[oneinthepipe]

This is my stupid question of the day.

If simultaneously connecting two amplifiers to a preamp creates a deterioration in the quality of the sound, why does my Insight SL preamp have two sets of output jacks? 

Then, depending on the reason, would something like a tape buffer work on the pair of preamp outputs?

(If this has anything to do with HT, I don't know anything about HT, either.)

[boead]

powered sub.

Tape loop needs to be line-level.

My McAlister has two preamp outs and a line-level tape loop.

[Wayner]

If you have 2 identical power amps, this is a convenient "y" cable for bi-amping. It really is just the cost of 2 more audio jacks. For those interested in bi-amping, this is a cheap almost "freebe".

Wayner

[oneinthepipe]

But the AVA literature states that simultaneously connecting two amplifiers to a preamp will degrade the quality of the sound.  Does that also apply to the amplifiers in powered subs?  What do you do if the there is only one powered sub with a single input?  For bi-amping, doesn't there need to be another crossover?  I thought to bi-amp, a single set of preamp outputs were connected to the crossover's input, and then the crossover's outputs were fed to the separate amplifiers' inputs.

[Wayner]

No, it says that connecting 2 different amplifiers may effect the quality of the other amplifier. The reason is that many amplifiers have different impedance ratings and that will affect how the amps respond in a parallel configuration. If you have 2 resistors in parallel and they are of different values, they will produce a different value altogether.

Wayner

[oneinthepipe]

No, it says that connecting 2 different amplifiers may effect the quality of the other amplifier. The reason is that many amplifiers have different impedance ratings and that will affect how the amps respond in a parallel configuration. If you have 2 resistors in parallel and they are of different values, they will produce a different value altogether.

Wayner

Thank you, I didn't understand why that happened.  However, while the quality of the output of the preamp will be the same, the quality of the sound of one of the amplifiers, if they are different amplifiers, could be worsened.  Then, wouldn't that also apply when connecting to the amplifiers in powered subs, since those amps would be different than the main speakers' amp, or when there are different amplifiers in a bi-amplified system, such as a tube amp driving the top and a solid state amp driving the bottom, for example?

[avahifi]

Since users are often going to use powered subs, and the cost of providing them the convenience is very low, why not do it.  I am not as concerned with acoustic mixing of the signals inasmuch as the sub electronics will have a low pass filter first.

Frank

[DSK]

Using a single power amp with an impedance (Zin) of say 47K, the pre-amp sees a 47K load. If you connect an additional amplifier (eg. active subwoofer) with 30K Zin, the pre-amp now sees a more difficult 18K load. The calculation is (Zin1 x Zin2)/(Zin1 + Zin2)

The higher the output impedance (Zout) of the pre-amp, the tougher job it will have. If a pre-amp has a Zout of say 250 ohms and is driving an amplifier with 47K Zin, the ratio is '188 x'. But driving amps of 47K Zin and 30K Zin, the ratio will only be '73 x'. The higher this ratio is, the better the drive, dynamics, lack of compression etc will be. The preamp will have an easier time, a bit like using overdrive on the highway rather than 4th gear.

I read somewhere just recently that sound degredation is even greater when the second amp (or subwoofer) is connected but turned off.

An amplifier designer once told me that adding a second amp will compress/flatten the wave form and degrade the sound (I hope I have remembered that correctly). I interpreted this is meaning that adding a second amp (regardless of whether the same type as the first amp) WILL degrade the sound but to what degree,and whether it is audible, will depend on various factors like preamp Zout, Zin of each amp, and maybe even other factors that I'm not aware of.


I would love to hear Frank's views on this.

[avahifi]

AVA Insight and Ultra preamps have a low output impedance and high drive current and are not load sensitive at all.  The T8 tube preamp is designed for flat response into a 10K input impedance in parallel with a 1000 pF capacitive load.  This should allow driving most any combination of amplifiers but not necessarily all if they are unusually load impedance combinations.

The output impedance of Insight preamps is 100 ohms, 560 for the Ultras, both set by simple series resistors.

Regards,

Frank Van Alstine

[DSK]

AVA Insight and Ultra preamps have a low output impedance and high drive current and are not load sensitive at all.  The T8 tube preamp is designed for flat response into a 10K input impedance in parallel with a 1000 pF capacitive load.  This should allow driving most any combination of amplifiers but not necessarily all if they are unusually load impedance combinations.

The output impedance of Insight preamps is 100 ohms, 560 for the Ultras, both set by simple series resistors.

Regards,

Frank Van Alstine

Frank, thanks for the response.

Forgive me if this is a stupid question (I can barely spell EE), but does this mean that the AVA pre-amps' outputs are 'buffered'?

BTW. Still loving the Ultra DAC you sent me in October. 

[avahifi]

Nope, the Insight and Ultra preamp line circuits are essentially self buffering as part of the design.

Frank

[oneinthepipe]

What I would have liked, which after reading this thread appears to be contraindicated, is simultaneously connect both my Insight 440, which drives Salk SongTowers, and my Super 70i, which would drive Spendor S3/5, to my Insight SL, then merely power up one amp/speaker combination and leave the other amp/speaker combination turned off, thus switching between the two sets of amps/speakers. However, moving interconnects isn't very inconvenient.

[stereocilia]

Speaking of connecting subwoofers (hope this is not too much of a thread hijack), it is my understanding that the left and right signals need to be summed by putting a resistor (usually 1K ohm?) in line with each output before they are tied together to be mono.  I could be wrong, but I think this is what most plate amps do.  Does this reduce the channel separation in the preamp?