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Old 11th May 2017, 1:03 pm   #21
paulsherwin
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Default Re: How to cure a noisy Bardwell amplifier?

As I said earlier, try a 9V battery to confirm or eliminate the PSU as the cause.

I agree that the sound on the youtube video is unlikely to be caused by bad transistors, and may well have more than one cause. I wouldn't describe it as 'hiss'.
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Old 11th May 2017, 1:18 pm   #22
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Default Re: How to cure a noisy Bardwell amplifier?

As well as using a linear regulated power supply instead of an SMPS, as suggested ( definitely the mostly likely cause of your problem, now you've provided video evidence ) it may be an idea for various reasons to investigate /improve decoupling on the module. By which I mean checking/ replacing/ upsizing if present any elderly electrolytic capacitor connected between Vcc and ground on your module....I don't know what decoupling there is locally on the chips right between their Vcc pins and their own grounds, either... these are far 'noisier' times than when these were designed!!!

But try the battery fix before doing anything fancier as it has the most probitive value and is simple!!
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Old 11th May 2017, 5:50 pm   #23
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Default Re: How to cure a noisy Bardwell amplifier?

Hi IG, the main thing from the graph is to observe the maximum working limits of the chips (the area under the curves), and under run them a little to be on the safe side. For an output of 10 Watts per channel, each chip will at a guess take about 1.5 Amps for full output when connected to 12 Volt supply. So your total current will be twice that, about 3 Amps peak for both channels at full tilt. A good airflow over the heatsinks is essential too. I would monitor the temperature after a while at your normal listening levels. With my amp I used a toroidal transformer in the power supply because hum was a problem due to the case being a bit cramped, and the transformer was too near the PCB. I think I used 15 Volts for mine. It may just be that this particular amp is susceptible to hum pickup. If you happen to be using a bluetooth link then that might be causing the buzz. Try a different audio source and see if the buzz disappears. Hope that helps.
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Last edited by Biggles; 11th May 2017 at 5:51 pm. Reason: typo
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Old 12th May 2017, 1:14 pm   #24
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Default Re: How to cure a noisy Bardwell amplifier?

Quote:
Originally Posted by astral highway View Post
As well as using a linear regulated power supply instead of an SMPS, as suggested ( definitely the mostly likely cause of your problem, now you've provided video evidence ) it may be an idea for various reasons to investigate /improve decoupling on the module. By which I mean checking/ replacing/ upsizing if present any elderly electrolytic capacitor connected between Vcc and ground on your module....I don't know what decoupling there is locally on the chips right between their Vcc pins and their own grounds, either... these are far 'noisier' times than when these were designed!!!

But try the battery fix before doing anything fancier as it has the most probitive value and is simple!!
Ok - I'll swap over the power supply next and see what happens. I have also drawn out the Bardwell circuit so we can see whats what. From this C115 and Cp might be worth changing (but I'll do the power supply trick first). Hopefully the circuit diagram and annotated PCB will be useful for future users also
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Old 12th May 2017, 1:50 pm   #25
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Default Re: How to cure a noisy Bardwell amplifier?

I have now powered the circuit with 25V using the DC from a rectified/smoothed voltage from a 1:10 step down AC mains transformer (part of the circuitry from a radiogram I have in bits at the moment).

The background noise is virtually eliminated - and the sound quality is excellent with no distortion at the high volumes. Interestingly, the ticking is still there but I think that this is due to the bluetooth module as it stops when I remove it from the circuit. However, I can live with that as its only heard at very high volumes and doesn't really interfere with overall sound output.

I will now have a go with a 9V battery and see if I can get a similar quality at lower voltage.
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Old 12th May 2017, 2:18 pm   #26
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Default Re: How to cure a noisy Bardwell amplifier?

The background noise will be the same or even less, but the maximum volume will be greatly reduced. It may well still be adequate of course.

Most of us here will have developed the habit of hoarding old wall warts - I always save them when I scrap equipment, I rescue them from skips, buy them for 20p in flea markets etc. I have a big box of them up in the loft. Old laptop supplies are particularly useful as they supply a nice steady 19V at a high current, and aren't usually too noisy.

As a general rule, wall warts containing a transformer are quieter electrically than the smaller switch mode ones, though there is a huge amount of variation. If you have a wall wart hoard you can experiment to find the best one.
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Old 12th May 2017, 2:26 pm   #27
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Default Re: How to cure a noisy Bardwell amplifier?

Note that two el-caps need to be changed (from 500uF to 1,000uF) if it's desired to use 4 Ohm speakers rather than 8 Ohm, as highlighted in yellow on the pic below. I guess these amplifier modules are of such an age (more than forty years), that they'd benefit from an all round electrolytic cap change. I make it 13 in total - all easy to get at, but I must admit that I've not changed mine!
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Old 12th May 2017, 2:40 pm   #28
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Default Re: How to cure a noisy Bardwell amplifier?

You were right Paul - with my 9V battery noise is still ok but there is a lot of distortion at the high volumes. I want to get up closer to the +20V I think.

so would something like this laptop power supply be ok? http://www.ebay.co.uk/itm/20V-3-25A-...YAAOSw9GhYd5Av

The trouble I'm going to have it finding a connector the right size to fit into my box. Or do you wire them straight it?

Last edited by indigo.girl; 12th May 2017 at 2:46 pm.
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Old 12th May 2017, 2:42 pm   #29
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Default Re: How to cure a noisy Bardwell amplifier?

Quote:
Originally Posted by David G4EBT View Post
Note that two el-caps need to be changed (from 500uF to 1,000uF) if it's desired to use 4 Ohm speakers rather than 8 Ohm, as highlighted in yellow on the pic below. I guess these amplifier modules are of such an age (more than forty years), that they'd benefit from an all round electrolytic cap change. I make it 13 in total - all easy to get at, but I must admit that I've not changed mine!
Thanks David - I have increased from 500uF and 1000uF - didn't really hear much of a difference. I think its the power supply thats my issue. At 25V this little amp sounds wonderful
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Old 12th May 2017, 2:52 pm   #30
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Default Re: How to cure a noisy Bardwell amplifier?

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Originally Posted by indigo.girl View Post
You were right Paul - with my 9V battery noise is still ok but there is a lot of distortion at the high volumes. I want to get up closer to the +20V I think.

so would something like this laptop power supply be ok? http://www.ebay.co.uk/itm/20V-3-25A-...YAAOSw9GhYd5Av

The trouble I'm going to have it finding a connector the right size to fit into my box. Or do you wire them straight it?
Very cheap Chinese laptop supplies do tend to be noisy. Why not ask in 'parts wanted' if anybody has a suitable wall wart in the junk box? A 12V unregulated supply is likely to give about 18V off load. Apparently these amps can run from 24V.
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Old 12th May 2017, 3:06 pm   #31
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Default Re: How to cure a noisy Bardwell amplifier?

BTW I have also used one of these 12V to 5V converters inside my box to feed the 5v USB bluetooth module. Is this type of module suitable for audio or will it have noise issues like the SSMP? http://www.ebay.co.uk/itm/1320733934...%3AMEBIDX%3AIT
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Old 12th May 2017, 3:50 pm   #32
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Default Re: How to cure a noisy Bardwell amplifier?

Good result ,IG! As far as the connector goes , why not hard-wire it in if there's no real advantage in putting in a special socket??

Do always strain relieve the cable, though. You can either use a cable clamp if you have an old pull from somewhere or just use a small cable tie or two inside, flush with the back or whatever surface you're running the cables through.
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Old 12th May 2017, 3:54 pm   #33
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Default Re: How to cure a noisy Bardwell amplifier?

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Is this type of module suitable for audio or will it have noise issues like the SSMP? http://www.ebay.co.uk/itm/1320733934...%3AMEBIDX%3AIT
That's a buck converter and is a noisy circuit with lots of harmonics , like other SMPS. So not really suitable at all...
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Old 12th May 2017, 4:14 pm   #34
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Default Re: How to cure a noisy Bardwell amplifier?

Is it based on the switching principle like the SMPs? To do it properly will I have to use a proper step down transformer inside the box?

Like this? http://www.ebay.co.uk/itm/DC-12V-24V...QAAOSwOyJX6npI
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Old 12th May 2017, 4:49 pm   #35
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Default Re: How to cure a noisy Bardwell amplifier?

I had problems with mine picking up hum from the mains transformer if it was mounted too close to the PCB. You may need to experiment with positioning the supply inside the box for best results. Also I think that the speaker coupling capacitors (500 microFarad 15 volt) are a bit underated for 24V operation. They should really be uprated to 500 microFarad 25 volt types, to cope with the higher supply voltage. In reality use 470 microFarad 25 or 35 volt ones as these are preferred values nowadays. Personally I would run the amp from 15 to 18 volts to avoid caning it too much.
Alan.

Last edited by Biggles; 12th May 2017 at 4:50 pm. Reason: more typos, pay attention Alan!
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Old 12th May 2017, 5:51 pm   #36
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Default Re: How to cure a noisy Bardwell amplifier?

Good thought Alan. 24V is ok for the chip but not for the circuitry. I have now found an old AC adaptor in my garage that supplies 16V so will use that.
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Old 12th May 2017, 11:27 pm   #37
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Default Re: How to cure a noisy Bardwell amplifier?

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Originally Posted by indigo.girl View Post
Is it based on the switching principle like the SMPs? To do it properly will I have to use a proper step down transformer inside the box?

Like this? http://www.ebay.co.uk/itm/DC-12V-24V...QAAOSwOyJX6npI
That's also a switched-mode buck converter.

An example of a linear regulator is the classic 7805. An example of a Chinese module using one: http://www.ebay.co.uk/itm/2Pcs-Modul...oAAOSwB09YI9mS

Note the heat sink. This might well get rather hot - it depends on the input voltage, and how much current the Bluetooth module draws. Do you happen to know that (or can you measure that for us?).
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Old 13th May 2017, 12:49 am   #38
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Default Re: How to cure a noisy Bardwell amplifier?

It is likely to be tens of mA if that. Bluetooth was specifically designed to minimise power use. (That's not to say that some poor implementations won't be power hungry of course).

I agree that a 7805 is the way to go, or even a 5.1V zener diode and limiting resistor. You will find 7805s in most scrap SMPSUs, or you can buy them from eBay sellers for pennies.
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Old 13th May 2017, 10:12 am   #39
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Default Re: How to cure a noisy Bardwell amplifier?

Thanks Paul and Mhennesy - I'll order one from china and have a play with it. It's tricky to know which is which as they aren't all labelled SSMPs etc. What it is it important to look for in the name to distinguish the two types of power supply?
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Old 13th May 2017, 10:30 am   #40
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Default Re: How to cure a noisy Bardwell amplifier?

If it uses LM75** type it will be a linear job, LM75** has a three wire lead out.

If it uses a LM25** type it will be a switcher, LM25** has a five wire lead out.

Also the PC board for a linear wouldn't normally have an inductor on it, whereas a switcher will.

Lawrence.

Last edited by ms660; 13th May 2017 at 10:42 am.
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