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Old 6th February 2014, 04:31 AM   #1
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Default Modding an old EQ for seperate main/sub inputs

Ok... I wanted to modify an old eq to take separate inputs for main and sub and have main and sub outs with separate gain and volume for each.
Not many companies are doing this and I wanted to keep the use of the time alignment from my HU. Plus like most, I hate fumbling through the menu's to change a setting.
This is what I did...
Used an old EQ form the late 90's and drew a schematic with TINA.
Added a small board to add one more 072 and removed the fader and the rear output jacks. I put in a power connector like the ones on audio control units.
I took out the main/aux switch and used the aux input for the sub input and wired it to the 072 I added.
Cut the trace that goes to the sub crossover section and wired to the out of the 072 I added.
It's dead quite at idle and clean sounding for old 072 opamps. I did replace all the electrolytic caps.

With 1.6 vrms in and sweeping from 20hz to 20khz the output stays at 4.6 vrms. It starts clipping at 6.4vrms.
The sub out with the same input but sweeping from 20 to 160hz is 4.7vrms. It starts to clip at 6.6vrms
Pretty even...
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File Type: jpg 100_4458.JPG (509.0 KB, 56 views)
File Type: jpg 100_4456.jpg (509.4 KB, 50 views)
File Type: jpg 100_4460.JPG (781.2 KB, 51 views)
File Type: jpg 100_4464.jpg (512.2 KB, 47 views)
File Type: jpg TL072MOD1 EQ.JPG (271.5 KB, 32 views)

Last edited by 90scaraudio; 6th February 2014 at 11:15 PM. Reason: none
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Old 6th February 2014, 02:46 PM   #2
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Schemi of EQ before mod.... Wasn't sure what to do with the fader circuit so me not being an engineer pulled the fader and put a 100k resistor in there. Maybe could have left it out, Don't know.
Any Ideas?
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Last edited by 90scaraudio; 6th February 2014 at 02:51 PM.
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Old 6th February 2014, 02:47 PM   #3
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And I was thinking about doing this.... It would be very easy...
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Old 6th February 2014, 11:14 PM   #4
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Default Modding an old EQ for seperate main/sub inputs

The reason I wanted to do this inexpensively, (except time), is I could not find much of what I could use in my car. To me there's nothing like a knob to turn quickly.
I found this item, ARC AUDIO XEQ but for $300.00+.... Wow!

This AudioControl isn't bad but they used 5% carbon resistors and cheap NJM opamps throughout!
AUDIOCONTROL OVERDRIVE PLUS $99.00

I have one in the car but the optional $18.00 ACR-1 BASS KNOB REMOTE CONTROL has a very NON-Linear taper, very sensitive above one-o'clock and up.


Been thinking about modding one of these..PLANET AUDIO PEQ15
..Cheap... $40.00 and newer than what I did already.


Last edited by 90scaraudio; 6th February 2014 at 11:18 PM. Reason: none
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Old 14th February 2014, 05:49 PM   #5
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Fader removed....
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Old 14th February 2014, 05:52 PM   #6
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Quote:
Originally Posted by 90scaraudio View Post
The reason I wanted to do this inexpensively, (except time), is I could not find much of what I could use in my car. To me there's nothing like a knob to turn quickly.
I found this item, ARC AUDIO XEQ but for $300.00+.... Wow!

This AudioControl isn't bad but they used 5% carbon resistors and cheap opamps throughout!
AUDIOCONTROL OVERDRIVE PLUS $99.00

I have one in the car but the optional $18.00 ACR-1 BASS KNOB REMOTE CONTROL has a very NON-Linear taper, very sensitive above one-o'clock and up.


Been thinking about modding one of these..PLANET AUDIO PEQ15
..Cheap... $40.00 and newer than what I did already.

!!!
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Old 15th February 2014, 12:40 AM   #7
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I like that mod
I have a pyramid crossover (CR73G) that amp trying to mod for some time.
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Old 17th February 2014, 12:55 PM   #8
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Quote:
Originally Posted by 90scaraudio View Post
The reason I wanted to do this inexpensively, (except time), is I could not find much of what I could use in my car. To me there's nothing like a knob to turn quickly.
I found this item, ARC AUDIO XEQ but for $300.00+.... Wow!

This AudioControl isn't bad but they used 5% carbon resistors and cheap BA opamps throughout!
AUDIOCONTROL OVERDRIVE PLUS $99.00

I have one in the car but the optional $18.00 ACR-1 BASS KNOB REMOTE CONTROL has a very NON-Linear taper, very sensitive above one-o'clock and up.


Been thinking about modding one of these..PLANET AUDIO PEQ15
..Cheap... $40.00 and newer than what I did already.

So why does AudioControl cost quite a bit, but use these "BA4560" They cost $0.64 from mouser and what about there slew rate???... I've found them in most everything they have....
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Old 17th February 2014, 02:39 PM   #9
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The BA4560 is better than what others use (TL072). PG uses the BA4560 in many (if not all, well not all) high end amplifiers such as the M series, MPS , ZX, TI's and others.

Trust me they cost much less than 0.64 when you purchase them by the thousands, that doesn't make them less suitable.


Could you imagine replacing all those with BB, you will spend around 40.00....that's a lot of $$$$, as a manufacture you would have to increase the MRSP of your product just to justify the use of the BB.
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Old 17th February 2014, 03:20 PM   #10
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Than whats the big thing about Slew Rates???
OPA604 SLEW RATE: 25V/μs THD 0.0003
BA4560 SLEW RATE: 1V/μs THD 0.005
TL072 SLEW RATE: 13V/μs THD 0.003

I thought the higher the V/us the better???
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