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Old 28th Nov 2015, 3:29 pm   #1
peter4076
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Default Reviving my pleasure of the past NAD 3020!

I've just dug out my trusty NAD 3020 amp from last century (confined it to the loft when it couldn't cope with all the peripheries), anyway I have a question to put, hope nobody minds?
Front of NAD a button states PHONO, I do not have my DUAL 505 anymore, so can I use the connections for example a CD?
Front of NAD a button states TAPE my reel to reel and Cassette player have gone, is it possible to use these connections for my lovely MINIDISK player?
Front of NAD a AUX button.
Your thoughts on the above would be most appreciated.
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Old 28th Nov 2015, 3:34 pm   #2
paulsherwin
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Default Re: Reviving my pleasure of the past NAD 3020!

The phono input is for a magnetic cartridge and applies RIAA equalisation. It can't be used with anything else.

The tape connections can be used with anything with a line level input/output.

The aux input is a line level input which is normally used with a CD player.
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Old 28th Nov 2015, 3:42 pm   #3
peter4076
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Default Re: Reviving my pleasure of the past NAD 3020!

Cheers paulsherwin, just letting the amp get to room temperature before firing it up, all my separates are over 30 years old, do they qualify as vintage?
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Old 28th Nov 2015, 4:43 pm   #4
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Default Re: Reviving my pleasure of the past NAD 3020!

That's a good question. When I saw the thread I thought NAD? Vintage? Do we have an age range that qualifies the term?
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Old 28th Nov 2015, 4:43 pm   #5
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Default Re: Reviving my pleasure of the past NAD 3020!

Just for completeness (and I think Peter4076 should ignore this!) I seem to recall seeing designes for 'inverse RIAA networks' that would take a line level signal (such as from a CD player) and convert it into the raw RIAA signal you get from a magnetic pickup cartridge. Thus allowing you to use a redundant pickup input for a CD player or similar.

I am sure feeding the CD player into the AUX input is a lot simpler and will sound better, so that's what to do if you have an AUX input available.
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Old 28th Nov 2015, 8:54 pm   #6
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Default Re: Reviving my pleasure of the past NAD 3020!

I think it's 25 years with exceptions roj but I might be wrong! That takes us to the end of the eighties-tempus fugit
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Old 28th Nov 2015, 9:49 pm   #7
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Default Re: Reviving my pleasure of the past NAD 3020!

Yes, we use a rule of thumb 'vintage' age of 25 years for most things, though we also use discretion at times. A 3020 certainly qualifies.
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Old 29th Nov 2015, 12:42 am   #8
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Default Re: Reviving my pleasure of the past NAD 3020!

Thanks - that makes even my CD player vintage! And makes me feel even older!
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Old 29th Nov 2015, 1:17 am   #9
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Default Re: Reviving my pleasure of the past NAD 3020!

The rich and/or upper middle class buy quality and hang onto it Roj!
Think furniture! It's your mental age that really counts.

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You turn around it's past
You don't get time to hang a sign on me!"
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Old 1st Dec 2015, 9:49 pm   #10
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Default Re: Reviving my pleasure of the past NAD 3020!

I bought an NAD3020 in 1981, the first piece of "serious" audio equipment I ever purchased. It survived two house moves before being retired in favour of an NAD T761 Cinema Amp in 2001.

I brought it out of retirement earlier this year for use with a Freeview STB and a pair of Leak Sandwich Speakers. It still works well apart from a bit of mains hum.
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Old 5th Feb 2016, 11:10 pm   #11
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Default Re: Reviving my pleasure of the past NAD 3020!

I would use all the line inputs such as CD, tape, aux etc. for cd players, tuners, etc. but if you run out of inputs (easily done with freeview boxes, sky and dvd players connected as well) then the you can easily build a reverse RIAA filter. This allows you to plug a line level source into the redundant phono input on the NAD. The circuit is passive and requires no power. Here are a couple of links:-

http://www.epanorama.net/circuits/phono.html

http://sound.westhost.com/project80.htm

Alternatively, try the middle circuit of the photo below.
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Old 6th Feb 2016, 1:56 am   #12
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Default Re: Reviving my pleasure of the past NAD 3020!

Probably easier to buy or build an external switch box though. You sometime find them at car boots or flea markets for little money.
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Old 6th Feb 2016, 9:09 am   #13
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Default Re: Reviving my pleasure of the past NAD 3020!

Quote:
Originally Posted by paulsherwin View Post
Probably easier to buy or build an external switch box though.
Cheap RCA switches are widely available (CPC, eBay, etc.) and by far the simplest option.

While we're on the subject of the 3020 though (I'm rebuilding one at the moment), could I maybe ask a Q. regarding the phono input circuit - specifically why the early phono input stage uses, or was at least designed for, C407 & C411 in parallel (both are specified as 0.0015uF / 50V, Mylar) ? Was this intended to reduce esr, or is there some other potential advantage of using 2 in parallel instead of a single Mylar twice the size ?

The main pcb is actually marked & drilled for both in parallel, although I've only come across a single 0.003uF Mylar cap actually being used in the couple of examples I've seen.

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Thanks, Alan
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Old 6th Feb 2016, 9:33 am   #14
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Default Re: Reviving my pleasure of the past NAD 3020!

Probably an attempt to use part values already used elsewhere on the board but later changed when view of costs changed.

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Old 6th Feb 2016, 11:06 am   #15
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Default Re: Reviving my pleasure of the past NAD 3020!

Cheers David - I'd not thought of that, and just assumed there was some techincal reason.

There's no similar values on the board, but I suspect you're right, there probably were on one of the other product lines in the same factory.

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Old 6th Feb 2016, 2:39 pm   #16
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Default Re: Reviving my pleasure of the past NAD 3020!

1n5 is an E12 value, but 3n is an E24 value. The latter would have been less readily available, so a wise designer would have included both options on the PCB and let Purchasing fight it out!

Also, putting components in series or parallel improves the tolerance. A pair of cheap 10% capacitors of equal value would have a tolerance of 7% (10/root-2). Not sure if that was on the designer's mind, but it's certainly the trick Douglas Self uses in his RIAA preamps.
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Old 13th Feb 2016, 9:34 am   #17
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Default Re: Reviving my pleasure of the past NAD 3020!

Thanks Mark - that's a good pointer. I just looked up some of the details of the Douglas Self RIAA pre-amps, it's interesting, and I can see I need to do a bunch more reading... but, it's good to see there probably is a good technical reason for the parallel caps, as well as cost.

In the mean time, I also found a photo of an early 3020, showing the parallel caps in position - so the early models apparently did indeed use them, presumably before purchasing won !
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