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Old 2nd August 2013, 12:49 PM   #3801
AndrewT is offline AndrewT  Scotland
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The B1 can share a PSU. But you must get the voltage for the B1 correct.

You must also arrange for the correct sequencing of the power up.
A single polarity supply to an amplifier will always give a varying DC pulse through the DC blocking capacitor at start up. Always !
If your sequencing cannot protect your speakers, then you need correct muting.
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Old 2nd August 2013, 12:58 PM   #3802
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The reason that you are seeing the higher voltage with the B1 than expected is because of its very low power drain. If it's measuring 33V then that is what it will be producing with such a low load. 33V is fine as long as the caps are rated sufficiently. I would consider 36V about the maximum voltage for the B1.
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Old 2nd August 2013, 01:00 PM   #3803
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You could use a relay to short the input of the F5 during power up for 5 seconds. In that way the relay contacts are not in circuit during normal use.
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Old 2nd August 2013, 02:56 PM   #3804
Rixsta is offline Rixsta  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
The B1 can share a PSU. But you must get the voltage for the B1 correct.

You must also arrange for the correct sequencing of the power up.
A single polarity supply to an amplifier will always give a varying DC pulse through the DC blocking capacitor at start up. Always !
If your sequencing cannot protect your speakers, then you need correct muting.
My B1 PSU is separate to the F5 PSU just both use same transformer which has 2 sets of secondarys one lower voltage than the other.

I Think ill go for upgrading the caps and powering the B1 with the 33v.
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Old 2nd August 2013, 02:57 PM   #3805
Rixsta is offline Rixsta  United Kingdom
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Quote:
Originally Posted by KatieandDad View Post
You could use a relay to short the input of the F5 during power up for 5 seconds. In that way the relay contacts are not in circuit during normal use.
I like it, having a think about this would be rather easy to do.

Now I need to find out whats wrong with the B1 or scrap it for a pre-amp which was the plan anway
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Last edited by Rixsta; 2nd August 2013 at 03:00 PM.
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Old 3rd August 2013, 09:04 AM   #3806
Rixsta is offline Rixsta  United Kingdom
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Iv'e been looking around for Pre-amps to replace the B1 but not having much luck, i know the burning amp pre-amp is available but I expect its not ok for driving F5t?

Do we know of any other Pre-amps ? other wise Ill try to get this B1 working

Quote:
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This seems broken.
Most properly built B1 have zero Output offset. The DC blocking cap and the leakage to signal ground resistor ensure the output offset is zero.

0.01Vdc = 10mVdc is wrong.
0.34Vdc = 340mVdc is broken.
When you say broken you mean something on the board may be blown ?
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Old 3rd August 2013, 09:08 AM   #3807
AndrewT is offline AndrewT  Scotland
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What are the voltages (to Audio Ground) before and after the DC blocking output capacitors?
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Old 3rd August 2013, 11:24 AM   #3808
Rixsta is offline Rixsta  United Kingdom
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C101 and C201 I just measured ?

Right Channel
After cap = 04.0mv slowly dropping lower over time
Before Cap = 7.3v

Left Channel
After cap = 24mv slowly dropping over time
before cap = 12 or 13v but is slowly changing over time too

I guess if i left it on some time it would become stable but it doesn't look to good!
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Last edited by Rixsta; 3rd August 2013 at 11:26 AM.
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Old 3rd August 2013, 12:50 PM   #3809
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Rixsta View Post
i know the burning amp pre-amp is available but I expect its not ok for driving F5t?
The BA-3 front end has gain, so it's actually much more appropriate to drive a F5T than the B1.

You would need to adjust the gain down for best results, but that's a ratio of 2 resistors. Easy. (I don't remember which off the top of my head...)
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Old 3rd August 2013, 12:51 PM   #3810
Itsmee is offline Itsmee  England
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If the JFETs are reasonably well matched, the output (before the caps) should be at half the supply voltage, looks like you have a problem with the right channel.

Quote:
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The BA-3 front end has gain, so it's actually much more appropriate to drive a F5T than the B1.
The BA2 would also be suitable.

Last edited by Itsmee; 3rd August 2013 at 12:54 PM.
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