Dual Chip Amp Question :

[DaveSail]

An amp built with a pair of LM4780 Chips would give more power , ( and, avoid grounding problems ? ) It contains two LM3886 chips on the same
" block " in parallel .

Would two " bridged " LM3886s on each side be more desireable ??

David V. Webber

[jcx]

depends on your load and wattage needs whether you want bridged or parallel (or both)

more singles make heatsinking easier since the heat sources are distributed

[DaveSail]

This amp , ( when built , ) is for my " Bedroom Speakers " ) . They are
two - ways . JBL LE14A and JBL LE85 Mid / High . [ Might add a pair of JBL Slot Radiators , but don't own them . ] 8 Ohms .

They are quite efficient , with massive magnets and voice - coils .
An actual 20 Watts is usually OK for me , but too loud for most of my family !

However , there are always the people who want to " borrow " a GOOD
amp for their slide - show or party , and I don't know what their needs might be !

David V. Webber

[tangmonster]

if your friends have 4 ohm speakers and you bridge the lm4780 or bridge two lm3886's they won't be able to cope.

For a safe bet i would rather parallel them with +-35V rails. For your 8ohm loads it is overkill and they will play at 50W all day long and for 4 ohm load you will easily get 100W.

[tangmonster]

if you want it to be stable into 4 ohm load with 2 lm3886's in parallel.

I would use a

400VA 25 0 25 ( 2 x 200VA 25 0 25 for dual mono)
2 x lm3886 per channel in parallel
I would use 30000uF per voltage rail ( or 20000uF per rail for dual mono)

[DaveSail]

I don't know how frequent 4 Ohm speakers are . What if I just did not
lend my amp out to folks with those ? [ A " Lend " situation might happen only once or twice a year , if ever . ]

For my own , pair of 8 Ohm JBLs , what would be the best choice ?
A LM4780 for each channel or a pair of LM3886s on each side ?

David V. Webber

[AndrewT]

A single chipamp driving a single 8ohm speaker is best advice for a newcomer.

[tangmonster]

Originally Posted by AndrewT

A single chipamp driving a single 8ohm speaker is best advice for a newcomer.

Hi davesail

I agree with Andrew.

[DaveSail]

Ok . That is probably wise . But , in case I later " upgrade " I may buy the 300 VA
Plitrons and a pair of the MUR860 Bridges ; ( or , for the added pair of chips would
one have to have FOUR bridges ? ) [ I've seen photos in galeries with single -
channel bridges with EIGHT diodes !! ]

While I am certainly a " newcomer " to Chip - Amps , I am not a newcomer to
electronics . Way back in the day , I built a Heathkit AR - 15 , with all the resistors having their gold bands either top or right . ( I know , very anal . )

I set - up the Quality Control Laboratory for a well - known Carbon and Metal Film
Resistor company . I was supervisor of a small assembly - line for Vishay , before
their production left this area . I have built four - pair of speaker crossovers , for fine DIY Speakers ; [ one custom designed just for me by Greg Timbers , the head JBL XOVER guy ! ] ( These are just composed of Coils / Caps / Resistors . ) I was
head of Final QC for a large , New Jersey Electronics firm , which made the communication gear for Philadelphia and NYC trains ; ( a lot of automated surface - mount boards . ) I make BEAUTIFUL solder joints !

David V. Webber

[tangmonster]

Read through these pages about power supplies. Study the various methods. The 8 diodes you saw was probably one of the versions with 2 bridge rectifiers (the method I prefer)

Solid State Power Amplifier Supply Part 1

A 300 VA philtron will be overkill for 1 chip per channel and will probably be good enough for 2 chips per channel.
A 400va will be great for 2 chips per channel into 4 ohm loads or 2 chips per channel bridged for 8 ohm load.

You cannot connect a bridged channel to 4ohm load.

If you want to use a single chip on 4ohm loads or bridged chips on 8 ohm load you need to use a 20Vac transformer not 25Vac

if you want to use dual rectifiers (8 diodes) you need to make sure you get a 25 0 0 25Vac or 20 0 0 20Vac transformer and not just a center tap (25 0 25Vac or 20 0 20Vac) one.