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I think i have some impedance(?) issues with my S&B based preamp...my amplifer's input is 47KOhm,
the CD's output stage is solid state so I think it can handle the load...for some reason the sound becomes blurry with the S&B...
Follow Ups:
Hello!I usually don't post here about the commercial stuff I do (I sell S&B stuff for North America) but I did not have any way to e-mail or PM you and did not want to leave you hanging!
The S&B is usually anything but blurry so something is definitely going on!
Extreme DC offset could maybe be the cause but I have not played with this so I don't know how it would sound. Measure your CD player output with a track paused (some players mute or disconnect the signal when not locked to a disk). Although the Transfomer pre-amp is not supposed to see any DC the Dac's I have read 1 to 2 mV or so typically at the outputs and have been working just fine. I suspect other users are also feeding small amounts of DC to the units without problems. It is something to check though.
A few other things to check - Do both channels behave the same? Does the unit function as you'd expect?
Please e-mail me with the full description of your setup and we'll try to get to the bottom of it.
Many Thanks!
John Chapman
john@bentaudio.com
perhaps your CD output is direct coupled and has got some DC and the transformer is overloading it? That (little) DC may not have showed up as a problem going directly into the amp or pre-amp's input previously.
...my autoformer volume control has not been a universal improvement everwhere I've tried it. It sounds fantastic in my system, but it has sounded *awful* in two other systems. SS or not, your CD player may not like the low load impedance presented by the transformer. Also, are you taking care that the transformers are not magnetically interacting with other transformers, or even each other? Try moving them or reorienting them.
If you don't have it already, toss a 600 Ohm resistor across the signal and ground on the output. This, if not done already, will increase the amount of current through the transformer.
If you don't have it already, toss a 600 Ohm resistor across the signal and ground on the output. This, if not done already, will increase the amount of current through the transformer.Er, why would you want to increase the current through the transformer?
se
hehe... just bustin' your balls.
Well, a couple reasons. These things are spec'd at a 600 Ohm load, and IIRC, these types, at lower levels, will act as a near-infinite load to the source, and cause some freq. extreme rolloff. Also, my experience has been that with a line-level signal, somewhat more current going through it tends to sound better (assuming the wiring remains overspecified for the amount of current).And as to sounding better? I put a 500 Ohm load on my own transformer-coupled passive design (Check out the 'Love Kitten' in Valve right now) and it sounded WAY better that way. More natural and less harsh, while retaining the extreme detail. So good, that someone who originally preferred a 7k tubed pre to the passive changed over, and now prefers the passive- the only change was the load resistor. In fact, I'm building the guy a cost-no-object version to replace his (extremely good) old pre.
So, in the end, whatever the reason, my own tranny coupled pre sounds WAY better with the load resistor.
hehe... just bustin' your balls.Oh, so that's what that was. I thought I was getting a case of jock itch. :)
Well, a couple reasons. These things are spec'd at a 600 Ohm load, and IIRC, these types, at lower levels, will act as a near-infinite load to the source, and cause some freq. extreme rolloff.
How it appears to the source depends on the transformer in question. In the case of the TX-102, it has either a 1:1 or 1:2 turns ratio (referenced to the highest tap). If it's wired 1:1, then a 600 ohm resistor across its secondary will appear as roughly a 600 ohm load to the source at the highest tap. In 1:2 mode, it will appear as roughly a 150 ohm load (both figures don't account for winding resistance which will add to those numbers).
Most tube sources and many solid state sources can't handle a 600 ohm load let alone a 150 ohm load.
Also, my experience has been that with a line-level signal, somewhat more current going through it tends to sound better (assuming the wiring remains overspecified for the amount of current).
But to have more current flowing in the transformer means having more current flowing from the source and depending on the source, it may not be able to deliver it and could get severely loaded down. Particularly tube sources.
And as to sounding better? I put a 500 Ohm load on my own transformer-coupled passive design (Check out the 'Love Kitten' in Valve right now) and it sounded WAY better that way. More natural and less harsh, while retaining the extreme detail. So good, that someone who originally preferred a 7k tubed pre to the passive changed over, and now prefers the passive- the only change was the load resistor. In fact, I'm building the guy a cost-no-object version to replace his (extremely good) old pre.
That's all well and good but the transformer used in the Love Kitten is a bit of a different animal than the TX-102. Its impedance ratio is 15k:500 which means it has a turns ratio of about 5.5:1 (in other words, it's a 5.5:1 step-down transformer). So if you put a 500 ohm resistor across its secondary, you get 15k ohms across the primary which is a very easy load even for tube sources.
So, in the end, whatever the reason, my own tranny coupled pre sounds WAY better with the load resistor.
But that 500 ohm load resistor isn't presenting the source with a 500 ohm load impedance as it would be with the TX-102. Try that 500 ohm load resistor on a 1:1 trannie and then tell me how it sounds. :)
se
Ah. That is something I was overlooking. Those variable impedance suckers can make big trouble for someone who's had a few.... I was overlooking the top settings, perhaps a bad idea to have such a low load resistor.... but then you still get some really high impedances, and likely a little rolloff.... perhaps a 10k load resistor might do the job without dropping loading down too low.
What do you think of the Love Kitten, btw? Pretty elementary, I know, but where it has enough level, it's a really great sounding, elegant solution. Your input is welcome, seeing as you use iso trannys, so know a bit about iron.
Best!
Jeff
Ah. That is something I was overlooking. Those variable impedance suckers can make big trouble for someone who's had a few.... I was overlooking the top settings, perhaps a bad idea to have such a low load resistor.... but then you still get some really high impedances, and likely a little rolloff.... perhaps a 10k load resistor might do the job without dropping loading down too low.Yes, for something like the TX-102, a 10k load on the secondary would work ok for most anything.
By the way, you keep mentioning high impedance and rolloff. What impedance exactly are you saying is high? The input or output impedance of the transformer?
What do you think of the Love Kitten, btw? Pretty elementary, I know, but where it has enough level, it's a really great sounding, elegant solution. Your input is welcome, seeing as you use iso trannys, so know a bit about iron.
I agree it's a simple, elegant solution. The source sees a sufficiently high input impedance and the transformer gives you a much lower output impedance than you'd get from a resistive attenuator.
The only caveat is that you need to have quite a bit of excess voltage gain to throw away.
By the way, another transformer that would work in this same type of "preamp" is the Jensen JT-10K61-1M.
se
The high impedance I refer to is the input impedance of the preamp.
Those Jensens look like a great cost-conscious alternative.
The 'Love Kitten' has not yet fallen short, level-wise, despite its very lossy nature.
Best,
Jeff
The high impedance I refer to is the input impedance of the preamp.Ok. It's possible I'm overlooking something obvious, but I fail to see how a higher input impedance can result in greater rolloff.
Those Jensens look like a great cost-conscious alternative.
I suppose. I've no idea what the MQs go for. They don't seem to have any information about them on their web site.
The 'Love Kitten' has not yet fallen short, level-wise, despite its very lossy nature.
Amazing what a few tabs of Viagra can do. :)
se
My understanding was that an extremely high load will cause rolloff with some sources. If nothing else, it would seem to make the capacitance of the ICs more relevant.The MQs are $200 the pair, wound with continuos cast copper magnet wire (6 9s, long crystal) use nickel laminates (or cobalt for a bit more $).
Yeah, the Love Kitten is great with the blue pills.... Waitaminnit... tradition causes the cobalts (cobalt oxide is blue, IIRC) to be called "blues" over on Bottlehead.... maybe I should call the cobalt version the Viagrified Love Kitten, rather than the Super Love Kitten. hehe...
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