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Old 30th September 2011, 02:24 PM   #1351
cersepn is offline cersepn  United States
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Not too sure if this is the right place to ask, but what will happen if one uses a dcb1 with an amp without input and output coupling caps (dc servo) like the parasound a21? Will it fry the amp/speakers or both?
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Old 30th September 2011, 02:48 PM   #1352
Salas is offline Salas  Greece
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Possibly if a failure occurs in the buffer and there is no DC sensor/protector guarding the power amp's output.
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Old 30th September 2011, 03:16 PM   #1353
cersepn is offline cersepn  United States
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Is there any way around it? It would be such a shame not to be able to use the DCB1...
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Old 30th September 2011, 03:31 PM   #1354
Salas is offline Salas  Greece
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An excellent capacitor on its output (second parallel output, non DC), or to pray nothing will ever fail. Second option is like beer after whiskey, i.e. definitely risky.
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Old 30th September 2011, 03:54 PM   #1355
Thago is offline Thago  Belgium
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What capacitance should that resistor have?
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Old 30th September 2011, 04:11 PM   #1356
Salas is offline Salas  Greece
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Well, difficult question because resistors don't have capacitance mainly. In case you mean what value an output capacitor should have, then 2.2uF should be OK with most main amplifiers input impedance.
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Old 30th September 2011, 04:17 PM   #1357
Thago is offline Thago  Belgium
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Right...
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Old 30th September 2011, 05:09 PM   #1358
cersepn is offline cersepn  United States
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Thank you, Salas. You're a great help as always

I was wondering more along the lines of.. since the amp has a servo to eliminate dc offset, then will it remove the offset coming in from the preamp side?
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Old 30th September 2011, 05:21 PM   #1359
AndrewT is offline AndrewT  Scotland
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The servo (or servos) could be adjusting either the input offset, or the output offset, or both.
What is more important is that there is a separate and effective output offset detection and shutdown system to help prevent damage to speakers
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Old 1st October 2011, 06:37 AM   #1360
cersepn is offline cersepn  United States
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Thank you, Andrew.

From the amp manual,
"The A 21 is direct-coupled from its input jacks to its speaker terminals. This advanced circuitry never needs adjustment or maintenance. It operates outside the audio signal path to keep the DC offset at the output of the A 21 at a constant 0.00 Vdc."

and
"Each channel of the A 21 has a high-quality protection relay with gold-plated contacts for long-term reliability. These relays function to protect either the amplifier, the speakers, or both. When the A 21 is first powered on, these relays remain open for three seconds as the positive and negative power supplies stabilize and reach equilibrium ...

Specialized current-sensing transistors are connected to the output stages of the A 21 to constantly monitor the current flow through the output transistors. If the current drawn by this stage exceeds a predetermined safe level due to a load impedance below 1 ohm or a short circuit at the speaker terminals, the output relay will open immediately to prevent any of the output transistors or other parts from failing.

Each channel of the amplifier has a separate fuse for its positive and negative DC voltage rails. These fuses provide backup protection in case the over-current protection does not work in time, or if an internal part
fails. In the event of a part failure, these fuses halt operation to minimize damage to additional parts."

Not sure if it's only marketing fluff... with what the manual said, is it still advisable to use the DCB1 capless with the amp?
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