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Old 7th June 2007, 05:47 AM   #1
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Location: Dona paula, Goa
Default Tri amp completed

Here is a tri-amp I constructed for a friend.

The chasis has...
a preamp with op-amps
ESP 3 ch Linkwitz-Riley crossover
a lightspeed volume control
ETI 480 amp for the highs
LM4780 for the mids
Symasym for the lows

There are four RCA inputs at the rear and one RCA at the front for connecting mini gadgets.

The amp originally had STK435 in another chasis for mid which is now replaced with the LM4780 and the lows have Symasym now instead of the TDA7285

The 3 power amps are powered by 3 separate EI transformers fitted in two other boxes.

For switching on the 3 transformers, this chasis has a small psu that drives a relay in the transformer chasis.

Gajanan Phadte
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Old 21st June 2007, 08:04 AM   #2
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heatsink for LM4780 is constructed from 5mm aluminium plate and area is incresed using copper pipes used in split air-conditioner.

photo showing the heatsink construction
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Old 21st June 2007, 02:07 PM   #3
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Default The Indian DIY!

Good Work Man!
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Old 21st June 2007, 04:30 PM   #4
Sashi is offline Sashi  India
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Nice work with the diy heatsink.
Are the Cu tubes sandwiched between two Al plates(with screws) ?
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Old 21st June 2007, 05:40 PM   #5
anatech is offline anatech  Canada
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Hi Gajanan,
Interesting project, and jam packed! Well done.

I am curious though. All the ETI 480's I've ever heard were a bit "edgy" sounding. The choice to use it for highs surprised me because of this. I was thinking the SymAsym was a nicer sounding amplifier, especially in the mids and highs. Even the LM4780 probably sounds better than a stock ETI 480.

Did you improve the ETI 480 by chance?

Anyway, well thought out and nicely executed cooling system.

-Chris
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Old 22nd June 2007, 05:52 AM   #6
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Thanks Workhorse.

Sashi wrote
Quote:
Nice work with the diy heatsink.
Are the Cu tubes sandwiched between two Al plates(with screws) ?
There is only one aluminium plate and the copper tubes are tightened to it using an aluminium T, fitted using 2 nut bolts. The copper pipes are not cut through into small pieces but a small portion is left and it is z folded like printer paper. It is single piece.

Chris wrote
Quote:
Hi Gajanan,
Interesting project, and jam packed! Well done.

I am curious though. All the ETI 480's I've ever heard were a bit "edgy" sounding. The choice to use it for highs surprised me because of this. I was thinking the SymAsym was a nicer sounding amplifier, especially in the mids and highs. Even the LM4780 probably sounds better than a stock ETI 480.

Did you improve the ETI 480 by chance?

Anyway, well thought out and nicely executed cooling system.

-Chris
It is jam packed and saved me the trouble of finding/making another chasis. Most of the time went in planning the placement of the circuits. It had to be serviceable. This took more time than I anticipated. In the course of its making, one of the TDAs blew naturally. Then I convinced my friend to go for a Symasym for the lows.

The ETI 480 had served my friend for many years without trouble, and he wanted to keep it.
Extra film caps were added from the outputs for bypassing. The o/p transistors 3055/2955 were replaced by MJ15003/04. Couldn't go for better plastics as the replacement becomes time consuming and are not easily available here.

Economics also was mainly involved as my friend was constructing his new house.

The Symasyms were the most time consuming to install as I found that the L shaped AL on which the o/p xtors were intalled gets too hot and needs lot of heatsinking. Finally I managed to fit them to the 3mm Alu bottom plate.

The LM4780 sounds better than the stock ETI480.
I will try this. Have 4780 ICs and have the ETI 480 amp left open for psu trials of the ideas read here. No esoteric component trials can be taken up as they are impossible to obtain here.

I was surprised when one of the Indian DIYer said that he couldn't buy the heatsinks in Mumbai,India. I hope this encourages the fellow members to construct their own heatsinks which are second costliest in an amp.

Gajanan Phadte

edited spellings
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Old 22nd June 2007, 07:51 AM   #7
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I have many rescued heatsinks but non had the real estate in the chasis. So I was forced to make one.

Gajanan Phadte
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Old 22nd June 2007, 11:13 PM   #8
anatech is offline anatech  Canada
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Hi Gajanan,
Thats what I had guessed. Thank you.

I was thinking that the ETI480 would be better on bass duty and the amp with the best highs could do tweeter duty. You may need power for the mids though.

You did improve the sound of the ETI480 when you subbed those outputs (good thinking).

-Chris
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Old 26th June 2007, 10:19 AM   #9
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Chris,
His(friends) speakers are too big to shift to my apartment for trials. Anyhow he is very happy with the silence and the sound.
I will keep your advice in mind, and do the necessary changes when he brings it to me. Time un-bound.

I should have asked the advice in advance while I was constructing it. I will keep this also in mind, as I am going to construct one for myself. It will mostly be all Symasyms. I have to procure the parts first. In India, u cannot order and obtain them from shops in Metros. The local shopkeeper will get it for me but the price will be exorbitant. I am in no hurry.
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It is a very good feature. We can scan what the Gurus and Mahagurus wrote.

Enjoy and let others enjoy

Gajanan Phadte
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Old 26th June 2007, 10:35 AM   #10
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Chris,
His(friend's) speakers are too big to shift to my apartment for trials. Anyhow he is very happy with the silence and the sound.
I will keep your advice in mind, and do the necessary changes when he brings it to me. Time un-bound.

I should have asked for the advice in advance while I was constructing it. I will keep this also in mind, as I am going to construct one for myself. It will mostly be all Symasyms. I have to procure the parts first. In India, buying over the counter is the only way. The local shopkeeper will get it for me but the price will be exorbitant. I am in no hurry.
..............................................
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It is a very good feature. We can scan what the Gurus and Mahagurus wrote.

Enjoy and let others enjoy

Gajanan Phadte
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