Bi-Amping Von Schweikert speakers

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duguyisheng

Re: Bi-Amping Von Schweikert speakers
« Reply #80 on: 2 Jan 2017, 02:22 pm »
I have been wanting to experiment with biamping but without a big expenditure and without worrying to much about sensitivities. After reading this thread, I found an older NAD amp as suggested on the board and it has a dial to adjust output for biamping. I then played some pink noise and using a multimeter adjusted the output so the readings on the upper and lower modules of my vr5 were about equal. it took just a few minutes to do this. For the top, I was using a BAT tube amp.

I am a believer. I knew the top amp was never strong enough to give me good bass. Now, I get good bass and the upper end sounds less congested (actually not congested) with big orchestras. Big difference. I am now ready to experiment with other big amps for the bottom. This has been a huge difference in my system.

kernelbob

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Re: Bi-Amping Von Schweikert speakers
« Reply #81 on: 2 Jan 2017, 11:29 pm »
I've been biamping VSA speakers for years, across three different models.  Currently, I'm using Tortuga LDR attenuators for both the primary preamp/controller that switches between inputs and another one with only one input to adjust the level of the bass amps.  I would recommend using a primary controller and bass amp attenuator that can be adjusted from the listening position.  Once you have the capability to fine tune the level of the bass amp relative to the mid/treble amp, you really come to appreciate the control.

I've found that different recording labels have very different approaches to the bass/mid-treble balance.  For example, the bass on Naxos recordings is unfortunately not as extended or dynamic as it should be.  In a word, it sounds polite.  I frequently bump the bass one or two dB's compared to, say, a London/Decca.  Similarly, different streaming services each have their own frequency profiles and often need a bass amp adjustment up or down a dB or so.

One other recommendation that I'd make is that the primary preamp/controller should include the capability to toggle the absolute phase of the system... from the remote.  Once you use that for a while, you won't want to be without it.  FYI, my Tortuga LDRxB has that feature.  The difference between the right and wrong setting is clearly audible on a reasonably good system.  Unfortunately, there's no consistency between labels (and even recordings within one label), so you'll need to confirm that you have the right setting for each recording.

Best,
Robert

mhconley

Re: Bi-Amping Von Schweikert speakers
« Reply #82 on: 19 Jun 2018, 11:49 pm »
From Albert Von Schweikert:
3.  The "secret" to achieve "killer" sound quality is to ensure that the amplifiers have exactly the same input sensitivity.  The amplifier with the lowest numerical rating, i.e. 100mV is much more sensitive than an amplifier with a rating of 500mV - the higher the number, the lower the sensitivity.  You'll need to reduce the higher sensitivity by using a series input resistor.  This can be installed inside your amplifier, directly at the RCA female jack leading to the input stage. If this sounds a little scary, then build an adaptor to house the resistor outside the amp.  If you contact Michael Percy at www.percyaudio.com, he will advise you on what you'll need to get from him.  Usually, a female RCA jack, a male RCA plug, a high quality metal film resistor, some plastic sleeving, and a short piece of high quality hookup wire is all that is required.  Basically, you're inserting the resistor between the "hot" connection from the female RCA jack to the male RCA plug, and then using hookup wire to connect the ground leads.  The entire assembly can be only a few inches long and installed into a plastic or Teflon sleeve to prevent short circuits.  This adaptor is inserted into the signal path between your preamp and the most sensitive amplifier. As you can infer from this description, the adaptor is used in between your interconnect and the input jack of the amplifier.
Michael Percy sells these parts for less than $100 for everything you'll need, and he'll also help you select the proper value of resistor to match the sensitivities.  Although this simple technique may sound like a "Micky Mouse" setup to "sophisticated" engineers that design chip OP AMPS and sell electronic crossovers to the PA industry, it is a very "pure" form of passive matching that will stomp the crap out of any electronic crossover I have ever tried.

Assuming I know the input sensitivity and gain of each amp - what is the math to calculate the resistor value?

Specifically, I am looking to use my DIY ICEpower 1000asp based monoblocks on the LF cabinet (2.96V input sensitivity) with a pair of VTA m-125 monoblocks on the HF cabinet (1V input sensitivity). From Albert's statement above the m-125 is more sensitive than the 1000asp so I need to add a series resistor to its inputs. Since I am building the m-125 from a kit I want to add the resistor inside the amplifier. What value will I need?

Martin
« Last Edit: 20 Jun 2018, 01:25 pm by mhconley »

KWF

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Re: Bi-Amping Von Schweikert speakers
« Reply #83 on: 16 Mar 2019, 05:14 pm »
It's been a few years since I originally posted in this thread, and I'd like to share what I ended up doing, along w/ some related observations, because I have solved this problem to my complete satisfaction, and perhaps someone else will find this information helpful.

Once you have the capability to fine tune the level of the bass amp relative to the mid/treble amp, you really come to appreciate the control.

Completely agree. This has been a guiding principle for me. I did not want any unnecessary component, not even passive attenuators, in the mid/treble signal path. Any adjustment should, ideally, take place on the solid state / bass end... but I was unable to pull this off, until, about two years ago, I found an add-on device to balance things out (see below).

Gear: I'm now on my second pair of VSAs, in this case VR4 SR MkIIs which I am in love with. Also, my tube and solid state amps have changed since I last posted... I now have a Cary tube amp on the top end and a Wyred4Sound solid state amp on the bottom.

A note re: the tube amp -- before I obtained the Cary, I had a Dared amp, and to achieve the correct balance between it and my solid state amp, I used passive RCA attenuators... I tried two different brands and a variety of db levels... since they were more expensive I expected Rothwells to sound cleaner, but to my surprise, the less expensive ones from Harrison Labs were a better fit for my system -- they simply were invisible, which is to say, if they added any sonic "veiling" (Albert's term) I could not hear it. However, once I switched to the Cary tube amp, I no longer needed any passive attenuators at all.

A note re: the solid state amp -- the Emotiva was a bit mushy, so I ended up going w/ a Wyred4Sound amp instead. I also have a really nice Parasound power amp which I've been quite happy w/ at my office running full range (i.e., not part of a bi-amp setup). I briefly tried it at home in place of the Wyred4Sound, and didn't care for it at all. In fact, I tried it on two separate occasions, because "on paper" it seemed to me that the Parasound was the better unit. Point being, do not assume all solid state amps are created equal (despite having similar or identical power ratings).

One other piece of gear worth mentioning is my pre-amp, an AR SP-16, which has a dual pair of outputs, i.e., perfect for bi-amping VS-es. And I'm guessing that for anyone who cares enough to bi-amp their VS-es, I don't need to point out that it's worth experimenting to find the right interconnects, especially the mid/treble pair.

Okay, having shared every bit of background info I can think of, here's what I ended up doing. As stated at the outset, my goal was to do all the "heavy lifting" on the bottom end, to allow the mid/treble signal path to be as simple as possible. So, I ended up purchasing an Eastern Electric BBA ("booster buffer amp")... the company is no longer in business, but you can find used BBAs typically in the $400-$600 range. For more information, see Doug Schroder's review here (https://www.dagogo.com/eastern-electric-minimax-bba-preamplifier-review/), though of course he was not contemplating using it as a bass adjustment component in a bi-amp scenario.

What I like about the BBA... 1. it's an amplifier, so it can boost the signal, as opposed to merely being a passive attenuator, and 2. it has both a "gain" and a "volume" control... I don't know what's going on technically, but in my system, "gain" equates to "punchiness" and "volume" equates to "boominess", and I tend to keep both controls in the 12-1 o'clock position, though depending on the recording I will sometimes go up to 2 or 3 o'clock w/ one or the other control. If I found that I was routinely wanting to push either gain or volume into the 4 o'clock range or higher (5 o'clock is the max), that would be an indication to me that it was time to insert a pair of passive RCA attenuators into the signal path between my pre-amp and the tube amp. (Which I had to do w/ the Dared tube amp, but not w/ the Cary.)

Between the gain and volume controls I can "sculpt" the bass to my liking on a track by track basis. Typically the adjustments are subtle (ranging between 12 and 1 o'clock), but the result is NOT subtle... I find that oftentimes the difference between "okay" and "incredible" is a small adjustment via the BBA.
« Last Edit: 17 Mar 2019, 12:01 am by KWF »

KWF

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Re: Bi-Amping Von Schweikert speakers
« Reply #84 on: 16 Mar 2019, 05:19 pm »
P.S. in case it wasn't clear in my previous posting, the audio chain on the top end is...

   pre-amp  >  tube amp  >  mid/treble

...and on the bottom...

   pre-amp  >  BBA  >  solid state amp  >  woofers
« Last Edit: 17 Mar 2019, 12:01 am by KWF »