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Yesterday (a Saturday in April 2003) I finished the GainClown and I decided to give it some time to break in before starting serious listening sessions. So I leave it on for a while. Not that I'm planning to wait forever before giving my honest opinion on it's performance, too many manufacturers claim months of listening before you are allowed an opinion on their products.
By that time it's not the hardware but your ears that have broken in, and your mind tells you that it's unwise to criticize a products you spent big $$$ on.
On the other hand, there are also enough people that tweak every major part in their hifi within days of building/buying and thus I have my doubts whether there is a strategy in this tweaking. I like to give myself enough time to listen and spot areas of improvement.
The day after finishing a project I expect it to be close to 90-95% of it's final performance. Major imperfections should show already in the first hours.
So one or two days of breaking-in ought to be enough, so lets play the music ...
Focus points for me were the things I admired in the GeenKloon. Not so much the control and the brutal force but the detail and musical capabilities.
I therefore grabbed some of my standard CD's I use to evaluate my diy projects, and continued evaluation with the above point in mind:
The overall impression is that there is enough bass. This might be an indication of less than total control over the speakers, so I need to to compare one-on-one with the main hifi set in the living room (playing two "identical" CD's at the same time).
Eva Cassidy has a voice that is capable of sounding both sweet and very strong with the latter risking a distortion-like sound in the high notes.
There is plenty of cymbal and drums details (too much?). I need to sort out whether there is indeed a difference with the other (commercial) amp or it's just me and are these details that strike me now I listen specifically for it.
<pls be quiet, I'm listening ;-) >
I did some testing with the function generator and scope (and a big old variable wirewound resistor). First I measured the DC offset which is about 17 mVolts (loaded or unloaded). I put the resistor on 6 Ohms and after some initial sinus waves tested the Gainclown with several square waveforms.
As far as I could see (I'm no expert, my scope is not calibrated, and you need better equipment than this anyway) the Gainclown behaves very well under such stress.
I did my experiments with frequencies of 20, 100, 200, 1K, 5K, 20K and 100K Hz. For the lower frequencies my old function generator was clearly unable to make perfect square waveforms. Under 20KHz the Gainclown had very good frequency response. At a 100KHz it became more difficult to output exactly the same shape as provided on the input.
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Here you see the frequency response for 500 Hz. Input shown on upper halve, output below. Output lines are not straight but is following input. | |
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On the right you see the scope output for a 6-Ohms load, 5KHz input on +/- 0.16V, Output +/- 3.4V (indeed a gain of about 20) |
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To the left the gainclown at 100kHz input. Rise and fall are not perfect (but I still think that it performs OK). | |
| BONUS Hmm, picture not sharp, but this is Gainclown with a 1.5 Ohms load, 200 Hz input. Not bad, but oscillations starting after 3 seconds are heavy and the SPIKE protection often kicks in. |
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Pictures above are taken by my Sony digital camera. One can see clearly how an inverted configuration inverts the output signal.
The transformer did it's job, but should I start this project over again I would select a stronger power transformer. Under heave load it starts to humm and it makes clear that it does not like such tricks at all.
Drawing conclusions about your own projects is never easy. The project started because I had some spare diodes, two LM1875, cheap housing left-over from another project and a junk transformer with the right secondaries. Looking back, I still added lots of components and a considerable amount of time so there is a legitimate question whether I should not have invested in another chip or transformer.
In other words, would I do it again, or would I start with other components.
Hmmm, tough answer. I like the amp but it's less versatile than a LM3875 based clone. I would probably advise others to consider the LM3875 over the LM1875. The LM1875 has musical qualities, no doubt, but most speakers appreciate a little bit more power and control.
Attention Points in this project were (and are):
As part of the learning process, there are some things I might want to do different or just try out in the next project(s):
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