Author Topic: Signal gain increase when engaged

April 26, 2021, 05:09:27 pm
Read 2979 times

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
Hi, 

I've built a EQP501 and I think that almost everything is working normal except for the gain level that increases a lot when the EQP501 is not on bypass mode. 

When on bypass mode it is the same volume/gain that I'm sending out. When it is engaged it gains some db, cant precise how much right now, but latter I'll let you know.


Is this the normal behaviour? What can I do to test/check for problems. 
I've already checked and reheat all the solders.

April 27, 2021, 09:14:01 am
Reply #1

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
This is not normal. The gain of the unit, when all the pots are at 0 is defined by 
R5, R6, R7, R8, R12, R13, R25.
Check you have the correct resistors in these places.
Also check you didn't swap some pots.
JPK

April 28, 2021, 11:03:30 am
Reply #2

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
Thank you very much for the answer. 

After analysing the Resistors are good and in the right place. But I noticed that the "2K2 Lin" is switched with the "100K Log" :/ need to change those and I'll let you know if this solves the issue. 

April 28, 2021, 06:16:24 pm
Reply #3

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
After changing the two swapped pots, the problem persists..

It gains some db, in bypass ok K20 it's around -6.5db and when active it goes around 3db .. it's a lot.
« Last Edit: April 30, 2021, 12:53:39 am by apok »

April 30, 2021, 03:27:43 pm
Reply #4

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
Send a 3VAC sine signal to the input and measure the AC voltage on:
TP1: 2VAC
TP3: 0.17VAC
TP2: 1.7VAC
JPK

May 02, 2021, 09:28:19 pm
Reply #5

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
After testing I've seen different values ???

0V -> TP1 : 1,999
0V -> TP3 : 0,564
0V -> TP2 : 5,804

May 03, 2021, 10:22:33 am
Reply #6

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
The issue is in the passive section :
Potentiometers P1...P5, R10, R24, R25.
JPK

May 04, 2021, 12:58:43 pm
Reply #7

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
The pots P1... P5 and the resistors R10, R24 and R25 that you mentioned are right and the ones from assembly guide.

Is there any possibility that this can be the Film Capacitors?

May 05, 2021, 10:14:48 am
Reply #8

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile

Quote
Is there any possibility that this can be the Film Capacitors?
No.

With the module unplugged, all pots at 0, 

- what resistance do you measure between TP1 and TP3 (?10k)?
- what resistance do you measure between TP1 and 0V (?11k)?
- what resistance do you measure between TP3 and 0V (?1k)?
JPK

May 17, 2021, 07:24:46 pm
Reply #9

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
Hi,

Answers inline

- what resistance do you measure between TP1 and TP3 (?10k)?
Yes

- what resistance do you measure between TP1 and 0V (?11k)?
No, ?15.7K

- what resistance do you measure between TP3 and 0V (?1k)?
No, ?4.6K

« Last Edit: May 21, 2021, 09:41:56 am by apok »

May 21, 2021, 11:38:48 am
Reply #10

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
It looks like your P3 pot is not correct. It should be 1k.
Can you measure it, between the 2 side pins, in circuit, after disconnecting the front PCB from the main PCB and with Low frequency ATTEN pot on 10 ?
JPK

May 21, 2021, 02:24:08 pm
Reply #11

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
It looks like your P3 pot is not correct. It should be 1k.
Can you measure it, between the 2 side pins, in circuit, after disconnecting the front PCB from the main PCB and with Low frequency ATTEN pot on 10 ?

I didn't get where to measure, can you please add some pics?

My pots pcb is like this:
http://imgur.com/a/7ZhfpTP
« Last Edit: May 21, 2021, 02:30:02 pm by apok »

May 24, 2021, 09:06:15 am
Reply #12

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
Measure between the circled pins with low frequency ATTEN pot on 10.

JPK

May 25, 2021, 11:34:14 am
Reply #13

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
The resistance is floating from 1 to 0.9

May 25, 2021, 05:49:18 pm
Reply #14

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile

Quote
from 1 to 0.9
What unit? ohms, kilo-ohms, megaohms?

It should not be floating. Check the pot solder joints.
Check the resistances between the center pin and the side pins for 3 pot positions : min, center and max.
JPK

May 26, 2021, 12:14:33 pm
Reply #15

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
I've made a new measurement today and it was 0.8 ohms 

The resistance for the others is like so:

Center and right:
Boost on minimum 0.6 ohm 
Boost on middle - 512.6 ohm 
Boost on max - 971 ohm 

Center and left:

Boost on minimum 0.2 ohm 
Boost on middle - 0.2 ohm 
Boost on max - 0.2 ohm 

May 26, 2021, 03:43:04 pm
Reply #16

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
Boost on minimum : you mean Attenuation on minimum, right? Because P3 sets the HF attenuation.
If so, then you have a short circuit between the center and left pins. Look for solder bridge on the pins or R24.
JPK

May 27, 2021, 11:34:55 am
Reply #17

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
Boost on minimum : you mean Attenuation on minimum, right? Because P3 sets the HF attenuation.
If so, then you have a short circuit between the center and left pins. Look for solder bridge on the pins or R24.
Maybe I misunderstood what you requested. 

So I measured on the P3 which is the Boost from the Low frequencies.. 

On this image https://www.soundskulptor.com/docs/eqp501-layout-01.pdf the pots are supposed to be placed when front facing the pcb? If so then I have all the pots wrong.

May 28, 2021, 11:13:11 am
Reply #18

JPK

  • Administrator
  • Hero Member
  • *****
  • Posts: 638
  • Karma: +19/-0
    • View Profile
On this picture, you can see the potentiometer shafts facing you.
JPK

June 07, 2021, 10:48:19 pm
Reply #19

apok

  • Newbie
  • *
  • Posts: 15
  • Karma: +0/-0
    • View Profile
I've already solved the problem, it was on the op-amp don't know how but one of the resistor 5R6 that are there to protect the pcb did not burn before but now it have.. I've ordered one from you and it is ok, I guess..

Thanks for the help