500 series pultec clone HELP!

[Studio Mollan]

Hi,
I'm drawing on a Pultec Peq clone as a 500 series module. I've worked out the filter part of it but I need some help with the input and output stages.
As Input I'm thinking a 600r to 600r transformer works fine, like the original design?
As output i want to make a DOA - transformer circuit.

I have made a drawing of it but I need someone to take a look at it as I don't really know what I'm doing. I took an API 312 amp and removed the input transformer.  Do I need anything before the amp? I put a 20k resistor to ground to set the input impedance but I don't know if thats needed or if it's the correct value.

I won't be using the 2503 transformer as i have a lot of 2603 already. The gain pot would be able to compensate for the gain loss with the lower turn transformer right?

Any help greatly appreciated!
/
Emil

 

[emrr]

Read the Analog Allstars 500 Pultec thread.  Consider buying their kit. 

 

[Studio Mollan]

Thank's I'll have a look through their thread.
I had a pair on loan a few years ago and they are truly amazing. I have so much stuff lying around here from past projects and i figured I'd give this ago on my own.  For learning, and hopefully have something useful at the end of it. Nice to be able to build something without being a full kit or pcb one day.  The Pultec seems to be a simple enough circuit and also well covers in this forum.
I'm building this for my own use alone. A pair of Peq1, and a pair of meq5 later if i get it working.
/
Emil

Read the Analog Allstars 500 Pultec thread.  Consider buying their kit.

 

[emrr]

good luck!

 

[Studio Mollan]

I went through the thread jut now and found some very valuable info.
Thanks for the tip!
/
Emil

good luck!

 

[john12ax7]

Do you really need 600 ohm on the input? If building from scratch I would say consider the more common 10k modern input. Makes interfacing with other gear easier.

 

[ruffrecords]

Do you really need 600 ohm on the input? If building from scratch I would say consider the more common 10k modern input. Makes interfacing with other gear easier.

If you use the original L, C and R values then you do need a 600:600 at the input because the EQ circuit is designed to look roughly like 600 ohms.

The 25K trim pot is probably too large. You will need about 20dB of gain make up so I would recommend a 4K7 or 5K gain trim pot which will give 20dB near the centre of its travel. I would also recommend increasing the 20K at the input to 200K.

Cheers

Ian

 

[Studio Mollan]

Thanks (again) Ian!!!

If you use the original L, C and R values then you do need a 600:600 at the input because the EQ circuit is designed to look roughly like 600 ohms.

The 25K trim pot is probably too large. You will need about 20dB of gain make up so I would recommend a 4K7 or 5K gain trim pot which will give 20dB near the centre of its travel. I would also recommend increasing the 20K at the input to 200K.

Cheers

Ian

 

[john12ax7]

If you use the original L, C and R values then you do need a 600:600 at the input because the EQ circuit is designed to look roughly like 600 ohms.

Indeed you can't just do a direct swap. I was thinking more of a partial redesign so things would work correct, so different L C R s. I should have mentioned that.

 

[ruffrecords]

Indeed you can't just do a direct swap. I was thinking more of a partial redesign so things would work correct, so different L C R s. I should have mentioned that.

OK, then check out my 3 band Pultec EQ design where the RLC values have been modified to work with a 10K:10K transformer:

http://www.customtubeconsoles.com/diy

Look in the 3BandPultec folder.

Cheers

Ian

 

[Studio Mollan]

I'll stick to the 600-600r transformer as the original schematic then. Thanks Ian. You are such a resource here on the forum. I think you alone have solved at least 10 issues for me over the last years.

Looking forward seeing more on your mastering pultec.
/
Emil

OK, then check out my 3 band Pultec EQ design where the RLC values have been modified to work with a 10K:10K transformer:

http://www.customtubeconsoles.com/diy

Look in the 3BandPultec folder.

Cheers

Ian