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Old 24th May 2005, 03:32 AM   #31
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Location: Puget Sound
I agree and am hoping that very little EQ'ing will be needed. That's why I bought the Behringer.
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Old 25th May 2005, 02:40 AM   #32
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The Rane is worth the money if you need its features. Being able to draw your own signal path with its CAD-style interface is a big plus. And it's quieter than the Behringer. However, it won't eliminate the need for a volume control. You can control digital gain blocks with a pot but the analog gain is set and forget. It works great for optimizing your gain structure but it can't be adjusted on the fly. The best you could do is set up 8 presets with different analog gains and change to them with a switch. That's actually not too bad an option. Maybe 4 presets, 0, -10, -20, -30dB (-30 is the max attenuation with the analog control.) Pick one for the mood you're in and you could do the fine tuning with the preamp without losing much digital resolution.
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Old 25th May 2005, 11:58 AM   #33
Keld is offline Keld  Sweden
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Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,

SNIP


Each RCA output pair receives two toggle-switches, one changeover and the other center neutral. These will become switches to select between the two polarities and -18/-12/-24db attenuation.

From pin2 & pin3 connect a pair each of 2K2 (1% or better) resistors in series to pin1 (ground).

The join between the two resistors for each polarity is connected to one of the two poles of the polarity selector. Thus at the flick of a switch the polarity of any given way can be inverted.

Further the "center neutral" switch connects a 2K2 resistor (-18db) or a 750R resistor (-24db) between the two junktions of the 2K2 pairs.
SNIP

Sayonara
I have tried to get this description down on paper, but I dont get it! Could anybody please help me draw the circuit.

DVC Keld
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Old 3rd June 2005, 06:49 AM   #34
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Quote:
Originally posted by Davey
Yes, I understand this is different than what is recommeded by Rane and Behringer.
I don't know how much clearer I can say it....don't connect pin 1 to 3 on the outputs. Pin 1 goes to your RCA shield and pin 2 goes to the RCA center. Pin 3 is unused and unterminated.

Davey.
So I just got around to doing this to the output cables and it didn't seem to affect the output level at all. It was supposed to lower the output, correct?
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Old 3rd June 2005, 08:04 AM   #35
AndrewT is online now AndrewT  Scotland
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Hi,
can I try?
Connect 10k to pin 3 and another 10k to pin 2.
Connect 200r between the two free ends of the 10ks, this forms a pi network that balances the outputs from the DCX.
Connect the screen to the far end of the 10k from pin 3. This is now your ground for the next stage.
Connect an RCA phono to both ends of the 200r. The ground (pin 3 10k) goes to the ground of the RCA and the hot end of 200r (pin 2 10k) goes to the input of the RCA.
you now have a source impedance of 200r to drive a cable and input greater than 2k.
attenuation is about -34db. 270r gives about -31db, 470r gives about -27db.
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Old 8th June 2005, 04:47 PM   #36
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Quote:
Originally posted by AndrewT
Hi,
can I try?
Connect 10k to pin 3 and another 10k to pin 2.
Connect 200r between the two free ends of the 10ks, this forms a pi network that balances the outputs from the DCX.
Connect the screen to the far end of the 10k from pin 3. This is now your ground for the next stage.
Connect an RCA phono to both ends of the 200r. The ground (pin 3 10k) goes to the ground of the RCA and the hot end of 200r (pin 2 10k) goes to the input of the RCA.
you now have a source impedance of 200r to drive a cable and input greater than 2k.
attenuation is about -34db. 270r gives about -31db, 470r gives about -27db.
I'm going to try this tonight. I have just enough parts on hand to do two cables with 220r and four with 470r. If I understand you correctly, the 220r will have a little less than-34dB of attenuation.

I'll use that on my woofers which are currently boosted to +15dB compared to my mid and tweet which are -13dB. It should allow me to bring the the levels closer together and allow me a little wiggle room.

As soon as my 12AT7s arrive, I'll swap them and a couple resistors into my grounded grid. Sure wish my foreplay was still operational. Seems like this would be a perfect use for it.
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Old 31st August 2005, 08:59 PM   #37
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I ended up building Kuei's interface unit which has worked well although I opted to not include the polarity selector.

At the time I didn't have any 750Rs on hand and other things to do so I just lived with it in -18dB mode.

But I finally got tired of the hiss and tried 540R (maybe it was 560R) to quiet things further but still not enough with 100dB/W drivers.

I want to try smaller values for more attenuation but I don't really understand how to determine the attenuation by the resistor value nor how low I can go in value.

Can anyone shed some light on this?

Thanks.
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Old 31st August 2005, 09:48 PM   #38
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally posted by ultrachrome
I want to try smaller values for more attenuation but I don't really understand how to determine the attenuation by the resistor value nor how low I can go in value.

Can anyone shed some light on this?
You can safely go down to a dead short.

Why not get a 1K adjustable resistorfor testing and turn it as low as you need?

Apart from that, if you look, the attenuation progresses in appx 6db steps with each step halving the value (to nearest preferred value), so halve the 750R to 390R for around 24db attenuation.

What Amplifier(s) are you using?

Ciao T
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Old 31st August 2005, 10:14 PM   #39
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That's easy enough to follow. Thanks.

I'm using an Adcom GFA-545II (150W @ 4ohm) for the woofers and four channels of a Panasonic XR45 receiver for the midrange and tweeter.

The panasonic replaced an AKSA55 and BrianGT LM3875 amps. That setup was too clumsy to move.

The volume control on the Panasonic is quite useful for helping match with the woofers and the convenience outweighs any SQ issues. Also allows me to easily adjust the relative woofer level to suit my mood.

Currently the Panasonic volume is set to -18dB. In the DCX my woofers are at +14dB and my Mid and tweet are around +6dB. So about 26dB difference between the woofers and mid/tweet.
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Old 31st August 2005, 10:33 PM   #40
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by ultrachrome
I'm using an Adcom GFA-545II (150W @ 4ohm) for the woofers and four channels of a Panasonic XR45 receiver for the midrange and tweeter.
Interesting, how do you like the pannie?

Quote:
Originally posted by ultrachrome
Currently the Panasonic volume is set to -18dB. In the DCX my woofers are at +14dB and my Mid and tweet are around +6dB. So about 26dB difference between the woofers and mid/tweet.
Wow, that is a lot. Try getting the woofers back to no gain, the add pads (fixed) for 26db on mid and tweeter. As long as the Pannie is quiet by itself (easily tested by shorting the inputs and turning the volume all the way up), it shuld be quiet after the DCX, it has around 110db S/N, so if it hisses you have miles too much gain.

Ciao T
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