ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #60 on: April 13, 2011, 05:40:07 AM »
This looks great, will somebody be drawing up a pcb so that we could home etch?  I'm thinking of making several and don't want to do a point to point...

I agree. I have built a version of the Pultec point to point and it was a royal PITA.  I am working on a layout right now (maybe we can do a group buy later if there's enough interest). In an attempt to keep this a poor man's project I have come up with an outline of one switch PCB that, by suitable component changes, can be used for both the hi and lo sections. I have excluded the pots as that gives lots of flexibility in their choice and mounting and its only a dozen wires to solder up. Here is a pic of the layout as it stands - the board is 2.1 inches wide and 1.4 inches high so it should fit in a 1U rack if required. I have tracked in two capacitors for each frequency for maximum tweakability.  The two resistors, R1 and R1 are only needed for the hi boost and cut and can be wire links or zero ohm resistors for the lo boost/cut. The terminals (pads really) T1 thru' T4 are the only external connections necessary. The only other component not on the PCB right now is the 56K resistor needed for the lo boost/cut. I am going to draw a version of the schematic using this PCB as building block so you can see how it would all wire together.

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'


mylesgm

Re: Poor Man's Pultec EQP1-A
« Reply #61 on: April 13, 2011, 06:24:41 AM »
Fantastic!  Thanks Ian.
Check my work at www.mylesmumford.com

ppa

Re: Poor Man's Pultec EQP1-A
« Reply #62 on: April 13, 2011, 06:46:17 AM »
very good Ian!



ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #63 on: April 13, 2011, 07:04:35 AM »
Here's a rough sketch of how the switch PCB would be wired up to the pots and the 56K resistor to make the poor man's EQP1A. As you can see, the 56K goes between T2 and T4 on the lo switch PCB and I think there is room for it on the PCB so I think I'll add it already connected to T4 and with a link to connect it to T2 if needed. That way the only external components will be the pots.

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'

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #64 on: April 13, 2011, 07:28:55 AM »
Here's the tweaked PCB including the 56K resistor (R3) and its link. I have checked with my favourite PCB supplier using his instant price calculator which tells me if we order 30 we can get them for about 3.50 GBP each. So a pair would be about 7 GBP and with post and paypal I reckon a pair could be delivered anywhere for less than 10GBP. I had to shuffle everything up a little to get that last track in and meet the design rules so the switch is now slightly off centre so I may make one further tweak to get it back dead centre as that makes it simpler from the construction point of view.

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'

ej_whyte

Re: Poor Man's Pultec EQP1-A
« Reply #65 on: April 13, 2011, 08:56:19 AM »
For £7 a pair + shipping I'd definitely be interested in 2 sets  :)

Joechris

Re: Poor Man's Pultec EQP1-A
« Reply #66 on: April 13, 2011, 11:25:41 AM »
Yeah, two sets here for shure  :)
j
musicians vary +/-9dB depending on mood, drugs, and line-voltage. (PRR)

Joechris

Re: Poor Man's Pultec EQP1-A
« Reply #67 on: April 13, 2011, 11:34:58 AM »
Well I know that this is to be without inductors, but I see you have space for one of those small 5mm footprint inductors besides C1.
Could be a nice option for a bell boost on possision one. Just add a small link if not used. Mabye just a messy idea..
j
musicians vary +/-9dB depending on mood, drugs, and line-voltage. (PRR)

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #68 on: April 13, 2011, 12:36:37 PM »
Well I know that this is to be without inductors, but I see you have space for one of those small 5mm footprint inductors besides C1.
Could be a nice option for a bell boost on possision one. Just add a small link if not used. Mabye just a messy idea..
j

Yes, I think I could move C1 and C1A over a little and put in a 5mm space component in series with them and you could just short it out if not used.

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'

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #69 on: April 13, 2011, 01:10:34 PM »
OK, here's the V3 PCB with the switch centred and space for a 5mm pitch inductor L1 at the bottom left hand corner in series with C1 and C1A. I have also moved all the tracks to the solder side (this is designed as a double sided PCB because at the small quantities we want there is no price advantage in single sided and double sided I find much easier to solder). I just need to check the switch footprint is correct for the Lorlin 2 pole 6 way switch (its designed from an RVFM equivalent).

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'


gemini86

Re: Poor Man's Pultec EQP1-A
« Reply #70 on: April 13, 2011, 01:25:58 PM »
are you able to put a calculation for l1 on the spreadsheet?
- Rodney

"...you better call Kenny Loggins, 'cause you're in the danger zone."

Albrebreton

Re: Poor Man's Pultec EQP1-A
« Reply #71 on: April 13, 2011, 01:55:29 PM »
Hi Ian, I am interested in 2 sets too (maibe 4)
Thank you.
Alberto

Re: Poor Man's Pultec EQP1-A
« Reply #72 on: April 13, 2011, 02:18:59 PM »
I'd be in for a stereo set please Ian. Good work.
C

culteousness1

Re: Poor Man's Pultec EQP1-A
« Reply #73 on: April 13, 2011, 02:28:29 PM »
Hi Ian, I am interested in 2 sets too

+1!

I just came along Igor's BA-283 output stage. Do you think it is suitable for this EQ?

Cheers,
Carsten
"What's all this analog stuff anyhow?" - Bob Pease
"My favorite programming language is ... solder." - Bob Pease

Joechris

Re: Poor Man's Pultec EQP1-A
« Reply #74 on: April 13, 2011, 04:05:21 PM »
I think the second Neve stage has a input imp around 50k, I could be wrong...
I think it would be safer to use the standard pulteck resistors/pot values if you want to use Neve as makeup.
Or make a fet buffer to put infront of the Neve.
Or use a hamptone fetboy as makeup for even more mojo :-)

musicians vary +/-9dB depending on mood, drugs, and line-voltage. (PRR)

ruffrecords

Re: Poor Man's Pultec EQP1-A
« Reply #75 on: April 13, 2011, 04:36:43 PM »
are you able to put a calculation for l1 on the spreadsheet?

I have just been looking into this in some detail. One of the problems is that raising the impedance at which the EQ works (so we can use a 10K bridging transformer) means the value of inductance needed to provide a reasonable Q (small bandwidth) is correspondingly higher and the value of capacitance is correspondingly lower. For a modest Q of about 1.2 (which is roughly mid way between the sharp and broad setting on the Pultec) then the calculated values of inductance and capacitance are:

Resonant f    Inductance mH    Capacitance nF
3000                  530                  5.31
4000                  400                  3.98
5000                  320                  3.18
8000                  200                  1.99
10000                 160                  1.59
16000                 100                  0.99


At the high frequencies, the capacitance values are becoming impractically low and at the lower frequencies I suspect the values of inductance are greater than can be obtained in a 5mm pitch inductor. If we aim for a more modest Q of 0.6 we get a more reasonable set of values:

Resonant f    Inductance mH    Capacitance nF
3000                  270                 10.61
4000                  200                  7.96
5000                  160                  1.37
8000                  100                  3.98
10000                  80                  3.18
16000                  50                  1.99


There is little point in aiming for an even lower Q because you get a Q of 0.3 just using the normal hi boost and cut together.

So, right now I am not absolutely sure that the inclusion of an inductor actually offers much unless you want to have a 16KHz 'air' setting at position 1.

What do you think?

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'

strangeandbouncy

Re: Poor Man's Pultec EQP1-A
« Reply #76 on: April 13, 2011, 05:50:24 PM »
Ian,

   I think you are a bloomin marvel . . . .


    ANdyP



 ps Thank you very much indeed . . .
. . . . RUH ROH . . . . .

strangeandbouncy

Re: Poor Man's Pultec EQP1-A
« Reply #77 on: April 13, 2011, 05:51:34 PM »
Oh,


  and I am in for a stereo pair too please
. . . . RUH ROH . . . . .

michal_k

Re: Poor Man's Pultec EQP1-A
« Reply #78 on: April 13, 2011, 06:25:03 PM »
a pair for me for sure. what's the width of the pcb? will it fit 51x front panel(1.5'')?

mylesgm

Re: Poor Man's Pultec EQP1-A
« Reply #79 on: April 13, 2011, 07:00:32 PM »
Count me in for 8.  Looking forward to this little beauty...
Check my work at www.mylesmumford.com


 

Related Topics

  Subject / Started by Replies Last post
8 Replies
3854 Views
Last post July 07, 2008, 11:56:08 AM
by bodega
991 Replies
166587 Views
Last post April 26, 2019, 04:17:05 PM
by ruffrecords
96 Replies
24039 Views
Last post August 09, 2013, 09:29:39 PM
by mikeyB
3 Replies
1243 Views
Last post May 27, 2018, 06:48:06 PM
by mylesgm