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F6 Illustrated Build Guide
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Old 16th May 2018, 07:57 PM   #1141
drewburn is offline drewburn
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have you looked at shielded toroidal transformers
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Old 16th May 2018, 08:12 PM   #1142
silasmellor is offline silasmellor  Denmark
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F6 Illustrated Build Guide
I was thinking about shielded transformers as i was moving things around today :P Toroidy makes some nice ones i might try in the future...
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Old 18th May 2018, 07:59 PM   #1143
silasmellor is offline silasmellor  Denmark
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Last night i had time to fiddle around with the amp some more. I reset the transformer to its original position flush with the base plate of the amp and instead switched the monolithic diode bridges for the breakaway boards from the diyaudiostore universal PSU with 250V/40A schottkys. Fast forward to the result - no change in the FFT nor noise. My current impression now is that we are back to a case of bigger is better - more distance between the power and input transformers is probably the way to go. Unfortunately, the leads of the PT are too short for me to put it anywhere else at the moment, and the chassis is too small to offer many more options, so i cannot really test it. I have bought some mu-metal samples from a german company and will try to make some cans for the Jensens with that and see if it makes a difference. So a lesson from that would be, if going with the 4U store chassis, its probably worth getting the deeper version for this amp if absolute minimal noise is the goal.

Bear in mind though, that this noise is still so low that i have to put my ear close to the speaker to hear it - no big deal really.

I will keep this in mind for the next build i plan to try (M2) and go for a bigger chassis and possibly a shielded PT.
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Old 19th May 2018, 03:08 AM   #1144
2 picoDumbs is offline 2 picoDumbs  Australia
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Add more filtering
Bloody bigger capacitors.
Or CRCRC, that would certainly reduce the rectification harmonics.
Something like 66000uF 0.07R 33000uF 0.07R 33000uF
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Last edited by 2 picoDumbs; 19th May 2018 at 03:12 AM.
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Old 20th May 2018, 10:59 PM   #1145
Bare is offline Bare  Canada
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IMO 'something' ( basic ?) Is amiss in your build.
My F6.. built exactly as per 6L6's guide, being too much of an amateur to adlib Anything.. is DEAD silent.
Vol pot to max.. ears pressed as close as I can get them to the HF compression dome(s) of my Tannoy Golds ...Zero noises.. period.
Same as when the amp is unplugged .. no difference.
Astounded me.. initially, now I simply take it for granted
Revisit your assembly perhaps ?
There is a Small possibility that your mains power my be extremely noisy.
Once had a Video monitor (cad station) that would flicker badly But only in one specific building.
Subsequent Electrical utility testings found that for reasons they wouldn't admit to.. the power being supplied was full of extraneous noises.

Last edited by Bare; 20th May 2018 at 11:04 PM.
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Old 21st May 2018, 07:12 AM   #1146
silasmellor is offline silasmellor  Denmark
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Well, as I said above, I’m leaning towards radiated noise from power transformer into input transformers and on the way to testing it. The build is faithful to the guide as well, within stated specs. Just because you follow the guide doesn’t mean everything will be exactly the same every time though, especially considering different component brands/series etc will not have identical performance.

Shielded pt was recommended specifically by 6L6 in the original F6 thread for the smaller deluxe chassis but I only just found that mention recently.

More filtering may help, the only way to know is to try, but I’m testing the shielding idea first.

Last edited by silasmellor; 21st May 2018 at 07:37 AM.
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Old 21st May 2018, 07:09 PM   #1147
silasmellor is offline silasmellor  Denmark
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Quote:
Originally Posted by 2 picoDumbs View Post
Add more filtering
Bloody bigger capacitors.
Or CRCRC, that would certainly reduce the rectification harmonics.
Something like 66000uF 0.07R 33000uF 0.07R 33000uF
So, what is more effective, CRCRC or CRC, assuming same total capacitance/resistance? I can get 100mF/40V caps that are actually reasonably priced here (somewhat at least), so was wondering if 100mF-0.12R-100mF for each side might be worth doing (over stock, 30mF-0.12R-30mF)? Or would it be better to run 30mF-0.12-30mF-0.12-30mF or something similar?

Bonus question, what determines the size of the R? i tried putting 0.12 vs 0.24R into PSUD2 and got much lower ripple with the higher R. do we simply go for the preferred tradeoff between voltage drop (lower R better) and smoothing (higher R better), or is that too simple? Can i compensate for higher R by using a transformer with higher secondary voltage?
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Old 22nd May 2018, 10:19 AM   #1148
fabrice63 is offline fabrice63  France
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more effective is by far CLC , more capacitance for reservoir ( the last caps ) and the shorter wire as possible , and one single point for all 0V ( per channel assumig your going dual mono ), the lowest esr for the second row of caps .

for example my F6 have : toroid trafo 2 x 220 va , then 16 x STPS30SM120ST, then 4 x 33000 uf then 4 x inductors 10 mH/0.47 ohm then 4 x 69000 uf

the all thing is dead silent on 15 Tannoys

because my trafos and inductors are near the boards i did that with 0.1 mm mumetal :

it won't harm for sure

Click the image to open in full size.



.

Last edited by fabrice63; 22nd May 2018 at 10:34 AM.
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Old 22nd May 2018, 11:06 AM   #1149
silasmellor is offline silasmellor  Denmark
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Haha that looks like a serious amp. Are those tubes for cooling fluid??

I ordered some mu-metal sheets so i will try my hand at making boxes for the transformers. How did you make those neat boxes? Cut and fold - are they welded shut (is that necessary)?

OK follow up: I just ran your numbers into PSUD2 to get a feel for them, and surprisingly 66mF-5H/0.22R-66mF gives me lower ripple than 66mF-5H/0.22R-140mF. Approx 100-fold difference, from 0.15 to 15mV. Any reason this might be?

I agree, the ripple reduction looks quite impressive. Is there any danger of radiation from chokes coupling into input transformers?

Last edited by silasmellor; 22nd May 2018 at 11:18 AM.
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Old 22nd May 2018, 11:57 AM   #1150
fabrice63 is offline fabrice63  France
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Yes the output are liquid cooled

To do the box , you may have the less cut as possible and the more fold , to ensure the magnetic conduction , no way to weld that stuff !!!

and the mumetal box may not be in contact with the input trafos core


psud2 is a great tool , but in real life ( measuring ) you find better result

regarding the chokes coupling into input trafos , i havent measured anything that prove anything , with or without mumetal protection, for me those protection were the cherry on the top of the cake

.

Last edited by fabrice63; 22nd May 2018 at 12:01 PM.
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