Passive Pre + F5 + Sub-woofer need buffer? - diyAudio
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Old 24th May 2015, 06:35 AM   #1
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Default Passive Pre + F5 + Sub-woofer need buffer?

Hi All,

I have added a B&W DB1 sub-woofer to my passive-preamp + F5 combination, driving a pair of B&W 805D. I have connected the newly added sub-woofer by inserting an RCA splitter at the power-amp output terminals of the Creek OBH-22 passive pre-amp.

After adding the sub-woofer, I perceive a decrease in loudness / drive to the music, now I have to turn the volume knob slightly higher compared to before even though with the sub-woofer the lower bass has been filled in, and I feel that the music has less drive / sounds thin.

I wonder whether it would help to put a buffer like B1 after the passive preamp?

Best regards
Liu
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Old 24th May 2015, 07:33 AM   #2
AndrewT is offline AndrewT  Scotland
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What is the sensitivity of the woofer channel compared to the sensitivity of the stereo channels?
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Old 24th May 2015, 08:07 AM   #3
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Hi AndrewT,

I am not sure. The stereo channel has a sensitivity of 88 dB as stated in the info sheet. As for the subwoofer, in the info sheet of the subwoofer, it is stated to feature a 1000W class-D power amp, but the sensitivity of the drive unit itself is not stated.
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Old 24th May 2015, 08:15 AM   #4
AndrewT is offline AndrewT  Scotland
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the stereo channel will have speakers driven by an amplifier.
You need the volts at the input of the amplifier and the output of the speaker in dB of SPL.

You need the same information for the woofer channel.

Then you can identify whether the same voltage or a different voltage needs to be fed to the woofer channel.

88dB/W @ 1m for the stereo channel is 1/4 of the information you need.
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Old 24th May 2015, 09:00 AM   #5
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Well, I have actually not given this any thought before. I always assumed that a commerically sold subwoofer is designed to take the same signal that goes to the main speakers channel and just amplifies the signal through its built-in power amp.

Anyway, in the setup menu of the sub-woofer, I have chosen a sentivity level that corresponds to 2V input signal. I assume that having chosen this setting, the sub-woofer takes care of the question of aligning the subwoofer channel and the main speaker channel?
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Old 24th May 2015, 10:49 AM   #6
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Hi All,

I would like to have your input to whether a buffer is necessary in this scenario:

Computer -> USB DAC -> Passive Pre-amp (output impedence 20k Ohms) -> F5 (input impedence 100k Ohms) in parallel with Subwoofer (input impedence 15k Ohms)

Looking at the output impedence of the passive pre-amp and the input impedence of the sub-woofer, I am thinking that it is probably a good idea to add a buffer. Appreciate your inputs. Thanks.
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Old 24th May 2015, 10:58 AM   #7
Zen Mod is offline Zen Mod  Serbia
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buffer must have

two , one for F5 and one for sub , even better
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Old 24th May 2015, 11:37 AM   #8
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Perhaps you have the gain of the sub set to high.
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Old 24th May 2015, 01:25 PM   #9
AndrewT is offline AndrewT  Scotland
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The sub is too quiet compared to the stereo.
That would indicate that it is not set to high gain.
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Old 25th May 2015, 02:34 AM   #10
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Thanks Zen Mod, I will try to start with 1 buffer first :-)

I am thinking of ordering the B1 kit from PassDiy store. However, since I already have a passive pre-amp with remote controlled input switch selection and volume control, I would like to just continue to use it. Refferring to the schematic, would the circuit work as a standalone buffer without volume control (so that I can connect any other source equipment or passive pre-amp to its inputs) if I bypass R100, R101, P100, R200, R201, P200 and connect the input RCA with a straight wire directly to R102 and R202?
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