Will repairing your amp change it's performance?

[@arianamirgholami9555]

Maybe the new fets are not the problem the fact that repaired one (at some point) had broken fets maybe something else is semi broken in it?

[@JasonWW2000]

Id try to look over the both amps to see what components look replaced. Even the nicer unit may have had something changed. You might be able to compare the LPF potentiometers just to make sure they are the same top, middle and bottom resistance. Sometimes people replace them with the wrong taper. Especially if they pull a used pot off a donor amp. The top and bottom resistance might be the same, but a different taper is going to change things. Try to eliminate as many variables as possible. Do the amps have a big gap in their manufacture dates? Maybe Alpine did a revision change. It's hard to say why there's a difference. I'm impressed that the repaired amp was actually more powerful. It seems like a small increase in THD was totally worth it. Maybe the nicer amp has an issue that's reducing it's power output? Does it seem to be meeting it's factory rated power specs?

[@buildmodrepeat2875]

if the transistors burned most of your caps even if they look fine are probably dry heat can dry up electrolytics with no noticeable residue

[@SubBassFrequency]

This is my thoughts as well

[@stuskustomshop]

I’d say to be a very valid comparison, there would need to be at minimum 3 stock unaltered/repaired amps tested o get a solid baseline. We can’t say for sure that one of these amps is really out of spec tbh. Great vid though!

[@ecpruthless]

I second this. Is it possible he just hit the silicone lottery on the good amp? Or, replace the fets in the good amp also and remeasure for a more direct comparison of the fets influence.

[@Adonis-qj1nq]

I love your videos and tuning guides they are so educational. Thanks so much for them. One question I have for you if you happen to see this comment. Unless I missed it in the tuning guides, do you use the Audiotech Fisher Dynamic Bass Enhancement feature in the DSP PC Tool or do you turn it off? How about the Real Center option in FX menu?

[@RAW-CAt]

I am not using any enhancements or other additional processing.

[@Adonis-qj1nq]

@@RAW-CAt Thanks so much, you are a treasure, really learned so much from you

[@jaimeteexplica5378]

It's important to understand that the broken amp might have gone through hell with the previous owner, so we don't know for certain what the rest of the circuitry looks like. So here are some educated guesses I could think of: 1. The replacement FETs might not have the same gain (transconductance) as the original ones, which can affect how the amplifier handles signals. 2. Differences in the gate threshold voltage between the new and old FETs can mess with the biasing and how smoothly the circuit operates. 3. The new FETs could have different internal capacitances, which can mess up the high-frequency performance and introduce distortion. 4. If the biasing isn’t adjusted to suit the new FETs, they might not operate in their ideal range, leading to less linear performance or even clipping and distortion. 5. The replacement FETs might not match the impedance of the output stage as well as the originals, which can reduce efficiency and increase distortion. 6. If other components like capacitors or resistors have aged or drifted out of spec, swapping out the FETs alone might not bring the amp back to its original performance. I can only assume that Alpine recalibrates every amp before boxing it and shipping it for optimal performance, regardless of transistor variations.

[@serwismusicinfo3008]

What You saying could be true if it's not a class D amp, so no biasing here. There is no gain in mosfets they are switches; amp power in this case is determined by supply voltages, current capacity of mosfets, filtering inductor current capacity. So power cant increase by changing mosfets without increasing supply voltages. Differencies in harmonics and distortion may be caused by decrease in capacity of supply voltage capacitos as well as filtering capacitors at the end stage of the amplifier, and all this due to heat stress and abusive usage by previous owner or just simply due to age of those components.

[@JasonWW2000]

I think you're forgetting that the repaired amplifier is actually performing better than the original. As if it's traded noise for power.

[@AcidDeathRitual]

So many variables here, and without metering or o-scoping side by side of both amps components it's up in the air. I'd be even more curious to see how a third one measures. Could be the "good" one was just exceptional, yet both are within Alpines allowable specs. Component level stuff like this can be extremely sensitive to even the slightest variances. Maybe swap the mosfets again and see if there's a change.

[@nickolaswilliams935]

considering it's a sub amp anyway, it's all academic. Human ear typically can't hear a difference in distortion below 1% anyway, low frequencies have even more room for error before you notice anything bad is happening. The harmonics might be an issue if the frequencies in question were higher, but no one listening to that amp will be able to tell any difference.

[@JasonWW2000]

Yes, the repaired amp is making more power. Seems totally worth it. Assuming the SQ hasn't suffered.

[@miri4885]

Q point or Operating point is set for max. Power i think. Ask your Freund how repairs it. Great Video 🎉

[@LatvianVideo]

Does sam have any theories on why there are differences?

[@RAW-CAt]

According to him, there should not be any differences🤷

[@jondonnelly3]

good enough for a sub

[@20smgreen]

The FETs might be the same model, but maybe there's an audio grade version?