Impedance Matching Question

atmasphere - thanks for your additional info, made an inquiry to Rolls about the bandwidth, but have not heard back. The box, RCA's, solder, and assemble would be no problem, however getting the proper transformer is beyond my expertise.

George - the preamp is an old VTL Maximal with a 5K ohm output impedance. I have tried a few amps with it. One was a 75 watt Belles with a 25K ohm input impedance. The result was poor, soft, rolled off, and no dynamics. That amp sounded great with a SS preamp. Surprisingly, the best sound with the VTL has been with the 18 watt power amp section of an Advent 300 receiver, quite a bit better than the Belles on the same speakers. It's input impedance is 100K ohms, so that proved to me that proper impedance matching is important. Thanks for the links to the buffers, however as I said previously, more than I want to spend in the location.

koestner - thanks for the info, that Burson RCA cable looks intriguing. Appears that it would solve the problem and it might be entertaining trying it on some other systems I have. I sold some cables in the past year, so it's easy to justify spending some of that money on new cables. :-)

VTL Maximal with a 5K ohm output impedance.

Wow that’s hi, I can understand it would be a no go (1:5) with the 25kohm of the Belles. But with an amp of 50kohms or higher (>1:10 ratio) as you found out with the Advent it was fine.

Remember back in those days the "industry standard" for input impedance of amps and preamp’s was 47kohm and that VTL would have been happy then as it was made then, and sources were very low in output volts phono ect and also high in output impedance, and you needed preamp’s for the extra gain they gave. But today gain is not the issue, as Nelson Pass says "we have too much."

Where today source have output stages that are the equal sometimes better than preamps, with high output voltage more than >2v, with low output impedance less than <100 ohms output impeance, and many amps today only need 0.5v to 1v for them to give their full wattage before clipping, and we have >2v available from our sources, do the math.

Cheers George

koestner
The Burson Buffer has not been made for quite a while now, and are hard to find. However Burson has this ingenious RCA cable with a small solid state buffer built into it. It is powered by 5 Volts DC. It will help with most any impedance mismatches.

Don’t know how good that would be, as it runs off the +5v usb supply, and from what I’ve seen it looks to be an opamp based buffer, and for audio these +5v single ended supply buffers are not too good, and I think they also would have to be capacitor coupled as they have dc offset with switch on/off thumps. 
Cheers George

George, thank you very much for your additional comments. I was already leaning toward not getting the Burson cable. I have found that the Polk Audio RTi A3 is on closeout for $240/pr, so not much more than the cable. It got an excellent review in Stereophile and made the Recommended Components list. It also has a real wood veneer cabinet, so definitely seems to be worth the current price. I'm thinking it's 89-90db sensitivity is likely enough that I'll just use the Advent 300 with the VTL. It's a small room and I don't need extreme volume. The Advent is surprisingly strong for 18 watts. Guess it was designed to have good current output since it was used with the original Advent speaker. Thanks again for your help.

Polk Audio RTi A3 is on closeout for $240/pr, so not much more than the cable.

Yeah definitely the money shot is for the speakers, how come we don’t get those kind of deal down here in Oz, it really ****** me off. Enjoy!


Cheers George