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Old 19th May 2002, 12:43 AM   #1
syl is offline syl  Sweden
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Default Powerful bass

A stiff power supply is needed to get deep and tight bass from a power amp. But there is another parameter that seems equally important.

It all started when I had my 100W Class AB power amp PCBīs on break-in with a 12 Volt PSU. I got curious how it would sound as a headphone amp. Said and done, I hooked up the headphones and put on some music. I was stunned by the immence power and control in the bass range compared to what Iīve heard from stand-alone headphone amps. OK, 16 pcs of 15A Sankens for a stereo headphone amp is quite an overkill, but I was totally surprised that the sense of power and control was still there even if just milliamps was delivered by the amp. Damping factor should not matter when driving 300 ohms, right ?

Theory says that a tiny amp will perform equally well when driving an easy load like a pair of headphones, but this is obviously not the case. If amplifier A sounds more powerful on speakers than amplifier B does, it will sound equally more powerful with headphones. This is counter-intuitive since damping factor really should be a non-issue when driving 300 ohms with a power amp. But the difference over headphones is real and very easy to detect - if fact just as easy as when listening to the speakers. Interesting indeed.

I have a range of power amps Iīve designed and built over the years. They all have a very stiff power supply (typically the transformer is 8 times rated power and the electrolytics are 180.000 uF or more). But they all have different "power" in the bass range. As can be guessed the smallest amp (with the smallest output devices) sounds smallest. All of them have a very tight bass, only the sense of "power" differs.

The observations has led me to the following conclusions:

- The stiff power supply gives bass control, i.e. the amp will be able to control what is there. If the output stage is small the sound will be slender, but still, very well controlled. I recall that builders of the Hiraga 8W "Monster" like the bass. Surely the control comes from the stiff power supply.

- The sense of bass "power" is a function of the output devices and is, it seems, INDEPENDENT OF THE RATED POWER OF THE AMP. My headphone experiment confirms this.

Class A amps are often praised for their powerful bass. I think that these amps would have the same powerful bass even if biased in Class B. The reason for the deep tight bass is probably the stiff power supply and the output stage, not the bias mode.

These findings suggest that a stiff power supply is simply not enough to achieve powerful bass. There is an absolute need to use powerful output devices. And it also suggests that a 10W power amp can outperform a 100W amp if the latter has a "smaller" output section. The rule is simple: use more (or bigger) output devices and the sense of bass "power" will improve (all of course given that everything else in the design is done right).

Kind regards

Syl
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Old 19th May 2002, 03:00 AM   #2
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Could this be a reason behind Pass Labs 1000W amps?
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Old 19th May 2002, 04:34 AM   #3
djk is offline djk
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How come an Ampzilla sounds like a brick house in the bass then? Only two 16A outputs per rail per channel, and they are in series.
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Old 19th May 2002, 04:51 AM   #4
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talking about power suplyes and their influence in the bass.
what about a regulated power suply. If the transformer is "man" enough for the job and enough capacitance before and after the
regulator circuit it wil end up with a very low output impedanceī...but as wallways life is that not simple...
regulator circuits have troubles taking the EMF from the woofer
because they are engeneared for suplying corrent not absorving it...
Life is not easy for making the "ultimate amplifier"...
but we never give up!!!!
Regards
Jorge
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Old 19th May 2002, 07:05 AM   #5
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Quote:
Originally posted by Tube_Dude
regulated power supply... regulator circuits have trouble taking the EMF from the woofer because they are engineered for supplying current not absorbing it...
A shunt regulator supplies and absorbs.

dave
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Old 19th May 2002, 09:12 AM   #6
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"A shunt regulator supplies and absorbs. " I'd like to see a high voltage shunt regulator for an amp like the Ampzilla. 30A?
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Old 19th May 2002, 11:53 PM   #7
syl is offline syl  Sweden
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Hello Djk,

I do not share your opinion on the Ampzilla so I think the findings still apply.

I have listened to the Ampzilla a couple of times, and in my opinion the bass is not very capable. At least it is not capable of playing musical bass on a pair of B&W 801īs. Even my tiny 20W amp outperforms the Ampzilla on the 801īs and those are not my words, it comes from the owner of the Ampzilla. The 20W amp starts and stops the woofer immediately all the way down to 30 Hz. The Ampzilla doesnīt. Maybe things would be more acceptable with book shelf speakers, we did not try that.

High rated power, yes. Brick house bass, not to my ears. For its age it is good though, most amps designed back then was worse.

Have you compared the Ampzilla with the LATEST models from Krell, for example FPB300 ? Thatīs the kind of bass I want. Unfortunately there is no shortcut available to get killer bass. You need big output devices, and a lot of them.

Regards

Syl
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Old 20th May 2002, 12:12 AM   #8
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Quote:
Originally posted by djk
"A shunt regulator supplies and absorbs. " I'd like to see a high voltage shunt regulator for an amp like the Ampzilla. 30A?
A bit of a design challenge, but i expect doable (it would no doubt be bigger & bader than the poweramp it feeds).

My needs are on the order of 300V, 500 mA max and i can mail order that shunt reg off the internet -- those aren't my bass amps thou.

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Old 20th May 2002, 07:03 AM   #9
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"My needs are on the order of 300V, 500 mA max and i can mail order that shunt reg off the internet -- those aren't my bass amps thou. " This makes sense to me. Rowland uses a shunt regulator in the voltage gain stages of the Model 7 amplifier, with the outputs on a brute force unregulated supply. "I do not share your opinion on the Ampzilla so I think the findings still apply. " I should have mentioned that I add power supply bypass caps to every amplifier I get, and film bypass to all the coupling caps in the signal path. An Ampzilla/Dynaco 400/SAE 2400 with these mods will have tighter bass and more slam than an unmodified Mark Levinson ML3 with its 20 parallel TO3 outputs per channel. The ML3 after my mods had more control and slam than the Rowland 7, which has a regulated front end and 32 TO3 per channel.
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Old 20th May 2002, 11:24 AM   #10
syl is offline syl  Sweden
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Hello Djk,

OK, so your Ampzilla is not the original design. That makes a difference. Adding caps to the PSU gives better bass control, such modifications are well spent money.

The differences you describe relative to the ML3 and Rowland 7 highlight the real issue with many commercial high-end amps. They use a lot of output devices but they donīt spend money on the PSU. Remember I wrote "all of course given that everything else in the design is done right". Just using a lot of output devices does not guarantee good bass. Thatīs why your mods are so successful.

I am not the least surprised that your modified Ampzilla beats the original ML3.

Regards

Syl
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