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Old 13th February 2007, 03:30 PM   #1
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Default Can I split line level input?

Hi
Please help.
Can I split the line level input into my power amp, so that I can input to a subwoofer that will then be able to be controlled by my passive pre?
Thanks in advance
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Old 13th February 2007, 03:44 PM   #2
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It depends on the output and input impedance of your devices.

if you are using a passive pre on one of the branches of the split. its impedance may change (does it? whats the set up) which might cause odd things to happen on the other input (main amp)

if the output impedance of the source is low enough you should usually be ok. watch out for ground loops. i can become complicated!
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Old 13th February 2007, 03:57 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
make sure BOTH power amps have a DC blocking capacitor on the input. Otherwise the input offset current will interact and may cause a problem.

If your two amps are high Zin then the preamp should be able to drive them.
Just try to get a 1:10 ratio between Pre Zout : Power Zin//Zin
eg. pre Zout=1k0 and both power Zin=20k works.
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Old 13th February 2007, 04:42 PM   #4
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Thank you for your replies.

This is obviously a little more complicated than I had thought (why I posted originally, I suppose), so I should have provided more details.

I will be using a cdp as transport, feeding a NOS DAC (powered by 12v DC). The signal will then go to a passive pre-amp, which will be a 50K stepped attenuator such as: http://www.diyfidelity.com.au/produc...products_id=32
After the passive pre-amp the signal will be powered by a Charlize T-amp.

I wish to use a sub/satelite combo for the speakers, so the sub (digital amp 12v DC) will need a feed after the stepped attenuator, in order to remain syncronized.

I do not want to feed the satelites through the subs XO, as I wish to preserve signal quality.

AndrewT: Is it simple to add DC blocking capacitors to both amps, without affecting the setup?
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Old 13th February 2007, 04:48 PM   #5
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by dublin78
......The signal will then go to a passive pre-amp, which will be a 50K stepped attenuator .........After the passive pre-amp the signal will be powered by a Charlize T-amp.........Is it simple to add DC blocking capacitors to both amps, without affecting the setup?
you're in trouble.
The maximum Zout of the passive is 50k/4=12k5 and worse, it varies as you adjust the volume.

Charlize? what input has it got?
No it's not simple to just add on a DC blocking cap without checking if the circuit suits it.
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Old 13th February 2007, 05:09 PM   #6
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The Charlize has Elna Cerafine input caps. Sorry, I can't see the values.

Would using an Alps Blue pot (50K) instead of the stepped attenuator make any difference? This is what the Charlize designer recommends.
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Old 13th February 2007, 11:49 PM   #7
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AndrewT: Thanks again.

Would adding a tube preamp like this http://www.autocostruire.com/catalog...roducts_id=329
be a solution? The output buffers are capable of sourcing 200 mA.

I am keen to diy, but I do not understand many basic principals. I am trying to learn as I go.
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Old 14th February 2007, 05:00 AM   #8
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I dont know about that thing. if it runs from 12 volts it must have an inverter or something for the tube high voltage? in that case ther would be high frequency electronics on the same board as your audio signal.
or may be the tube doesn't do anything

A simple op amp buffer ought to do the trick, you could also balance the main amp so it does not have to try and output the bass frequencies to the satellites. you could make an op amp filter or just block the lower frequencies by choosing the right input capacitor for the charlise.
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Old 14th February 2007, 08:51 AM   #9
AndrewT is online now AndrewT  Scotland
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Hi,
my Croft valve pre-amp has Zout~=1k. I have to be careful with cables for this.
All my other sources are below 200r.
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Old 14th February 2007, 10:07 AM   #10
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Neutron7: Thanks for replying agian.
Quote:
may be the tube doesn't do anything
I am a sceptic also (a healthy one).

An op amp buffer does seem to be the solution. I have spent an hour or so on Google, and have not found anything suitable. Do you know of anyone who makes a module that runs off 12V DC?
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