The brute has landed: NEC A820E integrated amp

[istari_knight]

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

Sounds like a nicer design than a couple of very well regarded amps I've got here which having now worked on them I must say I wouldn't touch them with a barge pole... It has in fact put me off the brand. I wont name name's but let's just say they were made in Japan but owned by the Dutch

Enjoy your bargain !

[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

[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

[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.

[Firebottle]

They wouldn't happen to be Ph****s would they?

It looks like the one electrolytic is probably there just so that the response does not go down to dc.
It's a non polar 4.7uF with no voltage across it, so I've added a 1uF foil cap across each one.

The regulator transistors feeding the phono board run really hot, that's the job of valves not semis, so I've also increased the series dropper resistors to cool them down a bit.

This amp is a seriously good performer, and cheap

Alan

[Gordon Steadman]

This amp is a seriously good performer, and cheap
Alan

Wadya mean cheap?? You've already had to spend almost £20 what with the manual and all. You are up to the amount I usually spend

[istari_knight]

No, Marantz

Got a couple of their higher end models from the early 90's here... Let me count the 'lytic coupling caps: on the phono input, on the phono output, on the buffer input, on the buffer output oh yes and on the power amplifier input as well !!!

As you say they were commonly used as high pass filters keeping out any sub 30hz grunge. Is the phono stage discrete or IC ? I couldn't make much of the SM... The schematics were pretty much illegible to me

[Firebottle]

Is the phono stage discrete or IC ?(

It's discrete, with an IC based servo around it for dc control.

[istari_knight]

It's discrete, with an IC based servo around it for dc control.

Ooh, this amp really is a nice surprise ! It must have been their top of the range or something ? I shall have to keep an eye out

[Macca]

Ooh, this amp really is a nice surprise ! It must have been their top of the range or something ? I shall have to keep an eye out

Yep see my post no2 I linked to a bit of info. According to that it is the amplifier from their 'Flagship Combo system' from 1980 - I wonder what the Combo speakers were like?