Poor Man's Pultec EQP1-A Build Support Thread

[anjing]

Hi all,
  I think i've read most the thread and i did not find anything that looks like the problem i have...I'm using the P3band pcb with carnhill inductors. What happens is when i choose low cut with the toggle switch everything drops of about 5db....I have a two position switch either dip or boost no bypass...The cut seems a bit thinner then the boost but if i understand correctly is normal.
  If i look at the schematic i see a 1k resistor to ground but on the pcb i see a 470 so i tried changing that but it's not the cause... 

If anyone has any idea of how i could solve this...

Big thanks in advance!

Pierre

 

[ruffrecords]

Hi Pierre,

If you lose 5dB when you switch in the mid, the first thing that comes to mind is that perhaps the mid pot is the wrong value. It should be 47K or 50K. Maybe you fitted a 4K7 or 5K?

Cheers

Ian

 

[anjing]

Good day Ian,
    I had a 50k log. Now i have a 50k lin and the response is more progressive but in both case i get the 5db loss...
Thanks again for your help!

Regards,

Pierre

 

[ruffrecords]

Good day Ian,
    I had a 50k log. Now i have a 50k lin and the response is more progressive but in both case i get the 5db loss...
Thanks again for your help!

Regards,

Pierre

Is the 5dB loss right across the spectrum?

Cheers

Ian

 

[anjing]

yes across the spectrum!

Regards!

Pierre

 

[ruffrecords]

yes across the spectrum!

Regards!

Pierre

Mmmmmm. Odd. The only other thing I can think of is perhaps one of the capacitors is faulty or there is a solder bridge some where. Does it work OK on boost?

Cheers

Ian

 

[anjing]

On boost it's ok, could it be a wrong value cap because i have the same problem  on all 4 channels so it is less likely to have a solder bridge.
If it was a wrong value cap would'nt the problem only be on that certain frequency?
Think of it it's hard to say if it's a 5db loss on the mid cut or a 5 db boost on low boost...

Regards,

Pierre

 

[ruffrecords]

On boost it's ok, could it be a wrong value cap because i have the same problem  on all 4 channels so it is less likely to have a solder bridge.
If it was a wrong value cap would'nt the problem only be on that certain frequency?
Think of it it's hard to say if it's a 5db loss on the mid cut or a 5 db boost on low boost...

Regards,

Pierre

I was thinking more of a faulty cap than a wrong value. If one of them was short circuit for example that might explain why the 5dB drop occurs right across the audio spectrum. But if you have the same effect on four boards that's still rather odd.

I am not sure about your last comment. Are you saying the 5dB cut is not the same across the audio band?

Cheers

Ian

 

[anjing]

yes it across the audio band. but if the pad was adjusted at unision with the switch in the cut position it would a 5 db boost.

regards!

pierre

 

[ruffrecords]

yes it across the audio band. but if the pad was adjusted at unision with the switch in the cut position it would a 5 db boost.

regards!

pierre

OK. Have you got the cut/off/boost switch wired correctly?

Cheers

Ian

 

[anjing]

yes it across the audio band. but if the pad was adjusted at unision with the switch in the cut position it would a 5 db boost.

regards!

pierre

OK. Have you got the cut/off/boost switch wired correctly?

Cheers

Ian

It's wired like this

Salutations,

Pierre

 

[ruffrecords]

It's wired like this

Salutations,

Pierre
[/quote]

OK, thewiring looks OK. The  picture shows a SPDT switch - you are using a centre off type yes?

Cheers

Ian

 

[anjing]

I'm not using a center off type, is it important?

Pierre

 

[anjing]

the one i use is the on-on type.

 

[ruffrecords]

the one i use is the on-on type.

OK, that is the wrong type. You need the type with a centre off position optherwise you cannot turn off the mid boost/cut. The compromise that had to be made to get a simple mid boost/cut was that even with the pot at its maximum there would be a small resifual mid boost or cut. So the centre off switch allows the mid to be disconnected.

However, this does not explain your problem so it is something you need to do but I do not think it is the solution to the problem. Are you sure you have a 5K pot for the hi cut?

Cheers

Ian

 

[anjing]

Yes Ian Hi cut is 5k lin..

Cheers

Pierre

 

[ruffrecords]

Yes Ian Hi cut is 5k lin..

Cheers

Pierre

I am running out of ideas now and it's 11pm here. I'll sleep on it. Is it the same at all frequency settings?

Cheers

Ian

 

[anjing]

Yes Ian Hi cut is 5k lin..

Cheers

Pierre

I am running out of ideas now and it's 11pm here. I'll sleep on it. Is it the same at all frequency settings?

Cheers

Ian

Thanks a lot Ian, i'm sure we will find a solution in time! No rush!

Regards!

Pierre

 

[ruffrecords]

Good morning Pierre. I think it is time to check basics. Can you confirm the hi boost pot is 47K. With all the pots fully anti-clockwise, can you measure the dc resistance from the top of the hi cut pot to 0V and also from the top of the hi cut pot to the input.

Are you using Chrion's inductors?

Cheers

Ian

 

[anjing]

Good morning Pierre. I think it is time to check basics. Can you confirm the hi boost pot is 47K. With all the pots fully anti-clockwise, can you measure the dc resistance from the top of the hi cut pot to 0V and also from the top of the hi cut pot to the input.

Are you using Chrion's inductors?

Cheers

Ian

Good morning to you Ian,
    I get 14.6k from the top of the hi cut and pot 0V and to the input, with all the pot's fully anticlockwise. The same left over pot outside circuit does measure 45k on my meter. With all the pots clockwise i get  29.2k with the post fully clockwise and just bass boost really matters.

I'm using the carnhill inductors. I'm also using the caps value that were for the europe pots and not the north american values. I was under the impression that this would only alter the fréquence response?

Thanks Ian,

Pierre