Can anyone identify this hipass filter?

[Hayman]

Hi,

I want to change the hipass filter in my mixer from 100Hz to 40Hz or something around that frequency.

This is a picture from the scematic:

I'm trying to figure out the values to put in for the cap and resistor. I have searched but I can't seem to find what type of design this is.

Can someone help me identify this filter? Any suggestions on values will be appreciated.

R15 is 22k. C12 and C13 are 47n


Thanks in advance.

Richard

 

[clintrubber]

Scaling the caps in value will do the trick. So from 100 to ~40 Hz just increase both caps to 120nF (gives ~39Hz).
This skips the question whether it's a 'Butterworth-dimensioning' or one of the other types, but simply scaling caps will just work.

(and if not then I learned something :wink: )

Regards,

Peter

 

[gyraf]

Can anyone identify this hipass filter?

My best guess is that it's from a Soundcraft board - placed right after the input mic/line amplifier.

But I agree with peter regarding dimensioning..

Jakob E.

 

[Hayman]

[quote author="gyraf"]

Can anyone identify this hipass filter?

My best guess is that it's from a Soundcraft board - placed right after the input mic/line amplifier.

But I agree with peter regarding dimensioning..

Jakob E.[/quote]


Yep, it's that Soundcraft series 600 that you guys helped me fix (powersupply).


Now I want to do more. The hipass filter is just one of several things I'll try to do.

Now I'm trying to figure out what opamps to put in the places where there now are TL072's. I was thinking OPA2604....good idea...bad idea...?

There are several Alps switches that need to be replaced.

....and of course caps. Wima's for the EQ and HP filter. Where there's electrolytics I'll use.......Nichicon?.......suggestions?

Would it be a bad idea to use tantalum caps on a couple of channels?


Well, I'm sure I'll have to ask you more later.

Thanks for the cap values.


Richard

 

[gyraf]

Don't use tantalum caps unless you're absolutely sure what you're doing!

If switches and pots are bad, change those first - that will be a much larger improvement than any esoteric opamp - and it will ensure that the desk is actually working..

Jakob E.

 

[pstamler]

[quote author="Hayman"]I want to change the hipass filter in my mixer from 100Hz to 40Hz or something around that frequency.

I'm trying to figure out the values to put in for the cap and resistor. I have searched but I can't seem to find what type of design this is.[/quote]

It's a Sallen-Key filter with a Q of about 0.707, which translates to a second-order Butterworth hi-pass filter.

R15 is 22k. C12 and C13 are 47n

R16 (47k) is also relevant to frequency setting. To scale the frequency from 100Hz to 40Hz, though, the easiest way is to change the capacitor values. 120nF will work; if the capacitors already installed are good ones, you could add 75nF in parallel with them, but more likely they're less than stellar, so I'd go ahead and replace with 120nF.

Peace,
Paul

 

[gar381]

This hipass is also used in the Soundcraft 1600/800B desks.

GARY

 

[pucho812]

Gary,
I have to ask. your avatar. What tape machine is that. Is it an ampex or an otari?

 

[PRR]

> your avatar. What tape machine is that.

Hint: right-click, Properties, URL ends with MM1000.gif

Does "MM1000" ring any bells? Sure sounds too-familiar to me.

 

[PRR]

What are the opamps? JFET like 353/072, or fat-BJT like 5532?

With JFET, don't fool with expensive capacitors, scale the cheap resistors 2.5 times higher. 55K and 118K. Round to 56K and 120K standard values.

With 5532, 47K is maybe as high as a worst-spec 5532 can use without excess offset error. What is the DC voltage on its output now? If you change the 47K to 120K, it will be 2.5 times higher.... is that acceptable?

I would add that it is the Unity Gain Sallen-Key, as opposed to the Equal Component Value Sallen-Key. Sometimes it is convenient if R1=R2, C1=C2, but you have to add gain to the opamp to raise the Q and corner-sharpness above "blunt weapon". The Unity-Gain does not mess-up your level diagram, but you have to severely offset the R/C values to get a sharp bend, leading to that 22K/47K ratio. Taken to extremes you get a very low-impedance input with a high-resistance bias resistor for the opamp; fortunately a ButterBump is not a real sharp bend or offset.

I would keep the channel filter 100Hz or 80Hz, and put any 40Hz/30Hz filter in the mains. I'm not real sure what the difference is between 40Hz and zero-Hz in most recording work. I do know that guitar, female (and some male) singers, horns, etc don't have balls below 80Hz and cutting-out room rumble (even 40Hz-80Hz rumble) really cleans up the mix.

 

[gar381]

Hi pucho

Its an Ampex mm1000 2" 16. Thanks for asking!

GARY

 

[NewYorkDave]

Master-Muncher 1000 :razz:

 

[SSLtech]

[quote author="NewYorkDave"]Master-Muncher 1000 :razz:[/quote]
No kiddin'!!!

I had one of those chew up a 2" one time when the long-ass tension arm got stuck... it wasn't in my studio, but a band that i engineered for had rented this place with an MM1000 and a BEL console (yeuch!)

I'm sure they sound great when in top shape, but this one was a dog... and it made me growl! :grin:

Keef

 

[gar381]

The chip used in the 800b for this hipass is half of a 072.

BTW.. I have heard lots of horror stories about tape handling
in the old Master Mucher 1000... after all it was a modded Quad
Video tape transport. The one I owned in the
early 80s never got hungry..guess I was lucky. I did
learn to rock stop it from FF and RW modes however!!
God this machine sure sounded GREAT!! ( the 440b electronics)
Wish I still owned it. :grin: Great memories
But on the other hand it required FULL TIME TLC and required
more space than my washer dryer combo!!

GARY