[magister]

I have a good tube amp (40 wpc) that I would like to use with my IV jr's, but it's not powerful enough in my largish room.  So I'm thinking about horizontal bi-amping, with a SS amp on the bottom.  I've never done this before.

The SS amp (NAD C 275BEE) I'm considering has an input trimpot to help keep the levels of the woofers and mid/upper in balance.  I was hoping I wouldn't need an external crossover, but some of the articles I've been reading say this is really necessary to get the benefits of bi-amping.  I'd appreciate any enlightenment that folks here can provide!

Thanks - David

[Delacroix]

David

Welcome to the VSA Circle here on AC. Since this question comes up a bit, I've moved an older thread on this up to the top as a 'sticky'. Albert gives some advice on this matter in that thread which you likely will find useful.

We do like new members to give us a little bit of intro too, so how about some background on your gear, music likes, and what got you to this point. Lots of helpful folks here.

Best

Patrick

[magister]

Thanks for the sticky, Patrick -- very useful.  I'm going to take the plunge and bi-amp, but may be back here for more help . . . I am reassured that one of the responses to Albert's original post mentioned good results with a NAD amp, a newer version of which I am considering, along with a tube amp that sounds similar to mine.  If I understand correctly, I don't need to worry about an external crossover, despite what I've read elsewhere.

I'm not really new here, just haven't posted in a long time.  Never felt the need to replace my IV jr's!  If anyone cares, my system is:

C-J Premier 17 preamp
SimAudio Moon phono stage and power supply
SOTA Sapphire turntable
Marantz SA8003 SACD player
Golden Tube SE-40 amp -- will be used with the upper/mids
VSA VR IVjr speakers

I have been using a pair of Transcendent Sound tube monoblocks (150wpc).  These are quite good amps but one blew a tube recently and apparently took some other bits of the amp out along with the tube.  While I'm waiting for the one monoblock to get fixed, I got my old SE-40 out of the closet.  The sound quality is terrific (harmonic richness etc.) but at 40wpc it won't handle the IV jr's in my largish room.  So I decided to investigate biamping.  I particularly like like acoustic music of many types (classical, folk, a little jazz), especially vocal music.

David

[JackD201]

There are three members here named dante, randybarba and vintage_dog that have done so with success. If you can't reach them here you can reach them via PM at www.wiredstate.com. Good luck!

[magister]

I've just purchased the NAD solid-state amp that I mentioned and am ready to bi-amp.  What's the best method to be sure that the two amps are in balance, aside from listening?  I have a Radio Shack SPL meter so I could take some measurements, but am not sure how to do this.

Thanks - David

[htradtk]

David,

Nice system! What speaker cables are you using? This past spring, I purchased a pair of the VSA Masterbuilts to be used with my VR-5 Anniversary speakers. Let me say that I thought I had great sound before, but after a few weeks with the Masterbuilds, my soundstage really opened up. My Anni's are currently at the the VSA factory as Albert and crew are upgrading them to the MKII specification. I surely do miss them! Enjoy.

Henry

[Jaco Pastorius]

David,
just trust your own ears! That is what counts.I like this possibility to dial in a balance that suit me,my room,my taste,my daily mood,and so on.
Do you have a volumcontrol on the tube amp? Many tubeamps have higher gain than SS amps,so worst case you might not be able to get the bass amp loud enough,but hopefully it will be no problem.

Rune

[magister]

Thanks, guys.

@Henry: I am using cables by Joe Mazzaglia of Auricle Audio.  They work well in my system, sounding noticeably better than the Nordost Blue Heaven that I was using before.  These are "minimalist" cables -- relatively small wires, no garden-hose style dielectric; kind of like the Mapleshade or Anti-cables, if you've seen those.  For whatever reason, they work, and they are very good value for the money compared to many cables on the market.  I have not heard the VSA cables, unfortunately.

@Rune: Ears will be the final arbiter, of course.  But it would be nice to get in the ballpark when I put the two amps together in the system.  My SS amp, an NAD C275BBE, does have a variable gain input, although the tube amp doesn't.

The VR-IV jr manual says that for bi-amping, if the two amps have input sensitivities that are fairly close, things should work out OK.  My tube amp has an input sensitivity of 100kΩ.  The specs for the NAD amp say that, If the variable gain selector is enabled, it also has an input sensitivity of 100kΩ.   (But is that true for all settings of the input volume pot, or only for the maximum?)

David

[srb]

The VR-IV jr manual says that for bi-amping, if the two amps have input sensitivities that are fairly close, things should work out OK.  My tube amp has an input sensitivity of 100kΩ.  The specs for the NAD amp say that, If the variable gain selector is enabled, it also has an input sensitivity of 100kΩ.   (But is that true for all settings of the input volume pot, or only for the maximum?)

The 100K Ohm spec is the input impedance.  The input sensitivity for the latest model NAD C 275BEE is 1.2V which is the input voltage that will produce the full rated power.  I didn't read the VR4 Jr. manual, but I would think that the spec that would need to be matched between the amplifiers is the gain, which is 29dB for the NAD.
 
Steve

[magister]

Thanks, Steve, and my apologies for not proofreading before hitting the "Post" button.  My quotation from the VR IVjr manual is accurate, though.  The input sensitivity of my tube amp is 1V, which I hope qualifies as "fairly close" to 1.2V.  I am trying to find out the gain of my tube amp, which is not given in the specs in its manual.

David

[roscoeiii]

This response to a post I made in an Audiogon thread may help:

From Almarg on Audiogon:

   Roscoeiii: Am I understanding input sensitivity correctly, as follows?: The higher the input sensitivity (say 2V to reach full power, as opposed to 1V to reach full power), the more travel I will have in my preamp volume control. So someone without sufficient fine tuning in volume control or who wants to move out of the 8-10 range and more into the 10-1 o'clock range should try to find an amp with higher input sensitivity.

    Do I have this right?

Almarg: Yes, provided that "full power" is the same in both cases.

But just to confuse the issue further, your statement would be more precise if it referred to a higher input sensitivity NUMBER, rather than to a higher input sensitivity. A higher input sensitivity number, properly speaking, corresponds to lower sensitivity. In other words, a more sensitive amp is one that requires less input voltage to reach full power.

 Roscoeiii:   I am not clear on if input sensitivity can give an idea of the amount of gain in dB (and what other specs might be needed to calculate dB gain from input sensitivity).

Almarg: If gain is not explicitly specified, and it often is not, it can be calculated to a reasonable approximation from the specified sensitivity and the specified maximum power capability.

As you realize, gain is the ratio of output voltage to input voltage, expressed in db.

The ratio of two voltages, V1 and V2, are converted to db based on the formula (20 x logarithm(V1/V2)).

The rated maximum output power into 8 ohms can be converted into voltage based on the equation P = (Vsquared)/R, where P is power in watts, V is volts, and R is resistance in ohms.

So for example in the case of an amplifier rated at 200 watts into 8 ohms and having 2 volt sensitivity, if we represent the output voltage corresponding to the 200 watts into 8 ohms as "Vout" and the 2 volt sensitivity as "Vin," we have:

200 = ((Vout)squared)/8

From which it can be calculated that Vout = 40 volts

Therefore the gain in db is

20 x log(Vout/Vin) = 20 x log(40/2) = 26 db

That is an approximation, as I indicated, in part because it does not reflect margin that may be built into the maximum power specification. But it will generally be a reasonable approximation for most purposes.

Regards,
-- Al

[magister]

Thanks, roscoeiii -- this is  helpful.  It seems that the gain of my tube amp is about 20 dB, compared to 29 dB for the SS.

[magister]

Followup: I just set up the bi-amp configuration: Golden Tube SE-40 amp on top, NAD C275BEE for the woofers of my IVjr's.  It's doing exactly what I hoped it would, that is, giving the wonderful tube midrange with bass power and control.  Definitely worth doing!  One thing I did not expect: I play some tracks a little louder, based on the volume setting on my pre-amp.  One song I just played begins softly, and to keep the level that I am used to hearing I raised the level above what I normally played this track at.  Of course when it got loud later, it was really cooking.  If anything, I expected to lower the volume since I have more power available with the addition of the SS amp; now it seems that a greater dynamic range is available, which makes sense.  On music I know well, I can hear no imbalance or discontinuity between the upper and bass units. 

David