The brute has landed: NEC A820E integrated amp

[Firebottle]

Just acquired this, bought as not working.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Pishanto/P1030710.jpg

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Pishanto/P1030711.jpg

Anyone know the model or have any experience or info? I can't find a date on any of the internal components.
It's certainly a big brute, rated at 80W into 8 ohm or 4 ohm speakers. It has a MM/MC phono input as well.

http://i601.photobucket.com/albums/tt97/Paramotorpilot/Pishanto/P1030712.jpg

Turns out the only thing wrong with it are the front panel indicator lights, result ;)
I did a softly softly approach to testing in case anything went bang, tested with headphones first.
Tried connecting a meter to the rear speaker terminals by inserting the 4mm plugs and got diddly squat, so thought the speaker switching or relays were US.
It turns out the terminals are not 4mm at all, I'm guessing they are for the old banana plugs :eek: Must be really old then :scratch:

I've listened to it and the bass seems a bit soft, would doubtless benefit from some modern replacements of the power supply electrolytics to sharpen things up. The frequency response seems wide but the loudness button is a bit excessive :mental:

...........and the price for this brute...........








all of €10...........whoa, hold on big spender...........

:cool: Alan

[Macca]

some info here:


http://www.audiokarma.org/forums/archive/index.php/t-451118.html

It's from 1980, apparently.

[Firebottle]

Ooh doctor doctor I'm feeling funny all over...........I think I've gone hi-fi :eyebrows:

Thanks for the link Martin, it looks like there's diddly squat for any other info.
Just had the brute linked up from an old Sony CDP into some very mediocre speakers with all replacement drive units (Audiolab 6 and a half inch) and it sounds remarkably good.

Whatever's happening to me?

:cool: Alan

[Audio Al]

Whatever's happening to me?

Looks like Pishantoitus to me :lol::D

[Firebottle]

Good one Al :)

It turns out the speaker outlets are not sockets at all, just binding posts for bare wire.
No wonder I got nothing when I tried to connect a meter :mental:

Alan

[synsei]

That is a great find for a euro-tenner Alan, looks to be very well constructed from here (man these binos are good) :D

[istari_knight]

Looks alright ! :)

Is the transformer potted or just a cover ? If the former it was worth the price alone just for that ! Cant help any with the light problem, I've looked for a SM but its only on one site & they want $$$ for it... Probably a reg gone down somewhere.

Can almost guarantee all coupling caps are cheap nasty 'lytics, always get a magnificent upgrade in clarity when replaced with a suitable film... Though I'm sure you know this anyway.

[Firebottle]

It's a potted toroidal transformer, agree that it's worth it for that alone.
I've tested the main supply electrolytics with a capacitance meter that has a 120Hz test frequency. They are marked 8000uF and they are all measuring 7900uF, amazing!

The front panel lights are tiny rice sized filament bulbs. Fortunately only one was blown and they are in a series string of 3. Two are used to light the 'Active Drive' symbol on the front panel with the third lighting the selected input button.
By cunningly fitting two LEDs to the 'Active Drive' with the same current draw, I now have all lamps working and a spare :carrot:

Onward and upward, probably have to fork out for an SM,

:cool: Alan

[istari_knight]

Sorted, that's what we like :thumbsup:

[Firebottle]

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.

:cool: Alan

[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.

:cool: 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 !

[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:eyebrows:

:cool: Alan

[Gordon Steadman]

This amp is a seriously good performer, and cheap:eyebrows:
:cool: 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:lol:

[istari_knight]

No, Marantz :D

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 !!! :doh:

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 :(

[MartinT]

I used to work for NEC, but from 1985 onwards. Their hi-fi division soldiered on until just after 1990, when they pulled out of the market. It's a shame as they made some good kit, especially a very high end 'statement' CD player that's as rare as hen's teeth. To think I could have bought one at staff discount :doh:

EDIT: here it is, the NEC CD-10
http://audio-database.com/NEC-AUTHENTIC/player/cd-10-e.html

...and this earlier beast, the CD-903 (love the remote)
http://audio-database.com/NEC-AUTHENTIC/player/cd-903-e.html

[Macca]

...and this earlier beast, the CD-903 (love the remote)
http://audio-database.com/NEC-AUTHENTIC/player/cd-903-e.html

Yeah that is tasty.

[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?

[istari_knight]

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?

Completely missed that :doh:

According to "wizargoz" on the link "Sound quality with original NEC Authentic Series Combo speakers is louder than A520E system, better definition but a sound quality far below 80 watt Technics 'New Class A'." ... Whatever that means.

[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.

:cool: 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.

:cool: 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.

:cool: 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 :)

:cool: 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.

[walpurgis]

This thread is 4 years old now

Still relevant though if Andi has one of these amplifiers. Alan may have some comments too.

[Macca]

I think I'd be wary of using it as a PA amp. I mean on paper it will be fine but it is surprising how much spl a room full of people soaks up. Your asking it to work hard continuously for several hours...I wouldn't take the chance.

[drrdf]

Although this is now a very old thread my NEC A820E is still going strong and giving a brilliant performance, just as it did the day it was new. (I have had this since I purchased it new.) I had the usual problem with mine that one or more of the indicator bulbs burn out with age. (They have now lasted more or less 40 years which is not bad.) However when I came to examine this my observation is that the bulb voltage of the originals is 4.5V not 12V. It is usually the two Active drive illumination bulbs which go first. As these bulbs are in series with the function switch bulbs none of them then illuminate. I made the mistake originally of thinking that these original bulbs were 6V; that was no doubt because I measured the available voltage supply when it had no load. I now believe and have observed that the proper voltage for these seems to be 4.5V. I did actually replace one of mine with a 6V bulb and that did work, but of course it does not glow quite as brightly as the other original 4.5V ones. That does not really matter with only one, since this will mean that the remaining bulbs will be under-driven, which should help them last a bit longer.

The circuit diagram and manual does not seem to indicate the correct voltage of these bulbs so this has to be determined by measurement. I note for anyone who may be interested that there is a guy selling these suitable 4.5V miniature bulbs on ebay. Do not forget to put the green translucent plastic sleeve over the new bulb to give a green hue to the display. If you cannot get 4.5V replacements then 5V will probably be near enough.