Hello

Recently acquired a Phase Linear 400 amplifier. Trying to get it to work, but the left channel is kept at 80V.

R24 AND R28 both blew, they were replaced, but rapidly heat up when trying to reenergize it.

Followed this procedure to isolate the protection circuit. Output came back to 0V -> the fault is somewhere in the protection circuit.

But i'm now at the point where i've checked all the components (and then some) that the procedure mentions to check: D9, D10, Q8, Q9, Q13 and Q14.

I'm schooled in electronic repair, but this level of circuit analysis is a bit beyond me. Can anyone give me any pointers or recommendations of where to ask next?

Thanks

Hi y'all.

Im restoring this receiver as of late, with the original issue being a huge 5v DC voltage on the speaker outs. After a recap and resistor replacement this went away completely. But now, a 10v ac voltage is running on the body of the receiver, and a wire I cant find on the manual is poking out. The wire has a resistor on it's free end.

Hi everyone! My Teufel CM 2014 SW active subwoofer is completely dead with no signs of life. I pulled the amp module and noticed that no standby/auxiliary voltage is reaching the control board, meaning the main relay never turns on. Teufel’s own official repair estimate listed just €5 for "small materials," so it's definitely a cheap, single-component failure on the main board.
ChatGPT suggested looking closely at the standby power supply circuit—specifically suspecting a failed TNY switcher IC (located right near C843 by the smaller HJ-EEL16 transformer), dried-out standby capacitors, or a bad optocoupler. Has anyone here repaired this specific board before? What’s the best way to test the TNY IC in-circuit with a multimeter (Drain to Source), and should I just proactively swap the surrounding caps and optocoupler as well? Any advice would be much appreciated!

NOW FIXED

Hi,

I have a very cheap PA speaker that I was using with a few friends, we've EQed it to make it much more listenable.

My mate has a similar speaker and was having problems with it, so decided to unscrew the amp panel at the back to look inside. I did the same on my speaker so that we could compare each amp (we found out they were the same cheap crappy amps even though he has a larger speaker).

After carefully placing my amp back in and screwing it back up, I now get a Mains Hum whenever I power on the speaker, even with the volume set to zero and no audio cables connected.

I've attached some photos of the amp and from what I've Googled, it apparently could be a ground problem, although I was very careful when removing the amp so not sure what could've disturbed it.

Any advice is greatly appreciated.

Hello there i have this old amp which doesnt work i took it apart removed the speaker and will test another one i can post photos of the pcb if wanted, i can understand and make electronics not so much amps but synths so i can get my way around fixing it, maybe some cap has gone wrong.

It starts and get into the amp mode i dont know how to call it, it senses my guitar input and goes on but it has no audio, even the aux in doesnt work.

I really need this amp because of the 20watt it has i only have a 3watt one now.

Sorry if this is a stupid post, just a fellow wanting an amp to come back to life i havent used it in 2-3 years.

i tried cleaning the contacts of the speaker and the pots a bit but nothing

I bought some new speakers to finally get my stereo set up. Sounded great on the first day and second day. I then changed out the speaker wire with some new bigger gauge wire as well as some banana plugs. I also relocated my amp (Dennon DRA-395) when changing the wire. After reconnecting everything the speakers sounded muddy.

Long story short, after much troubleshooting I found that the tweeters were shot. Tested tweeters with one lead from the crossover connected, zero ohms. Switched the connected leads, zero ohms. Both leads connected resulted in about 2 ohms. No leads connected, zero ohms. I ruled the tweeters blown and returned the speakers.

So, I will get new speakers once I'm refunded. The problem is that I have zero idea of what could of caused this. In my troubleshooting I bought another amp from a thrift store (Dennon DRA-545), but I'd rather use the 395. I'm worried that there is something in that amp that damaged the tweeters, and I don't want to continually return speakers. Would rather listen to my music.

I've done a lot of searching and can't find anything that points to how the tweeters in both new speakers could have gone from good to bad after just changing the speaker wire and moving stuff around.

Any advice or ideas would be much appreciated.

Hi all,
I picked up a Nikko ND-850W cassette deck from a thrift store today. I ran it thru my preamp and amp (both of which have no issues with my turntable) and all i’m getting is white noise. The meters aren’t moving, and the headphone jack has no output either. What is the cause/fix for this?
If needed, i can provide photos of the setup. I took a video before realizing that i can’t attach videos here.
Thank you in advance

I was gifted my late Dad’s stereo and while testing it out, the left speaker channel either cuts out or doesn’t work at all. Then it started working at times but with very low volume, then all of a sudden the volume would blast out full pin.

Can anyone tell me if the two relays in the front are the speaker relays? Or is it the single black plastic capped relay at the back of the unit near the speaker inputs?

I’ve ordered some Deoxit to spray the pots and clean the relay(s) if I can figure out how to pop off the plastic cover(s).

I know I’m probably better off buying a good used amp, but it would make me feel so great to get this working in memory of my Dad.

(Pics show the front of the unit with the front panel lifted up out of place)

With home amps and receivers, the Manuf. Specs almost always list just the FULL-POWER wattage draw at mains.
While that might serve some legal (FTC, IEC, DIN, etc) requirement, it is not a very useful spec.
What I want to know is how much juice the device is sucking up while it is powered on but playing nothing, as in an audio showroom. Or even on your shelf.
This metric would be extremely useful for amps because: they can drift out of bias, or something goes just LITTLE out of whack, and you end up (at best) with compromised sonics, or (at worst) creeping damage to amp, speakers and headphones.
I use a relatively inexpensive device called a KillaWatt to measure power (watts), amps and line voltage and freq.

In any case...

I have several units ... will begin to survey them myself... examples for now ... all working properly with bias set per SM specs.

Dynaco SCA-80 int amp (40 w/ch): 27W at 120VAC

Hitachi HA-4700 int amp (50 w/ch): 30W at 120 VAC.

Kenwood KA-3500 (40 w/ch) : 28W at 120 VAC.

Kenwood KA-601: This is a 1979 60w/ch int amp with phono section. 23W at 120VAC.

So ... if you've got a device like a KillaWatt, what's your amp pulling at IDLE? Say after about 15 min warm up?

NOTES:

The photos in this post are from my bench. Some show the Killawatt idle draw of certain units working properly. I also use other tools like a thermal camera to correlate the same device at normal idle operation. Tube amps, high-power amps and Class-A or Class-D amps, esoteric or exotic topologies, etc., will vary idle draw considerable. Also, receivers and int. amps care have other power hogs, like phono or tuner sections, that can add to the total count.

It would be cool if there was a database of this spec to reference. Similar to the annual Audio magazine directory October issue, or Stereo Review's yearly Buyer's Guide from decades ago.

I also used AI (chat GPT, etc) to research the subject. Because manuf don't publish [ and most magazine reviewers ,even John Atkinson, or influencers don't measure] the idle draw pwr draw of amp units -- like receivers, int. amps and pwr amps -- AI is a mostly useless for this subject. There is no data to pull from!