About make an audio power amplifier.

[tvtech]

I. don't.like.or.trust. Tants......for anywhere but timing applications or somewhere that there is no ripple current involved...

Make nasty little fires inside equipment if they get too hot. Ripple kills them.

Still got burnt fingers from a 10uF that was supposed to do final smoothing on a 20A supply designed around a Lm317 with outboard pass transistors...like 5 MJ 2955 I think...long time ago.

Used correctly and in the right application....they will probably outlive the rest of the parts....Military grade stuff (in the eighties) was full of them here in SA.
I know cause I was a guy that repaired the stuff that failed. Never replaced a Tant.....

Regards,
tv

 

[audioguru]

I used tantalum capacitors in the late 70's and early 80's and they all disappeared. Only their wires remained. I never saw the explosions. Most had the name brand ITT and their voltage rating was double the voltage used in the circuit.

 

[spec]

I. don't.like.or.trust. Tants......for anywhere but timing applications or somewhere that there is no ripple current involved...

Make nasty little fires inside equipment if they get too hot. Ripple kills them.

Still got burnt fingers from a 10uF that was supposed to do final smoothing on a 20A supply designed around a Lm317 with outboard pass transistors...like 5 MJ 2955 I think...long time ago.

Used correctly and in the right application....they will probably outlive the rest of the parts....Military grade stuff (in the eighties) was full of them here in SA.
I know cause I was a guy that repaired the stuff that failed. Never replaced a Tant.....

Regards,
tv

I used tantalum capacitors in the late 70's and early 80's and they all disappeared. Only their wires remained. I never saw the explosions. Most had the name brand ITT and their voltage rating was double the voltage used in the circuit.

Hi tv & ag,

Yeah, you have got tants pretty well nailed- they don't like current much, especially bead tants. But some of the later types are better.

Pretty much all of the capacitors, apart from reservoirs, we used on military equipment were axial can solid tants. I can't remember one blowing up though.

spec

 

[tvtech]

Good chat this

Never use a donkey in a horse race...simply not suited

Regards,
tv

 

[KeepItSimpleStupid]

And you should read about the early SMT tantalums in Tektronix equipment and poor IC sockets made by TI. Anyway, it loooks like the technology has improved. Then there were the bad electrolytic.

Now all you have to worry about is the low capacity batteries and capacitors inside intentionally wrongly labeled shells.

 

[spec]

And you should read about the early SMT tantalums in Tektronix equipment and poor IC sockets made by TI. Anyway, it loooks like the technology has improved. Then there were the bad electrolytic. Now all you have to worry about is the low capacity batteries and capacitors inside intentionally wrongly labeled shells.

Indeed Keep, there are many pitfalls with components. The rip off components are particularly annoying.

You do get batches of faulty components: in the early 1960s Wima, dark brown 250V solid capacitors were used everywhere because they were cheap and had a reasonable spec, and then they started going open circuit, especially when hot. Our company made scopes which had hundreds of them. It cost an absolute fortune to change them all. I never did use a Wima component for about 10 years after that.

In simpler days, many of the managers were ex engineers who laid down strict rules for us junior engs. Two were, write it all in a day book (sackable offence not too) and when you build a circuit for the first time check every individual component before fitting them so that you don't reject a good design because of a faulty component. The first is very good advice, but can you imagine checking each component in a modern circuit. How times have changed.

I can even remember the days when you had to produce flow diagrams for your software/firmware- I would love to see a flow diagram for Windows 10.

 

[spec]

tv,

just in case you haven't got it, here is a link to the service manual for the NAD 3020. It includes the full schematic:
https://p10hifi.net/planet10/manuals/NAD_3020_ServiceManual.pdf

​

Here is the specification:

​

I have also examined the circuit and it is pretty advanced, especially for the time and also for the cost.
Notable points are:
(1) High instantaneous current capability of 10mA * (hfe output tran * hfe driver) giving about 10A, which is exceptional.
(2) high open loop gain and low distortion by the use of a constant current drive from the input difference amp and bootstrapping in the Voltage Amplification Stage (VAS)
(3) Compound emitter follower output giving giving fast operation with no hang up as in complementary output stages.
(4) Zobel network to tame the wild reactive components generated by the speaker.
(5) Isolating inductor between output and speaker, improving the open loop frequency characteristics.
(6) Isolated + & - supply lines for drivers/output transistors and separate stabilized supply lines for the input difference amp and VAS.
(7) Two active transistors in VAS giving high gain and low difference amplifier modulation index.
(8) Current feedback giving wide band-width, high slew rate and low distortion.
(9) Balanced supply rails with no output capacitor and DC coupling to the speaker.
(10) Comprehensive open loop frequency response shaping, presumably to give a high slew rate and good frequency stability margin
(11) Surprisingly low distortion figures over a large range of conditions.

Yes, the RMS power of 20W at 8 Ohms is less than a lot of amps, but the instantaneous power is pretty good at 39W, especially as music has very little RMS power but huge peaks. The high peak output current capability of the 3020 would also build on this greatly and should produce a more solid sound than the rather thin sound of some higher powered amps.

It is clear that the manufacturer has saved money on the mains transformer which is quite small and, instead of being a toroid, is a conventional E&H type. The four 2.2 mF reservoir capacitors are adequate though.

I have never heard a NAD3020, but it is not surprising that they have a reputation for sounding sweet.

spec

​

 

[Nikolai Petrenko]

In theory you are quite right, but in practice not. Most high end audio amps need quite high input levels so even the line output from CD players etc is not sufficient to drive the amp. In general, the less gain that an amp has, and by implication the higher the input drive voltage, the less distortion, because for a given open loop gain, quite simply, there is more negative feedback to correct the open loop distortions.

But there is more to it than that. The source impedance into an audio amp effectively forms part of the amp circuit and can have a subtle effect on the amp sound. So it is advisable to drive the power amp from a consistent and well defined low source impedance.

There is also the question of Radio Frequency Interference (RFI). Any piece of wire will have unwanted signals in it. Of course with good system layout and screening and a good OV reference point these can be minimized but they will always be there. Not only are these unwanted signals a nuisance for the obvious reason, but they also cause various forms of distortion.

In short, having a preamp, while in theory is not essential, in practice it is. And don't forget you need a method of selecting the input signal any way.

And if I read you correctly, Nicolai, you will be wanting to add remote control to your HiFi system sometime along the line.

spec

The signal wires will be wrapped carefully with thin galvanized steel sheets.
Yes. Remote control but not now.

 

[audioguru]

The signal wires will be wrapped carefully with thin galvanized steel sheets.

Audio systems do not do that. The shield is braided copper strands or metallized plastic film which part of the cable.
Professional audio systems use balanced signals with a shield as above so that any electro or magnetic interference that leaks past the shield in the cable is cancelled. Home systems use ordinary cheap shielded unbalanced audio cables as described above.
I have used hundreds of shielded audio cables and have bought rolls of it. Most audio products come with the cables.

 

[Nikolai Petrenko]

Can you explain detail about "balanced" and "unbalanced"? I don't know certainly.

 

[KeepItSimpleStupid]

Look at this first: **broken link removed**

and this https://www.aviom.com/blog/balanced-vs-unbalanced/ second.

and this

third.

 

[Nikolai Petrenko]

Thanks KISS, I now understand!

 

[spec]

Can you explain detail about "balanced" and "unbalanced"? I don't know certainly.

Bit of chat about balanced audio here on ETO: https://www.electro-tech-online.com...s-differential-inputs-audio-amplifier.147226/

 

[tvtech]

NAD 3020 has nothing to prove to me...

In a TV environment that also does Amp repairs.... sad to see expensive (apparently) 300Watts RMS amps being brought in for repair...little speaker cable problem or accidental short and boof. 30 years of the 3020 never gave me boof.

So, small and with the balls of a elephant, the build of a budgie, and the sound of a canary in full song......

Keeps singing. 30 year old pets I have and keep happy

Till later

 

[spec]

NAD 3020 has nothing to prove to me...

In a TV environment that also does Amp repairs.... sad to see expensive (apparently) 300Watts RMS amps being brought in for repair...little speaker cable problem or accidental short and boof. 30 years of the 3020 never gave me boof.

So, small and with the balls of a elephant, the build of a budgie, and the sound of a canary in full song......

Keeps singing. 30 year old pets I have and keep happy

Till later

I know what you mean tv. I haven't got one, but I feel the same way about the Mission Cyrus 2 amp.

spec

 

[tvtech]

Ever heard a Krell class A before? There were the KSA 50 KSA 100 and so on. Worked for a company in JHB that had mates that imported those beasts.

Heard them and listened to them in the soundroom and was blown away. Now there is a beast that LOVES difficult speakers. Lower the speaker impedance..the cooler they run. Absolute bass control. No matter what you threw at them. Any speaker and clean input source and you will be gobsmacked.

Pink Floyd ...Dark side of the Moon were favourite demo discs then along with some classical stuff. Those WERE the days..

Regards,
tv

 

[spec]

Ever heard a Krell class A before? There were the KSA 50 KSA 100 and so on. Worked for a company in JHB that had mates that imported those beasts.

Heard them and listened to them in the soundroom and was blown away. Now there is a beast that LOVES difficult speakers. Lower the speaker impedance..the cooler they run. Absolute bass control. No matter what you threw at them. Any speaker and clean input source and you will be gobsmacked.

Pink Floyd ...Dark side of the Moon were favourite demo discs then along with some classical stuff. Those WERE the days..

Regards,
tv

Yeah,
Heard a lot of esoteric stuff, but mainly at audio shows. I was going to the Sound and Vision Show at Bristol last week but somehow didn't get around to it: https://www.bristolshow.co.uk/

Why past tense tv?

 

[spec]

I was at a mates house to see his new projector. While he was demoing it I noticed the very low clean base. He has only got a pair of KEF BD139s feeding into a huge horn which he made as part of the masonry when he built the house in the 1980s. I have visited the house many times since that time and had never known about the horn before. It acts as a base sub for two huge transmission lines at the front and a couple of KEF concertos at the rear (bought for next to nothing on the net). The sound was slightly better than the edgy racket that comes out of our TV.

 

[tvtech]

[QUOTE
Why past tense tv?[/QUOTE]

Quality quality quality. You in England spec....remember Rega RB300 arm and Rega 3 Turntable?

 

[tvtech]

I have both too...but my LP's were in storage and got damaged. Have not played a record in around 10 yrs