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I'm building my son his first amplifier and I'd be grateful for some advice

hacker said:
Just to be safe I'm going to assume the worst and proceed under the assumption that you mean +ve and -ve to be the +40V and -40V power rails (which is normally what +ve/-ve would refer to). Placing the inductor//resistor across those would effectively put a short across the power rails because the inductor//resistor has effectively zero impedance. Please don't do this! At best you'll blow a fuse, at worst...

The inductor//resistor combo should replace the existing 0R22 wirewound resistor between the output of the amplifier and the + speaker terminal, in line with the output signal. In other words, the amp drives the speaker through the inductor//resistor instead of through the 0R22. Installing it will probably be a bit of a hack on a Naim PCB because there's not much room for it. HackerNAPs and Avondale amps have space on the PCB for it, making the job quick, easy, tidy, and reliable.

The inductor//resistor combo is typically built by fitting the resistor inside the inductor coil. This page shows how I did it for the HackerNAP amp (which is a derivative/mash-up of the Naim power amp, Avondale power amps, and Acoustica modifications): https://www.pinkfishmedia.net/forum/threads/building-a-hackernap.124486/

Good luck!
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Thank you for this, it could have saved me from a very unfortunate outcome ! I had initially meant what you assumed I meant but, thanks to a bit more reading, had already realised that this was completely wrong. I had intended, though, to place the ind/res in series with the 0R22, rather than to replace it, so that is very useful advice. I had also thought about encasing the ind/res in heatshrink as it seems likely to be somewhat exposed floating above the board; is there any reason why this might be inadvisable ?

I have to say that your HackerNAP amp looks phenomenal; what a piece of work !

Thanks again for taking the time to respond.

Cheers,
Bo
 
can't help wondering if this amplifier is for your benefit, or your sons. If you had a good time building your first one (however it turned out), then doesn't your son deserve the same?
Recently, I bought some small class D amplifiers to power some exciters for vibration experiments. With wall warts (24v 6A) to feed each stereo amplifier, they are literally 'plug and play'. Up and running in a minute. Sound is excellent for such a small (and cheap) set-up, I ran each stereo amplifier into a two mid range loudspeaker. The sound beat my usual £1800 set-up!

Here is a pic of mine (a mono Class D with SMPS)



and a stereo one connected to a remote volume control (which sounded better! as did the silver plated loudspeaker cables!!)



 
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Helen Bach said:
can't help wondering if this amplifier is for your benefit, or your sons. If you had a good time building your first one (however it turned out), then doesn't your son deserve the same?
Recently, I bought some small class D amplifiers to power some exciters for vibration experiments. With wall warts (24v 6A) to feed each stereo amplifier, they are literally 'plug and play'. Up and running in a minute. Sound is excellent for such a small (and cheap) set-up, I ran each stereo amplifier into a two mid range loudspeaker. The sound beat my usual £1800 set-up!

Here is a pic of mine (a mono Class D with SMPS)



and a stereo one connected to a remote volume control (which sounded better! as did the silver plated loudspeaker cables!!)



Click to expand...

Well, I understand what you're saying, and it's certainly true that I shall be getting something from the build as well as my son, but it really is for him. Life's not the same for him as it was for me, vis a vis music listening, he already has a bunch of high tech ways to play music, and listens to it constantly, so there is no real driver for him towards traditional HiFi as such. I hope this amp inspires him to take it further but if not, that's fine.

Loving your system, by the way, but I think I'm going to have to put mine in a box, for safety 's sake. 8^)

Cheers,
Bo
 
that's fine, Bo, sometimes pushing our kids in a direction they may not want to take is usually counter productive.

As far as boxes are concerned, the amplifiers in the second pic were supposed to be set up and tested before more involved work, but it gave such an exciting sound (connected to the TiVo TV system) that we enjoyed it for some months as it is shown. The first pic was just to show what could be done with class D and SMPS, and was mains powered (the stereo amplifier was fed by a 24v supply).

Although my main TV system amplifiers cost over £600 and speakers about £1200, the little class D and JPW 'speakers provided a cleaner rendition of what was fed to them. Total price for two stereo amplifiers and two wall warts was under £50. So, with the JPW 'speakers they don't go as loud or as deep in the bass, but for 90%+ time, they were very good.

Good luck with your build!
 
Well, as part of my amp build I bought a Studer900 clone dual power supply (from eBay) to power the preamp board and have just connected it up for the first time. I have a 20-0-20V traffo connected to the AC side of the p/s and a NAC152 clone preamp connected to the DC side.

On power-up I was reading 22V DC from each side of the supply but over a period of a few minutes (I was thinking/hoping it might stabilise somewhere around that voltage) the voltage ramped up to 36V and seemed to stabilise at around that level. It was giving off a fair amount of heat, too, I noticed. My preamp needs dual 24V. Am I likely to have killed it with 36V ? I do hope not !

Under load the AC voltage measured as 19V, compared with about 21V no load. Is that sort of voltage drop normal-ish or a cause for concern ?

I have to confess that I am at a bit of a loss how to proceed with diagnostics. Any help or insight that anyone could offer would be very much welcome.

Thanks,
Bo
 
stevec67 said:
His son is 19, at university and has a girlfriend. I think we can guess how interested he is in soldering things together. That said, I don't think it matters.
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Do you think he would be into a job/life swap? I do lots of soldering things together:D

Nah thought not:rolleyes:
 
Jon Dennis said:
Well, as part of my amp build I bought a Studer900 clone dual power supply (from eBay) to power the preamp board and have just connected it up for the first time. I have a 20-0-20V traffo connected to the AC side of the p/s and a NAC152 clone preamp connected to the DC side.

On power-up I was reading 22V DC from each side of the supply but over a period of a few minutes (I was thinking/hoping it might stabilise somewhere around that voltage) the voltage ramped up to 36V and seemed to stabilise at around that level. It was giving off a fair amount of heat, too, I noticed. My preamp needs dual 24V. Am I likely to have killed it with 36V ? I do hope not !

Under load the AC voltage measured as 19V, compared with about 21V no load. Is that sort of voltage drop normal-ish or a cause for concern ?

I have to confess that I am at a bit of a loss how to proceed with diagnostics. Any help or insight that anyone could offer would be very much welcome.

Thanks,
Bo
Click to expand...

Pre amp should be OK but check the tants. Is this a 5 - 24v adjustable single supply such as I can see on ebay? If you are using the full 40V from it then that is way too much... if you have the centre tap connected to anything:eek::oops:
The first one I looked at which has a schematic well the schematic is almost randomly placed components...
Don't buy shite from China on ebay which costs less than the parts alone (just the parts... not including the PCB and their profit margin!) in the west! Too good to be true? Er Yeah!
 
Hi, thanks for responding. It's a "MJE15034 TL072 Regulator Power Supply Board For Pre AMP DAC Based on STUDER900" which can supposedly supply either +/- 5 to 28V or dual +5V to +28V. I am trying to use it in the latter mode. I have no idea about the cost of the components, especially in China, but the item itself cost about £25. Before buying it I scoured the web for reviews and did find a fair few folks (UK and US) that had bought the item and had found that it worked well so, recognising the risks, I took a chance. I now am where I am; I now have to decide to junk it and get something else or try to fix it (or maybe try to fix it then junk it and get something else 8^) ). I'm slightly reluctant to just bin it; not because of the [fairly small] cost of doing so but because there is an opportunity in this to increase my skills, if not my understanding, and it is interesting.

There are a number of aspects of this that I am struggling to understand:
1. The item's output is quite a long way out of spec; 36V is more than 25% over the specified maximum whilst the input AC voltage is well within the specified range. This implies to me that something is broken or that one or more controlling components have been implemented with wrong values. By controlling components I mean components whose specific value affects or controls the action of another component, such as a transistor. Is this assumption likely correct or is 25% over spec not uncommon ?
2. Both channels of the power supply are working the same way. This suggests that component failure is less likely to be the cause unless the failure has been caused by some common factor of the implementation such as components implemented with the wrong values leading to out of spec conditions for the failing components. Does this make sense to more knowledgeable people ?
3. Why does the output voltage increase so much from the value at switch on to the final value; a greater than 50% increase. I guess it's reasonable to expect some drift as the electronics warm up but 50%+ seems crazy. Does it reflect overheating, perhaps ? But caused by what ? Any comment ?

I guess my thought process is that if I can somehow characterise the actual behaviour relative to that expected then that will offer a starting point for investigations. Does that make sense ?

I believe that the following (fingers crossed I've correctly inserted the image file) is the schematic for one half of the supply (it is 'dual mono') :
49877544416_a17f772cdc_b.jpg


Any help or advice would be very welcome.
Thanks,
Bo
 
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