BAT vk-3ix and Parasound Halo A21 match?

I've been torn about getting a preamp at all since the NAD works quite well as preamp (as it was designed to do). Just saw that stereophile just did a review of my DAC and gave what seemed quite favorable review - for whatever that's worth. I don't put too much value on reviews anyway.

My concern is am I adding less transparency and purity by adding another component in the chain. However my hope is the "tube" opens doors to the music for my Thiels as many claim it do for mixing the tube pre with SS amp. Fingers X'd. I've wanted to add a BAT for a while but they were out of my price range, and though I really didn't need it the price was right and I grabbed it. Worse thing that could happen is I end up with a nice piece of equipment.

Zd542,
My passive unit is a dual mono TVC that is completely balanced. My source is a Marantz SA8260 SACD player with RCA outs. The CDP outputs 2.2V whereas the A21 has a sensitivity of 1V for full output. Even with the RCAs in place from TVC to A21, the volts were 2.2 as it is now. I do not understand how the XLR affected the performance. So I assume that the A21 is optimized for XLR connection.
Yes, I love the TVC. The only negative against the TVC is - it does not have a remote...but who cares?
The XLR from TVC to the Parasound A21 made the biggest difference in my system. I should have done it on day 1 when I got the A21...but who knew.

Here's what BAT has to say on this issue:

"Is the requirement for minimum input resistance dictated by the output resistance of your preamps?

No. However, this is a popular misconception. It is common to apply some old rules-of -thumb to things like preamplifier to power amplifier interfaces and state that there should be some magic ratio between the output resistance of the preamp and the input resistance of its load. People commonly mention numbers in the 10:1 or 20:1 area, some as high as 100:1. Unfortunately, there is no truth to such claims. As many of us know, one can perfectly transmit a signal in a system where the load impedance is equal or even lower than the source impedance (witness any cable TV system). The unusual design of Balanced Audio Technology's preamplifiers allows their gain stages to drive loads with resistance much below what their specified output resistance ratings would imply. For example, the VK-50SE preamplifier can supply a load with 65mA peak current - an amount well beyond that of the great majority of preamplifiers on the market today. However, it is also important to understand the role of the output coupling capacitor, present at the output of BAT preamplifiers. It is the size of this capacitor that will dictate the minimum power amplifier input impedance, not the output resistance of the preamp."

Having owned a 3ix for several years, I've been down this road (even owned a BAT 250SE SS amp for a while.)

If you like the 3ix, I would not limit the amp search to those with 100k Ohm or above input impedance.

Atkinson measures the frequency response with a 600 Ohm load and 100k Ohm load, which is very unhelpful as no consumer amps are anywhere near a 600 Ohm load and most are below 100k Ohm. A 10k Ohm load would have shown the response to be down a few dB at the frequency extremes.

BAT's stated spec of 10k Ohm is a sensible minimum bound for the amp's input impedence. 66k Ohm is no problem for it at all.

Milpai,

I took a quick look at the specs on the A21 and found this: Input impedance: 33 k Ω unbalanced; 66 k Ω balanced. Even though your CD player is single ended, you can sometimes get away with running a SE component into a balanced component; without having to switch the balanced unit over to SE mode. I've tried it myself and it doesn’t always work, but when it does, it usually sounds much better. Honestly, I'm not sure why. The only technical reason that I can come up with for the better SQ is that when running in balanced mode, the impedance goes up. With the A21 in balanced mode the impedance is 66k at opposed to 33k for SE. The higher impedance should be an easier load for whatever component is upstream; in your case, that would be the SA8260. Keep in mind, though, that’s just by best guess and could very well be wrong.

Regarding BAT's statement as quoted in Dave's post:

It is also important to understand the role of the output coupling capacitor, present at the output of BAT preamplifiers. It is the size of this capacitor that will dictate the minimum power amplifier input impedance, not the output resistance of the preamp.

That is absolutely true. It should be noted, though, that he refers to output resistance, not output impedance. The effects of the output coupling capacitor will be reflected in output impedance, which is what John Atkinson measures.

"Is the requirement for minimum input resistance dictated by the output resistance of your preamps?"

No. However, this is a popular misconception. It is common to apply some old rules-of -thumb to things like preamplifier to power amplifier interfaces and state that there should be some magic ratio between the output resistance of the preamp and the input resistance of its load. People commonly mention numbers in the 10:1 or 20:1 area, some as high as 100:1. Unfortunately, there is no truth to such claims. As many of us know, one can perfectly transmit a signal in a system where the load impedance is equal or even lower than the source impedance (witness any cable TV system).

The key factor is how much the output impedance VARIES as a function of frequency. A purely resistive output impedance will not vary at all. An output coupling capacitor will cause the output impedance to rise at low frequencies, to a degree that may or may not be significant in relation to the load impedance.

The 10:1 rule of thumb guideline is, IMO, properly stated as follows: The input impedance of the amp should IDEALLY be at least ten times greater than the output impedance of the preamp, at the frequency for which the output impedance of the preamp is highest.

The frequency for which the output impedance of the preamp is highest will usually be 20 Hz in the case of a preamp having an output coupling capacitor, such as most tube preamps.

That goal will assure that there is not an impedance compatibility issue. If that goal is not met, the results may or may not be ok, depending on the specific numbers that are involved, and especially on how much the preamp output impedance VARIES as a function of frequency.

IMO, based on JA's measurements the 10K minimum load recommendation for this preamp is marginal at best, and I would not assemble a system that way. Dave, I believe that the 10K/leg input impedance of the Bryston amp you referred to would be 20K as JA and others generally define it (the sum of the two legs), and even that resulted in a few db of rolloff at 20 Hz, as you indicated.

Regards,
-- Al