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Thread: Bass testing your favourite amps

  1. #1
    Senior Member Ian Mackenzie's Avatar
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    Bass testing your favourite amps

    This has been discussed many times before and bound to bring in many amps busters.

    Why Do so many amps sound different in the bass area?

    Okay allow me to qualify that, we are talking about quality amps, not so called multichannel wonder boxes and B grade consumer boat anchors.

    I recall a post recently where it was reiterated the quality of the power supply capacitors was the key.

    Oh really?

    Maybe for some amps, but not for others.....switch mode amps and other new classes, and perhaps even the tried and proven class A room heaters.

    Go here for a full explanation on power supply upgrades.
    The job of filter capacitors is also well explained here.
    http://www.tnt-audio.com/clinica/solid-state.html

    They act like a water reservoir tank, you pour water in and take water out, to a point the bigger the tank the better the capacity to cope with demand.

    Its also interesting to determine if the current demanded by the amplifier is constant or dynamic. As a rule, a constant load is a much tougher job for the filter capacitors because of the higher AC ripple current demanded.

    However, the impact of capacitors dynamic performance is far less pronounced on an amplifier that draws a constant load, where the supply rails remain relatively stable and the design has good PSSR and CMRR.

    With this in mind I recently did some comparisons with a conventional A/B amplifier, a class A SE amplifier and a 3rd class A amplifier having a true balanced output stage where the speaker output comes directly from the power transistors, not via the power supply.

    The subjective appraisal for the conventional A/B amplifier provided tight punchy deep bass, however there was obvious bloom and colouration in the upper bass and midrange, it had large power reserves but lacked subtle nuances on bass instruments. (Damping greater than 1000 @ 20 hertz and output greater than 300 watts).

    The class A SE amplifier exhibited an enlightened ambience in the bass and a feeling of space, individual instruments were clearly identified. There was a slight warmth in the tonality and good control of drum notes. (Damping factor 80, power output 100 watts).

    The full balanced class A amplifier showed impressive dynamic contrasts, 3 dimensional ambience and tantalising excitement of micro dynamics. The bass tonality was neutral and delineation of instruments outstanding. (Damping factor 30, power output 100 watts).

    Obviously I expect most will take this with a grain of salt and perhaps this belongs on another forum (although I would be preaching to the choir.) It would also appear damping factor is not the sole criteria for good bass performance.

    But I think its fun to challenge your equipment and your ears occasionally.

    By the way, the joke of this experiment was the reference speakers which were set up in near field operation. They are the much loved and unfortunately much bashed L100 Century.

    The moral of the story is except nothing as normal, blame the operator first and your speakers last.


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    Last edited by Ian Mackenzie; 06-07-2004 at 03:42 AM.

  2. #2
    PSS AUDIO
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    Re: Bass testing your favourite amps

    Originally posted by Ian Mackenzie
    I recall a post recently where it was reiterated the quality of the power supply capacitors was the key.

    Oh really?
    Hi all of you,

    When something is said about power amplifiers, here I am!

    All what will be said lies for AB amplifiers only.

    From my very little experience since 25 years from now, I can say that what is important in the quality of an amplifier is the following:

    The way the transformer is winded (we have several transformers able to deliver 2x300W, their power ability lies from 200Va to 1200VA; all listening test made around 25-30 watt, witch means that all transformers are powerful enough to drive the requested power).

    The bridge is also important. Once we have selected the right components (transformer, capacitor, and others) changing the bridge will affect the output tonality.

    Capacitors: From one brand to another, even with the best technical characteristics, you will have different tonality using one brand or another one (we finally went for several 10000MF100V capacitors instead of a big one – 47000MF63V from BC COMPONENT). One was nice but too shinny with a lack of mid bass … guess witch one?

    It is well known that replacing a power supply made by a transformer, bridge and capacitors by a battery will dramatically enhance the sound quality of your amplifiers and pre amplifier.

    Gain: the gain of the amplifier IS very important as we recently switched from 32 dB to 26 dB.

    Signal to noise ratio: This is perhaps one of the most important number and greater it will be; more micro details will be heard, and by lowering the gain of the amplifier you will increase his signal to noise ratio.

    CMRR: If you have a balanced input it is important having the better CMRR possible in conjunction with the signal to noise ration.

    After that the choice of good resistors, capacitors (void all capacitors in the audio link) the way the PCB is designed will also play on the tonality of the amplifier.

    Only A or AB amplifiers can play good music (other will just make noise, good enough for a football match in a stadium or for the next Olympic Games in Athens),
    Distortion has no real signification,
    Damping factor is just nuts,
    Slew rate is not that important as the rising time (there is a house …. The animals),

    This is just the beginning, for others climbing up the train just read a thread I opened month ago “Amplifiers are more significant than you may think”: http://audioheritage.csdco.com/vbull...=&threadid=347

  3. #3
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    Re: Bass testing your favourite amps

    Ian,

    Did you ever run across this - http://www.stereophile.com/amplificationreviews/674/

    Also, what all did you see at Pass Labs?

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    Re: Bass testing your favourite amps

    Originally posted by PSS AUDIO
    Damping factor is just nuts
    Here we go again.

    I'm not quite sure how a ratio of two numbers can take on a psychological "disorder" but here's what George had to say about DF way back when - The Damping Factor Debate

    It appears certain Marketing departments decided that damping factor was a "figure of merit" and we've been plagued with it as a selling point ever since.

  5. #5
    PSS AUDIO
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    Re: Re: Bass testing your favourite amps

    Originally posted by Giskard
    ... but here's what George had to say about DF way back when - The Damping Factor Debate

    We placed the same article on our website : http://www.pssaudio.com/english/art010.htm

    I was perhaps misunderstood.

    When I say nuts, it is between 17 and an infinite value, manufacturing an amplifier with less than 17, one must be ... very bad unless using an output transformer of poor quality!

    It is not because an amplifier will "show" a DF of 100000000000000000000000 or even greater, that it will handle bass properly!

    Neither if an amplifier has a DF of 20!

  6. #6
    Senior Member Ian Mackenzie's Avatar
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    Well that did something, Jeepers

    But the L100 misses the limelight again, Where are Bo and Tooths when I need them? Presumed missing in action.

    Reading the links to other threads, high damping factors and particularly varying with frequency may not be a good thing.

    Giskard, thats a nice review of the Aleph 3 and actually made one a while back. If you want a nice amp for your 4435 to biamp, thats the one.

    I saw many nice things at Passlabs, its was like a memorable experience, just watching the them build those great big poweramps. The biggest I saw was an X Series 600, thats a 600 watt mono block...this kinda say it all....a total mind f$%K

    The output follower stage consists of 48 power Mosfets per channel for a total of over 7200 watts short term dissipation. The power supply features a single massive toroidal transformers rated at 4 KVA, and over 180,000 uF of storage capacitance.

    Damping factor 60 ref 8 ohms nominal

    This stuff sounds really good as I found out at the invitation of Mr Pass.

    Ian
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    Senior Member Ian Mackenzie's Avatar
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    I am not here to promote Passlabs by the way but they seem to mate well with JBLs.

    Giskard, are you aware of Gt's attitude to amps and bass?

    Ian

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    Originally posted by Ian Mackenzie
    Giskard, are you aware of G.T.'s attitude to amps and bass?
    I'm pretty sure he likes bass, and I think there are a few amps out there he likes as well.

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    Originally posted by Ian Mackenzie
    I am not here to promote Passlabs by the way but they seem to mate well with JBLs.
    Ian
    Pretty interesting price on the XA200!

    Definitely in the audiophile range.

    John

  10. #10
    PSS AUDIO
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    Originally posted by Ian Mackenzie
    The output follower stage consists of 48 power Mosfets per channel for a total of over 7200 watts short term dissipation. The power supply features a single massive toroidal transformers rated at 4 KVA, and over 180,000 uF of storage capacitance.
    I am not here to promote PSS amplifiers but those numbers are quite normal as our next studio amplifier (2x150W/8ohms) will receive:

    2 x 1600 VA transformers,
    2 x 100 000 MF of storage capacitors (and perhaps more if we have some extra place on the PCB),
    2 x 6 output transistors (MJ15024) for a total of 7200 watts LONG term dissipation - 5A per transistor, it means 30A²x8=7200W per channel!

    Those numbers are made for the catalogue and it does not mean that an amplifier with such numbers will sound GOOD!

    Our will do ... from what we are said by several listeners!

    And his pricing is very honest!
    Last edited by PSS AUDIO; 06-07-2004 at 07:58 AM.

  11. #11
    Senior Member Ian Mackenzie's Avatar
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    Well the off topic now is going off topic.

    I though the comment in the literature about keeping some resisters handy in a pocket was interesting.

    I think the DCR or DCX as referred to in some literature, has to be taken into account when we are trying to assess and subject bass performance.

    ie DCR can be a good thing, an it can be a bad thing.

    If the drivers have un avoidably low QT its certainly one way to retune the enclosure, I did that with the Altec 515, the Qts was 0.17 as I recall.

    I doubled the Dc of the voice coil an ended up getting a usable response without having to resort to mis alighment

    The effective damping at FB appears to be sensitive to amplifer damping at least with some speakers.

    I have tried this with the 2245 woofer, but we are talking a magnitude of 0.5-0.8 ohms added DCR, thats 6 5 - 10% the value of the impedience, and 10% to 15% the coil DCR.

    The differences below 0.3 ohms added DCR are less discernable but sublte tonality and bass extension rather than bass over hang, for a nominal 8 ohms thats a Damping Factor of 26.

    Of course we are talking about added pure DCR to the exisiting network which in reality is not always the case. Depending on the speaker system and tuning, there most likely will be a threshold where the effect of DCR is such that it causes noticable ripple in the low rolloff response ( a bit like tuning the box a bit too high).

    These effects can be simulated in BassBox, and have to be considered with the box losses (fibre glass & leaks)

    Ian


    Last edited by Ian Mackenzie; 06-07-2004 at 02:54 PM.

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    Administrator Mr. Widget's Avatar
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    Hi Yuri,

    Since you are in the amplifier business I assume you have had a listen to the Pass Labs products. I know that Nelson Pass's stuff is audiophile and not Pro Sound, but it is highly regarded in both worlds. I have seen manufacturers use the Aleph amplifiers at AES Conventions to best show off their speakers or other gear. In fact Sony/Phillips used five or six of them to showcase SACD a few years back before SACD was released.

    What are your impressions of the Aleph and other "High End" amps?

    Widget

  13. #13
    Senior Member Ian Mackenzie's Avatar
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    Yuri would need to locate a Passlabs dealer for a demonstration , they can be found at Passlabs.com.

    The Aleph series has won countless awards in hifi circles. The newer X Series are far more powerful, up to 1000 watts and beyond when used together. They are benchmarks for Stereophile and Absolute Sound. The latest AX version uses concepts from both the Aleph and the X Series.

    Okay, here is an idea, I will have a look on diyaudio for a member who is in Yuri's area and see if we can organise a demonstration of a Aleph amplifier.

    Yuri, where do you live, drink red wine and entertain woman.

    The Aleph is now discontinued line and the diyaudio members have built some Aleph amplifiers for diy purposes. The design remains the interlectual property of Neslon Pass, however he is such a gentleman and a generous scholar of diy that he allows us mere formites to enjoy sharing his vast knowledge.

    The fact that I was able to met Pass at his firm in the Sierra's and tour the Passlabs facility was a rare treat, and then hosted some evening entertainment at his house, that was special.

    He is known in the industry as the Wizzard.

    Pass started out his career in audio designing crossovers for ESS, he then went on to form the Threshold Corporation, Telarc used the renouned Stasis amplifers for their cutting heads, in the early 1990's Pass formed a new company by his own name. From what I could gather Passlabs is one of the few hi end amplifer manufacters that has survived and flourished without entering the home theatre market.



    Ian
    Last edited by Ian Mackenzie; 06-07-2004 at 07:29 PM.

  14. #14
    Senior Member Ian Mackenzie's Avatar
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    I would love to hear from anyone else who has evaluated any amplifers for the purposes of bass peformance.

    Perception is 9/10 of reality after all.

    I recall the much loved Crown 300A was well regarded for bass end being able to drive 2 ohms, and in the same era the Harman Kardan 16, the kit version of the Dynaco 400 (Rob has one I think), the Marantz 510 monster, the Sae range and of course the Phase Linears.

    These days big power amps appear to have shrunk physically and grown in power. Such is the pace of technology and economics, but a BIG amp is a real turn on for me,and the girls likem......hey mate, I bet that one's got Big Balls. Yep.

    Unfortunately, power and it would appear finesse do not necessarily go hand in hand

    Actually, John Nebels nice Macs are BIG and they are transformer coupled. I recall the bass was quite articulate on all his wives.

    Perhaps John can give a us a run down on the Macs and his recent experiences..

    Ian

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    Originally posted by Ian Mackenzie
    I would love to hear from anyone else who has evaluated any amplifers for the purposes of bass peformance.
    Well, some of us here are sold on Crest amps, (at least in any range I can afford). I'm also a bass player, so I'm always interested and highly critical in that area. And though I really like them for general stereo also, I haven't ever done any really low-level listening, where undesirable artifacts would be most noticeable. But IMO they can't be beat for real honest output when driven at maximum for hours on end, and also for general stereo use... Note that since selling out to another "beatrice foods" of the audio industry, Crest now also makes lots of other low-cost amps that probably aren't worth looking at too much... But their top of the line stuff is real good.

    John

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