gpultec low end linearity improvement

[atticmike]

As I see it, you have a -3dB point of ca. 1500Hz

A quick calculation - e.g. http://www.muzique.com/schem/filter.htm shows that assuming a 220nF input capacitor at the filter board, you are likely to have a input resistor of ca. 470 Ohm.

Could it be that you by accident have a 470R at the 470K input resistor position (or possibly swapped the two)?

Jakob E.

thanks man, that was issue causing the culprit. The online shop banzai put 470R in 470k bags and the other way around.

 

[mitsos]

Aren't you glad you didn't trash it? 

 

[atticmike]

Aren't you glad you didn't trash it? 

haha, i was about to because I couldn't have imagined the issue was that simple.

I mean, considering I put a freaking fairchild together without an issue at the first powerup.

 

[mitsos]

well, once more, for anyone discouraged by apparently endless troubleshooting:

It's usually some small thing overlooked.

which reminds me, I have a dual 1176 to fix... 

 

[atticmike]

well, once more, for anyone discouraged by apparently endless troubleshooting:

It's usually some small thing overlooked.

which reminds me, I have a dual 1176 to fix...

my dual 1176 is busting and working

btw, here's the frequency curve, is that 30 hz bump alright? pultec-wise normal?

 

[gyraf]

Yes, normal at low loads. Resonance output impedance/capacitor/inductance. You can move it up and down by changing the 4u7 output capacitor - but I believe 4u7 to be optimal soundwise.

Jakob E.

 

[atticmike]

Yes, normal at low loads. Resonance output impedance/capacitor/inductance. You can move it up and down by changing the 4u7 output capacitor - but I believe 4u7 to be optimal soundwise.

Jakob E.

At what increments would I have to go up or down to lower the bump? Like up or down and what's the next value that's gonna drop it one dB or two?

Mike

PS: Would that cap drop it? http://www.banzaimusic.com/Mundorf-MCap-250-2-2uF.html

 

[gyraf]

You need to experiment, this is not a straight-forward area. But as said, i believe the chosen compromise to the best sonically.

Jakob E.

 

[atticmike]

You need to experiment, this is not a straight-forward area. But as said, i believe the chosen compromise to the best sonically.

Jakob E.

so there is no math that I'd have to go higher or lower with the cap's value?

are you saying it could deteriorate the sound?

I just think it could be a little flatter or how does the original pultec look like?

 

[mitsos]

How many dB's is that anyway? hard to tell in the pic. 

experiemntation is key.. you can put more caps in parallel (solder to existing caps under the PCB) to add more capacitance and see what that does. If you do, please post pics for educational purposes!

 

[atticmike]

My guess is that it'll be around 10 - 12 for a rather flat response.

 

[atticmike]

There we go, almost there, prolly 12uf.

at -10, it's looking like that:

 

[mitsos]

Nice! Thanks for posting!

 

[atticmike]

Nice! Thanks for posting!

No worries, anybody wants to know how it performs on a mix that's just EQd with original 4k channelstrips (242 black) without compression and a little balance? Wanted to hear how it affects a mix without adding compression.

 

[flaheu]

Of course we want to know 

 

[mitsos]

yes, otherwise it's just teasing.

 

[atticmike]

guess which one's the tube EQ:

https://dl.dropboxusercontent.com/u/70609905/a_bounce.mp3

https://dl.dropboxusercontent.com/u/70609905/b_bounce.mp3

BTW: I been at 16 uF so far and there is yet to be improvement:

 

[emrr]

You should go look at all the response plots I've posted all over this site.  A lot of the classic transformer coupled equipment has similar low end bumps.  I still really think you are chasing a 'problem' you see, and not one you hear.  Consider it a feature, it's like a tape machine head bump! That last plot looks like +0.5 at 20Hz.  I know I don't care about small bumps like this.  Make a list of things we record with musical response below 40Hz, and also the speakers that reproduce those frequencies with linearity. 

 

[atticmike]

You should go look at all the response plots I've posted all over this site.  A lot of the classic transformer coupled equipment has similar low end bumps.  I still really think you are chasing a 'problem' you see, and not one you hear.  Consider it a feature, it's like a tape machine head bump! That last plot looks like +0.5 at 20Hz.  I know I don't care about small bumps like this.  Make a list of things we record with musical response below 40Hz, and also the speakers that reproduce those frequencies with linearity.

any plots for original pultecs?

the new pulsebla pultecs are flat and they also got quite a big cap before the output trannie. but yeah, you are right but as a matter of a fact, I was actually bothered sonically by the low end bump, heard it out, checked the response and boom...

 

[emrr]

I might guess then you don't like tape.