audioxpress power amplifiers

ogp

Member
2001-09-17 9:27 pm
Ohio
Hi all. I would like to hear from anyone who has had any experience with either the OMP/MF Mono Power Amp Modules
from BK Electronics or the Power Amp Modules from ILP Direct Ltd, UK that www.audioxpress.com carries. I would like to get something that isn't too difficult. Does anyone have experience with either of these two products? If so, what else would I need to make a complete amplifier utilizing them? I was thinking about going with the amplifier kit from www.sound.au.com but that is just a bare circuit board and I would like something easier for my first diy audio project. Any info on these units would be greatly appreciated. Thanks.

Dave
 
http://www.bkelec.com/

If you do decide to use the modules I suggest buying them direct from BK, you will save many dollars. Maybe 40% or more.

Also check out the Asylum DIY board as I think there is a fellow there who used the modules in balanced mode and he says that that is the way to go with them.

There is another chap who lurks at the Madisound board who has used them and he also likes them, but again in balanced mode.

But all that aside, for a more tasty DIY experience may I suggest the AKSA from http://www.printedelectronics.com? You can either buy the circuit board and parts and populate it yourself or you can buy the boards pre-assembled and tested.

55watts or 100watts, your choice. Though the 100watter is not available pre-assembled.

Printed also offers a power supply for the AKSA and you can get the transformers from either Plitron (which will take a long time) or Avel Lindberg which will be quick and good.

I have no connection to Printed but I have built the 55watt amplifier (and I have the 100watter and Printeds' tube preamp kit on the way) and it is amazing for the price.

Very easy to listen to and not vieled or washed out, fully fleshed it is with detail in spades.

Hugh Dean, the designer is a class act and I can not recommend him or his products highly enough.

Regards


Tony D.
 
If you are looking for a cheap easy to build amp, check out the "Digi-125" at 'http://www.bettanet.net.au/GTD/kits.html'
This is a very simple circuit with readily available components that sounds good too. You have a choice of output devices you can use, from the cheap garden variety 2n3055/2n2955 devices through the MJ802/MJ4502 or MJ15003/MJ15004 pair for more output. I am running my current version with the NEC A1227a/C2987a outputs in a slightly modified form with about 10dB less nfb and an extra diode in circuit pushing it harder into class 'a'.
What I like about this circuit is its inherent simplicity with only 3 caps, a 10uf, 100nf and a 150p. Only one is strictly speaking in circuit the 150p bypass around one of the transistors the other two just decoupling. It is quite sensitive too so I am using it with a passive front end consisting of nothing more than an Alps pot and a selector switch. PS requirements are pretty flexible too so you can start off with something modest which also gives you the leeway to experiment.
Hope this helps,
tomcat
 
I lifted this from the PassLabs website (I hope that is okay) as Mr. Pass' description is better than any that I might supply.- Tony D.
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Balanced Operation
Let's review why balanced operation is desirable. Audio circuits operate in an environment of electrical noise; crosstalk from other channels, ground loops, magnetic pickup from transformers, power supply ripple and other noises. In a balanced circuit, two opposite phases of the signal are present on two otherwise identical input lines. The input of a balanced circuit has a plus and minus polarity, and the output of the circuit also has a plus and minus. The balanced amplifying circuit will amplify the difference between the two inputs and will display a larger difference signal at the output.

What the circuit doesn't do is as important as what it does; it does not amplify any portion of the signal which is the same at both inputs. Ideally it completely rejects the common input signal, and the quality of this rejection is referred to as the Common Mode Rejection Ratio (CMRR), which tells how much of the common input signal gets through.

Being that the noise picked up from the environment is usually common to both input lines, it is rejected at the input of the balanced circuit, and thus is much less of a problem. Actual home audio systems using balanced interconnects typically have about 1/10 the background noise and hum.

Another reason to use balanced preamplifying gain stages is that many high end DAC designs offer balanced outputs in which separate DAC circuits are used for each of the two phases of output. Using separate balanced DAC circuits reduces the random noise by 3 dB, the same as if they were in parallel, and reduces common noise by a larger figure. There is also the potential for reduction of distortion with such an approach, but to realize the full performance of these circuits, the gain stage following must have a balanced input.
 
Tony,
The other day, I forgot to install the shorting clip to the balanced input when I was using the single ended input of the power amplifier. I heard loud hum in the background even without signal to the amp. Would this mistake cause any harm to the amp?
Note: I think I have posted this question under a different subject in this forum.