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Old 16th October 2010, 06:14 AM   #1
Roushon is offline Roushon  India
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Default A bass-boost circuit for OB

I feel a bass-boost circuit is needed for the MJK OB I built sometime back.
The circuit is based on an application circuit in the datasheet of LM4562.
I look forward to your comments and suggestions. Especially if it is suitable
for the OB (it is the simple version one, not the U or H-frame one). The
circuit will be attached in between the cd-player and the amplifier. The
amplifier does not have any tone (bass, tribble) control.

Thanks and Regards
Roushon

P.S. C2 is also .05mF. by mistake I typed it nF
Attached Images
File Type: png bass-boost.png (8.2 KB, 854 views)
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Last edited by Roushon; 16th October 2010 at 06:16 AM. Reason: typo corrected in the attachment
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Old 16th October 2010, 07:40 AM   #2
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My dear friend !!! Are you going to put operationals along the path ,eh ??
I used to have the same problem ,like most of OBers !!! Firstly ,I just used a portable CD player which had a good bass-boost . When it went active ,as I didn't want to mess up the PURITY of the signal passing thru only the tube crossover , I let a single IC take care of boosting the subsonic frequencies . Linkwitz's site shows two shelving filters ,I used the one with 1uF in it!!! ..then below on the same page , also the same shelving filter+notch ,with 2 operationals.
Finished story !!!
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Old 16th October 2010, 08:24 AM   #3
Roushon is offline Roushon  India
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Default Thanks

Quote:
Originally Posted by picowallspeaker View Post
My dear friend !!! Are you going to put operationals along the path ,eh ??
I used to have the same problem ,like most of OBers !!! Firstly ,I just used a portable CD player which had a good bass-boost . When it went active ,as I didn't want to mess up the PURITY of the signal passing thru only the tube crossover , I let a single IC take care of boosting the subsonic frequencies . Linkwitz's site shows two shelving filters ,I used the one with 1uF in it!!! ..then below on the same page , also the same shelving filter+notch ,with 2 operationals.
Finished story !!!
Thanks. Thanks a lot Pico. This is exactly what I was looking for. The cd player (Marantz
cd5003) I have does not have a bass-boost facility. I will try the shelving filter+notch one
but tell me what kind of capacitor I should use. Is polyester OK?

Thanks and regards
Roushon
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Old 16th October 2010, 08:43 AM   #4
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Any will fit ,I had two BP around . But ...!! Remember that the examples shown on Linkwitzlab's page are for studying the stages for a fully active multi-way OB
system ,and each section would end on being connected to ampli-speaker only !
Are you sure that the circuit in exam is not giving any "ringing" or something
to the upper part of the frequency band ?
Also a passive RC net -yes ,a bass boost -might work ,without involving the use of ICs . I suggest to use each half of it and try the simple shelving one ,then ear and judge .
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Old 16th October 2010, 11:11 AM   #5
Roushon is offline Roushon  India
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Default OB with passive crossover

The MJK OB I am playing is with passive crossover exactly as in the
MJK's note. In an active system there are multiple number of Opamp
in the signal path as I see the Linkwitz's page. I know less is better. I
will remain in the passive setting but would like to raise the low frequency without bothering the high.

So if I do not use any buffer and use a non-inverting version of the circuit I
posted, then is it OK? Here I will have both boost and cut and in between.
On my desk I have two OPA627, one LME49710, one LM4562 and several
NE5532. Does the choice of a better Opamp make a diference? I am
reluctant to use the passive boost circuit as it attenuates the high
rather than raising the low.

Now what I hear from the OB is: the Fostex is a bit too loud compared
to the Eminence. No ringing from any of them. If I raise the volume to
hear the bass then the Fostex hurts my ear. The same OB I played with a
different cd-player which has a bass-boost and it sounded much better
though it did not have detail due to the ouput quality of the cd-player.

Roushon.
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Old 16th October 2010, 12:41 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

You could use a passive shelving circuit on the end of the CD lead.
similar to : Baffle Step Compensation or L-pad the Fostex.

rgds, sreten.
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Old 16th October 2010, 02:38 PM   #7
Roushon is offline Roushon  India
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Quote:
Originally Posted by sreten View Post
Hi,

You could use a passive shelving circuit on the end of the CD lead.
similar to : Baffle Step Compensation or L-pad the Fostex.

rgds, sreten.
Thanks Sreten, I like the Baffle step compensation circuit you mentioned.
I will try it.

In the mean time I made a simple modification in the Linkwitz' shelving
filter to have boost and cut options as attached. Is it OK?

Roushon
Attached Images
File Type: png bass-boost-mod.png (6.4 KB, 756 views)
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Old 16th October 2010, 03:27 PM   #8
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Are you using an LM3886 amp ? Searching for "bass boost " around the net , I arrived at this circuit :How to build 10W Audio Amplifier with Bass-boost (circuit diagram)
Would it be safe to put that network in the FB path of the 3886 ?!??!
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Old 16th October 2010, 05:14 PM   #9
Roushon is offline Roushon  India
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Quote:
Originally Posted by picowallspeaker View Post
Are you using an LM3886 amp ? Searching for "bass boost " around the net , I arrived at this circuit :How to build 10W Audio Amplifier with Bass-boost (circuit diagram)
Would it be safe to put that network in the FB path of the 3886 ?!??!
Hi Pico
I have seen this circuit while searching the net. It will be possible
to impliment it in LM3886. But in my case I am unable to do this for two
reasons.

1. It is difficult for me to take out the pcb from its cabinet, it is
in an air-tightly sealed cabinet with lots of wire (as I applied
`all grounds go to the star ground' principle literary). Although
this difficulty helped me to get a silent amp. I have spent long
time behind this amp.

2. Each channel consists of parallel of two LM3886. So if I employ the
bass boost circuit to both of them it will be very difficult to get
stability I think.

Simply I am afraid to try that. It will be a very very hard work.

Thanks and regards
Roushon.
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Old 17th October 2010, 06:05 AM   #10
Roushon is offline Roushon  India
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Default With some more flexibility

There is a buffer stage using OPA 627 in the amp which is easily accessible. I can
implement the idea as attached on this stage. But I do not know if it is OK.

Roushon
Attached Images
File Type: png bass-boost-mod.png (11.9 KB, 714 views)
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Last edited by Roushon; 17th October 2010 at 06:09 AM.
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