HTTP/1.0 200 OK Content-type: text/html
Can't connect to database, trying again....
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
69.159.136.52
Hello all,Once again i must ask for your valuable expertise. Last year i bought a pair of mr. Slagle's AVCs (Autoformer Volume Control), which are exquisite. Now i needed a balanced output, so i hooked a 20K:20K interstage like in the schemo.
It works, but is it "legit"? I used 20K because i didn't want to load the sources much more than they already are with the AVC (about 10K Z).
I am rather confused about primary loading vs secondary output. I guess my setup won't be able to drive a true 600-ohm load? But i hope the output Z of the sources will be reflected at the output with minimal signal loss (is it insertion loss?). The combined load of the AVC and interstage is 6K66.
Follow Ups:
Hey Joris,Of course it is legit. As for the load the sources see, you have to remember the "20K' load is reflected back by the turns ratio squared so as you attenuate the reflected load goes up. At low frequencies the inductance of the autoformer will dominate and for the most part when driving tubed stages without adding additional loading resistors the primary L will be the only number of interest since the reflected load will be at least a magnitude larger.
I personally do not like adding impedance numbers to magnetic devices that will not be terminated with the defined load. It is one thing to put a 5K number on an OT that will see an 8 ohm load, but for an IT where the load is usually not the defined value, it just serves to confuse the matter.
Hello Dave,> > for an IT where the load is usually not the defined value, it just serves to confuse the matter < <
Yes you're right and as a newbie it did a lot. Any transformer just reflects impedances by its turn ratio squared. if you operate a 20K:20K for coupling a stage with 100K input Z at the secondary, then 100K will be reflected at the primary. From what i understand now the specified Z for transformers is the optimal conditions where the manufacturers specifications are met.I wonder what are the consequences of operating the primary below or above its nominal Z? IIRC reading in some hammond doc that above (20K IT at 100K) there's loss of power handling, below (20K at 10K)implies loss of frequency response. Maybe it is the inductance of the windings that comes into play there?
The consequences are easy enough to find out by measuring them. This is really the only way to get the answers you need.typically lowering the source impedance extends bandwidth but can also cause ringing and increasing the source Z does just the opposite.
loading gets more complex, since it has different effects on the extremes.
Hi, Do you really need to drive 600 Ohms ? If so, first try with this setup, that you seem to like. It's the sound that matters, not the theoretical stuff. If it works, someone will create a theory why it did work. If it does not, they will throw in some other theory.
If the impedance mismatch is great enough, you will know. There will be a level mismatch and sonic degradation. Then, you will try a plate to line transformer, say a 10-20K Primary/150-600 Ohm Secondary. If you should do that, let me have first grabs at those 1:1 interstage bridging trannies...
Happy Listening...
Hello and thanks for your input.You're right i don't need to drive a 600-ohm line, was just wondering if it was a pre-requisite for the "pro-audio XLR output" status. The unit drives a tube input stage, input Z in the 300K range i guess? My concern rose because i read that using a trans below nominal Z would cause a narrowing of the response band. Anyways the sound is good.
Sorry but the interstages have such wide uses i ought to keep them! :o) They are 5K/20K dual primary and secondary which is a very versatile configuration.
This post is made possible by the generous support of people like you and our sponsors: