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Old 13th April 2006, 10:49 PM   #1
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Default Increasing Gain on Sub Amp

First I want to thank everyone who helped me fix my DH-200.

I have my Hafler driving my 2 subs. The amp is not bridged.

The problem I have is the gain on the reciever sometimes reaches the high+'s. I'm trying to figure out a way to increase the gain on the signal coming out of the sub preout on the reciever without raising the reciever's gain. Any suggestions?

My 2 subs are hooked in left and right channel and the sub preout is connected to a y-adapter then to left and right input on amp.
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Old 14th April 2006, 01:18 AM   #2
clem_o is offline clem_o  Philippines
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No quick way, I think. You'd have to put a small gain stage between your receiver's sub-out and your Y connector. Almost any single op-amp will do fine; configure it as non-inverting with a gain of 2. You'll have to build up a PCB as well as a dual-voltage power supply.

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Old 14th April 2006, 01:22 AM   #3
CBS240 is offline CBS240  United States
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Perhaps a small simple op-amp circuit/w a filter would be useful for a X2 gain of sub frequencies. Op-amps typically have a lower slew rate(not all of course) but that would not be such a factor for sub frequencies. Just be sure to use a PS regulator. Another option would be to go descrete, but that is much less simple.



EDIT>Aaaahhh clem_o, you beat me to it...
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Old 14th April 2006, 01:30 AM   #4
clem_o is offline clem_o  Philippines
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Just by a few moments, CBS240! Nice we agree on an arbitrary gain of 2.... :-)

Cheers!
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Old 14th April 2006, 10:32 AM   #5
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jakelm3075, if you can get the circuit diagram for the sub amp you could lower the feedback a LITTLE and that in turn raises the gain, all it takes is one resistor change in the feedback loop. Easy and bonus the amp becomes more stable as well.

Cheers George
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Old 14th April 2006, 11:04 AM   #6
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jakelm3075, I just looked at the circuit for the DH-200, if you change the resistor R25 100ohm for 80ohm, this should change your gain from 22 to 27.5 this could be enough, just try it, usually you don't need much to balance out, different amps, and you could vary that up and down a little to get it right, I've done many bi-amped system using this, it's much cleaner than adding gain stages, and sounds better also.

George
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Old 15th April 2006, 04:56 AM   #7
djk is offline djk
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I have changed R25 to as low as 50 ohms, and the amp worked fine.
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Old 15th April 2006, 07:33 AM   #8
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Quote:
Originally posted by djk
I have changed R25 to as low as 50 ohms, and the amp worked fine.


If you go as low as 50ohm, it would be a good idea, for the bipolar electrolytic 470uf (C5) above it to be changed to 680 or 1000uf as it controls the low fequency roll off of the feedback, with the 100ohm and the 470uf it's 3.3hz -3db, with the 50ohm it's 6.6hz -3db.

Cheers George
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Old 15th April 2006, 08:04 AM   #9
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My crossover had a hi-pass filter with a Q=2 at 31hz (for PA), I ended up with a pair of DH500 that were modified, and then moving them to MF and HF, and going BJT for the LF.

No matter what I did to them, I couldn't get the low end like I could out of the BJT amps. They are still in use for MF and HF though (25 years later).
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Old 15th April 2006, 08:11 AM   #10
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I will try the 80ohm for r25..I dont need much gain, so this should do just fine. Thanks all.

I dont think roll off from 6.6 to 3.3 will make that much difference, especially if its only 3dbs. But I appreciate the suggestion.


Jake
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