Adding 80Hz HP filter to a BA

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Re: Adding 80Hz HP filter to a BA

Postby Joe Malone » Wed Nov 11, 2015 12:37 pm

mikeyb wrote:Hi Joe, would you implement the filter like in my above jpeg?

Thanks

Mike


If Rload fixed or variable? What value is it if fixed?

Rf need to be low enough that the opamp output doesn't move to may volts offset as it will limit headroom and make loud bangs as HPF is bypassed.

e.g If Rf = 100k then Cf = 18nF = 88Hz or 22nF = 75Hz

If Rload is fixed it is best moved to the Rf position as it will be a lot lower in resistance so opamp offset will be a lot less.

Let me know the actual transformer and opamp and Rload values etc and I will be able to better advice what to do :-)
Joe :-)
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mikeyb
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Re: Adding 80Hz HP filter to a BA

Postby mikeyb » Thu Nov 12, 2015 2:45 am

JLM BA Settings.jpg
Hi Joe - thanks for quick reply.
I'm using OEP and want to try various DOA's including JLM Hybrid/2520/1731/990
I'm contemplating putting a Hi/Lo ratio switch and it says on attached jpg use low ratio parts but fit jumper to high ratio
So would i omit Rload and put in place of Rf 27k resistor, and for filter of 40Hz and 80Hz i would have cap values:

download/file.php?mode=view&id=211

C = 1/(2xPix27k x f

40Hz C= 1/(2xPix27k x 40Hz) = 147nF (150n)
80Hz C= 1/(2xPix27k x 80Hz) = 73nF (68n)



Thanks for your time Joe

Mike
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Re: Adding 80Hz HP filter to a BA

Postby Joe Malone » Mon Nov 16, 2015 3:06 pm

mikeyb wrote:
JLM BA Settings.jpg
Hi Joe - thanks for quick reply.
I'm using OEP and want to try various DOA's including JLM Hybrid/2520/1731/990
I'm contemplating putting a Hi/Lo ratio switch and it says on attached jpg use low ratio parts but fit jumper to high ratio
So would i omit Rload and put in place of Rf 27k resistor, and for filter of 40Hz and 80Hz i would have cap values:

download/file.php?mode=view&id=211

C = 1/(2xPix27k x f

40Hz C= 1/(2xPix27k x 40Hz) = 147nF (150n)
80Hz C= 1/(2xPix27k x 80Hz) = 73nF (68n)



Thanks for your time Joe

Mike


Yes all seems correct. Just cut track between transformer secondary and Rload fitted as 27k to insert HPF cap.

If thump is large when switching from HPF to normal. Switch a 10uF Non Polar cap across the HPF cap instead of shorting the HPF cap out.
Joe :-)

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mikeyb
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Re: Adding 80Hz HP filter to a BA

Postby mikeyb » Tue Nov 17, 2015 12:40 am

Thanks Joe - so like this?

Thanks

mikeyb

ps forgot to ask - do i still fit CLoad - i'd imagine i do
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Re: Adding 80Hz HP filter to a BA

Postby Joe Malone » Tue Nov 17, 2015 9:38 am

mikeyb wrote:Thanks Joe - so like this?

Thanks

mikeyb

ps forgot to ask - do i still fit CLoad - i'd imagine i do


Yes fit CLoad it will not effect the HPF function and it needed at the opamp input so it is stable while switching HPF.

Usually you would leave the 68nF permanently inline and switch a 68nF - 82nF or 10uF across it and have 1Meg resistor across any open switch contacts to minimise pops.
Joe :-)

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mikeyb
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Re: Adding 80Hz HP filter to a BA

Postby mikeyb » Tue Nov 17, 2015 10:19 am

Thanks Joe - should be trying it tomorrow

mikeyb

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Re: Adding 80Hz HP filter to a BA

Postby mikeyb » Wed Nov 25, 2015 4:20 am

Hi Joe - where do you get 10uF non polar caps from? RS used to do them but i cant find any reasonably priced ones on ebay?
Do they have to be non polar?

Cheers

mikeyb

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Re: Adding 80Hz HP filter to a BA

Postby Joe Malone » Wed Nov 25, 2015 7:20 am

mikeyb wrote:Hi Joe - where do you get 10uF non polar caps from? RS used to do them but i cant find any reasonably priced ones on ebay?
Do they have to be non polar?

Cheers

mikeyb


Since your Rload is 27k you could use a 1uF (5.5Hz) to 2u2 (2.7Hz) poly or mkt cap instead.

We keep 10uF 25v Non Polar in stock and can add them into a order if asked for at the time of ordering.
Joe :-)

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