quick solid state amp question

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perfect caps dont heat up, add the 2 resistors /one in series (ESR) one in parallel (leakage) that most real caps have and think again. One of the most common repairs in recording studio equipment (where they leave the gear on 24/7) is replacing electrolytics that have "dried up" If you let it sit for any periods shut it off. Its greener too!
 
But what about the sound?
What are we waiting for, after the turn on nob is swithed?

I think every amplifier are constructed and mesured for best performance at a given narrow temperatur range. And that temperatur is never stated in any commercial spec.

ClassA amps have some time to come upp till the temp that makes the heatsinks begin to flow air and stabilize, but what about classC or AB?
 
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Hi Ragnwald,
I think every amplifier are constructed and mesured for best performance at a given narrow temperatur range. And that temperatur is never stated in any commercial spec.
:confused:
Ahhhh, no.

Some amplifiers have poor control over the bias current. These take a long time to settle into the normal operating range (think Bryston 4B, etc ...). This is a defect in design actually. It is perfectly possible to design amplifiers that have settled in within 1/2 hour. Heck, that is the time needed for very accurate measuring instruments to stabilize. If an amp hasn't stabilized within half an hour, it will never settle in. As soon as you start playing music, all the circuit parameters will shift!

Hi Gain,
You were given correct answers early on. Hannes is bang on. If you are not going to listen to your gear for a couple hours, turn it off. Just avoid turning it on and off all day. A happy median is what you need.

Things to consider. Component failure is run time and temperature dependent. If you leave your stuff on all day, what percentage of the time on are you actually using it? Also, power companies like to play at night. Lightening storms come up quickly too. If your stuff is off, it will probably be okay. If it's on, I guess you wanted a new one.

Understand too. Older tube equipment was designed to be turned on and used, then turned off again. This "leave it on" thing is a modern misconception. If you are worried about temperature swings, then you must leave it on and listen to music very, very quietly. Recording studios leave some stuff on for a reason. Some of this is due to how much gear there is, and they get lazy. They also are subject to audio myths.

-Chris
 
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Hi cbdb,
Let's not forget the old MCI plasma meter bridges that often blew up on power up. A design error caused this and studio owners found that leaving these on was a matter of necessity. You never knew when the session had to be canceled due to those darn things. I guess the gave up and simply told people to leave it all on.

Then there is Bryston who gave the "leave it on" myth more momentum due to their own poor designs. The 3 and 4 B amplifiers had a bias control problem coupled with a power switch that couldn't take the turn on surge. How to you solve the warranty issues? Easy. Tell people they have to leave them on and that they were designed for that service. Now this poor advice is hard to stop.

Agree on the tube stuff as well. The effects racks are nice in the morning (that would be just after lunch for everyone else) when they are nice and warm.

-Chris
 
anatech said:
Then there is Bryston who gave the "leave it on" myth more momentum due to their own poor designs. The 3 and 4 B amplifiers had a bias control problem coupled with a power switch that couldn't take the turn on surge. How to you solve the warranty issues? Easy. Tell people they have to leave them on and that they were designed for that service. Now this poor advice is hard to stop.

Hi Chris,

I noticed in some Bryston schematics I've seen on their web site, that they have a soft-start circuit using triac phase control with a TDA1085C chip. Were the failures you saw in amps that use this circuit? Or do you think the circuit was a redesign to try to fix a previous design problem?

The circuit, or something similar to it, seems appealing because it doesn't require a big honking 50W resistor with an electromechanical relay in parallel with it to accomplish the soft start.

Sorry for the OT.
 
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Hi Andy,
That's a new addition that occurred later, after the 3B and 4B. For the money they charged, this ought to have been a no charge retrofit to those older amps. Output protection would have been nice too. Anyway, that is a fix to a glaring design oversight. Many amplifiers had these long ago.

The failures were that this switch would burn out. But then, the face plate used to tear off when roaded, making switch replacement easier. Kidding about replacing the switch being easier. Then there was the bias with it's very strong positive tempco. These amps start with severe crossover distortion with no bias. After 45 minutes, the heat sinks were very hot to the touch and the amp had reached it's iffy stable point. My understanding is that they hired a real designer and the Bryston stuff today sounds better and even stays together longer.

I like the idea of using a relay for the soft start job. The contacts are not under a great deal of stress and the second "click" is a nice audible cue telling you the universe is unfolding as it should. I would not tend to use a triac and trigger circuit unless there was another use for that circuit. Normally, most companies use 10 ~ 20 watt resistors. A 50 watt is overkill unless the power supply is massive. Although, a nice Dale 50 watt resistor mounts easily on the chassis. This resistor is designed to burn open if the relay drops out due to a fault. This helps limit the damage.

-Chris
 
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Hi cbdb,
And some of those old tubes might like to stay on all the time?
Actually, no. Only a few items were designed to run all the time. PA systems (that's why they are class B), computers (those tubes are designed to be kept in reverse bias) and some military or industrial things (like radars, telephone amplifiers - repeaters, etc..). Anything that was left on all the time had a maintenance schedule, even factory PA systems and early Terryphone systems.

If you leave tubes on with full heaters and no B+, you can "poison" the cathodes. The emission drops and noise increases. You are way further ahead to simply turn the item off (entertainment sound equipment).

These days, solid state equipment has lower maintenance if it has to be left on at all times, but there is still a maintenance program to look after that stuff. That is if the factory or installation actually expects their equipment to work when needed.

-Chris
 
anatech said:
Some amplifiers have poor control over the bias current. These take a long time to settle into the normal operating range. This is a defect in design actually. It is perfectly possible to design amplifiers that have settled in within 1/2 hour. Heck, that is the time needed for very accurate measuring instruments to stabilize. If an amp hasn't stabilized within half an hour, it will never settle in.

-Chris [/B]

Ok, if it´s not temperature dependent, what (more specific) exactly happens this 1/2 hour before we can lean back and listen to our favorite records under full control?;)
 
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