Spectra Sonics 110 pre with Opamp Labs 109 EQ

[craigmorris74]

grid suggested a transformer on the output of the 325eq section, or resistor isolation.
the concept of  fader after the Spectra preamp is apparently isn't such a good idea as the eq needs a low impedance source.

My bad, my reading comprehension sucks apparently.

Got it.

Okay, Craig, what's your plan here? I'm interested in what you do with this. I was talking to Cyrus M (Mount Cyanide) a while back about collaborating on a project to make the OAL 109 EQ in 500 series format and maybe also as small boards that connect directly to dual switches. But I haven't found time to get a layout done and source modern replacements for the inductors.

I was interested in making a preamp/EQ channel strip.  I already have the OAL inductors.

 

[rackmonkey]

Right. I just meant what specifically you decide on the options you asked about and what you think of the results. Keep us posted if you would. Watching with interest.

 

[craigmorris74]

Right. I just meant what specifically you decide on the options you asked about and what you think of the results. Keep us posted if you would. Watching with interest.

Gotcha.  Will do.  It may take a couple of months, but I'll make sure to report back.

 

[hodad]

I don't know if it would work with the passive EQ circuit you've got, but the old Spectra Sonics consoles would insert the passive EQ in the feedback loop of the amp card, substituting the EQ for the 10K7 resistor (Attached pic shows a 101 amp card, but I think they did the same with 110s.)

 

[craigmorris74]

I don't know if it would work with the passive EQ circuit you've got, but the old Spectra Sonics consoles would insert the passive EQ in the feedback loop of the amp card, substituting the EQ for the 10K7 resistor (Attached pic shows a 101 amp card, but I think they did the same with 110s.)

Thanks for the input and the picture.  The opamp labs circuit is actually a swinging input EQ.

 

[craigmorris74]

I don't know if it would work with the passive EQ circuit you've got, but the old Spectra Sonics consoles would insert the passive EQ in the feedback loop of the amp card, substituting the EQ for the 10K7 resistor (Attached pic shows a 101 amp card, but I think they did the same with 110s.)

Could I put the OAL EQ circuit (without the 325EQ) in the SS 101 feedback loop?

 

[rackmonkey]

If it were me, I'd use the 1204 channel schematic as a guide. A lot more straightforward and it will definitely work. Putting it in the feedback loop is going to be tricky.

 

[craigmorris74]

If it were me, I'd use the 1204 channel schematic as a guide. A lot more straightforward and it will definitely work. Putting it in the feedback loop is going to be tricky.

Looking at the 1204 channel schematic and considering what I want to do, it looks like I could use the SS pre card in place of the 360BM, or take the output of the SS pre and run it into a 10K:10K transformer, then to the EQ.  Am I correct?

 

[rackmonkey]

I would use it just like the 360BM and tweak as needed from there.

 

[craigmorris74]

I've got the Spectra Sonics pres working and in the case, and I'm thinking about the 109EQ.  I thought I had a couple of 325EQ modules left, but I don't.  Could I substitute another opamp for them?

Thanks,
Craig

 

[rackmonkey]

...Could I substitute another opamp for them?

Thanks,
Craig

The important thing will be to present a 10k input impedance to the eq circuit at the inverting input of the opamp so the eq will function properly. Look back at the circuit diagram of the 325eq that I drew for the teardown post. You could try a 5534 with the same network at the inputs as the 325eq (a 10k resistor connecting non-inverting and inverting inputs with a 15uF cap to ground, and a 10k series resistor at the non-inverting inverting input). Certainly easy enough to try.

 

[craigmorris74]

The important thing will be to present a 10k input impedance to the eq circuit at the inverting input of the opamp so the eq will function properly. Look back at the circuit diagram of the 325eq that I drew for the teardown post. You could try a 5534 with the same network at the inputs as the 325eq (a 10k resistor connecting non-inverting and inverting inputs with a 15uF cap to ground, and a 10k series resistor at the non-inverting inverting input). Certainly easy enough to try.

Thanks for the tip.  Could I use this idea and substitue a couple of Yamaha 80200 lamps I have lying around?

 

[rackmonkey]

Not familiar enough with those Yamaha amps. Post a schematic if you have one.

 

[craigmorris74]

Here the schematic.

 

[rackmonkey]

Same approach as I outlined above should work. Give it a try and see.

 

[craigmorris74]

Same approach as I outlined above should work. Give it a try and see.

Excellent.  I'll give it a try and see what happens.

 

[Whoops]

I've got the Spectra Sonics pres working and in the case

Hi Craig, could you please let me know how did you rack the SS 110 cards?
Like the wiring layout and how you took care of gain/attenuation?

I also have some cards I would like to rack

Thank you so much mate

 

[mjrippe]

Whoops, Have you read the document by Richard Guy?  He covers all aspects of wiring SS cards as preamps.  The one I have is for the 101, but should be nearly identical.

 

[craigmorris74]

Hi Craig, could you please let me know how did you rack the SS 110 cards?
Like the wiring layout and how you took care of gain/attenuation?

I also have some cards I would like to rack

Thank you so much mate

I'll make a detailed wiring diagram in the next few days.

 

[craigmorris74]

Here's a wiring diagram I whipped up.  If anyone spots any mistakes, I'll fix it.  I wired this according to what JLM and Matta posted on the "Racking Spectra Sonics 101"  thread.