Poor Man's Pultec EQP1-A

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
ruffrecords said:
Chris_V said:
ppa said:
this is the schematic

That's a lot of "gnd" for one design  ;)
BTW, there is still a mistake I think, the power supply of the upper left OPA604 differs from the others.

I think you will need to change the value of C250 as well if you want any HF response!

Cheers

Ian

yes, C250 needs to be changed,

BTW it changes the HF response a lot using Poor Man's Pultec EQP1-A.

Using my fet opamps it could be 10pF to avoid to change the HF response in your design.


PS: this my schematic cames from a trasformerless 16 channels summing amp that I am designing , so I have changed some values and also forgotten to change some others..........  ::) , I'm reviewing it another time and finishing the PCB.


thank you Ian


cheers
Pier Paolo


 
Chris_V said:
ppa said:
this is the schematic

That's a lot of "gnd" for one design  ;)
BTW, there is still a mistake I think, the power supply of the upper left OPA604 differs from the others.


I have separated the signal ground from the power gnd for lowest noise, this my schematic cames from a trasformerless 16 channels summing amp that I am designing , so it cames with the complex ground circuit needed for it , but BTW i prefer the separate grounds.

regarding the OPA604 it can work at +-24V power supply .
BTW the circuit is designed also for 2520, than can be used  many opamps can be used being the power rails at +-16V

However it's a good idea using some jumpers to use the same power supply voltages of the other IC opamps if needed, thank you  :D
 
ppa said:
regarding the OPA604 it can work at +-24V power supply.

I was wondering why such low 12V rails when many of your DOA's and OPA604 are happy with double that. But I wouldn't use OPA604 at all. LME49870 is a much better performing modern equivalent where you could still run 22V rails.
 
Kingston said:
ppa said:
regarding the OPA604 it can work at +-24V power supply.

I was wondering why such low 12V rails when many of your DOA's and OPA604 are happy with double that. But I wouldn't use OPA604 at all. LME49870 is a much better performing modern equivalent where you could still run 22V rails.



good question,

in my circuit is not required higher voltages for those
opamps that are used only as servo DC's,

on the contrary IC1 (as optional at the DOA1), that is used to sbalance the input signal, is connected directly to the main power supply voltages.

I have indicated the opa604 but the circuit is designed for many IC opamps, because as you have told , not all like the opa604.

I have added the regulators to use many IC opamps as possible, since that several opamps (as the TL071, for example) can not run at the same power supply voltage of the DOA's.  For the IC opamps that work at the same power supply voltage of the DOA's it's possible to bypass the regulators just with two wire bridges.

This circuit is designed for +-24V of power but also to operate at +-16V to permit to use the 2520 opamps and, since the 7815 and 7915 can not work with an input voltages of +-16V I have used the 7812 and 7912 regulators.
 
ppa said:
I have added the regulators to use many IC opamps as possible

I didn't see that at first but makes sense now.

The inductor-less pultec circuit with these buffers would make a great small form factor project. four channels in 2U rack, or api 500 (or whatever variant) comes to mind.
 
moreover, since the fet input is preferred for the inductor-less pulteq eq I am thinking to add a simple fet buffer, to use no fet input DOA's in the out stage, as , for example the 2520 or JE 990.
 
I have created a simple spreadsheet for calculating the capacitor values needed for the hi and lo cut and boost of the poor man's EQP1A. I have included a range of hi and lo frequencies but you can calculate your own simply by changing the values in the 'Switch f' column. The spreadsheet also gives an indication of where the lo dip and hi peak occurs when you use max boost and cut at any frequency.

The spreadsheet calculates capacitor values to 2 decimal places so you will have to work out the nearest available standard values or combinations thereof yourself. It is not necessary for the values to be exact for correct operation of the circuit.

http://www.ianbell.ukfsn.org/pics/capcalc.xls

Cheers

Ian
 
the new schematic with the fet buffer added to use bipolar DOA's. 
 

Attachments

  • IO section pulteq eq2.pdf
    270.7 KB · Views: 239
Lets make some sense of what you've got on that pdf.

Top left: a balanced Line input using a DOA and with a servo. I assume the servo is there to eliminate the need for DC blocking electrolytic capacitors.

Top centre: 12v Power supply circuits for the servos, standard stuff.

Bottom right: a DOA circuit to provide gain to boost the post filter signal back up to line level.

Bottom left: A FET circuit to present a high impedance to the signal from the EQ network

Is the FET circuit meant to be used with the DOA gain circuit or to replace it? I would expect the first option.
 
Ian, what would be the effect of using 5K, 50K, 500K etc pots rather than the ones shown in your schematic... or maybe somebody can point me to a source for (cost effective) pots in the values needed. Mouser/digikey is coming up short.
 
gemini86 said:
Ian, what would be the effect of using 5K, 50K, 500K etc pots rather than the ones shown in your schematic... or maybe somebody can point me to a source for (cost effective) pots in the values needed. Mouser/digikey is coming up short.

nevermind, just found where to change the pot values in the spreadsheet to adjust my cap values.
 
ah, but Ian was kind enough to give us a spreadsheet that will calculate the caps for whatever frequencies you want, giving YOU the choice of what eq you want to build... that maybe be difficult to  implement on one standard PCB, unless we give space for 2,3 paralleled and/or series caps to make precise values.

BUT, i know what you mean, I like when everything is nice and tidy, looking like a well organized plate of jelley-beans. (that's just what polyprop caps remind me of)
 
MikeClev said:
Lets make some sense of what you've got on that pdf.

Top left: a balanced Line input using a DOA and with a servo. I assume the servo is there to eliminate the need for DC blocking electrolytic capacitors.

Top centre: 12v Power supply circuits for the servos, standard stuff.

Bottom right: a DOA circuit to provide gain to boost the post filter signal back up to line level.

Bottom left: A FET circuit to present a high impedance to the signal from the EQ network

Is the FET circuit meant to be used with the DOA gain circuit or to replace it? I would expect the first option.

yes, they are, it's all correct

the FET circuit is to avoid the noise given by the bipolar input DOA's, so it is to used only with these ones , with the fet opamps as APP2055, FT992, JLM is not required
 
gemini86 said:
gemini86 said:
Ian, what would be the effect of using 5K, 50K, 500K etc pots rather than the ones shown in your schematic... or maybe somebody can point me to a source for (cost effective) pots in the values needed. Mouser/digikey is coming up short.

nevermind, just found where to change the pot values in the spreadsheet to adjust my cap values.

I was thinking about making the pot values alterable because it occurred to me that some people might want to make a closer copy to the EQP1A and use the same pot values that it does. You just need to bear in mind that the ratio of the pots to each other must remain the same. I'll tweak the spreadsheet and reissue it.

Cheers

Ian
 

Latest posts

Back
Top