rockford power 250m p/s cycling.

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so, i have this amp that i was just fixing the broken rca shield board connections. powered it up and went to test it, and noticed that it would cycle the music on and of. looked at my amp gauge on the poser supply, and noticed that the idle current bounces in an odd fashion... kind of reminds me of hitting one of those hanging punching bags. one spike, followed by bouncing current fluctuations that taper before the next spike.
 
I think it is the "newer" one. About 2k "waffle" design. i will try to post a picture of the board soon.

The bias adjustment was too high. Once I turned it down, it did idle just fine. Rail voltages rose back to +/-36v with 0.000v across the source resistors. I never touched the bias pot before this, but perhaps the previous owner attempted to adjust it because of the broken rca jacks.
What is the rail voltage supposed to be on this amp?
Thanks,
-Heath H-
 
So, i'm wondering if i adjusted the bias correctly. I started full ccw, then adjusted it cw to the point that it started to draw current, and backed it off a tad. I was watching the current meter on my power supply and measuring rail voltage on the source resistors (both sides of the resistor). I did this several times until i was sure of the adjustment. 37.82 and -37.94 @ 14vsupply. The adjustment left it 0.17v less.
The issues:
1-it does play clean audio and all preamp functions operate, but efficiency seems low. I did not set up the amp clamp, but i did measure the output ac voltage on both 4ohm and 2ohm sub loads, and, without knowing imp. rise, it is putting out roughly 50watts rms, while pulling 100 from the power supply.
is this normal at the lower power level for this amp? i cannot feed it 30a, like i would like to.
Should i re-adjust the bias so that there is no rail voltage drop?

2- It seems to require higher input signal to get a decent level of power out of it, even with the gain pot adjusted to max. I remember reading somewhere that there are a couple resistors, or caps that tend to be damaged sometimes when the rca shield legs break. which components are those, or should i be looking at something else.
3- is q110 supposed to be attached to the thermal board, or free-standing? It came free-standing, but i see the copper pad for it. I also have a rf punch75.2 that has the same thing, and the one on each side is bent over touching flush, but not glued down. The 75.2 looks to have been repaired, though.
 
That rail voltage drop is absolutely insignificant.

Class B and Class AB amps are very inefficient at low output levels.

Why can't you get 30 amps to it?

Drive a sine wave into it and measure the AC voltage at the RCA jacks and across the speaker terminals. Post the voltages.

I don't have any information on this amp but if this is the bias transistor, it's supposed to be in contact or in close proximity to the MEHSA insulator.
 
I suspected the rail voltage drop was unimportant, but I figured I would throw it up just in case. It did show more finitely the current draw, vs, my current meter, though.

All my other amps a/b/d seem to have significantly higher output with the same drain, even high current us amps, soundstreams, and just about every mainstream brand in between.

The power supply i built only has a 10a cb installed in it, which is pretty close to what it will currently sustain. i am about to order the rest of the parts to re-wire it with a 317-based adjustable regulator, and build another 75a+@12.5vsupply. This last spring, I think, tossed out 12 optimas, and then later, my 2 yellow tops that i had for benching higher power.
at 12.4v unloaded, i got +36/-36.25 at the rails, for reference.
198mvac input = 20vac output
400mv ac input= 29.98vac output
loaded:
200mvac input= 9.5vac output
could not drive it to 400mvinput due to the current draw
shouldn't this amp be 200mv sensitive?

thanks-
-Heath H-
 
A couple of problems...

With only 36v of rail, you cannot get more than 36v of rail without clipping. After it begins to clip, the voltage readings are inaccurate.

The output vs input should not change loaded/unloaded unless the output is clipped badly.

The only voltages usable here are the 198mv vs 20v. That's 40dB of gain which is more than some of the older Rockford amps, which had up to 36dB of gain (if I remember correctly).
 
I am aware that you could not get 36v+ with a rail of only 36, but i have run these line of amps many times in the past, and i could have swore that they were 200mv sensitive. I was expecting 32-34v by 250mv at max gain.

I do not understand what you are implying. It sounds like you are saying that rail sag does not exist without severe clipping
 
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