Colin Wonfor's SECA amp build
- Thread starter Marra
- Start date
Hi Colin
can I just check the value of SECA board R3.
I have 56R on the boom and 27R on my schematic.
Thanks
If it is the twin FET version it will sound better with 27R
Drive current = 0.6/R3
So for 56R we get approx 0.6/56 = 11mA
And for 27R we get approx 0.6/27 = 22mA
So the BD139/140 will get a bit warmer i.e 0.45W as to 0.18W but the extra current drive will drive the output fet better and give us a faster rise/fall time.
It can be done on the darlington / fet version but the constant current load which uses the darlington can,t follow the current as fast as the fet. and this can be heard as a high frequency clipping at full power.
NOTE please if using the twin fet version remove C4
as this limits the feedback control on the constant current and again makes it to slow and high frequency clipping can be heard.Hi Colin
Im building the twin fet version so 27R seems logical given that I noticed your comments in another post re asking the 139/140 to work a little harder.
Ive already omitted C4.
Thanks for the reply.
Ill post some pictures later.
The BD139/140 will love it, read Docfoster on the sound changes and improvements C4 (not P4) does when removed.
http://www.audiochews.com/discussion/1666/ben-s-one4-wonfor-seca-build-ready-populated-boards#latest
Now I am going back to the ward for a snooze before the Quacks start drilling new hole in me.
Sorry to hear that you are still confined.
Hope things get better soon.
But Ive been slowly picking away at the project.
Just a few snapshots of my build.
(The Rakes progress)
Started out in the usual way with components lowest to the board first.
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And then worked upward
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Finished SECA mounted on heat sink.(you may notice that R3 has magically changed to 27R)
[/URL][/IMG]
All caps are 50V Pany FC except for the 10uf IP cap which Ive used BP Muse. PS caps are as specified in the BOOM.
Most of the 1/2W Resistors are bog standard Maplins
A little more of the dreaded metal work and then Ill be ready for some testing.
Hope things get better soon.
But Ive been slowly picking away at the project.
Just a few snapshots of my build.
(The Rakes progress)
Started out in the usual way with components lowest to the board first.
And then worked upward
Finished SECA mounted on heat sink.(you may notice that R3 has magically changed to 27R
)
All caps are 50V Pany FC except for the 10uf IP cap which Ive used BP Muse. PS caps are as specified in the BOOM.
Most of the 1/2W Resistors are bog standard Maplins
A little more of the dreaded metal work
and then Ill be ready for some testing.Thanks Keith
Given your long and illustrious history with Papa’s amps your build fired up my interest and this thread made it worse.
Yes that R3 change was easy to miss but I remember Colin discussing it on one of the threads. Still managed to solder the wrong one in though. I'll be interested in your thoughts RE the sound after that mod.
Extra speed and band width is sometimes welcome.
The cap across the trimmer should just squeeze into the spare holes next to it so not a big job.
and on Cap choices.
well I've tried to go with Colin's choices just for a start but from what I've read it's about HF stability so maybe a Mica would be a better choice in that spot than the MKP. interesting to find out though.
i'm much more interested these days in building in a way that I would not do ordinarily.
lets hope for the best @ switch on.
Given your long and illustrious history with Papa’s amps your build fired up my interest and this thread made it worse.
Yes that R3 change was easy to miss but I remember Colin discussing it on one of the threads. Still managed to solder the wrong one in though. I'll be interested in your thoughts RE the sound after that mod.
Extra speed and band width is sometimes welcome.
The cap across the trimmer should just squeeze into the spare holes next to it so not a big job.
and on Cap choices.
well I've tried to go with Colin's choices just for a start but from what I've read it's about HF stability so maybe a Mica would be a better choice in that spot than the MKP. interesting to find out though.
i'm much more interested these days in building in a way that I would not do ordinarily.
lets hope for the best @ switch on.
Hi All
Fired up the first of the SECA mono’s today.
Here it is.
Errrr frankenSECA
[/URL][/IMG]
A bit of a make do just to size up the heat factor and I suspect that bigger sinks will be needed For the full SECA effect. I’ve become a little jaded with doing all the expensive case and metal work approach only to find that the electronics are not to my taste. So I’ve made do with what I have just to taste the wine before getting down to a more serious build if I like the taste.
I’ve used a DC protection relay to avoid the SECA bump at start up but this will be replaced later when the soft start goes in. so just as an anti bump.
OK
Don’t forget that I have the 18V transformers ready to use with the PSU module so temperatures may be running higher than expected.
Room temp constant @ 20 Deg C
1.5A @ 45 Deg C on the Heat sink.
Offset ridiculously low at less than 1MV but setting up is a little skittish due I suspect in some part to the open plan case I’m using. Stable enough though.
Just number two to set up now and then the music test.
A few comments on the build.
The boards are really nice to build with. Great attention to detail and easy to follow component markings on the board. Really nice quality, well fabricated boards are supplied with thick copper traces which made swapping out R3 for the required 27R a breeze (no vaporising of tracks or pads that I’ve experienced with cheap boards) as did my go to Cardas solder which helped that process also.
Initial set up @ power on took some time just to allow the heat to stabilise. I found it easy to initially set a low bias current and slowly edge up.
It’s been fun so far.
I’m intending to build the regulated PSUs but that will be after Santa’s visit and add some big daddy heat sinks should the sound testing prove successful.
Fired up the first of the SECA mono’s today.
Here it is.
Errrr frankenSECA
A bit of a make do just to size up the heat factor and I suspect that bigger sinks will be needed For the full SECA effect. I’ve become a little jaded with doing all the expensive case and metal work approach only to find that the electronics are not to my taste. So I’ve made do with what I have just to taste the wine before getting down to a more serious build if I like the taste
.
I’ve used a DC protection relay to avoid the SECA bump at start up but this will be replaced later when the soft start goes in. so just as an anti bump.
OK
Don’t forget that I have the 18V transformers ready to use with the PSU module so temperatures may be running higher than expected.
Room temp constant @ 20 Deg C
1.5A @ 45 Deg C on the Heat sink.
Offset ridiculously low at less than 1MV but setting up is a little skittish due I suspect in some part to the open plan case I’m using. Stable enough though.
Just number two to set up now and then the music test
.A few comments on the build
.The boards are really nice to build with. Great attention to detail and easy to follow component markings on the board. Really nice quality, well fabricated boards are supplied with thick copper traces which made swapping out R3 for the required 27R a breeze (no vaporising of tracks or pads that I’ve experienced with cheap boards) as did my go to Cardas solder which helped that process also.
Initial set up @ power on took some time just to allow the heat to stabilise. I found it easy to initially set a low bias current and slowly edge up.
It’s been fun so far
.I’m intending to build the regulated PSUs but that will be after Santa’s visit and add some big daddy heat sinks should the sound testing prove successful.
Hi Quickie
I’m using these from Jims Audio
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=220718917152
Which were left over from my Voyager re-build.
These can be split to accommodate mono blocks and just need a 12Vac supply but you have the regulated PSU so why not just build the anti-thump circuit on those boards.
I’m thinking of doing that.
Just for the switch on delay.
Colin's soft start board looks like a much more elegant solution.
Love your SECA builds BTW.
Nice and compact.
I’ll be finding some bigger sinks and then building the cases around them.
If I get anywhere near your great work I’ll be happy.
Hi Keith
Yes I suspect that the soft start is helping to keep the bumps at bay but I won’t be adding my SS units until later.
The way that I have my SECA board mounted on the sink may not be doing the dissipation factor any favours. My temperature measurement was taken from the hottest part of the sink BTW.
Could use a spreader but I’m planning to do a re-build at some point so did not bother. I just have room to squeeze the PSU on which will also allow for shorter secondary connections which are far from optimal ATM.
Maybe room to squeeze the standing current up a little but I’ll start off conservatively and see how it goes.
I’ve enjoyed the build so far but really wonder how Colin can supply ready built boards for such a low price.
My own build was only a little less than that but hey we like to build so no matter.
For the novice those ready-made boards look like VGVFM IMHO.
One down and one to go.
I’m using these from Jims Audio
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=220718917152
Which were left over from my Voyager re-build.
These can be split to accommodate mono blocks and just need a 12Vac supply but you have the regulated PSU so why not just build the anti-thump circuit on those boards.
I’m thinking of doing that.
Just for the switch on delay.
Colin's soft start board looks like a much more elegant solution.
Love your SECA builds BTW.
Nice and compact.
I’ll be finding some bigger sinks and then building the cases around them.
If I get anywhere near your great work I’ll be happy.
Hi Keith
Yes I suspect that the soft start is helping to keep the bumps at bay but I won’t be adding my SS units until later.
The way that I have my SECA board mounted on the sink may not be doing the dissipation factor any favours. My temperature measurement was taken from the hottest part of the sink BTW.
Could use a spreader but I’m planning to do a re-build at some point so did not bother. I just have room to squeeze the PSU on which will also allow for shorter secondary connections which are far from optimal ATM.
Maybe room to squeeze the standing current up a little but I’ll start off conservatively and see how it goes.
I’ve enjoyed the build so far but really wonder how Colin can supply ready built boards for such a low price.
My own build was only a little less than that but hey we like to build so no matter.
For the novice those ready-made boards look like VGVFM IMHO.
One down and one to go.
This site contains affiliate links for which pink fish media may be compensated.
quickie
pfm Member
Thanks for the link
It was more the DC protection bit I was interested in.
The SECA's are pretty good at switch on.
This site contains affiliate links for which pink fish media may be compensated.
Thanks for the link
It was more the DC protection bit I was interested in.
The SECA's are pretty good at switch on.
No Worries
I had those boards in my Voyagers for over a year without issue.
Not expensive and just the job for mono's.
S-Man
StrivingON
A bit of a make do just to size up the heat factor and I suspect that bigger sinks will be needed For the full SECA effect. Ive become a little jaded with doing all the expensive case and metal work approach only to find that the electronics are not to my taste. So Ive made do with what I have just to taste the wine before getting down to a more serious build if I like the taste
I've taken this approach for ages and I haven't done a "serious" power amp build for many years.
I currently have 5 non-serious amp projects on the go. It's a sad affliction but probably less pitiful than online bingo!
Anyway looking forward to your views on the SECA sound. Hope it gives you a hit like your first DIY amp