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[OPA541 chip amp built using a Resurrector]
[Italian version]

It's a chip amp Jim, but not as we know it!

Product: Resurrector - chip amp enhancement module
Manufacturer: Marek Klimczak
Cost: 99 € (Resurrector, not chip amp).

Reviewer: Nick Whetstone - TNT UK
Reviewed: December, 2008

There are two ways to go through life. You can keep your head down, take the easier options, and hope to avoid most problems. Or you can be a risk-taker, accept the highs and lows with equal magnanimity and see where that takes you. It's the same with reviewing. There are 'safe' subjects for review where you will attract the least come-back, and there are the other ones that you review at your peril. I've already run into a couple of those and you may have thought that I would have learned my lesson. But no, I just can't turn down a challenge so here we go again.

[Resurrector module]

As some of you may know, I've been putting together Gainclones (or more accurately chip amps) for some years now. I've tried a lot of the variations, and thought that I had been there, done it all, and come back with the postcard. My experience was that nearly everything that I tried with a chip amp sounded slightly different, often neither better nor worse, just slightly different. Only the different power supplies really made any significant improvements as you would expect. So when somebody pointed me to an auction on Ebay for something called a Resurrector, I read the listing with a certain amount of indifference. Toward the bottom of the listing were some pictures, and in one of those pictures, I saw the familiar name 'LM3875', one of my favourite chip amp chips. Still something told me to ignore it and I surfed off somewhere else. But the next day, I had an overwhelming urge to find out if the Resurrector was the answer to a chip amp builder's prayers, or yet another over-hyped tweak. So I contacted the seller and offered him the chance of a review on TNT. I've done that before and it does tend to weed out the vendors who are shall we say less confident in their product. But on this occasion, I received a fairly quick reply urging me to take a sample of the Resurrector and try it for myself. It meant building a new chip amp but I had most of the necessary parts here so I agreed.

The designer of the Resurrector, Marek Klimczak is a native of Poland and doesn't speak any English. My Polish is non-existent so we relied on his daughter to translate as best she could with a technical subject. As a consequence I don't know quite as much about the Resurrector as I would have liked to but I will try and describe it as best as I can in this review. Of course, my hands-on experience has revealed plenty. In a nutshell, the function of the Resurrector is to reduce the amount of EMF that is sent to the drivers thus reducing the current inside driver coils of the speaker drivers. What is EMF? Well rather than re-invent the wheel, I'll point you to this link for a description.

The Resurrector is actually part of the chip amp circuit that has been modified. Quite understandably, having spent years researching his solution to the EMF problem, Marek Klimczak wants to keep his secret from prying eyes, and the important parts of it are hidden inside a small plastic tube that is then filled with resin. Emerging from the resin are a pair of ribbon cables that the user connects to various parts of the chip amp. As with anything new, it initially appears complicated, but a careful study of the diagram supplied with the Resurrector is all that is needed to build it into the chip amp. Although I've built many chip amps I did find building one with the Resurrector a little harder, mainly because I couldn't actually see items like the resistors that set the gain. I also have to confess to somehow frying a chip along the way, mainly because I was too blasé to use my light bulb tester when I powered it up!

[Resurrector circuit diagram showing external connections to an LM3875 chip]
The Resurrector circuit built into an LM3875 chip amp

The Resurrector will work with almost any chip amp. In fact it could be made to work with almost any transistor amplifier that has inverting and non-inverting inputs. For those of you interested in this sort of thing, here is the specification of the chip amp built and used for this review.

In other words a fairly basic chip amp. This amplifier had no nasty noises when powered up or down and was totally silent when not playing music. In other words, the Resurrector has no negative effect. Like some of the other chip amps I've built, this one ran warm to begin with and then much cooler after a day or so of use. Using fairly efficient speakers meant that I didn't need large heatsinks.

The Resurrector as supplied is only part of the solution. The other part is a pair of 'phantom drivers' as Marek Klimczak refers to them. These should have a similar (if not the same) impedance as the drivers that you will be driving with the chip amp. Apart from that, size and shape don't matter too much. In fact you can achieve different results by trying different phantom drivers. You then need some 3 watt resistors approximately twice the value of the driver impedance. It is also recommended that you use some more 3 watt resistors in the position marked R1 on the diagram. These play no part in the battle against EMF but they do allow you to switch the Resurrector circuit in and out so that you can see if it is working. The resistors marked R1 simply adjust the volume level (when the Resurrector is switched out for comparison) so that it is the same whether the Resurrector is switched in or out, making the comparison more meaningful. A simple double pole double throw (DPDT) switch can be used for this purpose. I found an old one in my parts box and was able to switch the Resurrector in and out while the amplifier was playing without any ill-effects or unwanted noises.

Having run some tests to make sure that I had no significant DC on either the output to the main speakers, or the output to the phantom drivers, I connected the chip amp up with some cheap 8 inch full-range drivers acting as phantoms. The system used for the initial test consisted of an SB3 feeding a modified Monica2 DAC. I was advised by Marek Klimczak that the input impedance of the chip amp using the Resurrector was on the lowish side, so I included the Autocostruire Tube Pre between the DAC and the amp to prevent any impedance mis-match problems. (The Resurrector that I reviewed makes an inverted chip amp. All future Resurrectors will form a non-inverting chip amp with a much higher input impedance) Cables were what ever was lying about, and with everything connected and checked, it was time to hear if the Resurrector did indeed do what it said on the tin.

Having set the SB3 to play random tracks, I listened for a few minutes with the Resurrector switched in. Initial impressions were that it sounded good so I switched it out. It was quite obvious from the moment the switch was thrown that there was a big difference. Despite the resistor values of R and R1 being matched to provide the same volume level, it sounded as though the volume has been turned down. There is simply less of everything with the Resurrector switched out! Such was the difference that I only needed to switch the Resurrector in and out a few times to be totally convinced that it was doing something quite significant.

Of course, at this stage it was very tempting to start assuming that the output from the phantom drivers was making the difference, despite having them situated in the far corners of the room under several cushions. In fact I had to go and lean my head over the cushions to even detect that there was any sound coming from the phantom drivers (they play at a much lower level than the main speakers). And if the difference was made by the sound coming from the phantom drivers, it would surely have made things worse (by diffusing the sound stage and imaging), not better.

I turned the volume up a bit and sat back to take it all in. The first impression that you get with the Resurrectored chip amp is one of sheer enjoyment. Initially you don't think things like "that's good bass, that's great clarity, that's good timing" etc. The overall impression is that the music is just 'better', very musical, very enjoyable, very uplifting. It's only after you start to analyse why it is so enjoyable that you notice what the Resurrector is doing. You can hear each element of the recording much more clearly on its own, and that element be it voice or instrument sounds more real. Despite that the coherence of everything is perfect (assuming a good recording of course). The bass is clear, tuneful and oh so natural. Imaging is excellent and the sound stage is wide. In fact I forgot that the speakers were there, as a wall of sound pressurised the smallish listening room. After an hour that went by very quickly I left the amplifier on to burn in. Returning to the system later in the day, the sound quality was even better. If anything slightly clearer than with the earlier session (not unusual for a new amplifier having a few hours use behind it). I switched the Resurrector out one more time, but only for a few seconds as the sound appeared poor compared to it switched in. Despite the cold of an unheated room in late November, I was riveted to my seat while I listened to track after track.

The next morning I went up to try tuning the Resurrector to see if it could be made any better. There are two methods of tuning. One involves trying different phantom drivers, the other is adjusting the value of R (in the diagram above). There is little point in adjusting R1 as it is only in circuit when the Resurrector is switched out. Believe me, very early in one's experience of using a Resurrector, you will forget about wanting to switch it out (although it is enlightening to do it from time to time after you have made changes). I found some 20 ohm wire-wound pots in my parts box and soldered on some tails. I then replaced the 15 ohm resistors (that I started with) with the pots. The pots were initially preset to 10 ohms and I powered up the system to take a listen. The sound was clearly different again. I thought initially that it sounded more focussed, but it somehow had less off what I had enjoyed the day before. I increased the resistance of the pots by a couple of ohms and listened again. Once more the sound changed, becoming much more like it had been. It appeared that as I increased the resistance, the Resurrector had more effect. I went right up to 20 ohms and then back to 16 noting a slight difference in the changes. I think it would take a while to determine the exact sweet spot - and that may even be different for different recordings, or with different ancillary equipment.

The next day I swapped out the 'phantom' cheapo full-range drivers for some SEAS P21 bass drivers. Again it was easy to detect the change in sound, slightly more 'bassy' while the full-rangers were a bit more 'airy'. I guess the ideal phantom drivers may be exact copies of the woofers in the main speakers. Of course that could make things a bit expensive in some cases. But don't be deterred, even my full rangers, costing less than 20 pounds for the pair, produced a fantastic sound with the Resurrector. What I can tell you for sure is that there is plenty of tuning potential. That may deter some while it will appeal to the fanatical tweakers amongst us! And some may say that if the phantom driver affects the sound, isn't that poor hi-fi? Well I don't see it like that. You many as well say any loudspeaker affects the sound that you hear from a system but that doesn't make them 'bad'.

The next day (yes I hope you guys realise how much time we put into reviews at TNT) I moved the Resurrectored chip amp to my main system. I did a quick room correction ( 35hz to 300 hz to tame the bass) using the Behringher DEQ2496 and sat back to listen. The effect was not quite so pronounced as it had been upstairs but was clearly audible. Perhaps this was due to the speakers being open baffle, or the listening room being larger and more open. The effect was still very pleasing. The music sounded more musical, more coherent. I could detect a bit of softness, although not enough to make things unpleasant. If you are obsessed with clinical detail, this sound may not have been to your taste. On the other hand, if you like music to be how it is when you hear it live, it would be. And remember that this is all circumstantial because with a different phantom driver and resistor value, things can and do change quite significantly. I suspect also that choice of cables, particularly speaker cables will be more critical too. I've already noticed that changing an IC seems to have a greater effect than I have noticed pre Resurrector. May I also remind you that all this is with a fairly basic chip amp, there are all sorts of potential improvements with regulated power supplies etc. I don't feel that I have nearly exhausted the potential of the Resurrector but I've heard more than enough to justify writing the review at this stage.

The dynamic range of the system is also improved with the Resurrector. One of my regular test albums for reviews is 'Sister Drum' by Dadawa. Most of the tracks have sounds that range from a feint whisper, eg Dadawa singing very softly, or finger cymbals, to a crescendo of large drums and mass Tibetan horns. With the Resurrectored GC I found those quietest sounds much more tangible without having to turn up the volume level as much as I would normally do. I also heard some sounds coming from the end of one track several seconds after I normally think it is ended! In fact as the day went on, I constantly noticed tracks continuing for a few seconds after I thought they usually ended. It's like a huge magnifying glass has been put over the music and the minutist details are much more perceivable, or even audible for the first time! This increase in detail also enhances the music by providing more clues to aspects such as ambience so you get a much better perception of the venue with live performances, and even the studio with some recorded music.

The overall presentation is relaxed. I don't mean dull or uninteresting, far from it, but you could listen to it all day and not get listening fatigue (I did and didn't!). The music is relaxed when it should be, eg with quieter classical music, but is 'electric' when the material dictates it, eg Rodriguo y Gabriella flamenco guitar. The presentation is also large, as though the music (effortlessly) fills the room. Each element in the sound stage is clearly located but at the same time, it is not separated, or should I say disconnected, from the other elements in a way that makes the whole performance sound artificial. On some recordings the performers really appear to be in the same room. There is a great sense of realism too. Complex passages of music are handled with ease. The overwhelming impression is 'musical' and 'nice' to listen to. There's a massive 'feel good factor' with the Resurrector, and that is pretty much what the inventor is trying to get over in his Ebay listing.

I could go on and on about the Resurrector. But I'm trying to walk a very thin line here between singing its praises, and not wanting to sound OTT. Traditionally any hi-fi tweak attracts scorn and derision, more so if it isn't cheap. In many cases that scepticism has been justified, and many an unscrupulous individual has made a good profit out of unsuspecting audiophiles. I'm sure that many will write off the Resurrector as yet another scam so I'm going to put on the heaviest flak jacket that I can find and nail my colours to the mast. I think that the Resurrector is possibly the biggest advancement in amplifier/speaker interfacing since we stopped using horns on top of a wind-up gramophone! Perhaps I'll live to regret that statement and I look forward to somebody with much more technological knowledge than I have, assessing the Resurrector and publishing their findings. For me, what my ears are telling me is enough to recommend the Resurrector without hesitation. I know some will say that it costs as much as building a complete chip amp, but you have to look at this item in terms of how far it will improve your listening experience. This isn't a small tweak, like some new cables, a mains conditioner, or some exotic resistors or capacitors. It's something that will transform the way that you hear recorded music and it makes more of an improvement than anything I have ever heard in the world of hi-fi. I'm almost over that thin line now so if I may borrow something from another movie, it's over to you - are you feeling lucky today punk?

To help overcome the language barrier, I will be adding a Resurrector section to the Gainclone pages at Decibel Dungeon where I will try to answer most of the questions that may arise when building a chip amp using a Ressurector.

I would also like to express my sincere thanks to Marek's daughter who translated our countless emails despite being a busy mother.

© Copyright 2008 Nick Whetstone - www.tnt-audio.com

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