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EQP501 Passive Equalizer
alternative opamps
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Topic: alternative opamps
April 15, 2021, 05:22:39 AM
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conorc
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alternative opamps
Hi there,
I’m wondering if i can use a capi ca-0252 or a gar 1731 in the 501?
thanks!
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April 15, 2021, 06:56:16 PM
Reply #1
JPK
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Re: alternative opamps
Probably yes, as long as they do not output too much DC offset.
Check the DC volts on TP2. If it stays lower that a few millivolts then it's OK.
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JPK
April 16, 2021, 05:08:18 AM
Reply #2
conorc
Newbie
Posts: 18
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Re: alternative opamps
Great, thanks!
I have another question.
I finished the two 501s this evening and one seems to be working great (but need to take them in to the studio to check audio). The other one was fine initially and gave the correct + and - 16v readings on the test points, but my probe touched off something (possibly the mosfet?) and now the positive rail is down to a steady 0.7 volts and the DOA LED no longer illuminates.
Do I need to replace Q1 maybe?
And if so, would this do the job?
https://www.newark.com/microchip/2n7000-g/mosfet-n-ch-60v-0-2a-to-92/dp/31AC2702?gclid=Cj0KCQjwyN-DBhCDARIsAFOELTkqyoyp0yevUdIfvNucXoHB6yvPcb0Kc78KrM68g0tM06Z3Sy4rm88aAhsgEALw_wcB&mckv=sV3NYpyb3_dc
|pcrid|492622077317|plid||kword||match||slid||product|31AC2702|pgrid|108905520690|ptaid|pla-932219301484|&CMP=KNC-GUSA-GEN-Shopping-NewStructure-MPN-Semiconductors-Discretes#
Thanks!
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April 16, 2021, 11:09:12 AM
Reply #3
JPK
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Re: alternative opamps
A damaged Q1 could not put the +16V down.
Remove the DOA and check the +16V again.
If not the DOA,
check
the diode D1 (can be done in circuit).
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JPK
April 16, 2021, 04:39:56 PM
Reply #4
conorc
Newbie
Posts: 18
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Re: alternative opamps
Ah ok. I measured D1 and it gives a voltage drop of 0.563. D2 and D3 also seem normal.
Thanks!
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April 16, 2021, 05:32:08 PM
Reply #5
conorc
Newbie
Posts: 18
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Re: alternative opamps
Removed the DOA and the + voltage is still down at -0.7
Also, I built 2 501s, so I checked the DOA in the other unit and it illuminates normally and the voltages at the test pins are normal in that unit with either of the 2 DOAs installed, so I don't think the DOA is the problem
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April 17, 2021, 04:51:04 AM
Reply #6
conorc
Newbie
Posts: 18
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Re: alternative opamps
Update: now both units have the same issue (the functioning one stopped working!), so I guess it must be a misplaced component as i built them side by side. Here are some images.
https://imgur.com/IGuXBTT
https://imgur.com/drFhves
https://imgur.com/dhbglzV
https://imgur.com/dhbglzV
https://imgur.com/dhbglzV
https://imgur.com/dhbglzV
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April 17, 2021, 09:45:02 AM
Reply #7
JPK
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Re: alternative opamps
Look for a reversed electrolytic, C10, C11, C14, C15 in particular.
Remove U1, the DOA and the front PCB and check the voltage rail again.
Check value of R21, R22, R23, direction of D3 and RLY1.
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JPK
April 19, 2021, 11:51:08 PM
Reply #8
conorc
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Posts: 18
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Re: alternative opamps
It looks to me like all of the resistors and EL caps are in the right place, but maybe you can see something in the pictures linked above?
I removed the opamp and pots panel, now the positive rail is zero (wandering up and down around 50mA to be precise).
Thanks!
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April 20, 2021, 08:54:03 AM
Reply #9
JPK
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Re: alternative opamps
Check the value and solder joints of R19. It is 1 ohms in series with the + rail.
Also check that the +16V rail comes through to the module. The issue could also be in the extender.
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JPK
April 20, 2021, 06:00:41 PM
Reply #10
conorc
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Posts: 18
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Re: alternative opamps
I checked the power headers of the extender, and they do indeed provide +16 and -16 as normal.
Measuring R19 at the top leg of the resistor I get +16v and at the bottom leg of R19 I get -0.7v.
Keep in mind that both modules initially worked perfectly, and failed after a few minutes of being powered up.
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April 21, 2021, 08:21:49 AM
Reply #11
JPK
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Re: alternative opamps
What value do you get when measuring R19 in circuit?
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JPK
April 21, 2021, 11:32:04 PM
Reply #12
conorc
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Posts: 18
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Re: alternative opamps
On one unit it's 0.38M, on the other I don't get anything (0.L on the DMM). That's with the units not powered up. Thanks!
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April 23, 2021, 03:08:16 PM
Reply #13
JPK
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Re: alternative opamps
Quote
on the other I don't get anything (0.L on the DMM).
This one looks damaged. Try replacing it.
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JPK
April 26, 2021, 04:48:43 PM
Reply #14
conorc
Newbie
Posts: 18
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Re: alternative opamps
Have ordered some replacement 1Rs (and some diodes and a couple of other parts just in case), will let you know!
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May 08, 2021, 09:41:51 PM
Reply #15
conorc
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Posts: 18
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Re: alternative opamps
Replaced the 1Rs and all is working perfectly
There was no visible damage to them but maybe they were defective from the factory? Might be worth testing the remaining ones in stock....
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May 10, 2021, 05:34:30 PM
Reply #16
JPK
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Re: alternative opamps
Congratulations!
I checked some 1R0's from our stock randomly and they are all OK. Although rare, defective parts can occur.
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JPK
May 10, 2021, 05:39:32 PM
Reply #17
conorc
Newbie
Posts: 18
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Re: alternative opamps
Yeah who knows really! The EQs sound excellent. The multiple low frequency options really allow you to dial in a very solid kick sound, great for electronic stuff.
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January 23, 2022, 06:44:08 PM
Reply #18
conorc
Newbie
Posts: 18
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Re: alternative opamps
Hi there,
After a few months of use, one of my EQP 501s has developed a problem: the gain has lowered considerably, especially in the low end. You can see images from Room EQ wizard here where I compare it to my other unit which seems to be doing great:
https://imgur.com/a/vgwcUQy
The first images are of the unit with all gains down to zero, the second has them up to about 50% (and the low attenuation also at 50%). Any thoughts on what might be causing this? Thanks!
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January 23, 2022, 07:50:13 PM
Reply #19
conorc
Newbie
Posts: 18
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Re: alternative opamps
PS: I have swapped the DOAs with no difference in the results. Also, the tests were conducted using the same 500 slot and cables, so no variables there.
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January 24, 2022, 09:30:03 AM
Reply #20
JPK
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Re: alternative opamps
With all the gains at 0, does the low frequency attenuation changes when changing the low frequency CPS?
In sucha case it would suggest an issue with the low freq attenuation potentiometer.
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JPK
January 25, 2022, 09:25:05 PM
Reply #21
conorc
Newbie
Posts: 18
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Re: alternative opamps
I just tested it and yes, the CPS does change the frequency response when all gains are at zero. Here's images of the CPS at 15hz and 100hz:
https://imgur.com/a/Fz0N3LB
If it is the low frequency pot that's the problem, what would you suggest to resolve it?
Thanks!
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January 26, 2022, 05:33:38 PM
Reply #22
JPK
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Re: alternative opamps
Can you check the P5 pot by measuring the resistance between the 2 extreme pins. It should vary from 0 to 100k.
If it doesn't you will need to replace the pot: Contact me by mail
here
.
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JPK
January 27, 2022, 07:47:15 PM
Reply #23
conorc
Newbie
Posts: 18
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Re: alternative opamps
I tested the pot and it actually seems fine: it moves smoothly from 0 all the way to the left to 10k all the way to the right. Anything else that might be a likely cause? Again, this unit has worked perfectly for 6 months before recently having this issue.
Thanks!
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January 28, 2022, 04:30:32 PM
Reply #24
JPK
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Re: alternative opamps
It must be the connections between the pot and the mainboard:
Check solder joints of:
- the pot,
- CN2A & CN2B the lower 2 pins, near the spacer.
You can check the continuity between the center pin of P5 and TP3 and C12 top pin.
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JPK
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EQP501 Passive Equalizer
alternative opamps
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