• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join freeLog in
    Want zero display ads or expanded classifieds tools? Compare plans.

Wiring

Most power amps have quite a few volts on the output - higher voltage supply rails seem quite popular in recent designs, because it reduces current demand.

The main feature of well designed equipment is that it is resistant to abuse - outputs that can stand reverse phantom being stuffed up them, mic inputs that can cope with +4 levels being stuffed into them, amps that can survive being plugged into awful generators that have wildly fluctuating output voltages. It's amazing any of this kit works, but good design means most of these things are tolerated with no lasting damage.

Everyone here is quite right saying DON'T plug speaker level feeds into a mixer channel - but have you seen how tiny some of those surface mount capacitors and resistors are? There really isn't much to go up in smoke, so they just fail. They can be secondary components, perhaps designed to prevent DC or RF entering the device, and they may fail safe - with just protection gone, and you will never know until something else happens.

So if somebody says should I, and the answers come back no, don't, stop, whoa, then surely common sense says hang on, everyone is saying this is a dodgy thing. Reading this, and then actually doing it, is foolhardy in the extreme - even perhaps stupid. To then tell everyone you did it with no harm just makes everyone sigh a little with relief you may not (not did not) do any damage, but they also think how stupid you were to ask for an opinion and then ignore it. Why ask a question if you really are going to ignore the response?
 
The main feature of well designed equipment is that it is resistant to abuse - outputs that can stand reverse phantom being stuffed up them, mic inputs that can cope with +4 levels being stuffed into them, amps that can survive being plugged into awful generators that have wildly fluctuating output voltages. It's amazing any of this kit works, but good design means most of these things are tolerated with no lasting damage.

Damaged output stage (exploided coupling capacitors) on 19" effect racks was a very popular damage at the time when I did repairs for a friends music store.
 
I see the results of "bad ideas gone wrong" in the service department.

On another point, why do folks who have no idea how something works, and can't understand a schematic think they can repair everything themselves. These units usually come in in body bags and ALWAYS cost more than they would have ifthey hadn't fiddled with it themselves. This is the ultimate fail IMO.
 
  • Like
Reactions: Sartori and ddnidd1
Yep people complain when somebody wants to charge them $100 to fix an amp...

Okay, let's see what I've got floating around in the shop. A scope, a couple of sig gens, a signal tracer, a good soldering iron, a desoldering station, several multimeters, a dim bulb tester, isolation transformer, Variac, heavy duty dummy load, transistor checker, several power supplies, etc, etc. So there's a ton of money tied up in test gear. Then of course there's my time. I guess after all that, we're supposed to fix amps for minimum wage?

So when people try to fix their own amp, invariably they get on the Internet, find out what somebody else's amp had wrong with it, and so they then attempt to repair their amp by installing the same parts that the other person needed to fix their amp. No troubleshooting, no logical method, just parts-swapping. They wind up replacing perfectly good parts and sometimes wind up damaging their amp even further. Since the amp no longer works, they then junk the amp (and proclaim loudly that Brand X amp is a piece of s**t). Had they brought the amp to a qualified tech, a little bit of troubleshooting and then the amp is fixed by replacing just the parts that needed to be replaced.
 
Not just a tech's time as generic time, but EXPERIENCED time.

Say I can fix a problem in 15 minutes and charge $50, and another "tech" can fix it in 2 hours and charge say $100, why would they complain that my labor rates are too high but think the tech with the lower labor rate is such a deal? Good techs are quick BECAUSE they have experience and know their stuff.
 
Not just a tech's time as generic time, but EXPERIENCED time.

Say I can fix a problem in 15 minutes and charge $50, and another "tech" can fix it in 2 hours and charge say $100, why would they complain that my labor rates are too high but think the tech with the lower labor rate is such a deal? Good techs are quick BECAUSE they have experience and know their stuff.
+1 :)
 
Test equipment can be very expensive. The fancier stuff can get really expensive. A Keysight U8309B audio analyzerInvalid Link Removedis around $13K. A basic spectrum analyzer can cost over $50K. A good reason to buy used. Some jobs specify the equipment that you have to use and they require that the calibration be certified.
 
Test equipment can be very expensive. The fancier stuff can get really expensive. A Keysight U8309B audio analyzerInvalid Link Removedis around $13K. A basic spectrum analyzer can cost over $50K. A good reason to buy used. Some jobs specify the equipment that you have to use and they require that the calibration be certified.
And if you are not forced to a certified calibrations of your equipment, doing calibration or service on equpment only for your own is already costly because you have to charge some fee for the service documents.

Many years ago I had to pay around $300 for the service document of a programmable signal source HP 8165A.
 
Reading this, and then actually doing it, is foolhardy in the extreme - even perhaps stupid. To then tell everyone you did it with no harm just makes everyone sigh a little with relief you may not (not did not) do any damage, but they also think how stupid you were to ask for an opinion and then ignore it. Why ask a question if you really are going to ignore the response?

Because I was under the mistaken impression that people here would know the answer.