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A Very Compact Hybrid Amp - Page 87

post #1291 of 2213
Thanks for the hard work cfcubed, I think I have some 1000uF/35V in the closet. :P Any measurements of post switcher and if post switching affects anything? Some of us are going to start chasing a 1A version, and according to the spec sheet using 220uF C2H would be advisable. I was wondering how bad it is to not follow that, though if I add 220uF to C2H, ~180uF would go to C1H also. I would like DC as smooth as possible just to be DC.

I could scope it too, but I've been pulling some long days these past few weeks and amp building is not what I want to do when I have 1 hour to eat before sleeping.
post #1292 of 2213
holland - based on my battery vs SM heater testing, which someone could confirm if they wish, there should be no audible benefits for stock heater loads from raising C1H or C2H, only raising C3H to 330uF -> 470uF range.

Keep in mind though that I use D2000s are fairly sensitive/efficient to make these judgments. And these suggestions w/those cans *should* bring hum/noise down to the unavoidable(?) hiss/white noise level present w/battery heater. I'll find this out for my CTH by tomorrow AM EST.

But to support higher than, say 4W of heater load (6.3V / 630ma & 12.6V / 310ma), I'd consider raising both C1H & C2H to 180uf or so... As well as C3H to 470uF or so. Low impedance caps are a must for all these I think, based on my scoping & switcher spec sheet.

Again my bet is there is likely no further audible benefits to be gleaned from "improving" heater circuit beyond the above suggestions. I'd look to general A/C shielding for entire CTH PCB A/C area for any further noise/hum reduction. And this is a tube amp folks
post #1293 of 2213
Quote:
Originally Posted by cfcubed View Post
Please use a low-impedance 330uF cap rated @ 35V or better & lead-length as short as possible.
Thanks for following through with this Chris.

Is 35v the absolute minimum rating we can use? I have 470uf 25v here which would fit flush to board(8mm dia) otherwise the 35v caps I have would have to be mounted off board with longer leads.
post #1294 of 2213
Quote:
Originally Posted by Forte View Post
Is 35v the absolute minimum rating we can use?
Yes, I'm measuring 29V or so across existing C3H leads. A 25V cap might last a while tho.

Know you are doing this, but consider removing existing C3H & putting cap there OR mounting below PCB if using non-std case that supports this.

Again, will do this to my CTH & boxup within 24hrs but would like confirmation of this "fix" w/tubes supported by stock CTH.
post #1295 of 2213
Will give the 25v caps a miss then, I have some 35v caps, will see if I can squeeze them in there as best I can. I put in a 100uf cap this morning and the hum definitely reduced even with R18 at 47R.
post #1296 of 2213
Have just put in a 35v 470uf Panasonic FM cap in and noise seems to be gone. The amp is still out of the case and the pot is not currently grounded but seems to be all good.

The cap is a tight fit(10mm diameter) and sits about 5mm off the board, but it is in. My build used the original proto BoM with the larger C5P cap, the newer smaller cap used on the production board should give more room.

Listening with a 6n1p , have a couple of tubes which have been more noisy (6h23, 6bq7a), will try these in the morning as well as listening with some more sensitive headphones.
post #1297 of 2213
Quote:
Originally Posted by Forte View Post
Have just put in a 35v 470uf Panasonic FM cap in and noise seems to be gone. < snip >
Excellent.
Quote:
Originally Posted by Forte View Post
Listening with a 6n1p , have a couple of tubes which have been more noisy (6h23, 6bq7a), will try these in the morning as well as listening with some more sensitive headphones.
Sounds good. WRT 6bq7a & noisy tubes in general, consider what I found in testing "With 4 D cell heater supply 6922 has NO hum. 6BZ7 has faint hum." That with R18s shorted tho.
Going further, think we'd need to bark up another tree. Perhaps better then to just write off a few of the dozen or so varieties of tubes that work in the amp (at least when used w/sensitive cans).
post #1298 of 2213
just tried it..... and the noise is dramatically reduced. I can still here a bit, but its substantially quieter. I'll dig out a 6n1p again and report back.
post #1299 of 2213
Quote:
Originally Posted by Forte View Post
Will give the 25v caps a miss then, I have some 35v caps, will see if I can squeeze them in there as best I can. I put in a 100uf cap this morning and the hum definitely reduced even with R18 at 47R.
Mine's a proto board with the smaller cap, so I scooted C5P over a bit and got a 470 pretty nicely (and I think it was a 63V)...
post #1300 of 2213
wow, that was quick. Nice job all!
post #1301 of 2213
Quote:
Originally Posted by cfcubed View Post
Have to credit others for this but adding 330uf to C3H looks to be enough to virtually eliminate the noise/hum contributed by SM heater circuit.
I think it was the first suggestion Alex made

We should look for a drop in substitute for the BoM (as soon as Alex blesses it...) There should be some tall skinny Nichicon models that would work...
post #1302 of 2213
Quote:
Originally Posted by HeadphoneAddict View Post
But what if I get a CTH?

Hmmm, what if you do? I keep thinking about a special HeadphoneAddict Edition.
post #1303 of 2213
It's nice to know even a barely perceptible hum can still be reduced even more is definitely a big plus!

Thanks for all your hard work guys.
post #1304 of 2213
I am still hearing too much noise for my liking, but i have horribly long leads on the 'too big' cap. I'll try and source somethihg that fits.
post #1305 of 2213
Quote:
Originally Posted by adamus View Post
I am still hearing too much noise for my liking, but i have horribly long leads on the 'too big' cap. I'll try and source somethihg that fits.
It is boxed up? I had to box & move everything to an EMI-quite area of the house to conduct my SM heater vs battery heater testing. And, yes, shortening the leads should help.

If this solution becomes an "answer" for most then we'll find a way to accommodate it on the PCBs. D5H of 1N5818 (1A) instead of 1N5820 (3A) would help and that's a perfectly fine thing to do.
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