Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Powering Up Audio System (Read 4367 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Powering Up Audio System

I have a mid-fi system that includes a JBL B-380 subwoofer driven by a very powerful monoblock amp (powerful enough that it dims the lights when I switch it on).  My mains amp is a Adcom GFA 555 Mark II.  I am careful to switch on the preamp, CD player, etc., prior to the power amps to avoid any sort of turn on thump making its way to the speakers.  I want to automate this by using some sort of "timed" or "staged" power-up device.  (All of this would apply to turning off the system safely, too.)  I'm imagining some sort of modified power strip with individual solid state relays and timer delay circuits.  Is there a commercial product for this purpose or has anyone else tried building their own?

Re: Powering Up Audio System

Reply #1 –
There are many power sequencers out there, just google a bit.  Here's just one manufacturer: http://www.furmanpower.com/products/all/power-sequencing/all

But...it's all a band-aid.  If anything in the system causes a transient during power on or off at the speakers, it's designed poorly.  All of that should have already been taken care of.  Find the offending device and separate it from yourself.  A power sequencer should not be necessary just to eliminate transients during start up of shut down.

Re: Powering Up Audio System

Reply #2 –
Thank you for your response.  I will try to determine where the startup thump is coming from and fix it.  The other half of  the problem is that the two amps create a very large current spike upon powering up and I need to address that.  When I turn them on one at a time, as I always have, there is no particular issue but if I want to power everything up at the same time (remotely), I would probably pop a breaker.  I am thinking of adding an inrush current limiter (say, 5 amps) to each amp and see if that helps control things.  Actually, I originally put a larger valued one in the subwoofer amp (which I built) but I may need to go with a smaller value.  Is this approach common practice with audio equipment?

Re: Powering Up Audio System

Reply #3 –
Yes, multiple amps with a high current spike can be an issue, and that one is correctly solved with a power sequencer.  The inrush current limiter would solve the high current spike but may also likely compromise peak recovery.  You might want to use a scope and monitor AC line current under demanding audio peaks to see if the amp ever spikes as high or higher than the startup cap-charge spike.

'm not aware that inrush current limiters are common in audio power amps.  Some of the newer power supply designs work around that another way.  I doubt there are many still using the brute-force linear method that puts the filter cap on the power supplyl looking like a dead short until it charges.  There are other ways to get these things started, like the good old "step-start" concept, just as one example, or a more modern version with some sort of ramp-up on power on that gets out of the way once the caps are charged.

Re: Powering Up Audio System

Reply #4 –
Quote from: dc2bluelight on
You might want to use a scope and monitor AC line current under demanding audio peaks to see if the amp ever spikes as high or higher than the startup cap-charge spike.

Ever actually do this?   The results are usually very stunning for what they don't show.

Quote
I'm not aware that inrush current limiters are common in audio power amps.

The basic design of a naively designed simple linear power supply creates high inrush currents.  Switchmode power supplies which are becoming more common can accomplish this with very little expense or trouble.

In a simple linear power supply the inrush current is limited by things that are always there to some degree, such as the maximum saturation current of the power transformer, the CD resistance of its windings, and the ESR of the rectifiers and filter caps.

As long as power amps are designed to satisfy imaginary requirements created by audiophile myths such as all channels driven power ratings, there is a strong exposure to excessive inrush currents.

One simple solution to this problem might be to use a more realistically sized power amp to drive the subwoofer.

BTW turnon thumps and inrush currents need not have any relationship to each other.  They are separate problems that can easily have separate causes.


Re: Powering Up Audio System

Reply #5 –
Quote from: Arnold B. Krueger on
Ever actually do this?  The results are usually very stunning for what they don't show.
Yeah, that was sort of my point.  Unless the amp is repeatedly asked to dump nearly clipping level power into a load you really don't see line current wobble.  What people don't realize is now far from that condition normal operation really is.
Quote from: Arnold B. Krueger on
As long as power amps are designed to satisfy imaginary requirements created by audiophile myths such as all channels driven power ratings, there is a strong exposure to excessive inrush currents.
Ah yes, "all channels driven"... the mythical, statistically impossible condition.
Quote from: Arnold B. Krueger on
One simple solution to this problem might be to use a more realistically sized power amp to drive the subwoofer.

BTW turnon thumps and inrush currents need not have any relationship to each other.  They are separate problems that can easily have separate causes.



Yes, that was the source of my "band-aid" comment.  I see people solving the transient problem with power sequencing when it's source is bad design. 

Re: Powering Up Audio System

Reply #6 –
For commercial banks of LV lighting (12v dichoic) soft starters were sold to limit the inrush current, smooth out the voltage and extend the life of what used to be an expensive lamp when they were first developed, not sure how successful this bit of kit was. Voltage spikes and current inrush was a stated cause of early lamp failure. Would something like a soft starter be available/useful, soft starters are also used in power tools such as single phase table saws to stop them tripping the breaker.

Re: Powering Up Audio System

Reply #7 –
Can't believe this, but today I just ran into a piece of gear with the inrush protection devices!  Now, it's not a piece of audio gear, it's an older low power FM broadcast transmitter, 200W, uses a HUGE linear power supply. Their design calls for a moderate 6A slow-blow input fuse, and the power goes through a combo IEC filter/fuse holder/voltage selector, then on to the inrush devices and a pair of MOVs.  Since the inrush devices (yes, 2 of them) toasted themselves,  (we took a surge that took out the MOVs too), I bypassed the inrush devices temporarily until parts arrive so I could get the TX on the air.  Couldn't actually get the thing started...at all...with anything less than a 20A fuse because of the inrush! 

The product is older, and new designs of this product use switching PS, so this issue is over.  But I'm amused that I was just posting in this thread and just a day later that design lands in my lap. 

Re: Powering Up Audio System

Reply #8 –
The other alternative is a speaker relay. Also a bandaid of sorts, true. I never turn anything on or off without the speaker relay disconnected.

Re: Powering Up Audio System

Reply #9 –
OP here.  To reiterate my original questions, I want to be able to start up my entire system with one switch, but I was afraid of the large current inrush.  (Each power amp alone causes the lights on the same circuit to blink momentarily).  To get around these problems, I took a well made industrial (metal, not plastic) eight slot power strip and installed an inrush current limiter inside.  Coupled with the ones already in the power amps, this works well: I can now power up everything without any current load problems, and I don't need to buy a power sequencer to do it.

The second issue was the turn on thump, which was one of the reasons I always powered things up manually and in order.  I examined my system component by component and found that the preamp is causing the turn on and off thump (as I mentioned earlier, there is a very small thump without it, and I can live with that).  The culprit is my Sumo Athena preamp and it seems to be working well except for this problem.  So, my remaining question is about how to diagnose and repair this problem.  I am going to start a separate thread for that question.  Thanks for the help and advice so far.

BTW, my system consists of:

Harmon Kardon  HD7600 II CD player
Sumo Athena preamp
Adcom GFA555 II mains power amplifier
Mirage M-3 speakers
Sumo Delilah active crossover
Leach DBA monoblock subwoofer power amplifier
JBL B380 subwoofer (aka Sumo Sampson)

Like I said, mid-fi at best, but I like how it sounds.  The Leach base amp does indeed use a very heavy duty "naively" designed linear power supply that uses isolation - not step down - transformers to power the two rails.  The filter caps are massive.  This simple design gives me a very loose power supply that is more than capable of driving that little 15 inch woofer driver.  The low end is plentiful and very, very tight.  As a result of biamping, the GFA555II also has more power than I could ever use to drive the Mirages.