ruffrecords

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1000 on: January 16, 2020, 06:36:49 PM »
Hi Ian
It's possible to use your tube make up stage in original pultec filter section?
I need to change something?
I' using sowter  3603 as input
Carnhill 2281 as output.
Thanks!
I am guessing you mean the poor man's tube gain make up stage - yes you can use this. The Sowter 3603 will be fine at the input. The Carnhill VTB2281 may not be so good at the output. The reason is that this particular tube amp design does not work well into a low impedance load. The VTB2281 is fine across most of the audio band but its impedance drops rapidly at low frequencies so you may lose low end response. If you want to use the amplifier then it is best to use the recommended Sowter output transformer since this has a much higher inductance than the VTB2281 and so it suffers a lot less from low end loss.

A better tube gain make up amp would be one half of my twin line amp design. This uses a VTB2291 output transformer wired 2K4:600 and will drive a 600 ohm load to well over +20dBu. It also has a simple adjustment for gain which simplifies set up. But if you only need one amp it is a bit of an overkill.

The alternative is to modify the original poor man's tube gain make up amp to use an 6922 tube instead of a 6CG7. This has extra gain and can also use a VTB2291 output transformer.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


ilfungo

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1001 on: January 22, 2020, 08:58:00 AM »
Yup, that's the way it should be!

Cheers

Ian

Hi Ian


I did some experiments and
I do not know why,
if I put a 100k resistor from the G point (mid inductor) on the ground,
all problems with the middle band are solved.
the 1db bump at 16000 is gone.
The strange curve that came out with extreme middle frequencies has disappeared.
I don't understand what I did ... can it create problems?

ilfungo

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1002 on: January 22, 2020, 09:00:27 AM »
Hi Ian just for info:
The bump at 16KZ come out only with mid on.
With eq in and mid out the responce is near flat...
Thanks!

Sorry...
« Last Edit: January 22, 2020, 09:22:35 AM by ilfungo »

ruffrecords

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1003 on: January 22, 2020, 03:04:29 PM »
Hi Ian


I did some experiments and
I do not know why,
if I put a 100k resistor from the G point (mid inductor) on the ground,
all problems with the middle band are solved.
the 1db bump at 16000 is gone.
The strange curve that came out with extreme middle frequencies has disappeared.
I don't understand what I did ... can it create problems?
pin G on the  mid inductor is supposed to be connected to 0V. It is on the 3BPultec PCB. Which PCB are you using?

Cheers

ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ilfungo

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1004 on: January 22, 2020, 05:16:57 PM »
The 3 band green pcb.

ruffrecords

www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ilfungo

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1006 on: January 23, 2020, 02:47:00 AM »
Yes!
Sorry not the G point but the H point 
100k to  ground...
« Last Edit: January 23, 2020, 04:28:15 AM by ilfungo »

ruffrecords

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1007 on: January 23, 2020, 05:26:04 AM »
Yes!
Sorry not the G point but the H point 
100k to  ground...

OK, that makes more sense.

The 3 band Pultec design was always a bit of a compromise. Originally I designed the poor man's EQP1A. Then I got loads of requests to add a mid band but unfortunately there is no straightforward way to do this. I tried to resist adding it but there were so many requests I felt I had to come up with something. The result is what is now the 3Band Pultec. The mid band of this is a compromise because when the boost/cut is engaged you can never turn the boost/cut down to zero. You can only turn it down to a small value. This is why the mid band has a centre off position. This means that with the mid engaged there will always be some small boost or cut but it should not happen around 16KHz. I think the problem is due to a spurious resonance in the inductor which can occur due to the capacitance between turns of the inductor. Other people have reported something similar.

Exactly why your 100K from pin H to 0V fixes it I do not know. The interesting thing is that pin H is the highest value inductance so the one most likely to create a spurious response in the  audio band. I have checked the schematic and I do not think the 100K will materially affect the overall performance so if it fixes the spurious 16KHz response I think you should leave it in.

Cheers

Ian
« Last Edit: April 29, 2020, 05:16:45 AM by ruffrecords »
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ilfungo

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1008 on: January 23, 2020, 07:41:39 AM »
Thanks Ian
Th 100k remote the 16khz bump and create a more gentle curve between the mid and hi band...
Thanks!!!

3nity

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1009 on: April 28, 2020, 08:02:42 PM »
ian.
Thanks for creating this project!
Im using the basic config. and its very smooth eq.
Thanks God for analog gear. What a difference it makes.
Life is a path, death the destination.


ruffrecords

Re: Poor Man's Pultec EQP1-A Build Support Thread
« Reply #1010 on: April 29, 2020, 05:19:48 AM »
ian.
Thanks for creating this project!
Im using the basic config. and its very smooth eq.
Thanks God for analog gear. What a difference it makes.

Glad you like it. Pierre Petit hosts a gallery of completed DIY projects based on my designs. So if you have any pics of your completed EQ you can email them to me and I will pass them on to him for inclusion in the gallery.

The gallery is here:

http://theworldin35mm.com/projectgallery/

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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