simple chip bass amp

[jamie1107]

hi
im relatively new to chip amps i have built a couple of lm3875 gainclone kits and some valve amps
i would like to build a bass amp next 200-400wrms @8 ohms
i have looked at maybe 6 3875 s or possibly using 4780s does anyone have any ideas or simple schematics as i dont quite understand how to bridge 4 or 6 together so the more simple the design the better
many thanks

[dave_gerecke]

Go to the National Semconductor website:

www.national.com

type in the LM3875 or LM3886 p/n into the search box. When the page comes up, scroll down. You will find a listing for an app note that shows how to build Bridge, Parallel or Bridge/parallel combination amps. I'm not sure of the app note number.

Good Luck,

Dave

[ionomolo]

If you want such a high power go for a driver with discrete output stage.

LME49810 can deliver up to 500W on 8 Ohms and there are a lot of threads here discussing it.

http://cxem.net/doc/amp/LME49810.pdf

It's only slightly more complicated than a gainclone but it's possible to wire these on veroboard (I've done a 7.1 system and can tell that it's exhausting, but if you are looking for a mono design you hit it)

[InlineTwin]

AN-1192 is the BRP LM3886 circuit. LME49810 and LME49811 are more expensive and complicated. Not really what you are looking for in a low frequency amp IMHO. Skip the servo app and go for the basic BRP.

[ionomolo]

I didn't succeed in getting a BPA-200 to work (by far too many connections for a veroboard), but with LME49810 i've always had good results (even air-wiring).

the idea is: Stick to the datasheet "Typical application" and replace darlingtons with mosfets, place a gate stopper resistor (take the value from AN-1645) and replace the Vbe multiplier with a 5K pot.

Use the same layout techinques that you would with a gainclone.

Current price at digikey for the 150W versionis $13.55 for the driver, $6.99 for the N-channel fet and $6.96 for the P-channel fet so total cost from active parts is $27.5. 4 LM3886 cost $24.77. The BPA-200 will also need an input buffer since the inverting part has a low input impedance and will have problems with current sharing that don't exist if you build one of these. The BPA-200 also has a lot of passive parts. If you place an LM4562 as a buffer you are actually paying more!

The LME49810 has soft-clipping which turns to be a must in a musical instrument amplifier because you will be playing uncompressed (unlimited volume) audio. There are boards arround that are easier (and faster) to build than a BPA-200.

I've attached a picture of mine so you can see the complexity (this is 150W) and has one small heatsink because the picture was taken during the first tests. Sound quality is amazing and puts almost all LM3886 amplifiers to shame.

EDIT: This was the first try, these can be made better-looking and better layouted.

[InlineTwin]

Originally posted by ionomolo
I didn't succeed in getting a BPA-200 to work (by far too many connections for a veroboard), but with LME49810 i've always had good results (even air-wiring).

the idea is: Stick to the datasheet "Typical application" and replace darlingtons with mosfets, place a gate stopper resistor (take the value from AN-1645) and replace the Vbe multiplier with a 5K pot.

Use the same layout techinques that you would with a gainclone.

Current price at digikey for the 150W versionis $13.55 for the driver, $6.99 for the N-channel fet and $6.96 for the P-channel fet so total cost from active parts is $27.5. 4 LM3886 cost $24.77. The BPA-200 will also need an input buffer since the inverting part has a low input impedance and will have problems with current sharing that don't exist if you build one of these. The BPA-200 also has a lot of passive parts. If you place an LM4562 as a buffer you are actually paying more!

The LME49810 has soft-clipping which turns to be a must in a musical instrument amplifier because you will be playing uncompressed (unlimited volume) audio. There are boards arround that are easier (and faster) to build than a BPA-200.

I've attached a picture of mine so you can see the complexity (this is 150W) and has one small heatsink because the picture was taken during the first tests. Sound quality is amazing and puts almost all LM3886 amplifiers to shame.

EDIT: This was the first try, these can be made better-looking and better layouted.

Wow. What fet's are you using to get 150w from one pair?

[ionomolo]

2SK1530/2SJ201, but power rating is based on power at 1% thd, not on continuous dissipation! Its colder than the gainclone at twice the volume, but this probably has more to do with having dissipation shared between two huge heatsinks.

[jamie1107]

hi
thanks for all your help i think as you say the lme49810 circuit is simpler and theefor the best bet
could you clarify a couple of thing s
the best circuit to use is the first one on the data sheet rather than the dc coupled
what powersupply voltages and transformer ratings are people using
and does anyone have a power supply circuit schematic i could have a look at please
looking at the pic of your amp project i(thanks for that ) i assume most of the capacitors are electrolitic type and what transistors did you find worked best for q1-4 sorry if this seems a little simple its just the bp 200 amp had a parts list which made life a whole lot easier as im just starting out im not that good on working out which components to use
thanks for all your help

[ionomolo]

I'm at the university right now so i can't post any schematic. I will tell you hopw i did mine this evening (Evening in spain ).

What i've to write is exactly a part list since i need to do a second channel amplifier for my bedroom one and i must buy identical parts to get good stereo matching.

[garage1217]

Post away! Very interested!