[apok]

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.

[JPK]

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.

[apok]

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. 

[apok]

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.

[JPK]

Send a 3VAC sine signal to the input and measure the AC voltage on:
TP1: 2VAC
TP3: 0.17VAC
TP2: 1.7VAC

[apok]

After testing I've seen different values 

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

[JPK]

The issue is in the passive section :
Potentiometers P1...P5, R10, R24, R25.

[apok]

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?

[JPK]

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)?

[apok]

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

[JPK]

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 ?

[apok]

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

[JPK]

Measure between the circled pins with low frequency ATTEN pot on 10.

[apok]

The resistance is floating from 1 to 0.9

[JPK]

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.

[apok]

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 

[JPK]

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.

[apok]

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.

[JPK]

On this picture, you can see the potentiometer shafts facing you.

[apok]

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

[jziemba001]

Hi,

I’m having a similar result, though maybe not as extreme.

When I send the unit a 0dBu (.775V) 1 kHz signal, I get the following reading from the output pins:
Bypass: .769V
Engaged: .852V

So if my math is correct, that’s roughly a ~ .89 dBu increase when the unit is engaged.

Following this thread, I’ve checked the following:

R5, R6, R7, R8, R12, R13, R25 all correct
R10, R24 correct

3V 1kHz signal
TP1: 2VAC (1.963)
TP3: 0.17VAC (.168)
TP2: 1.7VAC (1.731)

With the module unplugged, all pots at 0, 

- what resistance do you measure between TP1 and TP3 (?10k)? 
(9.87R)
- what resistance do you measure between TP1 and 0V (?11k)? 
(10.82K)
- what resistance do you measure between TP3 and 0V (?1k)? 
(.943K)

P3:
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 ? (9.87R)

I also checked all solder joints on all the potentiometers and they look good.

Is this less < 1 dBu increase in level I’m measuring at 1 kHz when engaging the unit considered normal behavior?  Or should I investigate anything?

Otherwise all functions seem to be operating normally, both with test audio signal generation (sine and white noise) and also musical material passing through it…and the unit sounds quite fantastic!

The small level bump is barely noticeable if at all when engaging and disengaging the unit with music playing through it.  Though I do here a small tick when it passes through the “off positions of the KCS switch, but I think this is normal as it is with most 500 series units since it uses an active relay?  The clicks are not present when switching without audio passing through.

I can send mdat files or screenshots of sweep measurements I took in REW with the unit in bypass and also engaged with all knobs set fully counter-clockwise if that's helpful.

Please let me know what you think!

Cheers,
Joe