khstudio
Well-known member
I'm pulling my hair out with this one.
I didn't realize the Pultecs were so sensitive to input loading.
When I looked at all the schematics & saw that Jacob & the Manley's had 10k resistors to GND before the circuit... I "assumed" they were using 1:1 (10k:10k) input trannys.(until I did more research )
So that's what I did... I got Cinemag 15k:15k and loaded the secondary with 10k.
After I started sweeping the unit I noticed I couldn't get the high boost to boost enough & spent days looking for wiring errors... then, the LAST thing I tried was dropping the 10k on the secondary of my input tranz to 620 ohms & BANG... the whole EQ changed & sounded great + fix the high boost... what a difference.
So now I'm a little pissed at myself for not researching this further & have two Nice Cinemag inputs that probably aren't optimal being loaded by the 600 ohm.
What I'd like to do :idea:
Build a few universal 10k:600 buffering circuits that I can patch thru when needed for my Pultecs & Black Face 1176's.
But even after researching this I'm still confused on HOW to do this.
This is a PM I sent to Matt from JLM:
I didn't realize the Pultecs were so sensitive to input loading.
When I looked at all the schematics & saw that Jacob & the Manley's had 10k resistors to GND before the circuit... I "assumed" they were using 1:1 (10k:10k) input trannys.(until I did more research )
So that's what I did... I got Cinemag 15k:15k and loaded the secondary with 10k.
After I started sweeping the unit I noticed I couldn't get the high boost to boost enough & spent days looking for wiring errors... then, the LAST thing I tried was dropping the 10k on the secondary of my input tranz to 620 ohms & BANG... the whole EQ changed & sounded great + fix the high boost... what a difference.
So now I'm a little pissed at myself for not researching this further & have two Nice Cinemag inputs that probably aren't optimal being loaded by the 600 ohm.
What I'd like to do :idea:
Build a few universal 10k:600 buffering circuits that I can patch thru when needed for my Pultecs & Black Face 1176's.
But even after researching this I'm still confused on HOW to do this.
This is a PM I sent to Matt from JLM:
Funny you mention this as Ive just finished 2 pultec type eqs for mastering similar to what you describe.
They use JLM pultec boards that we no longer make and a dual 99V MB PCB with two JLM Hybrid opamps to provide electronically balanced in and quasi balanced out. We did some rewiring and used the PAD relay to bypass the eq. I chose the Hybrid opamp to drive the eq circuit because it stays very linear with unchanged THD into any load down to 50 ohms, so it can easily cope with the low and changing impedances of the pultec circuit no matter what the settings. I was going to use a 99V for the output amp but tried some Hybrids to start and loved the sound so Ive left them in.
M
Could you PLEASE tell me how you set up the JLM Hybrid opamps as the Input Buffer to your Pultecs or even better, send me a schematic that shows how to set the JLM Hybrid opamps as a buffer for this.
I just finished a dual Pultec & I need to be able to use it with my 10k inserts on my board (& other 10k gear) & with my mic pre's (which don't have a problem driving it as is.