building my own high end power-amp for passive studio monitors

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Btyre2013

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I'm thinking of building my own power amplifier for my newly purchased mono grotbox. I am using a single speaker the littlepapercone, check out welcome to littlepapercones: studio reference monitors - speakers for more info. It's basically an auratone clone.

I could build a mono only amp, but may as well build a stereo one with the option of bridged mono so that if I decide to ever go stereo, the option is available to me.

I'd like to know some info on building one, seeing as I'm new to this,

I've modded amps before, built my own guitar pedals, cables and am confident with my soldering skills. I can't seem to find any DIY kits here in the UK, so am now thinking of building my own from scratch, including designing the circuit or cloning a circuit that is already proven.

Ideally I'd like to spend no more than £200 and buy ALL the parts myself, including the chassis e.t.c.

looking forward to opinions and thoughts. If any of you are electronics engineers I'd REALLY appreciate the help,

thanks,

Ben.
 
There's a lot more to an amp than the circuit. Heat management is critical, especially for a studio amp that runs without fans. That sort of stuff benefits from industrial R&D.
 
bouldersoundguy said:
There's a lot more to an amp than the circuit. Heat management is critical, especially for a studio amp that runs without fans. That sort of stuff benefits from industrial R&D.
Click to expand...

ok I'll take that into account, so heatsinks are pretty crucial. I don't plan to use fans, I've seen some linn power amps going for cheap on ebay, they look very well made, what do you think?
 
I've built a two channel power amp for my home stereo system. I used amplifier kits from one of our local electronic enthusiast magazines, and built it all into a 3RU case. Took quite a while to finish, and I find that the metal work is the most challenging!

I think that £200 may be a little tight, particularly for a higher powered unit. You need to figure in amp modules, suitable heatsinks, power supply reservior caps (big 'uns), a decent power transformer, a decent enclosure, and sundries like cabling, connectors, switch, etc.

Importantly, you need to consider electrical safety, particularly if you are new to this. There is the matter of safely hooking up a mains power supply, and correctly setting up your chassis earthing.

As a slightly less ambitious option, amps built around the National Semiconductor chip amplifiers (LM3886 or LM3875 from memory) are widely acclaimed in DIY and audiophile circles for their great sonics.

A great resource for DIY audio and technical information is Rod Elliot's site. He also sells circuit boards for some of his projects.

Hope this helps. Building stuff is amazingly fun! (at least in my opinion :))
 
PRHunt said:
I've built a two channel power amp for my home stereo system. I used amplifier kits from one of our local electronic enthusiast magazines, and built it all into a 3RU case. Took quite a while to finish, and I find that the metal work is the most challenging!

I think that £200 may be a little tight, particularly for a higher powered unit. You need to figure in amp modules, suitable heatsinks, power supply reservior caps (big 'uns), a decent power transformer, a decent enclosure, and sundries like cabling, connectors, switch, etc.

Importantly, you need to consider electrical safety, particularly if you are new to this. There is the matter of safely hooking up a mains power supply, and correctly setting up your chassis earthing.

As a slightly less ambitious option, amps built around the National Semiconductor chip amplifiers (LM3886 or LM3875 from memory) are widely acclaimed in DIY and audiophile circles for their great sonics.

A great resource for DIY audio and technical information is Rod Elliot's site. He also sells circuit boards for some of his projects.

Hope this helps. Building stuff is amazingly fun! (at least in my opinion :))
Click to expand...

thanks for all that, some good info on rod's site
 
I ended up getting a Rotel RB 970 BX amp, and it worked great...until it blew the speaker lol, then I got the guy who makes my monitors to send me a new one and low a behold...the second speaker blew, looks like the power amp is already broken.
 
Rated at 60W per chan that amp should not blow any speakers worth the name.
I strongly suspect it has an output "offset" problem which should be repairable.

Check the DC conditions at the speaker terminals, you should not have more than 10mV DC there and preferably bugger all!
A "get out of jail" fix is to put a 4,700 mfd, 63V cap' in each speaker line.

Dave.
 
thanks dave for the advice,

would it make any difference to the cap value if it's 180W not 60W? because I'm using it in bridged mono mode, which is rated at 180W. I could do with a quick fix as I really want to get this up and running ASAP,

Ben.
 
ok...been taking some measurements: It surprised me!

in bridged mono mode it measured an average of 100vDC! lol

then I measured the it again in stereo mode, Left channel = 50vDC Right Channel = 27mV DC, so I presume that means there is a problem with some of the capacitors on the LEFT channel only? They must not be filtering out the DC properly?

Having now looked inside at some point 2 of the resistors have been replaced on the left channel only, at some point the original resistors must have blown because there is a burn mark underneath and the new resistors are carbon not metal film....

I've not had a chance to fully take off the PCB and see underneath yet, but it's going to be interesting. Makes me wonder if the guy I bought it off knew it was on it's way out....if so he deserves negative feedback for hiding some of the details, I might have to report him, he claims that it all worked before posting it though and seems genuine. Also the mono-stereo switch is in bad shape, yet he described the item as 'in full working order'...

any thoughts?

regards,

Ben.
 
"any thoughts?

regards,

Ben.

My thoughts are unprintable in polite society Ben! I question the circumstances of the vendor's conception. Right! Now that we "know" let's nail this down....

Get hold of two 1k 1watt resistors and fit them across each speaker line. It is best to have a DC path when checking offset volts.

What are the left and right DC readings? In stereo mode, all controls at zero, no input.

As I said, 10milli volts is just acceptable.

There will be no capacitors inside as DC blockers all modern amps are DC coupled throughout. (well, ok, maybe not some "retro" guitar jobs!)

Carbon resistors are totally unacceptable in audio equipment.

I think you have a good case for money back.

Dave.
 
ecc83 said:
That is a mess!
Get your money back.

Dave.
Click to expand...

it is indeed, I've contacted him about getting a refund, so hopefully it will be resolved, if not I'll be onto ebay, this is the first time anything like this has happend to me on ebay after 9 years.
 
got a full refund in the end! so no amp again, I'm definitely building my own now from that experience, will keep you all updated
 
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