The brute has landed: NEC A820E integrated amp

[dowser]

Ooh - I remember the Cd10 - they had one on display at a Hifi shop in Bondi Junction I briefly worked at - great sound, I remember popping the cover to see the internals & not being that impressed at what I saw...but sounded bloody good!

I reckon the amp would seriously benefit from a rewire with some attention to cable management - looks like a bloody dogs dinner

Richard

[drrdf]

I've had to bite the bullet and buy (cough) a service manual. It's a scanned copy and almost impossible to make out component values, but the circuit arrangement is well shown.

I'ts a sophisticated circuit with dual FETs on the inputs of the different gain blocks and it appears there is only 1 electrolytic in the signal path, on the output of the phono stage.
Those will have to get changed.

If anyone would like a copy of the manual please shout up. It's a PDF of 1.2MB.

Alan

I have one of these amplifiers which I have owned from new. In my opinion they are brilliant amplifiers, and the fact that they are Active Drive gives them an incredible bandwidth (virtually flat over the audio range). Indeed this can be a problem sometimes if you have a speaker system with an exceptional infra bass range; even on studio broadcast transmissions general studio rumble can be a problem, and as for the idiot announcers who believe they have to get up close to a wide-range microphone - well you know the problem? They were also designed in the days before "micro-miniaturization", so you can actually get at everything quite easily to carry out any necessary repairs.

You were very fortunate to get hold of one for that price, I think. They seem to be becoming sought after as vintage items and fetching some amazing sums.

You mention the problem with the indicator lamps; they originally had one for each of the buttons as selections were made, as well as the main one for the "Active Drive" logo. That lamp chain seems to be the only longer-term real weakness in the design, and they all fail after some years, and are not easy to instantly replace. The only other weakness seems to be the main power-supply reservoir capacitors, which like all electrolytics get leaky after some years.

I have sourced some suitable replacement indicator lamps; they are those used in model trains and are just the right size. I would be interested to have a copy of the service manual if you could be so kind as to e-mail me the pdf? If you are prepared to do this I will PM you my e-mail. Thanks.

Ronald

[Firebottle]

No problem Ronald, pm your e-mail address.

The indicator lamps are 12V each, with three in series, two being behind the Active Drive logo and the last behind whichever input button is pressed.
For the Active Drive logo I fitted two LEDs in parallel with a series resistor for each, resistor + LED to drop 24V.

Alan

[drrdf]

No problem Ronald, pm your e-mail address.

The indicator lamps are 12V each, with three in series, two being behind the Active Drive logo and the last behind whichever input button is pressed.
For the Active Drive logo I fitted two LEDs in parallel with a series resistor for each, resistor + LED to drop 24V.

Alan

Thanks Alan. I will PM you my email. Your solution using two LEDs is probably a better one than the original as they will probably last longer than bulbs?

[Firebottle]

Aye, the LEDs should last forever, or nearly, plus the series resistors for the LEDs act to limit the cold inrush current of the last bulb in the chain.

Doing this will always extend the life of filament bulbs

Alan

[awkwardbydesign]

I reckon the amp would seriously benefit from a rewire with some attention to cable management - looks like a bloody dogs dinner

Richard

I saw that and wondered if it had been fiddled with.

[drrdf]

I saw that and wondered if it had been fiddled with.

Hi Richard,

That is mostly how they made them in those days. I have had mine from new and it was always like that. The key point I feel is that although it may not look too tidy the overall hum and quiescent noise level is very low, even compared to many more modern amplifiers. Clearly having a potted toroidal mains transformer also helps. One of the danger always can be that if you re-route wiring and move wires in amplifiers of this era to attempt to make them look more tidy, you can impair the low hum level charecteristics, due to induced eddy currents resulting. Most people do not look at the internal wiring unless they need to undertake some maintenance or repairs, so it is normally covered up by the case.

Ronald

[DiscoTex]

Hi Alan

I'd love a manual, I've had this amp for over 10 years, but only keep it on 2/10 as it's in a house with neighbours. However, I'm thinking of using it for a disco, I have 2x150w rms 300w peak speakers, so it may be under powered; but someone has suggested that if I wire each speaker into BOTH channels, that would provide 160w to each, or did I understand this wrong?

I also want to get the panel lights working so any guidance on this would be much appreciated.

Thanks in advance

Andi

[Audio Al]

This thread is 4 years old now

[walpurgis]

someone has suggested that if I wire each speaker into BOTH channels, that would provide 160w to each, or did I understand this wrong?

Andi

I take it you mean connecting each speaker to both sets of terminals for each channel? Eighty watts is still eighty watts, no matter how many terminals you connect to, so whoever told you that is wrong.

The eighty watts would be the RMS power rating per channel. If you want to 'glam it up' like some manufacturers do, you could call it 640 watts PMPO, which is all bollocks of course.

Assuming you are using a pair of DJ type speakers with a sensitivity of say 92db @ 8 ohms each, your eighty watts per channel should give you an overall working loudness of around 115 decibels before the amp starts running out of steam and that's not taking into account the amp's capability on peaks, which could be a lot more. Probably more than enough loudness for a room with 250 people in it.