Testing power amps - am I doing it right?

[Deleted member 214]

Dug out some old car power amps. I have a 12v benchtop power supply giving juice. Output tests good. Plugged a known good CD player in the RCA jack inputs, known good speakers to the speaker terminals, and neither amp made a sound. Neither has a "power" light to check. Both had good fuses. Is there something else I should check, or are these scrap???

 

[cbunt1]

It's been a *LOONG* time since I messed with car audio...BUT if memory serves:

You don't say exactly how you hooked the known-good CD player up, whether you came from a headset jack, speaker-out terminals or RCA jacks, so forgive me if I'm covering ground you've already covered.

The RCA-style input is not the same as standard output from a speaker or headphone jack. I don't remember what the impedance is, but I'm thinking it's significantly different than what you get from a speaker wire. As I remember, you couldn't just go from the audio outputs from the head-unit, unless it was either native RCA or you used a converter.

To bench test an amp, I would use a phono (dating myself here) or CD player with native RCA outputs. If you're getting no audio from known good input and known good speakers (are they 4 ohm? Many car amps are looking for 4 ohm loads).

I'd also check your power source and put a meter across the terminals to ensure it's pulling some load. As I remember most older amps would "pop" the speaker when they powered up -- the 'soft start' is a newer feature...but as I type that, I'm thinking that the "pop" may have come from the head-unit instead of the amp, because thinking of the startup sequence we used to use for auditorium audio (not car audio) we powered the mixer, THEN the amps or we rattled windows with the POP.

Most of what I'm telling you is old, and I was in high school last time I wired a auto sound system, and it's been probably 10 years since I ran a mixer board...I'm sure someone here is both more knowledgeable and "fresher" with it than I am.

Hopefully it can give you a start...

 

[q-ship]

Unless they are really old low wattage (1960's) amps, you will need to apply power to the "power-up/start circuit" also.

Can you post a picture of the terminals?

Also, be careful about using anything other than a car battery to power them as most any amp will require far more amperage than a power supply can provide. This can fry a power supply, or trip internal protection circuits in the amp and shut them down.

 

[Deleted member 214]

It's been a *LOONG* time since I messed with car audio...BUT if memory serves:

You don't say exactly how you hooked the known-good CD player up, whether you came from a headset jack, speaker-out terminals or RCA jacks, so forgive me if I'm covering ground you've already covered.

The RCA-style input is not the same as standard output from a speaker or headphone jack. I don't remember what the impedance is, but I'm thinking it's significantly different than what you get from a speaker wire. As I remember, you couldn't just go from the audio outputs from the head-unit, unless it was either native RCA or you used a converter.

To bench test an amp, I would use a phono (dating myself here) or CD player with native RCA outputs. If you're getting no audio from known good input and known good speakers (are they 4 ohm? Many car amps are looking for 4 ohm loads).

I'd also check your power source and put a meter across the terminals to ensure it's pulling some load. As I remember most older amps would "pop" the speaker when they powered up -- the 'soft start' is a newer feature...but as I type that, I'm thinking that the "pop" may have come from the head-unit instead of the amp, because thinking of the startup sequence we used to use for auditorium audio (not car audio) we powered the mixer, THEN the amps or we rattled windows with the POP.

Most of what I'm telling you is old, and I was in high school last time I wired a auto sound system, and it's been probably 10 years since I ran a mixer board...I'm sure someone here is both more knowledgeable and "fresher" with it than I am.

Hopefully it can give you a start...

Thanks. CD player line out jack with mini plug at CD end and RCA at the other. It plays fine through the RCA inputs of my band's PA system.

Checked power supply output with a multimeter - 12.6v.

Next!

- - - Updated - - -

Unless they are really old low wattage (1960's) amps, you will need to apply power to the "power-up/start circuit" also.

Can you post a picture of the terminals?

Also, be careful about using anything other than a car battery to power them as most any amp will require far more amperage than a power supply can provide. This can fry a power supply, or trip internal protection circuits in the amp and shut them down.

Thanks. I'm using a pair of tiny Radio Shack bookshelf speakers to test with. I'll try a car battery.

The little Coustic amp has only hot and ground. The big Kenwood has hot, ground, and pcon (remote). Should I supply 12v to that terminal too? Never thought about it. I've never used separate power amps before, just head units with built in amps.

 

[Deleted member 214]

Charged up my spare car battery. Found an orange wire on the Coustic. Hooked that to the hot along with the main power wires - it works great! Jumped the Kenwood remote terminal to hot - all four channels work. Strange thing: the Coustic is rated at a lot lower WPC than the Kenwood but when the input sensitivity is at max on both, the Coustic is a lot louder. I have only a pair of 6x9s in back right now and will probably use the Coustic for them, run the pair of 3 1/2s in the dash with the head unit. If I find some slim line speakers for the kick panels I found an Alpine 4x45 unit that is super efficient and super small I might buy. Thanks everybody for your help!

Greg

 

[daredevil]

Charged up my spare car battery. Found an orange wire on the Coustic. Hooked that to the hot along with the main power wires - it works great! Jumped the Kenwood remote terminal to hot - all four channels work. Strange thing: the Coustic is rated at a lot lower WPC than the Kenwood but when the input sensitivity is at max on both, the Coustic is a lot louder. I have only a pair of 6x9s in back right now and will probably use the Coustic for them, run the pair of 3 1/2s in the dash with the head unit. If I find some slim line speakers for the kick panels I found an Alpine 4x45 unit that is super efficient and super small I might buy. Thanks everybody for your help!

Greg

Sounds a lot like what I set up yesterday. Dual 50 x4 on 5" in the doors with a 600 watt Sony pushing my 6x9 Lanzars in the rear deck with my sub outlets run to a 1200 watt Boss amp pushing two 10" Rockford Fosgates in a lexan box in the trunk. With my fade slightly higher to the rear and the sub output level at a 2 on the radio its like being at a concert when I crank it.Clear and loud not that boom boom boom ****.