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bobsinclar 19th July 2006 10:10 PM

citation 12 mos fet
while waiting the parts to complete my aleph 30, I was impatient to get into the groove, so I ran across the citation 12 modified by nelson pass with complementary fets, schematic is really easy and quick to build, and I had all the spare parts here, so I made the first channel, and it immediately worked very well, no hum or noise, good bass but I can't juge as it's only mono, and my test speaker is quite small (bw solid 5 inch boomer!)4ohm
the only thisgs I changed from the original nelson modified schematic is that :*
for the complementary fets I used IRF 530/9530
the power supply is regulated (+/-32V) with 30Amps ballast darlington bipolars

my question to those who are familiar with this schematic, would concern the replacement of the end drivers with IRFP 240/9240
I already put them in place of the IRF 530/9530, and turned the bias resistor for a minimum bias, but should I put source resistors between the fets? (as in the actual schematic there aren't any kind of resistors...) whould they be necessary knowing that i intend to bias alittle high?
any input would be appreciated!

bobsinclar 19th July 2006 11:05 PM

2 Attachment(s)
I am afraid to fire it up like that , so I prefer to wait for your comments before
here is the pict of the first card finished with the IRFP 240and 9240

Nelson Pass 20th July 2006 05:43 PM

Source resistors on the MOSFETs are desirable in that they
help thermally stabilize the outpus and provide a resistance
where you can measure the bias. For this I suggest about
.47 ohms.

bobsinclar 20th July 2006 06:30 PM

Thanks Nelson,
I 'll try the 0.47 Ohms , and will try to run it in class A ,the second card is almost done, so I'll probably have stereo soon!

By the way just received the PASS DIY stickers they are great! again many thanks!

Nelson Pass 20th July 2006 06:35 PM

I don't think you're going to get Class A off the Citation 12
heat sinks, or 60 watts Class A with a single pair of devices.

bobsinclar 20th July 2006 08:33 PM

actually I have big heatsinks here , and I just intend to push the 2 IRF240/9240 the just the highest I can , maybe 500mA each
would that be too much? this way I thought I'd expect the first watts to be class A , anyway this is my very first amp built from scratch, so I may be mistaking? would it make sens to try this kind of bias?

bobsinclar 21st July 2006 12:45 PM

2 Attachment(s)
I finally fired it up with the source resistors I could find (about 0.3Ohms)and a bias of about 100mA , worked great without any kind of problem of oscillation , and concerning the sound compared to the irf 530/9530 the 240/9240 are just terrific IMO, but I also made modifications to the PSU so maybe the improvment isn't due to the fets change only...
anyway this is a very simple circuit that just sound great, anyway I'll try a bit more bias , but I don't want to take much risk as it's well like that, so if anybody has advice concerning the improvement by setting a higher bias I'd be interested, I'm too scared to try it myself without advices before, as I heard so many times people getting their amps blown trying to search for perfection!
anyway great schematic Nelson minimalist and very efficient!!!
here is the pict of the amp under test:

Nelson Pass 21st July 2006 06:32 PM

Nice test rig - much cleaner than anything I do.

As to what you can get away with on 240's and 9240's, I
have run them as high as 50 watts dissipation with a 60 deg
heat sink temperature. Any more than that and I think you'll
be over the edge for reliability.

bobsinclar 21st July 2006 07:21 PM

thanks for the info Nelson,
now I know how to stay around the safe area for them...
I am completing the second channel ...
much fun with this amp!
hope the Aleph 3 will also go smooth like that!

stoN_Cold 21st July 2006 08:36 PM

Hi Bob S
Sorry, for Q.
Do you have schemayic of Citation 12, I think it is very cheap amplifier & Ihope very good sound.

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