sontec eq amp with passive eq? any chance to work?

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michal_k

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Nov 12, 2008
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I know these are totally different beasts but I wondered if I could use amp board with a passive eq like NYDave's or Pultec?
If not, why it wouldn't work? do I need anything besides buffer on input and simple output stage? insufficient gain makeup?
I've got two melcor DOAs lying around and thought I could finally use them.

differential diagnosis, gimme your ideas.  ;D
 
michal_k said:
I know these are totally different beasts but I wondered if I could use amp board with a passive eq like NYDave's or Pultec?
If not, why it wouldn't work? do I need anything besides buffer on input and simple output stage? insufficient gain makeup?
I've got two melcor DOAs lying around and thought I could finally use them.

differential diagnosis, gimme your ideas.  ;D

The Sontec eq amp has a different function to the makeup gain amp in a NYD EQ or Pultec.  In the Sontec there is no overall gain, the filters are in the feedback loop of an amp.  In the Pultec or NYD you are looking to makeup a level drop  (not sure off the top of my head how much).  There is also the issue of amplifier input impedances to consider, this is always an important consideration with passive eq networks.

If you have Melcors I would suggest looking at how the solid state Pultecs were done using the API 2520 op amp.  Someone (maybe Dr. PAt?) posted a nice schemo here one showing how their original unit was setup.

Cheers,
Ruairi
 
 
I've always thought that building a Nevetec was a pretty cool option. 31267 step-down step-down for low-impedance drive, BA283 for make-up and output drive.
 
thanks for the answers.
ruairioflaherty said:
If you have Melcors I would suggest looking at how the solid state Pultecs were done using the API 2520 op amp.  Someone (maybe Dr. PAt?) posted a nice schemo here one showing how their original unit was setup.

I saw that eq. But I don't want anything ready to build and rather figure out something on my own(with your help ;D). Besides, I'd like to avoid use of transformers cause I'm aiming into transparent in/out stages. I know that If I used lundahls there would be hardly any colour added by trafo, but again, that has been done before(opamp in/out in passive eq was probably done before too, but I haven't seen any schematic so it doesn't count ;D).
On the other hand, melcors aren't the most transparent DOA's but I can always swap them for 990 or any other opamp If distortion would be audible.

ruairioflaherty said:
The Sontec eq amp has a different function to the makeup gain amp in a NYD EQ or Pultec.  In the Sontec there is no overall gain, the filters are in the feedback loop of an amp.  In the Pultec or NYD you are looking to makeup a level drop  (not sure off the top of my head how much).  There is also the issue of amplifier input impedances to consider, this is always an important consideration with passive eq networks.

I've read about impedance considerations in eq meta. As far as I understand, a passive eq network can have extremaly low input impedance and that's why we use stepdown transformers on the input. Now, If I used simple differential amp stage to unbalance signal and transform impedance it should do its job as well as trafo, wouldn't it? DOAs are able to provide enough current to drive 32R headphones so passive LRC network shouldn't be a problem ethier.

Output stage should only provide enough gain to compensate loss in eq section. it seems to be simple, especially that I don't even need balanced out.

What do you think?

 
anybody? I'd like to hear that there's at least light chance it's gonna work before I start soldering. Or please point me to any materials that may help me. I've already read through both metas, for passive and active eq but found no answer so far.

thanks,
Michał
 

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