Modifying amplifiers for better bass

[retsel]

I have a Hafler P7000, a 500 w/ch amp into 4 ohms. While it is not a large amp in terms of watts, it should be sufficient for decent bass. While Hafler amps are known for their reliability, they are only so-so in terms of bass quality.

I use this amp with my open baffle subwoofers. I have a part of 18 inch drivers (Avalanche), and a pair of 15 inch drivers on open baffle for the bass. This is plenty of surface area. However I wanted to improve the sound quality of the amps with my open baffle subwoofers.

I had read that by parallelling a set of smaller, higher quality capacitors with the power supply capacitors, that it can improve the sound quality. I opened the Hafler up and noticed that there are 6 x 4700 caps per side, which is around 28000 uF per side - a lot of capacitance. Also, because there are 6 capacitors per side, which should lower the ESR of the bank of capacitors, it would seem that there would be little to gain by paralleling some additional capacitance.

Just the same, I figured that I would give it a try. I had several 68 uF Black Gates around, so I added one each to each side. I was really impressed at the improved tightness in the bass in the midbass region (i.e., 100 hz), which helps a lot with bass slam and also for articulate double bass. Because Black Gates take so long to break-in, the sound quality improved even more after the first week.

When I have some time, I will add a second set of 68 uF caps, one each per side, to see if this helps the sound quality even more.

Retsel

[ThomasW]

I don't think using bypass caps is going to make much of a difference when the amp is used for low frequencies. These kind of tweaks are usually most noticeable when the amp is reproducing higher frequencies.

[retsel]

You are probably right Thomas. If you crossover your infinite baffle subwoofers at 40 hz or below, you may not notice any benefit. However, if you crossover your IB subs above 40 hz, I might still give it a try.

Retsel

[ThomasW]

I have a number of fairly high-end amps at my disposal, this includes an Aragon 8000BB and a Ayre V5-xe.

If I swap out my Face 1200TS and put in the Aragon or the Ayre there's a noticeable difference using a standard 80Hz XO point. That said the difference isn't enough for me to leave a multi-thousand $$$ amp powering an IB sub, because those amps make a much bigger difference when used above 80Hz

[retsel]

My thinking is similar for my Open Baffle bass system. Why pour a lot of money for a lot of watts, when only brute strenght is needed. By modifying the Hafler, I got very good quality bass at a low price.

Perhaps you should modify your Face amps like I did, by adding a high quality electrolytic capacitor as a bypass. Crossing over at 80 hz is likely high enough in the frequency region that you will notice a substantial improvement.

The other tweak to make would be to switch out the rectifiers with Harris high speed, quick recovery diodes. Eventually, I will make this tweak to my amps, or I will pick up a set of Class D amps instead.

Retsel

[ThomasW]

I'll keep the warranty intact thanks...

[retsel]

...wait a year then...

Retsel

[ThomasW]

5 years

[tvrgeek]

68 u not much, I built a box of 1/2 F per rail ( yea, 2F in a box) for my first sub back in the 70's. Now that made a difference. Of course, I had to charge them through a light bulp, and the sub would make odd noises for 3 days after it powered down. It was only a 100W amp, but that was big back then.

Have not looked in my Haflers, but my B&K had a small cheap 10u electrolytic as an input blocking and a similar one in the feedback. I doubled them and added a 1u poly. It was like an octave showed up!