Poor Man's Pultec EQP1-A Build Support Thread

[ruffrecords]

Thanks Ian
yes the pot slide is connected to the top of 47uf cap.
Sorry I'm not an expert :
"Loss of low frequency usually means the EQ is loaded too much" ?
Can you explain what could be?
I'm using a this circuit with Carnhill 2281...
Thanks!

The output of the EQ needs a gain make up amplifier. This needs to have a high impedance input;preferably at least 470K. If it is much lower than this it loads the output of the EQ too much which results in loss of bass response.

It is not deigned to be fed directly to a transformer, Check out the documentation in the PMEQP1A folder under the DIY tab of my web site:

http://www.customtubeconsoles.com/diy

Cheers

Ian

 

[krabbencutter]

Hi Ian,

after jumping through some more hoops and wiggling with some other stuff I'm ready to built your suggested amplifier stage.
As this will be part of my Eurorack, it will run from +/-12v and the input/output signal will be unbalanced.
- Do I need to take any special measures to separate signal & power ground?
- I guess the input signal should be buffered before hitting the EQ? If so I could just use the second opamp of the TL072.

Thanks

 

[L´Andratté]

Check ruffrecords folder posted above. There´s exactly the schematic you want in there! 

 

[krabbencutter]

Check ruffrecords folder posted above. There´s exactly the schematic you want in there! 

Thanks, my questions are regarding his schematic (the TL072 dual supply output stage).

 

[ruffrecords]

Hi Ian,

after jumping through some more hoops and wiggling with some other stuff I'm ready to built your suggested amplifier stage.
As this will be part of my Eurorack, it will run from +/-12v and the input/output signal will be unbalanced.
- Do I need to take any special measures to separate signal & power ground?
- I guess the input signal should be buffered before hitting the EQ? If so I could just use the second opamp of the TL072.

Thanks

The input signal does not have to be buffered. The EQ input impedance is nominally 10K but varies as you vary the controls. As long as your driving source can work happily into a 5K load it should be fine to go in direct, especially as you are working unbalanced.

For advice on what to do with the various sorts of ground check out my Grouding 101 document in the Power folder under the DIY tab of my web site.

Cheers

Ian

 

[ilfungo]

Hi Ian
I want to try your  TL072 make up stage.
It's possible to drive directly from output a 600 ohm transformer?
Thanks!

 

[ruffrecords]

Hi Ian
I want to try your  TL072 make up stage.
It's possible to drive directly from output a 600 ohm transformer?
Thanks!

The smallest load a TL072 will drive is 2K ohms. So you might be able to get it to drive a 600:600 transformer provided the transformer secondary is loaded with 2K or higher. I have not tried this so I cannot be sure.

Cheers

Ian

 

[ilfungo]

Hi IAN!
The  TL072 make up sound good!!!
Just last info I'm using ll5402 transformer on input
I need 12k resistor on secondary?
If yes can you explain why?
Thanks!

 

[ruffrecords]

Hi IAN!
The  TL072 make up sound good!!!
Just last info I'm using ll5402 transformer on input
I need 12k resistor on secondary?
If yes can you explain why?
Thanks!

According to its data sheet. the LL5402 is an output transformer designed for use in special feedback outputs. It is not really suitable for use as an input transformer.

With the controls set to flat. the input impedance of the poor man's EQP1A is about 55K. In order to ensure the 10K:10K input transformer sees a load close to 10K the 12K resistor is used. 12K//55K = 9K8.

Cheers

Ian

 

[shot]

I'm having issues with high frequency roll off similar to this post on page 29.
But since I've built a different filter section, I've opened another thread for it.
Please chime in with some solution if you can!



Luka

 

[Alexwfm]

Hello,

Was just looking for some PCB's to make a stereo version of the eq with tube make up, does anyone know how to possibly get hold of them?

I tried writing Ian an email but afraid I might have ended up in the junk!

Cheers,
Alex

 

[ruffrecords]

Hello,

Was just looking for some PCB's to make a stereo version of the eq with tube make up, does anyone know how to possibly get hold of them?

I tried writing Ian an email but afraid I might have ended up in the junk!

Cheers,
Alex

I still have some boards left. My current email address is in my groupDIY profile and also on my web site. I checked my spam folder and you are not in there. Try emailing me a gain and I will look out for it.

Cheers

Ian

 

[3nity]

Hi Ian.
If using a bA283 output style is there any changes that i would have to do?
Thanks in advance.

 

[ruffrecords]

Hi Ian.
If using a bA283 output style is there any changes that i would have to do?
Thanks in advance.

Unfortunately the BA283 has a relatively low input impedance and this EQ prefers to work into an input impedance of at least 470K. So, if you want to use the BA283 then it would be a good idea to consider using a FET follower after the EQ and before the BA283.

Cheers

Ian

 

[skal1]

Hi Ian,

just a quick ? about  TL072 circuits for the PMEQP1A and all my other passive EQs:

https://drive.google.com/open?id=0B_n67A1hN3qtSkg5MW9wRDBWS1k

can i use this to work with the  original pultec filter circuit , without any changes to your  TL072 circuit.

Regards

skal

 

[ruffrecords]

Yes you can.

Cheers

Ian

 

[skal1]

Yes you can.

Cheers

Ian

cool

skal

 

[winner]

I want to ask, if I need to adjust the bandwidth（HI BOOST） like Pultec PEQ1A, what should I do Thanks for your patience

 

[ruffrecords]

I want to ask, if I need to adjust the bandwidth（HI BOOST） like Pultec PEQ1A, what should I do Thanks for your patience

One of the cost reductions used in the PMEQP1A was to remove the hi boost inductor and replace it with a simple RC circuit. Unfortunately this means there is no option to alter the bandwidth.

Cheers

Ian

 

[ilfungo]

Hi Ian
It's possibile to use your tube make up stage in original pultec filter section?
I need to chenge something?
I' using sowter  3603 as input
Carnhill 2281 as output.
Thanks!