[Albert Von Schweikert]

From Albert Von Schweikert:
Hello Fellow Audiophiles,
Over the past 32 years, I've used bi-amping as a method to achieve more realistic sound quality.  A decent, high powered solid state amplifier will give you explosive and tight bass power, while a smaller tube amp will give you the "air" and image float you are seeking from your sound system.  Here are a few tips:
1. The bass amp does not have to necessarily be expensive, but make sure it has a large transformer and power supply to ensure "tight" bass.  All of our speaker designs employ 4-ohm woofer systems, with a dip down to 3.5 ohms, so make sure the amp is stable into a 4 ohm load.  Power requirements depend on your room size and how loud you want to go.  I suggest 200-300 watts per channel if you have a large room and want an explosive dynamic range.
2. The tube amplifier can have as little as 20 watts per channel in a small room, but in a large room, you may want to have 50-100 watts per channel to avoid clipping at high volume levels.  Due to the distribution of power over the frequency range of 20Hz to 20kHz, you can use a much smaller amplifier on the midrange and tweeter module.  Use the 8-ohm taps on the tube amp, but feel free to experiment - it won't hurt anything to try other taps.
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.
4.  Brands and Models: basically, put your money into the tube amp, since even inexpensive solid state amplifiers have stiff power supplies and enough quality to drive woofers with high speed transient response, high volume levels without clipping, and tight bass.  Twenty years ago, Adcom built a 200-watt amplifier for around a thousand bucks new, and half that price used.  Today, there are many expensive amplifiers that sound great, but you're paying for an expensive chassis, face plate, branding (advertising), and so forth.  Instead, look for an amp with a large transformer and high quality power supply.
Tube amplifier choices abound, at all price ranges.  Some of the best values are from China if you are on a budget, but large American tube amps from long established companies will be a good investment, with good resale value and the ease of repairs. Don't worry about the availability of tubes, they're going to be around for another 50 years or more due to the ever-expanding market for tube amplifiers.
Happy Listening from Albert Von Schweikert

[JackD201]

Hi Albert,

I'm asking this question on behalf of "you know who" and his VR-11 SEs. He'll have a 7m (W) x 11m (L) x 4m (H) listening room being built from the ground up to be acoustically treated as a recording space as opposed to a control room. He also likes listening fairly loud at times. If he were to use amps with these input sensitivities for the bass modules:

         1.076 Volts RMS ± 2% for 220 Watts into 8 Ohms.

Which of the three below would work under the conditions noted above

         0.85 Volts RMS ± 2% for 30 Watts into 8 Ohms. (Single Ended Triode)

         1.2 Volts RMS ± 2% for 80 Watts into 8 (Push-Pull)

         0.775 Volts RMS ± 2% for 18 Watts into 8 Ohms. (Single Ended Triode)

and also

Would there be a need for extensive modification/manipulation of input sensitivities required or would the higher sensitivity to the preamps output actually help balance out the discrepancies in wattage with regards to the SET amps?

Thanks in Advance!

Michael

*for others reading this my name is Michael John. I get my nickname from my second name

[slinco]

Hello Albert! Great to have you join in the discussion here.

I've been bi-amping my MkI VR4jr's for about a year now and the results are truly fantastic. I can heartily recommend the NAD C272 for bass duties. It's a screaming bargain at $750 new, and around $350 used. It's rated at 150W continuous into 8 ohms, but NAD amps are well known for their "dynamic headroom"  - NAD specs it at 410W @ 4 ohms and 520W @ 2 ohms. This amp is ideal for bi-amping because it has a gain control on the back with +/- 12dB adjustment, making it a snap to balance it with the M/T amp. This also gives the option of boosting the bass a dB or two if you're a bass head like me, or to compensate for a bright room.

For the top end I'm using an AES (Cary) AE-25 Super Amp Signature DJH. It's a triode wired push-pull amp rated at 35W with KT88 tubes, and a bit less (25W or so) with the EL34's that I'm currently using.

The sound? Nothing short of breathtaking - all the beauty of a triode amp up top with deep, rich bass and explosive dynamics. I couldn't be happier with the sound.

Some of you may also be interested to know that the M/T cabinet of the VR4jr can also be driven with a "flea power" amp. I've used a 3 watt "spud amp" (6cl6/6197 tubes), also matched with the NAD on the bass, and the results surprised me - great sound and plenty of volume (LOUD!!). The M/T cabinet must be a very easy load to drive.

[mfsoa]

The M/T cabinet must be a very easy load to drive.

I don't know if this observation means anything in reality, but I try to stare at the midrange driver at loud volume and it doesn't move. You can feel it move with your hand but it doesn't do much.  So yeah, it seems like the M/T isn't taking too much power.

Thanks for the flea-power comment - Makes me more interested in getting my amp rewired for triode.

-Mike

[Delacroix]

I've been bi-amping my MkI VR4jr's for about a year now and the results are truly fantastic. I can heartily recommend the NAD C272 for bass duties. ....
For the top end I'm using an AES (Cary) AE-25 Super Amp Signature DJH. It's a triode wired push-pull amp rated at 35W with KT88 tubes, and a bit less (25W or so) with the EL34's that I'm currently using.

Hi slinco -- what are you using as a preamp here?

[slinco]

Hi slinco -- what are you using as a preamp here?

I bounce back and forth between a Monarchy Audio NM24 and an NAD C162. The Monarchy is also my DAC (fantastic!!), and has a minimalist tube linestage that's very pure and pristine sounding, and fabulous with great recordings. Definitely puts the spotlight on bad recordings though, and being more of a music lover than an audiophile I find the NAD suits me better more often than not. It's also got something the old fashioned side of me enjoys - defeatable tone controls. It's really a great sounding preamp, a real sleeper.

Oh yeah, the C162 also has two sets of pre outs, one of which is adjustable 0dB to -12dB for bi-amp matching. Very versatile.
When I want to listen to the Monarchy linestage I have to use a Y-connector from it's single pre-out.

[PLMONROE]

Albert, If you were bi-amping a speaker with tubes on the top that had a 300hz crossover and then added to the mix a ss powered sub woofer below 80hz I guess you would actually be tri-amping. My question for this set up is -- which type of amp would you recommend  for the 80 to 300hz range, ss or tube?

Paul

[PLMONROE]

Anyone else have thoughts on which type of amp would be the better choice?

Paul

[JackD201]

That is the range where Mr. Punch lives so I would say Solid State

[PLMONROE]

That's kind'a what I was thinking too.

Paul

[JakeJ]

Is there a formula that I can calculate the resistor value to match one amp's sensitivity to another. Amp 1 has a rating of .72 VRMS for full output and Amp 2 is 1.5 VMRS for full output. I just need to change one resistor and I'd rather not put a potentiometer in due to mounting issues.

So, how do I match two different amplifiers?

Thanks,
Jake

I probably should post this in the Lab circle. 

[Delacroix]

Is there a formula that I can calculate the resistor value to match one amp's sensitivity to another. Amp 1 has a rating of .72 VRMS for full output and Amp 2 is 1.5 VMRS for full output. I just need to change one resistor and I'd rather not put a potentiometer in due to mounting issues.

So, how do I match two different amplifiers?

Thanks,
Jake

I probably should post this in the Lab circle. 

Hi Jake, if you get an answer from anyone in the lab section, be sure to point it our way. All I know, from asking Victor K at BAT about biamping was that he told me not to think about input sensitivity but to try instead to match the gain on any two amps used. He was of the view that small gain differences might not even be noticeable but if they were, attenuators could be used. Reading Albert's post above has given me more food for thought, so I'd love to hear from others more knowledgeable than I am.

[blownrx7]

This thread is very  interesting to me because I have seen so many other opinions that seemed to make it very complicated to bi-amp.
Active crossover, bypass the internal speaker crossover, set the crossover frequency above the speaker crossover frequency, etc, etc.

Now here comes Mr Von Schweikert.  Certainly someone we all feel is an authoritative source of knowledge and he promotes the easiest of solutions to implement. Now, I don't need to stress over buying yet another piece of equipment (the crossover), and I don't have to mess with the internals of the speaker and I don't have to figure out if the crossover frequency I've chose is correct.

All I have to do is run the amps to the speakers and if the amps have different sensitivities, pop in a resistor. What could be easier?
Am I missing something?
If someone get the resistor value formula, please post it here.
TIA

Proud VR4.5 owner

[randybarba]

I probably should post this in the Lab circle. 
[/quote]

Hi Jake, if you get an answer from anyone in the lab section, be sure to point it our way. All I know, from asking Victor K at BAT about biamping was that he told me not to think about input sensitivity but to try instead to match the gain on any two amps used. He was of the view that small gain differences might not even be noticeable but if they were, attenuators could be used. Reading Albert's post above has given me more food for thought, so I'd love to hear from others more knowledgeable than I am.

[/quote]

A problem that I find is that not all manufacturers put both input sensitivity and gain in their specs. For example, Mcintosh only puts input sensitivity while BAT only puts gain. So if I were to biamp using amps from these companies for example, I wouldn't know how to match their amps. Is there a formula to derive gain from input sensitivity and vice versa?

[Albert Von Schweikert]

Albert, If you were bi-amping a speaker with tubes on the top that had a 300hz crossover and then added to the mix a ss powered sub woofer below 80hz I guess you would actually be tri-amping. My question for this set up is -- which type of amp would you recommend  for the 80 to 300hz range, ss or tube?

Paul

Hi Paul,

I would go solid state for 80Hz to 300Hz - that midbass range needs to be tightly controlled.

AVS

[Albert Von Schweikert]

Hi Albert,

I'm asking this question on behalf of "you know who" and his VR-11 SEs. He'll have a 7m (W) x 11m (L) x 4m (H) listening room being built from the ground up to be acoustically treated as a recording space as opposed to a control room. He also likes listening fairly loud at times. If he were to use amps with these input sensitivities for the bass modules:

         1.076 Volts RMS ± 2% for 220 Watts into 8 Ohms.

Which of the three below would work under the conditions noted above

         0.85 Volts RMS ± 2% for 30 Watts into 8 Ohms. (Single Ended Triode)

         1.2 Volts RMS ± 2% for 80 Watts into 8 (Push-Pull)

         0.775 Volts RMS ± 2% for 18 Watts into 8 Ohms. (Single Ended Triode)

and also would there be a need for extensive modification/manipulation of input sensitivities required or would the higher sensitivity to the preamps output actually help balance out the discrepancies in wattage with regards to the SET amps?

Thanks in Advance!

Michael

*for others reading this my name is Michael John. I get my nickname from my second name

Hi Michael,

Depending on the actual gain of the amplifier's input and output stages, the most sensitive amplifier (as rated by "input sensitivity" in mV) may be the loudest amplifier in a "passive bi-amp" configuration. However, as we don't know the actual gain configuration of these amplifiers, the closest input sensitivity value would be the "best guess" at this time.  It is actually best to use a solid state bass amp with a higher gain and input sensitivity, and use an outboard attenuator to reduce this amplifier's output, see below.

In truth, the best choice for a tube midrange/tweeter amplifier would be the amp that actually has the best sound quality driving the midrange-tweeter enclosure of the speaker, int his case, our VR-11SE.  The volume level differences can be handled by using an external attenuator to find the correct resistor value, then installing that value into the input jacks of the amplifier.  However, for best results, the amplifier designer should be consulted, as adding a resistor inside the amplifier may void the warranty, while using the outboard attenuator will not. 

Channel Islands Audio, one of the Audio Circle Members, offers the VPC-3, which can be inserted in the signal path before the amplifier that is playing the loudest. Use Pink Noise and a RTA (or your ears) to match the levels of bass-to-midrange/treble. 

I have found that using the attenuator for the bass amplifier works the best, since the very slight sonic "veiling" is not readily apparent in the bass, but is more audible in the upper midrange/treble area.  This is not due solely to the potentiometer in the attenuation box, but also the extra connections and necessary interconnects.  In the bass range, the added "veil" is not audible.


Best regards,

AVS

[mfsoa]

Hi all,

I got some good advice from the Lab here:  http://www.audiocircle.com/index.php?topic=59057.0

I was making the mistake of thinking linearly when that's not the case. See Mr. Jeffreybehr's helpful comment at the bottom of the page.

-Mike

[JackD201]

Hello Albert,

This reminds me of a conversation we had some time back and the possibility of you designing a stand alone amp that uses the primary amp as the input stage of the solid state bass driver. This would guarantee a match with practically any amp of less current or voltage. You have done this for the DB-100 and DB-99 SEs. I think it would make for a great option for all double stacked models. Even the triple stacked VR-11s. I remember when Keith and I hooked his 99s up to 220wpc Lamm Hybrids and the sound remained as ballanced as with 3 watt 2a3s. The difference was that they were playing so cleanly even at extreme levels, Security finally showed up.

If you want to build up a prototype. I volunteer to do some beta testing. Do make 'em pretty from the get go though because in all probability I'll buy them! The thought of using VR-9s with the 30 watt Lamm ML3 GM70 SETs bi-amped this ways has got me in agony while the thought of using them with SRs and say a QUAD II is just as enticing. :twisted:

Jack

[es347]

I am just about to pull the trigger on buying a VR-4 SR MK II but have questions...1) if I biwire (or I think you can even biamp with the MAC 252 amp) running separate cables to the mid/high freq top unit and the bottom bass unit, where does the crossover or filtering occur?  Long ago I owned Snell Type A speakers which also had separate mid/tweeter and bass cabinets.  I biwired them but had to use an external crossover.  What am I missing here?...2) I am looking at McIntosh electronics but am wondering if there is a better way to go...Classe? McCormack?  I am not particularly fond of tube amps...sorry to those tubers here...2) I have listened to Wilson watt puppies/sophias, B&W 802D and Martin Logan summits most recently and would be interested in hearing, if anyone has heard any of those, how the VR-4 SR MK II sound compares.  I have never heard the AVS speakers as we have no dealers here.  If someone would care reply rather quickly it would be greatly appreciate as I my trigger finger is itching badly.  Thanks in advance for your replies.

[JackD201]

I am just about to pull the trigger on buying a VR-4 SR MK II but have questions...1) if I biwire (or I think you can even biamp with the MAC 252 amp) running separate cables to the mid/high freq top unit and the bottom bass unit, where does the crossover or filtering occur?  Long ago I owned Snell Type A speakers which also had separate mid/tweeter and bass cabinets.  I biwired them but had to use an external crossover.  What am I missing here?...2) I am looking at McIntosh electronics but am wondering if there is a better way to go...Classe? McCormack?  I am not particularly fond of tube amps...sorry to those tubers here...2) I have listened to Wilson watt puppies/sophias, B&W 802D and Martin Logan summits most recently and would be interested in hearing, if anyone has heard any of those, how the VR-4 SR MK II sound compares.  I have never heard the AVS speakers as we have no dealers here.  If someone would care reply rather quickly it would be greatly appreciate as I my trigger finger is itching badly.  Thanks in advance for your replies.

Hi ES,

You won't need an external crossover. The High Pass circuits are are on the MT modules and the Low Pass Circuits are on the bass modules. I really don't want to ruffle any feathers by comparing the SR IIs to the speakers you've mentioned. I mean I'm bound to since clearly I'm biased!   Just let me say that before I became a dealer, I auditioned loudspeakers from all three companies you mentioned (and many more) and was left unsatisfied. I heard a pair of VR-4 Generation 2s at a friends house and never looked back.

So what did the VRs do that the others didn't? Well to me they sounded more coherent, had realistic weight, didn't have any phase-y artifacts, had a more substantial soundstage (tactile as opposed to pseudo-visual) but, as the ultimate compliment , had me just enjoying the music instead of acting like a high school student dissecting an amphibian. As always, your mileage may vary!

Best of Luck and Happy Hunting!

Jack

Oh by the way, VRs go very well with both Mc'Is  and Mc'Cs if you like palpable midranges with nice oomph Never heard them with Classe amps though. If clarity and top-end sweetness is your cup of tea then Plinius is a good option too.