John Curl's Blowtorch preamplifier

Status
Not open for further replies.
Jump to Latest
#15,506
john curl said:
Joshua, haven't you anything further to say? How about what usually breaks in hi fi equipment first? You have the experience, we don't.
Click to expand...


Well, first to go are relays, when their contacts loose good conductivity, especially when switching fairly high currents.

Also, electrolytic capacitors seem to go off, sometimes explode, especially as the years go by. Often, they don't go off completely, but change their capacitance and characteristics drastically.

Next come semiconductors. Here there are no rules, as some maintain operation for decades, while others may go off within few years, sometimes even within few months. Sometimes the semiconductor will operate, but produce considerable noise.

Fuse holders sometimes have loose contacts with time.

Connectors may corrode with time.

As for tubes (valves), their operation lifespan is limited by definition, by their construct, when their filament gradually evaporates.

Corrosion on PCBs also happens some times, especially with hand held or mobile equipment. It seems to me that it's good practice to dust the inside of equipment every once in a while, as moist dust may cause leakage.

Years ago, with tubes equipment, sometimes resistors and even capacitors would break.

In production, good soldering is of utmost importance. Also, cleaning the PCBs after soldering.

All the above relates to all electronic equipment, Hi Fi gear isn't different from any other equipment.
 
#15,507
Soldering
Capacitors
Resistors
semiconductors/tubes
everything else

Relays don't count except as a special case, because you don't see them all that often at all, or if present in a position of importance or where they are likely to have caused a failure - of course if you do, they're fairly obvious...

Anything mechanical can and will fail... so you can put that on the list anyplace you want... but imho %wise the above list is accurate over the last 40 years or more. 😀

_-_-bear
 
#15,513
Hi John,
Everybody hates relays, but relays in audio are few and far between. Caps can be pretty bad, AND often just about anything can go wrong.
Click to expand...
I don't hate relays. They are far better than using fuses any day. Good relays have low contact resistance, and if you don't abuse them, they will last. For input switching, they are the way to go as long as you do use reasonable relays. Sure, a switch with silver contracts might be better, but there are times when that is not a possibility.

When stuff goes horribly wrong in an amplifier, I really want to have some way of disconnecting that energy. A triac might work just as well, shorting the signal to ground.

As far as failures go, Bear has it right.

-Chris
 
#15,517
Hi John,
Personally, I think that less junctions are better than more junctions.
Click to expand...
I will assume you are talking about electrical connections. I would then agree with you. We can extend what you said by adding "I think that less junctions are better than more junctions except where needed". For example, we could push the comment the other way to argue a signal switching IC is better than your input selector switch. This is something I don't accept as your selector switch is going to perform (measure) better, and sound better. There are relays used in test instruments that are better than your garden variety DPDT switch arrangement. They would probably come close to the performance of the rotary switch you chose, or they may equal it.

For speaker output protection, I think there are two main ways to do this. Either use a good relay to make the connection, or use a device to short the output signal to it's return in the event of a fault. The latter method guarantees a lot of amplifier damage, but safe speakers. The relay option may not be able to reliably interrupt the fault current if the relay is not up to the application.

I am wondering about something John. have you ever tried putting a capacitor across relay contacts and evaluated the performance? I haven't yet, but I will try this at some point. A high current film or foil type will be needed.

-Chris
 
#15,519
It is my opinion that diode biasing can create its own distortion under dynamic conditions, and I tend to use less diodes rather than more diodes, UNLESS there is a good reason for using more diodes, such as integral output stage diodes.
I have never put a capacitor across a relay, but it 'might' make sense and 'might' do some good.
 
Status
Not open for further replies.
Top Bottom