Roender's FC-100 prototype and builder's thread - Page 53 - diyAudio
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Old 10th September 2012, 06:00 PM   #521
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Original the FC100 uses a 2x25Vac toroid is used after the rectifier is this 2x35Vdc.The shunt regulator gives 4 volts more around 39Vdc.I,m planning to us a 2x27Vac transformer after rectifying is this 38Vdc.The front-end is using 4 volts more,my question what to I've to change of the shunt-regulator to get 42Vdc?
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Old 12th September 2012, 04:43 PM   #522
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Patrick, you need not change anything.

Go and use your 27VAC transformer for the backend and the 30VAC that I sent you for the frontend.

I am absolutely sure that Mihai (I consider him to be a real expert) took account of 10% deviation on the primary voltage!

Best regards - Rudi_Ratlos
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Old 12th September 2012, 05:01 PM   #523
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Rudi, I will try it but the frontend transformer is 2x35Vac which gives 49Vdc after rectifying.Is this a problem?
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Old 12th September 2012, 05:20 PM   #524
zsaudio is offline zsaudio  Europe
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I feed my shunty with 49,5VDC and have no problem just the heatsink gets a little bit warm but it passed my finger test.
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Old 12th September 2012, 06:06 PM   #525
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Doesn't the shunt voltage for the front-end need to be 4 volts higher as the back-end voltage?
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Old 12th September 2012, 06:19 PM   #526
zsaudio is offline zsaudio  Europe
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yes it does.
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Old 12th September 2012, 10:36 PM   #527
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Now the shunt is using 36volts zener and the output is 38-39 Vdc.Doesn't I need a 40volts zener to get my 4 volts more(42Vdc)?
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Old 13th September 2012, 08:23 AM   #528
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by meanman1964 View Post
Rudi, I will try it but the frontend transformer is 2x35Vac which gives 49Vdc after rectifying.Is this a problem?
35Vac for the output stage of the amplifier is too high for a 4ohms rated amplifier. The temperature de-rated SOAR gets exceeded too often by reactive IV when working with near maximum volumes.

However, it is my opinion that 35Vac for the whole amplifier would be really good for an 8ohms specified amplifier. If you do not have any 4 to 8ohms speakers and never intend testing any low impedance speakers then building an 8ohms only based on a 35Vac transformer may well give you a very good combination of high sound quality and the ability to send unclipped signal when the going gets towards high SPL.

Conversely, having studied the details, I reckon that a 28Vac transformer would give a very good 4ohms rated amplifier, capable of driving any true 4ohms rated speaker and all the others of higher impedance.
If I had some 4ohms speakers I would be very tempted to use a 30Vac transformer and a very big heatsink, along with 35Vac regulated down for the front end.
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Last edited by AndrewT; 13th September 2012 at 08:31 AM.
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Old 13th September 2012, 08:24 AM   #529
AndrewT is offline AndrewT  Scotland
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The front end does not NEED to be supplied with a higher voltage. The amp works well with the same PSU supplying both ends of the amplifier.

One advantage of using a lower front end voltage is that the output stage does not approach rail voltage and thus the output transistors do not approach saturation. When the output becomes very close to rail voltage the transistor betas become lower, the transistors become slower, the capacitance becomes higher. and most importantly if the output clips the stage can become very slow to recover from that clip.

Limiting the front end maximum output such that the output stage never approaches clipping makes for a better "sounding" performance if you like listening at high powers.
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Last edited by AndrewT; 13th September 2012 at 08:29 AM.
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Old 13th September 2012, 09:11 AM   #530
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Andrew,thanks for the explanation you're a big help
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