300W gainclone

Hi!

My threshold 4000 is dead.
I have a good chassis with big dissipators, and I would like to install 6 modules LM3886 for channel or better the double modules, maybe 4780 or something like that.

I have more or less 75V and a big transformer of 1000VA and I like gainclone.

If anyone have any practical suggestion to make the cards or purchase preassembled kit and how much money they costs and where.

Thanks in advance.
 

Mihkus

Member
2012-07-22 8:01 pm
Some say that 4780 sounds worse than 3886 yet the package is great for mounting and heat dissipation is way better than the TF of 3886

It might be a bit more compact if useing 4780 but the price of the chip is pretty expensive.
Two LM3886t costed around 9€ few months ago when i built little surround amplifier
for cheap 5.1 system with TDA8954 driving 12" monster STX subwoofer in mono, sounds great.

Well, these cheap ebay kits sometimes blow very easily they dont even have good traces
and filter caps, the stereo version were terrible Vcc and Vee were thin as 3mm and longer than the power cord i plug to wall...
Terrible design, make ur own pcb.

I found that STX is selling super nice 2,2uF paper in oil gold legged filters for 8€ each,
Also many cheaper parts.
 

rjm

Member
Paid Member
2004-05-02 2:41 pm
Kyoto
phonoclone.com
You should probably look into whipping up a clone of the Jeff Rowland Design Group Concentra, or similar amplifier circuit based on a massively parallel array of chip amps.

I always though the Concentra was a neat design for its use of input transformers to split the signal phase to two separate banks of output devices, positive and negative phase.
 
+/- 75V is nearly twice as much voltage that a gainclone can hande.

However you could get by using them as one set on each of the 75V supply's side in a BTL configuration.
It would be even better if you can separate the to halves to just two 75v sections if the transformers winding's are not Center tapped types.

There are other configurations of amps that are better suited for utilizing a +/-75V supply if you choose to use it as it is.

FWIW

jer :)
 
Your PSU is absolutely unsuitable for any gainclone.
Try to rebuild the Threshold (we are at DIY audio, after all ;) ) or mount there some big puppy which is happy with +/-75V raw voltage.

Edit: I think the translator you used which like most relies on a preloaded dictionary, matched "piú e meno" to "more or less" , but here it should have been literally "plus / minus".
Just for fun I just translated equivalent Spanish "más menos" into Italian and if separate gave me correct "piú " and "meno" but together gave me "circa", go figure ;)
Salute quasi paesano !!! ;)

Google translator is a minefield.
 
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Check it yourself:
pa150_schematic.gif
 
Not sure that you'll be happy going from a Threshold to a chip amp. I've built three 3886 amps and while they don't sound bad, they're not in the same tier as a Threshold, Bryston, etc.. They punch above their weight for what they cost, but at least to my experience they're not in the same league as high-end kit.
Jim
 
As your rails are too high for a chipamp in balanced supply mode, you could consider going single ended and put 3 amps on the positive side and 3 on the negative. This might give probs with grounding though - depending on whether your trafo has two separate windings or is centre-tapped.
Sorry but even so they are *way* too high.
Plus, as you say, grounding will be a nightmare, both amps will be "on the opposite sides of ground", one of them will have a grounded +V rail amd and the ground -76V from the real one, etc.
A mess.

The solution to recycle that dead amp is to place a new one one that's happy with what's available.
Trying to fit a square peg into a round hole is a waste of time.
 

Sangram

Moderator
Paid Member
2002-09-25 11:01 am
India
LM4702/LME498xx series will work well for your application, add about 6-8 output pairs per channel and you can have a pretty nice amplifier.

You could use the 3886 if you are very determined. But the topology would be very complicated - either single rail opposed drive like suggested above, or directly driven outputs with rail cascodes (see the many opamp hybrid solutions suggested in patent applications), or simply rewire the supply to provide a single +75V rail and run the 3886 in single-supply mode. You'll have to parallel many chips to be able to run loads at this voltage, to be safe maybe twice the recommended number (i.e 2 chips for 8 ohms, four for 4 ohms per channel).

It can be done, but why would you?