Tonecontrols for the LeachPreamp

roger-k · 21st February 2005, 08:10 AM

I will make the Wide Bandwidth Preamp construct by W. Marshall Leach:
http://users.ece.gatech.edu/~mleach/papers/wbpreamp/feb77article.pdf]http://users.ece.gatech.edu/~mleach...eb77article.pdf <http://users.ece.gatech.edu/~mleach/...b77article.pdf[/URL]
I will make the preamp with tonecontrols and put in a relay which can bypass the tonecontrols.
But I have a problem:

The pot for bass and treble should have revers log taper, but I can't find any pot with shaft and reverse log thaper.

How can I solve this problem?

udip · 21st February 2005, 03:33 PM

Hi,

You can use standart log pots wired backwards, so the bass/treble boost will be when you turn them anti-clockwise.

Udi.

roger-k · 21st February 2005, 05:03 PM

Yes, I know that but bass and treble shall boost when I turn the pot clockwise.

audiofan · 21st February 2005, 05:06 PM

if you check in this site there is a section potentiometers .com or so they should have what you need

http://www.state-elec.com/

roger-k · 22nd February 2005, 08:19 PM

Thank you for the tip. I have sent them a mail, and they have the pots I need. But it is a little expensive: $21.50 each and quantity purchased below 25 pieces will incur a $50.00.

It tells nothing to me but the pot is "388 series".

roger-k · 24th February 2005, 07:55 PM

I also want to make the preamp with a balance control.
The value on the volume pot have to be 20k.
What value do I need for the balance control?

udip · 25th February 2005, 04:58 AM

Hi,

If you want to add balance control check this link,
figure 3.
You can make the balance pot 50k and each volume pot
100k.
You should also change R18 (M.Leach article) to about 5k,
and omit R17.

Regards,

Udi.

roger-k · 25th February 2005, 08:41 AM

I will try to do that.
Thank you very much for the help.

AuroraB · 25th February 2005, 09:25 AM

Depending on how the pot is used, you can achieve various tapers by using lin pots and parallelling resistors across the wiper and/or the whole pot. This may require some experimenting, but is absolutely possible.
At some point I saw a calculator for this somewhere on the net... try some googling.............

OTOH, may I suggest using another tone circuit....- there is a lot of different tone control circuits out there, which uses "normal" components. Anti-log taper has always been quite rare.....

EDIT:
HAH-knew I had seen it somewhere....
( or actually- this is not a new trick )
http://sound.westhost.com/pots.htm#chg-law

roger-k · 25th February 2005, 10:32 AM

Thank you very much!
I will try to do as Rod Elliot explain (a lin pot with two resistors connected).
I will save much money by doing this.

21st February 2005, 08:10 AM	#1
roger-k diyAudio Member Join Date: Mar 2004 Location: Karmøy in Norway	Tonecontrols for the LeachPreamp I will make the Wide Bandwidth Preamp construct by W. Marshall Leach: http://users.ece.gatech.edu/~mleach/papers/wbpreamp/feb77article.pdf]http://users.ece.gatech.edu/~mleach...eb77article.pdf <http://users.ece.gatech.edu/~mleach/...b77article.pdf[/URL] I will make the preamp with tonecontrols and put in a relay which can bypass the tonecontrols. But I have a problem: The pot for bass and treble should have revers log taper, but I can't find any pot with shaft and reverse log thaper. How can I solve this problem? __________________ Roger

21st February 2005, 03:33 PM	#2
udip diyAudio Member Join Date: Oct 2004 Location: Israel	Hi, You can use standart log pots wired backwards, so the bass/treble boost will be when you turn them anti-clockwise. Udi. __________________ "Things should be as simple as possible, but no simpler" Albert Einstein

21st February 2005, 05:03 PM	#3
roger-k diyAudio Member Join Date: Mar 2004 Location: Karmøy in Norway	Yes, I know that but bass and treble shall boost when I turn the pot clockwise. __________________ Roger

22nd February 2005, 08:19 PM	#5
roger-k diyAudio Member Join Date: Mar 2004 Location: Karmøy in Norway	Thank you for the tip. I have sent them a mail, and they have the pots I need. But it is a little expensive: $21.50 each and quantity purchased below 25 pieces will incur a $50.00. It tells nothing to me but the pot is "388 series". __________________ Roger

24th February 2005, 07:55 PM	#6
roger-k diyAudio Member Join Date: Mar 2004 Location: Karmøy in Norway	Balance control? I also want to make the preamp with a balance control. The value on the volume pot have to be 20k. What value do I need for the balance control? __________________ Roger


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21st February 2005, 05:06 PM	#4
audiofan diyAudio Member Join Date: May 2003 Location: quebec	if you check in this site there is a section potentiometers .com or so they should have what you need http://www.state-elec.com/

25th February 2005, 04:58 AM	#7
udip diyAudio Member Join Date: Oct 2004 Location: Israel	Hi, If you want to add balance control check this link, figure 3. You can make the balance pot 50k and each volume pot 100k. You should also change R18 (M.Leach article) to about 5k, and omit R17. Regards, Udi. __________________ "Things should be as simple as possible, but no simpler" Albert Einstein

25th February 2005, 08:41 AM	#8
roger-k diyAudio Member Join Date: Mar 2004 Location: Karmøy in Norway	I will try to do that. Thank you very much for the help. __________________ Roger

25th February 2005, 09:25 AM	#9
AuroraB diyAudio Member Join Date: May 2001 Location: Norway, -north of the moral circle..	Depending on how the pot is used, you can achieve various tapers by using lin pots and parallelling resistors across the wiper and/or the whole pot. This may require some experimenting, but is absolutely possible. At some point I saw a calculator for this somewhere on the net... try some googling............. OTOH, may I suggest using another tone circuit....- there is a lot of different tone control circuits out there, which uses "normal" components. Anti-log taper has always been quite rare..... EDIT: HAH-knew I had seen it somewhere.... ( or actually- this is not a new trick ) http://sound.westhost.com/pots.htm#chg-law

25th February 2005, 10:32 AM	#10
roger-k diyAudio Member Join Date: Mar 2004 Location: Karmøy in Norway	Thank you very much! I will try to do as Rod Elliot explain (a lin pot with two resistors connected). I will save much money by doing this. __________________ Roger

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