Rockford Fosgate 800.4 - Distortion Ch RR - Page 4 - diyAudio
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Old 1st March 2013, 06:26 AM   #31
Witwe is offline Witwe  Germany
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Location: Schwerin
the klick while powering up the amp (like you can see at the scope video) is away.
the DC Voltage at Idle:

RL - 11,3mV
RR - 17,1mV
LF - 5,6mV
RF - 1,3mV

but when disconnecting the power, all channels still increase dc voltage to 300mV like before. or is that normal?
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Old 1st March 2013, 09:14 PM   #32
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You should not have 300mv of DC on all channels. Are you measuring the DC voltage directly across the two speaker terminals for each channel.

I don't watch the videos people post.

Reconnect those two transistors. Remove Q316. Post the DC voltage on all legs of Q300-Q304.
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Old 2nd March 2013, 11:43 AM   #33
Witwe is offline Witwe  Germany
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yes, directly across each speaker terminal!
is that wrong?

DC Voltage:

Q304
B : 12,75V
E : 13,37V
C : 11,6V

Q303
B : 12,75V
E : 13,39V
C : 12,75V

Q302
B : -29,9V
E : -646mV
C : 12,75V

Q301
B : -33,1V
E : -645mV
C : 12,52V

Q300
B : -7,06V
E : -7,73V
C : -685mV
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Old 2nd March 2013, 02:00 PM   #34
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Directly across the speaker terminals is the right way to check the DC offset.

Re-check the DC voltage on the bases of Q301 and Q302. These should be very near 0v. Compare the voltage to the voltage on the bases of the corresponding transistors in the other channels.
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Old 4th March 2013, 11:47 AM   #35
Witwe is offline Witwe  Germany
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Ahh, sorry. i have missed the mV....

here the measurings again:

Q304
B : 12,75V
E : 13,37V
C : -11,57V

Q303
B : 12,75V
E : 13,39V
C : 12,75V

Q302
B : -30,6mV
E : -648mV
C : 12,75V

Q301
B : -33,3mV
E : -645mV
C : 12,52V

Q300
B : -7,06V
E : -7,73V
C : -685mV

i have compared everything with Q400-Q404 but with Q416 in circuit.

Q404
B : 12,77V
E : 13,40V
C : -11,55V

Q403
B : 12,77V
E : 13,42V
C : 12,77V

Q402
B : -40,5mV
E : -653mV
C : 12,77V

Q401
B : -35,6mV
E : -652mV
C : 12,55V

Q400
B : -7,06V
E : -7,73V
C : -693mV

I have also compared it to the bases of the other channels:

Q101
B : -35,8mV

Q102
B : -38,2mV

Q201
B : -37,8mV

Q202
B : -38,5mV

Last edited by Witwe; 4th March 2013 at 11:50 AM.
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Old 4th March 2013, 06:07 PM   #36
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I don't see a problem.

When you saw the distorted signal on the scope (with Q316 in the circuit), was a speaker connected to the channel?

Does the bias pot cause an increase in current draw in the 300 series channel? The transistors must be clamped when you check this.
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Old 5th March 2013, 06:09 AM   #37
Witwe is offline Witwe  Germany
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there was no speaker connected during the test:
Click the image to open in full size.

when I connect a speaker, the signal looks like this
Click the image to open in full size.

the bias pot don't increase the current much.
full ccw: 1,27A
full cw: 1,39A

the other channels increase the current draw over 11A when setting there bias pots!
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Old 5th March 2013, 03:48 PM   #38
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Does it produce a clean audio signal with Q316 out of the circuit and a speaker connected?
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Old 6th March 2013, 05:54 AM   #39
Witwe is offline Witwe  Germany
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yes it does!
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Old 6th March 2013, 12:08 PM   #40
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What is the DC offset across the speaker terminals with the speaker/load connected?
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