Oh here is the family, 20W,50W,100W,200W,300W.

10981614_1406623902989303_1108928776440984274_n.jpg


So it can be done if you can afford the heatsinks and the electric bill.

P.S.

Just a after thought the 300W had 80 MOSFETS and 80 Darlingtons and 3 banks of 1.5F of caps and a 3KVA transformer, a mere toy.
:D
 
Stop messing about ;) , if you can make sound adjustments to your listening room then with just another small tweak...

A2%20Wind%20Tunnel%20Test%20Section.JPG
 
Could also check how aerodynamic my paunch is:D

Any way back on track. Col would you mind explaining in easy to understand terms ow the tracking p/s works for those of us(me) with only a little electronics knowledge. Thanks.
 
Marra said:
Could also check how aerodynamic my paunch is:D

Any way back on track. Col would you mind explaining in easy to understand terms ow the tracking p/s works for those of us(me) with only a little electronics knowledge. Thanks.
Click to expand...

Have just spent 20min writing a explanation the PC switched off I hate digital crap.
So I will start again. grrrr;)
 
The Sliding or Dynamic PSU

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As you can see the +V and –V regulator are based on the LM317 and LM337 chips, these drive current gain stages and have a very simply current fold back current limit using 0.1R resistors to set this to about 6A.
This current limit allow the 10,000uF and the SECA’ s 33,000uF capacitors to charge much slower and this will increase their life and reduce the ON thump.

The basic just SECA board has a ripple voltage of about 500mV but with the PSU this is reduced to approx 5mV, this will show itself as more detail at low levels when using the PSU together with the SECA.
The losses across the FET are there because we have a Gate Source voltage of about 4 – 5V so the FET cannot drive to the +V rail, the Darlington in the original has a voltage across it of about 2V and thus it cannot swing to the –V. So to use the full range of the power/volts available we use the PSU board with all the advantages mentioned before. In version 2 with the 2 FET’s the –V is not such a problem as we only lose about 200mV max.

Now as the output approaches the max regulated +V or –V on peaks the PSU ref is also moved and as it approaches 10V peak the PSU output voltage changes and allow the FET/Darlington to get to the max voltage it can, this gives you more punch and dynamic, this will show up on deeper bass and fresh top end.

Does this help ??
 
CJ14 said:
Having tried that 10,000uf 50v worked very well indeed.

But link out the correct diodes, and get rid of that long bit of wire.
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just a quick question re the SECA PSU caps (the ones on the SECA board not the dynamic PSU) which I believe can be changed in value once the Dynamic PSU is installed.


my question seemed to get a little lost in the fan dance:D


I was going to change my SECA PSU caps to 10,000 50V as mentioned in the above post. my understanding is that the regulated supply allows smaller cap values to be used On the SECA board and letting the reg to do most of the work. ripple should as you've mentioned be much lower so any need for the bigger cap value in that spot?


But maybe I've missed something (which would not be unusual).:cool:


Thanks for the PSU explanation which makes sense and helps plenty.
 
shoom said:
just a quick question re the SECA PSU caps (the ones on the SECA board not the dynamic PSU) which I believe can be changed in value once the Dynamic PSU is installed.


my question seemed to get a little lost in the fan dance:D


I was going to change my SECA PSU caps to 10,000 50V as mentioned in the above post. my understanding is that the regulated supply allows smaller cap values to be used On the SECA board and letting the reg to do most of the work. ripple should as you've mentioned be much lower so any need for the bigger cap value in that spot?


But maybe I've missed something (which would not be unusual).:cool:


Thanks for the PSU explanation which makes sense and helps plenty.
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I have tried 22,000uF and it worked fine, with 10,000uF I found that the deep bass sounded a bit thin, but on small speakers like Sabre it was fine.
Try and use LOW ESR type and with large ripple current specs.
 
''I found that the deep bass sounded a bit thin''

I'll skip that then and keep the 33000 in that spot.


Thanks for the Info:cool:


Santa's list is growing nicely:)
 
Hi Colin

Nearly ready to fire up the dynamic PSU’s and was starting to wonder what’s the best way to test before fitting to the SECA.

Any tips welcome.:cool:
 
shoom said:
Hi Colin

Nearly ready to fire up the dynamic PSU’s and was starting to wonder what’s the best way to test before fitting to the SECA.

Any tips welcome.:cool:
Click to expand...

Ah Stig or Shoom?:)

Power up check +20V and -20V tell me results please.

Col
 
here's the report back.

fired up the first PSU.

plus and minus 26V rails.

un loaded

Minus 17.6V not to bad

Plus 10.2V not so good.

second board

Minus 17.6V

Plus 10.2V

Exactly the same which makes me wonder if I’ve missed something.

I’ll post some photos.



any thoughts.:)
 
Here are some picture.:cool:

No power transistors fitted yet but it measured the same with or without those.

psu%20top_1.jpg
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psu%20side_1.jpg
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psu%20back_1.jpg
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It’s going to be something obvious I’m sure.

also can I aske the values of R4 R6 which I've seen listed over on AOS as:
R4 3K6 250mW 1206 1646735
R6 3K6 250mW 1206 1646735

but my boom both are 2k7

But I just don’t see it.:)
 
I really must make a note to myself:D

don't give up smoking and start a new project.

it just does not mix well with my E line blindness.

yup no matter how many times I've looked over the board I failed to notice the E line soldered in reverse.:eek:

a sort of Line E.

SO NOW

Positive 17.8V

Negative 17.8v

Good to go.:D
 
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