Suggestions for testing a never installed, 20-year boxed amp.

I have a new Pass Labs X5 power amp that has never been installed (boxed up for over 20 years). I'm looking for suggestions about powering this unit up. I'm concerned about connecting it up to my current speakers the first time I power it up. Should let it cook while connected to some load resistors? Should I leave the inputs unconnected or loaded? 


You can turn on a solid state amp without a load connected to it.  But, just to be safe, you should contact Pass for their recommendation.  I would not hook up any speakers until the amp has been turned off and on several times and has been allowed to run for a while with no obvious signs of distress (the most obvious sign of trouble will be a strong odor of something burning, repeated blowing of fuses or tripping of any safety relay that cuts the amp off).  

The concern with an amp like this sitting a very long time unused is the state of the electrolytic capacitors in the power supply.  With tube gear, you can soft start them by attaching them to a variac and using that to slowly bring up the voltage which allows the capacitor to "reform."  But, some solid state gear do not like under-voltage conditions so this is not recommended unless Pass Labs says that this can be done.

Before I powered up my long dormant Pioneer SX-1050 I found a current limiting device on eBay. It used a light bulb to someone limit current. It powered up OK. I then used a multimeter to check for DC on the speaker terminals. Luckily there was none. 

Yes, good advice about checking for DC with a multimeter.  Unlike a tube amp with output transformers, some solid state amps can pass DC.

I’d contact Pass Labs. They may tell you to run the amplifier through a variac in order to allow the capacitors to reform safely. Best of luck. 👍

Just curious: How did you end up coming upon an unused for 20 years boxed up amplifier?

Many years ago I rebuilt a handful of very old (circa 1870-75) Acoustic Control Corp. solid state guitar/bass amplifiers.

I had this same question. Yontz, at Mad Scientist Audio (? - been a long time) suggested using a light bulb current limiter, basically a light bulb socket spliced into a short extension cord with a 60 watt bulb.

NEW electrolytic caps AND old, discharged ones appreciate slow voltage build-up. Worked like a charm.

Lately though I use a 20 amp variac on recapping projects. ADCOM preamps, amps, tube amps, 1.5 kW HF linear amps, etc.

Curious to know what you do and how it works out for you.


Buy a Chinese variac on eBay for around 100$. Power up slowly over 24hrs. Make sure you get the proper amp variac. You should be ok. Good luck. 

All good ideas. I'll try to contact Pass Labs Monday before doing anything. I already have a lightbulb current limiter setup, a variac, and some 250W 8ohm resistors.

My acquisition of this amp is a long story. The company I worked for, at the time, set up a number of QC stations and 3rd eye approval stations for mastering DVD movies for major studios. This amp was never used in any of the setups. It sat in the shop for years until the US operation was closed. I purchased this and some other equipment from the company before moving on. My plan was to set up a better home theater system with this amp. I also purchased a new Marantz AV7005 that's also still in its box. Basically, I couldn't find speakers that my wife could live with. Now I'm trying to decide what I should do with these items.

I'll let you know what Pass Labs tells me. Thanks again!

I think the advice being given about contacting Pass Labs before powering up is sound. Not being familiar with Pass equipment, is there any current limiting circuitry in them? I have a Mark Levinson ML335 that's been boxed for 25 years or so. When I asked a similar question here about powering it up, it was recommended I send it to a shop to have the capacitors checked first. I found a shop in Austin (Pyramid) that I'll be sending it to BEFORE I put it in my system.

Incidentally, I had occasion to visit my daughter in Austin recently so took the opportunity to visit the shop. I was very pleasantly surprised at the facility and evident expertise available. 

Good luck waking up your amp and as always...

Happy listening.

I used a Variac and 2, 8ohm 10watt resistors on the output with volt meters across them.  Short the inputs.  Take the covers off.  As I easy up the variac, I watch the meters, sniff around and look for smoke.  Now I would use an infrared thermometer.  Before I used to use my trusty finger.  Hoping B+ doesn't get me.

I had a laughed watching Vice Grip Garage.  When he connects a battery to a car he's resurrecting, he sniffs around and looks for smoke.

OK - I took your advice and contacted Pass Labs. Someone actually answered the phone and referred me to Kent who was very helpful. His concern was with the capacitors as some of you mentioned. Kent recommended a "current limited power up" using a 120vac current limited power supply. I asked if a light-bulb limiting circuit would be Ok and he said to cook the amp for a day with a 60w bulb then move up to a higher wattage bulb for another day. Of course, he cautioned me about safety concerns. No connections to inputs or outputs are necessary. 

Kent offered to do this for me if I wanted to ship it to them for a nominal fee. He said he could also re-cap the amp if it becomes necessary. He also offered to send me instructions to make the speaker connectors banana plug ready. 

I don't have any decent speakers for this amp. If this amp tests ok I will have a tough decision to make. Do I keep it and build a system around it or get rid of it? Either way, I need to know if it works.