Those who have been reading my pages for a long time will have noticed that solid state equipment rarely appears here. In fact, almost every time someone has asked me to repair an amplifier of this type, I have refused the job. The reasons are several. The main one is that I chose to specialize in tube equipment first of all. Secondly, repairing equipment of any kind requires having a large assortment of spare parts, ready and immediately available. With tubes this is feasible, because the types produced and used over the years have been a relatively limited assortment, and today they are still fairly easy to find. The advent of the transistor, on the other hand, also marked the beginning of a much more aggressive era of planned obsolescence: manufacturers often created “custom” transistors for specific products, then stopped producing them as soon as the commercial life of that model ended, because it was convenient to make repairs increasingly difficult after a certain number of years.
As a result, it is not uncommon to come across strange part numbers with no documentation and no reliable spare parts. Of course, there were also more “standard” components, produced by several manufacturers and for many years. However, there is another problem: unlike NOS tubes, which can sit in their cardboard boxes even for 100 years and, in most cases, still work perfectly, silicon ages badly. Old NOS transistors can be affected by phenomena such as dopant migration, become noisy, unstable, or simply no longer meet their original specifications. On top of this comes the now chronic issue of modern replacement parts of uncertain origin: the market is flooded with counterfeits, devices that do not meet the specifications of the original, often with lower quality and a very high probability of failure. Exceptions exist, but the problem is that the person selling you the fake does not tell you, and you only discover it when the unit is already on your bench.
In short, repairing solid state amplifiers “as a profession” is, in most cases, pure masochism. That is why, when I am told about problems that could involve the circuitry, I refuse. I know very well that often these amplifiers “only” need a recap, but trouble is always just around the corner. Once you have the unit in your hands and you are halfway through the job, all it takes is one unexpected fault, and if you cannot find a replacement part you are stuck. At that point you either go crazy trying to find it, or you have to abort the repair, with the real risk that the customer will not want to pay for the time you spent, because you are returning a unit that still does not work.
In recent months I have accepted a couple of solid state units because, at first glance, they seemed like manageable jobs. After all, work is work and, as the ancient Romans used to say, money does not smell. The first unit was this beast, the Jungson JA 99 D, as heavy as a nuclear reactor. So much so that I had to take advantage of a friend who happened to stop by to get it out of the crate. Just to spite those trolls who hate tube gear and say that tube amplifiers are big and heavy, while solid state ones are supposedly “light”.
In any case, this Jungson JA 99 D was “working” and only had a vibrating power transformer. So in that case, things went well for me. Later on, I accepted a Quad 405, with exactly the same problem: “it works but the transformer vibrates”, according to the customer.
Attention: this is not a criticism of Quad or of solid state amplifiers in general. It is the account of a real experience, and a personal reflection on the repairability of this type of equipment.
I forgot to take a picture of the original transformer. It was a UI type core with a double bobbin, potted and housed in a metal case. I disconnected the rectifier bridge, isolating the transformer from the circuit, and powered it up for testing. The result was that it vibrated violently and drew about 70 watts at no load, without any load connected. Such current draw is a very clear sign of shorted turns, so in practice the transformer was scrap. On top of that, several electrolytic capacitors on the boards had already leaked electrolyte, and those also had to be replaced.
When informed about these additional problems, the customer was a bit taken aback: “but how, they sold it to me as working and perfectly preserved…”. Then I started looking for a replacement power transformer, and here comes the painful part: the only practical solution was a toroidal. Having custom toroidal transformers wound, especially as a single piece, is quite expensive. In practice, the new replacement transformer alone cost me almost as much as the entire amplifier had been paid for. At that point the owner’s comment was: “it might be better to buy another one instead of repairing this one, I saw one…”. The problem is simple: this one was sold to you as good, and it was not good. And what if instead of one broken Quad you end up with two broken Quads? It might go well, but it can also go very badly.
All right, let us go on and repair this one…
The installation of the toroidal transformer turned out very well. I then replaced about ten electrolytic capacitors on the two channel boards. When measured, they were all completely exhausted: for example, a 100uF capacitor measured 16uF, with an ESR of 20 ohm. The only ones I did not replace were a pair of non polarized capacitors, because they were perfect. I also replaced the speaker binding posts, because the originals were damaged, and added a pair of RCA inputs, since the owner did not like the DIN connector.
I performed a gradual power up using a variac, monitoring current draw and the oscilloscope. I injected signal and signal came out, everything seemed fine, and the new power transformer was perfectly silent. Then I connected the small bench computer and played some music. I also recorded a video, but I cannot publish it because it contains copyrighted music, so you will have to take my word for it. I let it play for about an hour, then came back, lowered the volume, and from one channel there was a clear “frying” noise.
I removed the faulty board, cleaned all the contacts on the transistor collectors, which are not soldered but use the screw as a conductor, without any improvement. I desoldered all the transistors and tested them one by one on the BJT curve tracer, and they worked cleanly. Even when heated, the curves remained regular, so they did not appear to be the problem. All the resistors were fine, so the conclusion was that the culprits were these “red things”…
Which are nothing more than modules, small circuits with a number of SMD transistors embedded in red resin. An unobtainable spare part. After all the effort to restore the rest of the unit, you find yourself facing a wall. The only realistic solution is to salvage them from a donor unit. I still requested my fee: I had been assured that the amplifier was good, I was asked “only” to replace the transformer, and that is what I did. However, the unpleasant feeling remains that part of the work was useless. The owner has spotted some replacement boards around, but it is not clear where they come from.
My work cost a lot, so the installation of the replacement board will be done with the help of a friend: “it is easy anyway”. And I wonder whether they will have a variac with an ammeter, whether they will take the care to use a load and monitor everything with an oscilloscope while injecting signal, slowly increasing the voltage step by step to check that everything starts up gradually as it should. Or whether, as often happens, they will apply full voltage all at once and burn everything if something is wrong. And then maybe the friend will say that my transformer was no good, that I worked badly, that I ruined the amplifier. Yes, because that is how it sometimes ends. Fortunately, I have a video showing the amplifier powered on and working.
Too many “what ifs” for my taste. Talking with a friend who works in telecommunications systems and who in the past repaired (in the past, and the repetition is intentional) transistor amplifiers, he confirmed the poor state of this entire sub sector. Apparently, the best used listings, with a higher probability of being “good”, are often abroad. However, the average Italian does not trust them and looks in Italy first. Foreign listings are also often more expensive. On the other hand, the average Italian also has the bad habit of trying to cheat others, so it is not rare to see units sold as “good” that are not good at all, perhaps at a lower price. Then the listings from honest sellers seem expensive, but everyone claims to sell good equipment. Exactly like in this case, where the unit was supposed to be good and was not good at all.
Anyone claiming that a unit has never been touched by anyone and “works” should already raise some doubts. A 40 year old unit (or more) almost certainly needs some work on the electrolytic capacitors, but done properly. Because not all old capacitors need to be thrown away: for example, the two main electrolytic capacitors in this unit were perfect, and the smaller ones I replaced were checked one by one. The problem is that many audiophiles ask for advice on forums or Facebook from people who often know less than they do, and the answer is always the same: “replace everything”. At that point they buy the cheapest capacitors they can find online, because “it is enough to match capacitance and voltage” and “they are all the same”. This is taught by the usual amateurs, who have never used a proper LCR bridge and check capacitors with an 8 euro tester.
As a result, they end up installing capacitors that perform worse than the original old ones. Or they try to have the unit repaired “on the cheap” by the local basement technician, who often ends up messing things up and causing more damage than before.
And when they finally reach a serious technician, they are holding a battered “thing” that requires enormous effort to fix. So I often ask myself about the utopia living in the minds of certain audiophiles: they want a vintage solid state unit, they want to pay little for it, and they want it to work perfectly. They want to buy something old hoping it is healthy. They want to find the under the table repairer who, with 50 euro, does not destroy everything. They want the luck of taking two broken units and making one good one. Or worse, they buy a unit full of dead electrolytics that “works” but sounds bad. Or they buy a unit where all capacitors have been replaced with junk, so it sounds bad anyway. The problem is that they have never heard how it was supposed to sound back in the day, so they have no reference.
I could also tell the story of someone who had a solid state amplifier, a high end one, that worked and sounded good, but had a limited problem due to a few electrolytic capacitors on one input. The “technician” suggested a complete recap of the entire unit, carried out with cheap capacitors, about 1 euro each. Because “the expensive ones are a rip off”, and “matching capacitance and voltage is enough”. The amplifier came back fully working, yes, but it sounded so bad that in the end the owner threw it away.
I am sure there are skilled enthusiasts out there who repair their own equipment and do it well. But doing it as a job, repairing equipment for others, does it make sense today given these premises? In my opinion, no. For me, what remains are old and new tube amplifiers, which due to costs and technology are repairable, while modern gear is designed to be disposable.
