1

EQP501 Passive Equalizer / Re: alternative opamps

« on: February 03, 2022, 11:08:11 PM »

Reflowed all of the solder joints at the pot and the headers, and we're back in action! Thanks for the help.

2

EQP501 Passive Equalizer / Re: alternative opamps

« on: January 27, 2022, 07:47:15 PM »

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!

3

EQP501 Passive Equalizer / Re: alternative opamps

« on: January 25, 2022, 09:25:05 PM »

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!

4

EQP501 Passive Equalizer / Re: alternative opamps

« on: January 23, 2022, 07:50:13 PM »

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.

5

EQP501 Passive Equalizer / Re: alternative opamps

« on: January 23, 2022, 06:44:08 PM »

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!

6

EQP501 Passive Equalizer / Re: alternative opamps

« on: May 10, 2021, 05:39:32 PM »

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.

7

EQP501 Passive Equalizer / Re: alternative opamps

« on: May 08, 2021, 09:41:51 PM »

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....

8

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 26, 2021, 04:48:43 PM »

Have ordered some replacement 1Rs (and some diodes and a couple of other parts just in case), will let you know!

9

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 21, 2021, 11:32:04 PM »

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!

10

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 20, 2021, 06:00:41 PM »

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. 

11

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 19, 2021, 11:51:08 PM »

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!

12

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 17, 2021, 04:51:04 AM »

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/dhbglzVhttps://imgur.com/dhbglzVhttps://imgur.com/dhbglzV

13

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 16, 2021, 05:32:08 PM »

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

14

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 16, 2021, 04:39:56 PM »

Ah ok. I measured D1 and it gives a voltage drop of 0.563. D2 and D3 also seem normal. 
Thanks!

15

EQP501 Passive Equalizer / Re: alternative opamps

« on: April 16, 2021, 05:08:18 AM »

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!

16

EQP501 Passive Equalizer / alternative opamps

« on: April 15, 2021, 05:22:39 AM »

Hi there, 
I’m wondering if i can use a capi ca-0252 or a gar 1731 in the 501? 
thanks!

17

TS500 Tape Simulator / Re: types of OPA2134

« on: April 15, 2021, 05:20:10 AM »

Fantastic, thanks!

18

TS500 Tape Simulator / types of OPA2134

« on: April 13, 2021, 03:19:59 PM »

Hi all,

I have just finished building a pair of TS500s and everything went smoothly except for one little issue. On one unit, the OPA2134 was in backwards, so when i plugged it in I noticed some magic smoke. I powered it down in a hurry and there's no major damage done it seems –the 2134 from the other unit works fine in there and it all sounds great, but I have a couple of questions as I want to use these 2 units in stereo and to make sure that there's no issues.

1. I can get Texas Instruments OPA2134s more easily and cheaply than Burr Browns. Would there be a sonic difference if I used one in one unit? (again, thinking about stereo applications)

2. Might the power transistor (Q1) have been damaged by the reversed opamp and should I replace that too?

Thanks!