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argonrepublic 20th January 2013 01:46 AM

Active studio monitor amplifiers
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I dont like my current Blue sky monitors. I have included shematic. I have available to me some compact amplifiers, two per enclosure using STK4044. I have also included a schematic. How will the STK4044 rate in comparison to Blue sky? The SYK4044 are pre built, two per PCB.

Ian Finch 20th January 2013 03:27 AM

The TIP142/147 darlington output transistors used in the Blue Sky monitor design don't have a lot of respect as audio power amplifiers. They are there for cost and compactness reasons but the rest of the circuit appears to be generally a competent, low cost design.

Hybrid amplifiers can have similar shortcomings but the specifications of the basic amplifier will be known and you can read them from the datasheets. or the finished module supplier's specs. It's likely then, that these assemblies will significantly outperform the original amplifiers. This guy seems very keen to sell them to you, too.

These days, chipamps like TD7294 are more economical, powerful and well protected internally, saving many DIY assemble and test problems with relay and external safety design. Usually, they perform better again than hybrid modules like STK 4044.

If you are looking for better or just different sound quality, be aware that the amplifier is not the only part that affects it. There are the drivers, cabinets, crossover design and to a small extent, the preamp controls and safety devices that all have a hand in shaping the sonics.

I think it's a bit optimistic though, to ask for opinion whether your idea will make the sort of improvement you want unless someone had already done it and knows what sort of audio you actually want to hear.

argonrepublic 20th January 2013 03:54 AM

Your response is extremely helpful. I am kind of shooting in the dark. My Blue sky are decent, well balanced. As much as they are transparent, detailed and linear, they seem to lack life.
I just worked on and old Yamaha receiver and was looking to replace an STK. I tested the old Yamaha and found it soothing in comparison to listening to my Blue sky. That was when I noticed a pair of STKs on a board it reminded me of the pait of outputs in my monitors.
I know it may be a process. The idea of an STK per driver fed by and active crossover intrigues me. I know I can't have everything but If I could have a consumer studio monitor/ Vintage hi fi hybrid, I'd be happy

Ian Finch 20th January 2013 05:25 AM

I imagine that you used different speakers with the Yamaha amp. and possibly they have more bass extension without the need for a subwoofer. This profoundly changes the sound of stereo systems IME, because we either don't have that bass warming up the overall sound or it is not crossed over correctly when we simply listen for what seems OK when we are up close and adjusting any sub. controls.

I'm not suggesting there is anything wrong with your preference but sometimes the reasons we are not happy are obscured by basic issues like the inadequacy of budget, powered monitors in say, 2.1 systems. You have to spend a lot of money for good wide-range sound monitors and properly matching sub, regardless of how impressive most seem to be for short periods in near-field listening. Good active crossovers can make even craptanium drivers sound great that way. Fatiguing sound is usually associated with amplifier distortion but I suspect the issue here is more basic and is in the limitations of the speaker system itself.

Still, 'no harm in exchanging amplifier designs to test the ideas out. Do check what extra provisions are necessary (if any) for protection of hybrid amps as DIY lash-ups can usually find the weaknesses of any solid state amplifier! :D

argonrepublic 20th January 2013 06:15 AM

I have been bouncing back and forth for a few years. I have bought quite a few nice drivers crossovers from Solen( morel, scan-speak, litz inductors, good caps). It was just my 4" tag band 2 ways that I tested the Yamaha with. I have a broad selection of nice homade 2 ways. I wasn't running a sub. Just nice clean bookshelf audio. After the placebo wore off, I found my Blue sky to be another pair of Mackie, Behringer, KRK, M-Audio, Futureshopmusic store monitors. The hype and the convenience takes me shopping and my ears always return me to my old faithfuls. I would like to stop bouncing back and forth. I think what I need now is a pair of 35-0-35 250VA torroids. What is the best place for me to get these? I live in Canada.

argonrepublic 20th January 2013 06:18 AM

I think my plan here is to get some decent 2 way active crossovers, use these amp pairs and try it with my Morels or Scan speak.

Ian Finch 20th January 2013 07:14 AM

Well, Plitron for toroids is in Toronto, right? However, 250VA may not be as common a stock size as 225 or 300VA styles which are international standards.

Yes, that's my view of that list of popular active "monitor" speakers. They are really about making more money from cheapest parts. I think you are on a more promising path there with quality drivers in your own builds, at least.

argonrepublic 20th January 2013 07:48 AM

Thanks for the help. I don't think I will regret even the learning. I will feel better about dumping the twice repaired Blue sky. Proceeds will pay for transformers etc.

stratus46 20th January 2013 08:43 AM


Originally Posted by argonrepublic (
I dont like my current Blue sky monitors. I have included shematic. I have available to me some compact amplifiers, two per enclosure using STK4044. I have also included a schematic. How will the STK4044 rate in comparison to Blue sky? The SYK4044 are pre built, two per PCB.

We replace lots of power supply caps in Blue Sky speakers at work. I don't remember any mention of solder joint failures. IIRC the units I saw have LM3886 amps.


JMFahey 20th January 2013 10:47 AM

I agree that maybe you don't like your present monitors, fine with me.
And that "another" system sounds better, smoother, whatever.
As mentioned above, a system is built out of many elements, but I think the *less* p`roblematic of them all is the amplifying section.
Nowadays amps are incredibly low-distorting and flat as rulers, and although they still contribute some mud, distortion or whatever, it's orders of magnitude below what speakers, crossover choices, tuning, cabinets, acousting damping, etc. cause.
I *think* that the main improvement you heard comes from using standard classic *unprocessed* Hi Fi cabinets.
Just get a couple of them, your choice, and if you wish to drive them with STK or any other choice, "just do it".
What I fear is that you build the new power amps, hook them to the same Blue Sky components and ..... get basically the same sound you don't like very much :(

Somebody around here has a signature which roughly says: "People should tweak rooms and speakers .... since they can't, they tweak amps or buy miracle wires, connectors, etc." .... or something like that.

EDIT: the Blue Sky electronics look competent for their job, only thing I do not like at all is the mute or anti turn on thump built out of 4 4N26 optocouplers.
Don't like at all adding crummy switching very non linear transistors in series with audio ampifying ones.
*Maybe* permanently shorting them with a short piece of wire (can be done pin to pin at the very optocouplers) removes that harshness or fatiguing sound that now bothers you.
But you do it on your own risk, of course.
Good luck.

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