LM3886 bass amp

thomasst · 5th July 2008, 01:37 PM

Hi,

I need/want to build a power amp to drive a 150w/8ohm bass speaker, can the LM3886 kit do this?

I understand any power amp would do the job, but everything I have read relates to hi-fi amps. Does this matter? I'm not looking for bells n whistles just something to boost the preamp into the speaker (sounds simple I know!)

A pointer in the right direction would be most appreciated.

Thanks

e_fortier · 5th July 2008, 01:47 PM

Hi,

The LM3886 is normally used for 4 ohm load but can be used for 8ohm with less output power.

If you want you could use their bridge/parralel configuration to get your required 150W but in my opinion the few gainclone I have built kinda lack the bass punch required for a sub. I would recommend going with a Class D amp for a sub.

Regards,
Eric

tpsorin · 5th July 2008, 02:12 PM

You will need to use 4xLM3886 /channel in bridge-parallel configuration. See national site for schematics.

Any chip amp is better to be used with 8Ohm than 4ohm.

thomasst · 5th July 2008, 02:41 PM

I should also point out that getting 150W is not necessary, getting sound is! 50W will be fine for the moment, even 20W would do to start.

This is for a bass guitar, not some kinda sub woofer, does this matter, does the speaker care?

I have just finished a college course in electronics, so know mostly what is going on here, although none of the stuff I did was specifically amp design, I just need a eureka moment to meld all this together.

Thanks

e_fortier · 5th July 2008, 02:47 PM

Hi,

Then if 50W is enough just build a nice Gainclone based on LM3886 or LM3875, nice very nice kits available via the people of this website or via e-bay like this link (I have not tried their kit); GC Kit

Regards,
Eric

eketehe · 6th July 2008, 07:06 AM

Maybe a bridged tda 7294 for enough output. You'll still need a tweeter or a fullranger i/o a single woofer for bass
brgds

pacificblue · 6th July 2008, 11:23 AM

LM3886 and LM3875 will do just fine. The lack of punch is only an issue, if you make one of those gaincard copies with 1000 µF per rail. If you need more punch, increase the power supply capacitor(s) to a reasonable value. For a bass guitar you won't need the "magic in mids and highs" that people use as an argument for low capacity power supplies.

Both ICs are designed for 8 Ohm loads and give you the 50 W you want (@1%THD) with a transformer from 2x26 V upwards. 160 VA will be sufficient. If the 50 W should be peak only (@10%THD), use 2x20V. 80VA will do then.

Don't use a transformer with more than 2x30 V.

With 4 Ohm loads you have to be more careful about heatsinking than usual. That's one of the main reasons why BPA-200 exists. And with 4 Ohms you shouldn't use a transformer with more than 2x20 V for LM3875.

The applications notes and the Overture Design Guide on http://www.national.com/analog/audio/ will be helpful.

Brett · 6th July 2008, 11:30 AM

Quote:

Originally posted by thomasst
IThis is for a bass guitar, not some kinda sub woofer, does this matter, does the speaker care?

50W is insufficient for a bass guitar amplifier if used on stage for monitoring and especially if it's used to provide audience sound if not going through FOH. In the studio it's predominantly DI'd. Would be fine as a solo practice amp.

Minion · 6th July 2008, 06:32 PM

Maybe a Bridged TDA7293 would be good, it will give you about 160w+ with 2x50v rails ,but I wouldn"t know were you could get a kit but I"m sure there are some arround....

Cheers

pacificblue · 6th July 2008, 07:04 PM

Kits for the TDA7293 are available at http://www.diy-selbstbau.de/diy-en.htm. 80 W single and 200 W parallel versions are available.

5th July 2008, 01:37 PM	#1
thomasst diyAudio Member Join Date: Jul 2008	LM3886 bass amp Hi, I need/want to build a power amp to drive a 150w/8ohm bass speaker, can the LM3886 kit do this? I understand any power amp would do the job, but everything I have read relates to hi-fi amps. Does this matter? I'm not looking for bells n whistles just something to boost the preamp into the speaker (sounds simple I know!) A pointer in the right direction would be most appreciated. Thanks

5th July 2008, 02:47 PM	#5
e_fortier diyAudio Member Join Date: May 2001 Location: Montreal	Gainclone kit Hi, Then if 50W is enough just build a nice Gainclone based on LM3886 or LM3875, nice very nice kits available via the people of this website or via e-bay like this link (I have not tried their kit); GC Kit Regards, Eric

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5th July 2008, 01:47 PM	#2
e_fortier diyAudio Member Join Date: May 2001 Location: Montreal	Hi, The LM3886 is normally used for 4 ohm load but can be used for 8ohm with less output power. If you want you could use their bridge/parralel configuration to get your required 150W but in my opinion the few gainclone I have built kinda lack the bass punch required for a sub. I would recommend going with a Class D amp for a sub. Regards, Eric

5th July 2008, 02:12 PM	#3
tpsorin diyAudio Member Join Date: Jun 2005 Location: Timisoara	You will need to use 4xLM3886 /channel in bridge-parallel configuration. See national site for schematics. Any chip amp is better to be used with 8Ohm than 4ohm.

5th July 2008, 02:41 PM	#4
thomasst diyAudio Member Join Date: Jul 2008	I should also point out that getting 150W is not necessary, getting sound is! 50W will be fine for the moment, even 20W would do to start. This is for a bass guitar, not some kinda sub woofer, does this matter, does the speaker care? I have just finished a college course in electronics, so know mostly what is going on here, although none of the stuff I did was specifically amp design, I just need a eureka moment to meld all this together. Thanks

6th July 2008, 07:06 AM	#6
eketehe diyAudio Member Join Date: Nov 2007	Maybe a bridged tda 7294 for enough output. You'll still need a tweeter or a fullranger i/o a single woofer for bass brgds

6th July 2008, 11:23 AM	#7
pacificblue diyAudio Member Join Date: May 2008	LM3886 and LM3875 will do just fine. The lack of punch is only an issue, if you make one of those gaincard copies with 1000 µF per rail. If you need more punch, increase the power supply capacitor(s) to a reasonable value. For a bass guitar you won't need the "magic in mids and highs" that people use as an argument for low capacity power supplies. Both ICs are designed for 8 Ohm loads and give you the 50 W you want (@1%THD) with a transformer from 2x26 V upwards. 160 VA will be sufficient. If the 50 W should be peak only (@10%THD), use 2x20V. 80VA will do then. Don't use a transformer with more than 2x30 V. With 4 Ohm loads you have to be more careful about heatsinking than usual. That's one of the main reasons why BPA-200 exists. And with 4 Ohms you shouldn't use a transformer with more than 2x20 V for LM3875. The applications notes and the Overture Design Guide on http://www.national.com/analog/audio/ will be helpful.

6th July 2008, 06:32 PM	#9
Minion diyAudio Member Join Date: May 2006	Maybe a Bridged TDA7293 would be good, it will give you about 160w+ with 2x50v rails ,but I wouldn"t know were you could get a kit but I"m sure there are some arround.... Cheers

6th July 2008, 07:04 PM	#10
pacificblue diyAudio Member Join Date: May 2008	Kits for the TDA7293 are available at http://www.diy-selbstbau.de/diy-en.htm. 80 W single and 200 W parallel versions are available.

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