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Old 10th January 2017, 12:31 PM   #1361
alibear is offline alibear  United Kingdom
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Hi Everyone, perhaps a stupid question, but here goes.
I am making the power supply for an earlier version of the TO3 Symasym using Carlos Mergulhao PCB. The build manual suggests to wind the inductor for the Pi filter using 40 turns of enamel copper wire around a 33Ohm resistor. Is the resistor necessary or could I wind the turns around a former and then remove the former to create an air cored inductor?
Thanks
Alan
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Old 10th January 2017, 01:32 PM   #1362
AndrewT is offline AndrewT  Scotland
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what's the inductor for?
40 turns is too many for an amplifier output Thiele Network
and too few for a PSU filter.
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Old 10th January 2017, 05:39 PM   #1363
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Alan, do it as Greg Erskine is telling you:

40 turns of 1.0 mm enamelled copper wire wound in 4 layers around R7 and R8 (approx. 13mH) (well: need not be 40 turns, can be 30 as well - LoL).

But: always use a resistor (Greg proposes to use a 33 Ohm resistor) to wind the enamelled wire around it.

Best regards - Rudi
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Old 11th January 2017, 08:49 AM   #1364
AndrewT is offline AndrewT  Scotland
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40T in 4 layers will not get any where near 13mH.
Like I said, 40T is too few for a PSU filter.

A large diameter bobbin like 19 to 25mm with 100T to 200T (14layers of 14turn) is probably more like what is needed to get a reasonable inductance affect to roll off the higher harmonics.
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Last edited by AndrewT; 11th January 2017 at 08:52 AM.
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Old 11th January 2017, 03:16 PM   #1365
alibear is offline alibear  United Kingdom
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Thank you for your replies. The question now is, if the inductor is too small a value to have any useful purpose in the power supply ( as Andrew T points out ) why is it there? Can it just be substituted with a low value resistor, say 0.1 Ohm?
If I had more space available I would wind larger inductors as suggested but this is not possible.
Thank you for your help.
Alan.
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Old 19th January 2017, 09:08 PM   #1366
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any boards left for this amp?
thank you
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Old 20th January 2017, 07:57 AM   #1367
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Asuslover, I have sent you a PM.

Regards - Rudi_Ratlos
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Old 1st February 2017, 09:25 AM   #1368
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Gentlemen, I want to offer you the SYMASYM shown on the picture below.
It consists of:

- 2 PCBs "Black Beauty SYMASYM", with Backend PSU, Frontend CapMultiplier and Speaker Protection on board
- 2 pairs of matched NJW0281G and 2 pairs of matched NJW0302G
- 4 capacitors Nichicon 10.000F/80V

The price: 65 with shipping worldwide inclusive.

Best regards - Rudi_Ratlos
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Old 1st February 2017, 04:53 PM   #1369
alibear is offline alibear  United Kingdom
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Hello everyone, I have just completed one channel of the TO3 version and am conducting some listening tests. The bias set up easily and the offset appears to be 1mV either side of 0 volts. The amplifier appears to be completely silent with no input and ear next to speaker cone.
Quality seems very nice, but have not as yet carried out comparisons with my regular amplifier.
One query that I have is that the gain appears to be slightly too high when using my normal pre amp ( Quad 44 ). I have included the 22ohm resistors on the input pair as advised. Could I alter the ratio of the 2k and 22k resistors on the input network to reduce the gain, or is this not a good idea?
Regards
Alan
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Old 1st February 2017, 05:38 PM   #1370
AndrewT is offline AndrewT  Scotland
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Have you tried a 1kHz square wave at a few mVac input with 22nF to 100nF across the output. Output 200mVpp to 2Vpp.
Both my To247 builds oscillated, or rang badly.
I gave up trying to suppress this and both builds sit on the shelf.

Reducing the gain increases the feedback. This would reduce the stability margins and may make the ringing worse.
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