I found a scrapped realistic amplifier, from possibly the 70s or 80s.
Its a nice amp, has the dual analogue VU meters on the front, silver face, has all the knobs, and all kinds of stuff, the only thing wrong, it is missing the amp board. but the other boards are there.
Im assuming, that someone didnt finish the repair job, and left it for the destind trash.
Anyway, I was thinking about building a 4 - chip lm3886 amplifier module in it.
the system will power on, the meter piolet lights still work, and the power supply has a 4amp fuse, and the unit spits out +/-44v rails with no ripple as seen on my scope.
So, is it possible to build a lm3886 amp in this thing? I would love to, as I like the look of it.
I was thinking about a 2-chip parallel per channel, totalling about 4 chips.
Anyone got a schematic?
i read somewhere that +-42 volts already pushes it on the edge, which tells me I might need regulation, but the datasheet clearly says that it will work with a span of 96 volts I think?
well this only has a span of 88.6volts, according to the measurements of my meter.
Any thoughts on this?
Its a nice amp, has the dual analogue VU meters on the front, silver face, has all the knobs, and all kinds of stuff, the only thing wrong, it is missing the amp board. but the other boards are there.
Im assuming, that someone didnt finish the repair job, and left it for the destind trash.
Anyway, I was thinking about building a 4 - chip lm3886 amplifier module in it.
the system will power on, the meter piolet lights still work, and the power supply has a 4amp fuse, and the unit spits out +/-44v rails with no ripple as seen on my scope.
So, is it possible to build a lm3886 amp in this thing? I would love to, as I like the look of it.
I was thinking about a 2-chip parallel per channel, totalling about 4 chips.
Anyone got a schematic?
i read somewhere that +-42 volts already pushes it on the edge, which tells me I might need regulation, but the datasheet clearly says that it will work with a span of 96 volts I think?
well this only has a span of 88.6volts, according to the measurements of my meter.
Any thoughts on this?
The data sheet clearly states, that the LM3886 max. can handle +/- 42 Volts. So no worries there. The 96 volts (=+/- 48 volts) can be applied, if it is not playing music. Normally - when the music starts - you will also start to draw current from the PSU, and then the voltage will drop *if* it is an unregulated one.
If you have some power resistors you can try this test: Connect them to the PSU and see, if the voltage drops.
As for parallel coupling schematics: Look into the other threads in this "chip amp" forum.
If you have some power resistors you can try this test: Connect them to the PSU and see, if the voltage drops.
As for parallel coupling schematics: Look into the other threads in this "chip amp" forum.
You cannot go beyond 84V supply on the LM3886. I wouldn't even think about 84V because of the thermal issues. Atleast you would have to parallell them and use massive heatsinks or a fan. How about regulating it down to +/-30/35V? (depending on transformer regulation).
see http://www.national.com/an/AN/AN-1192.pdf#page=8
for parallel schematic
see http://www.national.com/an/AN/AN-1192.pdf#page=8
for parallel schematic
mbates14 said:
If you lack funds there's little you can do. You will need them to buy the parts for an LM3886 project, particularly if it's in parallel.
With that kind of voltages, I would try to find the original Realistic circuit and see if the amp can be repaired. They are too high for the LM3886 or LM3875. You can only use them if you regulate them.
Using two chips in parallel is good if you have low impedance speakers. But for that you would have to go lower in the PS voltage too.
So the choices are not that many.
Perhaps a different chip, like an STK type, would fit your bill better.
Carlos
thing is, I already have the 3886 chips.
I have a +/-35 supply, but its an SMPS, and I dont think it would handle the currents required for parallel. but im not sure.
Also, I have a stereo circuit bult and functioning already, but from a much smaller power supply. I wanted to go parallel, because I want 100W per channel instead of 50W per channel.
my question is this:
I have a stereo circuit that is operating. it contains two circuits. if I build two more circuits (like two stereo amps in a way). Can I put the output resistors between the first two circuits, and that makes one complete circuit in parallel? or no.
they are inverting designs.
I have a +/-35 supply, but its an SMPS, and I dont think it would handle the currents required for parallel. but im not sure.
Also, I have a stereo circuit bult and functioning already, but from a much smaller power supply. I wanted to go parallel, because I want 100W per channel instead of 50W per channel.
my question is this:
I have a stereo circuit that is operating. it contains two circuits. if I build two more circuits (like two stereo amps in a way). Can I put the output resistors between the first two circuits, and that makes one complete circuit in parallel? or no.
they are inverting designs.
I have a good chip for you: TDA7293 It takes a total of 120 volts, 60 volts per rail and they are 100 watts per chip.
About stk modules, they are very nice and user friendly to use. I have never had one fail even tho i ran a commersial amp using one at the max volume the power supply could withstand for atleast 30 minutes with no problem. The heatsink was too hot to touch when i turned it off and it still runs fine, so you have done something wrong if you fry them.
About stk modules, they are very nice and user friendly to use. I have never had one fail even tho i ran a commersial amp using one at the max volume the power supply could withstand for atleast 30 minutes with no problem. The heatsink was too hot to touch when i turned it off and it still runs fine, so you have done something wrong if you fry them.
OT: Exactly the same as any discrete amp will do when a component on the board fails, stk modules are small discrete amps in a plastic case.
On Topic: Try the TDA7293 as suggested, no need to modify any transformers and no need of paralelling as they are 100 watt per chip. You could sell the LM3886:s to fund the TDA:s, they are on ebay for $54 for a lot of ten. Thats what i bought.
On Topic: Try the TDA7293 as suggested, no need to modify any transformers and no need of paralelling as they are 100 watt per chip. You could sell the LM3886:s to fund the TDA:s, they are on ebay for $54 for a lot of ten. Thats what i bought.
mbates14 said:
You could try the SMPS supply, as long as it can handle the current. Nuuk has had good results from this.
A parallel circuit must fulfill some requirements, like mated resistors and all that, in order to work well. National recommends them to be close to 0.1% in matching. You certainly need the output resistors, which should be matched to 1% in the paralleled amps.
But to go to 100W at 8 ohms you will need to bridge them. But if you need that power at 4 ohms it's much easier.
To parallel the amps and bridge them you will need lower voltage supplies than the ones you have now, unless you regulate them. But that would also be a waste of power.
The 7293 seems to be a good chip too and takes more voltage. They seem to be more stable than the STKs.
Carlos
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.