Daemon4x4 - 4x4 & Off Road Technical Board

Daemon4x4 - 4x4 & Off Road Technical Board

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#2620-10-2011 20:02:12

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Apache wrote:

Cant stand up across the whole area upstairs.

John, no B&O suff. Not something I've ever really been attracted to. 'All show and no go'  wink
I have to agree about the B&O stuff we bought ours from the PSI Shop at Gutersloh (BFPO47) tax free The 4000 wasn't so flash but gave good sound quality, came back to blighty got Denon and Technics stuff and big Omar speakers,kept telling ex wife that the sofa would be next year....

#2720-10-2011 20:13:04

Re: Classic / old hifi for the hoarders out there!

Bawbags.  No room at the moment and no need for another set of speakers comes the verdict.  Sorry, Andy, someone else will have to lighten the load for you.

#2821-10-2011 06:57:11

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Matt wrote:

how big is your back garden? Sounds like it's like a Tardis. big_smile
Hard to say - so much of it is covered by sheds big_smile



At a guess, shed free, it would be around 30ft wide by 40- 50 ft long, then a bit about 12ft wide by 30ft long. If I was careful I could get more sheds in...

#2921-10-2011 11:49:04

Re: Classic / old hifi for the hoarders out there!

lol What you ain't got out front you definitely made up for at the rear then. big_smile

#3021-10-2011 20:55:58

Re: Classic / old hifi for the hoarders out there!

Magnums are now spoken for!

#3106-11-2011 18:37:45

Re: Classic / old hifi for the hoarders out there!

Andy, is the Module 80 still up for grabs?  I've just had another 'flameout' on the NVA power amp.  I don't even know what I did this time but it took exception to being moved....It's so poncy it doesn't have any protection circuitry.  I'm not paying another 80 quid and going round that bloke's house to get it working...

I'm more than happy to swap your old receiver for a broken NVA A40 and a Rotel RC850 pre amp, but I suppose you're going to want to sell?

#3206-11-2011 19:49:40

Re: Classic / old hifi for the hoarders out there!

Hahaha, NVA, yes. Is it made of plastic, or am I thinking of DNM?

Anyway, yes, the Module 80 is still here - no-one seems to want proper hifi in these download days.

I find myself being drawn towards saying 'yes' to a swap - even though the shed is full I just can't say no to a project...

#3306-11-2011 20:03:11

Re: Classic / old hifi for the hoarders out there!

NVA is made of plastic these days.  This one is mostly aluminium - it's a proper old school one.

#3406-11-2011 20:06:20

Re: Classic / old hifi for the hoarders out there!

Probably why it's blown up. Soldering not good enough and shorting to the case big_smile

Happy to swap, but PLEASE take some speakers too! big_smile

#3507-11-2011 12:50:24

Re: Classic / old hifi for the hoarders out there!

Andy, sorry to dick you around here.  Just tested the pre, which is working fine, as expected.  Curiosity got the better of me and I decided to have a peak insider the power amp.  It looks like this:

http://i235.photobucket.com/albums/ee48/adampreece/IMG_0688.jpg

Now, to me, that looks like a transformer, two massive capacitors and a couple of boards. 

Investigating the boards, it looks like my usual resistor inferno has taken place:

http://i235.photobucket.com/albums/ee48/adampreece/IMG_0690.jpg
http://i235.photobucket.com/albums/ee48/adampreece/IMG_0689.jpg

My question for you (or Matt or anyone else) is then whether I am right in thinking that I can just buy a couple of 'power amp kit' boards off ebay and swap them over.  The wiring looks pretty simple (I am not good at electronics) and it might be better for me to just do a straightforward swap in the case, than try to work out how to exchange about a ton of old hifi between here and Malvern. 

What do you reckon?  I'm really keen to make it work if it's something within my meagre skills.  Help me out and I'm more than happy to send you the old boards as a thank you if they're any use to you.

#3607-11-2011 21:28:08

Re: Classic / old hifi for the hoarders out there!

Never seen inside an NVA before, and if he charges significant money for them, I'm surprised he doesn't weld the lids on so you cant see your money went on shoddy crap.

I can see at least two design faux-pas immediately. I'm amazed NVA ever gained any acclaim! I built better as college projects!

To answer your question, yes you could simply buy power amp boards, but it is likely to be as expensive as just buying a half decent amp off eBay, unless you fancy a project. Sanch, I'm happy to send you the Goodmans for the cost of shipping it + a pint to save you pouring any more money into that rubbish. smile

#3707-11-2011 23:38:18

Re: Classic / old hifi for the hoarders out there!

You mean both inputs being grey and having the mains and the audio out using the same colours? That seems weird to me, anyway. I like the.goodmans as a bit of.furniture anyway so would love it even if I do decide to play with the nva. Let me know how much postage and beer would be.

By the way, nva still trade but only on eBay. Type those three letters in and get ready to shit yourself.

#3808-11-2011 01:28:04

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Sancho wrote:

You mean both inputs being grey and having the mains and the audio out using the same colours?
I've no idea if what's making me cringe is what Apache is referring to, but the fact that none of those FET's are bolted to the heatsink and that wiring on the caps and rectifier are a bit disconcerting. Seems weird that the outputs are so close to the TX too, IMHO. How are those PCB's secured in place Sanch?

#3908-11-2011 08:48:47

Re: Classic / old hifi for the hoarders out there!

Well, PSU wiring, colours aside...

All wiring to PSU should go to the same points at the reservoir caps. This reduces noise current transfer. It's called star earthing and is a basic fundamental in electronic design for low noise and distortion. Looking at the track layout on the PCBs suggests no thought has been given to that sort of thing there either. As it is, the RF oscillation he's so concerned about (use his 'special' speaker cables etc) is going to be almost unavoidable with all those earth paths and consequent stray capacitance.

Your resistors keep boiling up because the amp is oscillating at RF because it has no stability. This is partly because his design philosophy is off with the fairies thinking that he cant use a low inductance in the output for the amp to allow it to remain stable. So an amp that is always on the edge of RF oscillation sounds better? Really?? Hmmm... Would like to see him get them CE marked and thus legal for sale in the UK... lol

Sanch, I'm well aware of the prices he charges for his kit. You'd have to be as mad as someone who believes Bobboxes, electric turbos, those air inlet diffusers etc work to pay any kind of money for them. But there's plenty who do, so good luck to him!

Anyone want to do a Surf Train with a Goodmans amp on board?

#4008-11-2011 12:46:49

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Matt wrote:

Icon - Post link Sancho wrote:

You mean both inputs being grey and having the mains and the audio out using the same colours?
I've no idea if what's making me cringe is what Apache is referring to, but the fact that none of those FET's are bolted to the heatsink and that wiring on the caps and rectifier are a bit disconcerting. Seems weird that the outputs are so close to the TX too, IMHO. How are those PCB's secured in place Sanch?
You'll like this, Matt.  The PCBs are glued, as are the FETs.  NVA's design philosophy is all about minimising metal, hence the cases now being plastic.  Part of that is that all fixings are glued unless unavoidable.

There are actually two wires coming out of the transformer that don't connect to anything other than the rubber on the end of them (kind of pointing towards the front of the case).  I'm sure that's not 'best practice' either.

#4108-11-2011 13:43:37

Re: Classic / old hifi for the hoarders out there!

If you read the twaddle on his website, it's pseudoscience which could run with the best of them from the automotive snake oil world.

He might like to note that if he employs a proper earthing strategy like I alluded to, he wont actually HAVE any casework eddy currents to worry about! What a tit!

#4208-11-2011 14:46:26

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Sancho wrote:

You'll like this, Matt.  The PCBs are glued, as are the FETs.  NVA's design philosophy is all about minimising metal, hence the cases now being plastic.  Part of that is that all fixings are glued unless unavoidable.
You ain't going to tell me that it's hot melt he's used too, are you? big_smile


There are actually two wires coming out of the transformer that don't connect to anything other than the rubber on the end of them (kind of pointing towards the front of the case).  I'm sure that's not 'best practice' either.
End of the day, there's not really much you can do with stray leads other than to insulate the ends and secure them to stop them flapping around. In that scenario, I'd use a similar technique. Heatshrink both ends, with a half inch or so of sleeving extending past the end of the cable, and then double them back and secure them to themselves with a second single, larger diameter length of heatshrink, so that there's not a cat in hells chance of them being exposed or contacting anything. Then secure it up to something to stop it flapping around.

Not sure whether that might tally up as being best practice with the RF geek, (audio/radio chaps are a breed of their own big_smile), but it's safe.

#4309-11-2011 14:57:36

Re: Classic / old hifi for the hoarders out there!

Just out of curiosity Sanch, have you not considered having a try at repairing it yourself? You can hardly bugger it up much more if it's already knackered, and seeing as you're considering board swaps anyhow. What are the numbers on those transistors/FET's? I'm assuming at least one output circuit is intact so that you can see the values of those burnt up resistors?

#4409-11-2011 15:49:36

Re: Classic / old hifi for the hoarders out there!

When it was last plugged in (and the time I killed it before that), one channel was working and one was dead.  From what I can see, one channel is pretty much burned out, the other looks like it's been a bit warm. 

When it went back to NVA before, his view was that the components would now be 'stressed' so they all needed replacing if I wanted optimum quality.  The fact that he had a big pile of modules lying around and couldn't be arsed soldering individual components was not a factor....

I could have a crack at repairing it myself.  My soldering is not great, but I can probably do it.  The reason I didn't is partly because my brain still half believes that I shouldn't bother swapping individual components, and partly because usually when I touch anything involving electricity I either start a small fire or find myself on the other side of the room with a sore arm and lots of people laughing.

#4509-11-2011 15:58:57

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Sancho wrote:

The reason I didn't is partly because my brain still half believes that I shouldn't bother swapping individual components
Component level repair is what the trade has survived on for years. smile Certain components will be damaged and need replacing, but some will be totally fine as they are.


and partly because usually when I touch anything involving electricity I either start a small fire or find myself on the other side of the room with a sore arm and lots of people laughing.
That's half the fun of electronics. big_smile If I had a quid for every time I'd got a shock I'd be rich. Those bloody old Hitachi TV's were the ones which always got me. They made it so that it was practically impossible to reach the chassis release catch and extract the chassis without touching the reservoir cap. I feckin hated those things. big_smile Wooden cabinet too, so when you pulled your hand back you were guaranteed to tw@t it on the extremely sturdy cabinet and be in even more pain. big_smile

You're welcome to send it up here, or pull the boards and send those up. Won't promise owt, (although if I couldn't repair something like that I'd eternally hang my head in shame big_smile), but I can take a look if you wish.

#4609-11-2011 16:55:24

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Sancho wrote:

the components would now be 'stressed' so they all needed replacing if I wanted optimum quality.
<titter>

<Harry Enfield> "Yes, I'm afraid I saw you coming"

In all seriousness, I would't bother repairing it unless you live in a faraday cage and can therefore stop it going unstable at radio frequency again. The design is always going to be prone to blowing up becasue as I said, it has no natural stability because 'this is bad for sound quality for reasons no-one can explain'  whistle

If you REALLY want to keep it, build a couple of kit power amps from Maplin and fit those (or Velleman - bit expensive, but they are sensible designs). You'll have to measure the rail voltages and get something compatible if you don't want to change the transformer too.

IMO though, I wouldn't piss on it if it was on fire - and it probably will be again soon.  lol

Matt - if you repair it, put a series inductor (not much, just half a dozen turns of something like 16awg) on the output. That will go some way towards stabilising the piece of crap. A metal case would help too, but 'they're bad for sound quality' in the same way the tooth fairy is reducing UK debt.

#4709-11-2011 17:18:49

Re: Classic / old hifi for the hoarders out there!

Measure?  Voltage?  As far as I know, multimeters are only for attaching to your tongue to prove that you conduct electricity...

The transformer that's in there currently says 30v + 30v so I presume I'd be looking for a module that takes 30v - a couple of the Velleman ones seem to work and, from what I can see, are actually those that Maplin sell these days. 

I'm assuming the two big caps are there for 'technical' reasons either to do with the wires being too long or trying to achieve some kind of soft start. 

I shall ponder what to do with it.  As you might know, I have some investment in a business making and selling acoustic and electric guitars and am polishing up my (lame, but rapidly improving) woodworking skills so that I can hopefully change over to working there full time in a couple of years.  I've already had to give myself some soldering lessons, done a bit of reading about pots and caps (an NVA amount of mystery involved around those in guitars) and knocked up a simple circuit for a single pickup guitar (with sound, not fire, coming out of it) so I'm getting there. 

One thing we don't do at the moment, and very few do, is make amps.  I think there's a pretty big gap for someone to make decent looking guitar amps and an even bigger one for reasonably priced amps that aren't shit.  The very concept of screwing a driver to a chipboard cab with no back and very little bracing would make most speaker designers sick. 

So.....I'm considering learning a bit more about amps so we can see how that goes.  I'm thinking that something like a guitar just needs a nice clean signal, simple circuits and as little interference as possible, then going to a speaker that doesn't just vibrate everything in a 5 foot radius. 

I guess guitar amps have a lot more gain than hi-fi amps. but it's kind of tempting to butcher the pre and power amps I have now and stick them in a wooden cabinet with a shiny speaker.....

#4809-11-2011 18:26:34

Re: Classic / old hifi for the hoarders out there!

If the transformer is 30V, it is likely that the rail voltage you need to look for is +/-45V. The voltage on the transformer will be it's AC voltage. Once rectified it will be around 42.2V (30V x 1.414) and as there is no blocking capacitor on the O/P, the amplifier will use a split supply. ie a -ve and a +ve rather than a +ve and a ground.

The two big caps are reservoir caps. Primarily they are there so you don't hear a 50Hz (mains) hum on the output. Also known as 'smoothing' caps. They also act as a 'reservoir' of current for high power musical transients.

Guitar amps are as much prized for the way they 'colour' the sound. A completely neutral sounding guitar amp / speaker combo may not be as popular as you might think!

I did build some 1kW power amps for someone about 20 years ago, when amps of that power cost thousands. These days you can pick a Beringer 1kW amp for £300! I couldn't build one for that.

#4909-11-2011 19:37:59

Re: Classic / old hifi for the hoarders out there!

Now I'm baffled.  I had a look at this Velleman module:

http://www.esr.co.uk/velleman

Ignore the price and the 'music power' for a moment.  That says 25-30Vac.  I took that to mean a transformer with 30 volts on it would work.  Because it's AC.  Guess who didn't even do physics at school?

What you say about guitar amps colouring sound is certainly true.  One of the issues we have on our guitar adventures is that I want everything crystal clear, my mate who makes them insists on having them 'coloured' a bit.  Still, I think you can build an amp with all that tonal richness etc etc without making it out of chipboard.

#5009-11-2011 20:38:59

Re: Classic / old hifi for the hoarders out there!

Icon - Post link Sancho wrote:

Ignore the price and the 'music power' for a moment.  That says 25-30Vac.  I took that to mean a transformer with 30 volts on it would work.
It'll work fine with that transformer of yours. The whole AC/DC thing Apache was referring to was if an amp needs a recified & smoothed supply, but that kit sorts that side of things itself. You just feed it the raw AC from one of the outputs on that TX.
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