[darkmoebius]

I've had an S&B TVC for a couple fo years now and love it. It works spectacularly with my upgraded Museatex Bitsream dac that has an output of 3V@300 ohms. My SET amps, Art Audio PX-25 & Welborne DRD 300B monoblocks, have inputs of 0.7mV@180k ohms and 1.5V@100k ohms, respectively. The problem comes when I use my Gram Slee Era Gold mkV phono preamp which has an output of 1.08V max(don't know the impedence).

This highlights one of shortcomings of all passive volume controls along with the varying impedance issues of TVC's.

Anyway, I've been planning on adding a fully balanced,  6GM8 version(24V battery powered), of John Broskie's Aikido amp into my TVC chasis as a switchable buffer/gain stage to maximize the preamps versatility.

[Edit: I missed your recent post on "CD Player Output Impedance and Opamps" which touches on buffers, Burson, and Jensen transformers]

But, I was reading the new 6Moons review of the Bent/Music First Audio TAP fully remote controlled TVC when I came across a mention of your upcoming Magnequest collaboration for an optimized TVC:

(To be complete, there's yet another form of transformer-coupled passive preamp that uses a 1:1 input transformer with a resistive attenuator plus fixed resistor across the secondary to create an idealized constant rather than varying load for the transformer and insure linear impedance matching regardless of attenuation. MagneQuest's forthcoming Ingot designed in collaboration with Steve Eddy is one such device and will eventually be offered with optional valve or battery-powered JFET buffer.)

The idea sounded brilliant even though I couldn't fully picture how it worked. But, something about that description tweaked a dark recess of my 1970's rotted Nerf ball of a brain. I'd heard something very similar before, but couldn't remember what or where. All I knew was it was long ago.

Late last night, I was going back through all the buffer designs I'd bookmarked over the years, and I stumbled across a little kernel of creativity that you'd dropped on the public years ago on another website(which shall stay unnamed).

As I stared at the design and read your description, and here's where "The Tao" comes in, bells began to ring. I understood! This is the buffer/amplifier that has become the new volume control:

You can also replace the fixed resistor R1 with a 20k ohm pot or stepped attenuator and call it Sistah Steve's Buffered Passive Preamp.

But, even better, and this is where kismet comes in, I just happen to have an exact pair of your (then) suggested Jensen 1:1 transformers sitting on my desk awaiting Eight Part Harmony.

Any advice or component changes (learned since back then) if I want to wire one up for comparison with my own S&B TVC? 

How much effect does the quality of the series/stepped attenuator across the transformers output have?

How does this volume control's sound compare/contrast with regular resitor based and TV's?

Should I point everyone to the old post/discussion?

[Steve Eddy]

Hehe. Kismet indeed.

But, even better, and this is where kismet comes in, I just happen to have an exact pair of your (then) suggested Jensen 1:1 transformers sitting on my desk awaiting Eight Part Harmony.

Any advice or component changes (learned since back then) if I want to wire one up for comparison with my own S&B TVC?

Well, first let me figure out what it is you're wanting to do exactly.

You started off by indicating that you weren't getting enough output from your phono stage and were looking to add some signal gain into the mix (i.e. John's Akido). However EPH has no voltage gain to speak of. And here you're saying you're wanting to compare it to your S&B TVC.

Are you still wanting to get some signal gain? Or are you looking to compare EPH with the S&B TVC and still use the Akido for gain?

Reason I ask is because depending on your answer, there may be a better use for those 11P4-1s you have.

se

[darkmoebius]

Hehe. Kismet indeed.

I've been waiting a long time to work that word into a post.

Well, first let me figure out what it is you're wanting to do exactly.

Nothing big, just make the perfect preamp! (just joking)

Sorry about the confusing post, I ended up mixing two seperate issues; 1) your Jensen buffered volume control, and 2) my TVC needing an optional gain stage for my phono.

In reality, to solve #2, I just need to get another phono pre that puts out a full 2V or better. Unless switchable, the 24V Aikido stage's needed 15dB gain would boost my dac's output to 6V. That's going to push the TVC deep into distortion territory below 40-50Hz. So that won't work.

So, back to #1. One thing I have noticed is that my TVC has amazing dynamics, transparency, ease, tonality, and space. But, I have also noticed that a few active preamps have greater drive (the tension or force within dynamics) and a "meatier" presentation.

I was wondering if your buffered transformer volume control(b-TVC) might have both the positive sonic traits of a TVC along with the drive and meat of an active?

If so, I'd like to use my pair of Jensen JT-11P4-1-1 to build a buffered preamp and compare it with my TVC.

One thing though, the spec sheet says the 11P4 has a typical input Zi of 11.8k Ohms and an output Zo of 3.36k Ohms at 1kHz. Would the constant load seen by the source be the 20k attenuator across the transformers secondary? What would be the output impedance?

hope this makes mroe sense

[Steve Eddy]

I've been waiting a long time to work that word into a post.

Hehe. Well glad I was able to help you there. It's certainly a word you don't see every day.

Nothing big, just make the perfect preamp! (just joking)

Oh is that all? Why didn't you say so?

Sorry about the confusing post, I ended up mixing two seperate issues; 1) your Jensen buffered volume control, and 2) my TVC needing an optional gain stage for my phono.

In reality, to solve #2, I just need to get another phono pre that puts out a full 2V or better. Unless switchable, the 24V Aikido stage's needed 15dB gain would boost my dac's output to 6V. That's going to push the TVC deep into distortion territory below 40-50Hz. So that won't work.

No, it wouldn't work too well that way, but I thought you were thinking of using the Aikido after the TVC rather than ahead of it. That'd still give you a lot of excess gain, but you wouldn't have to worry about saturating the TVC.

As for the phono stage, see if you can find out what its output impedance is. If it's reasonably low, say 100 ohms or so, what you could do is use say a 150 x 4 line output trannie wired 1:2. That would give you about 6dB more from your phono stage

So, back to #1. One thing I have noticed is that my TVC has amazing dynamics, transparency, ease, tonality, and space. But, I have also noticed that a few active preamps have greater drive (the tension or force within dynamics) and a "meatier" presentation.

Yes, that's been an observation made by a number of people out there.

I was wondering if your buffered transformer volume control(b-TVC) might have both the positive sonic traits of a TVC along with the drive and meat of an active?

Personally I think that it does. I've always thought that much of what people have liked about TVCs has had less to do with their acting as a volume control than their simply being a transformer. I mean, until the TVCs came along, input transformers were virtually nowhere to be found except in some pro gear and offerings from the likes of Jeff Rowland. Other than that, no one was using them, including DIYers.

If so, I'd like to use my pair of Jensen JT-11P4-1-1 to build a buffered preamp and compare it with my TVC.

Would you be up to buying a second pair of them?

Reason I ask is because the design has evolved a bit since the original. It's now fully balanced, push-pull using a Gilson source follower and has about 6dB of voltage gain. Here's the basic schematic:



Reason I asked about getting a second pair is that the 1:2 input trannie is made up of two trannies (which gives you the voltage gain). That's not an absolute requirement however. You could use a single transformer and a pair of 10k attenuators and let those form a virtual center tap.

Using a center tapped choke on the sources means it can only drive a balanced or transformer input, but you can also use a line output transformer with a center tapped primary which would allow it to drive both balanced and unbalanced inputs.

One thing though, the spec sheet says the 11P4 has a typical input Zi of 11.8k Ohms and an output Zo of 3.36k Ohms at 1kHz. Would the constant load seen by the source be the 20k attenuator across the transformers secondary? What would be the output impedance?

Yes, the load seen by the source would effectively be the 20k attenuator across the secondary accounting for the turns ratio and winding resistance provided you're driving a reasonably high load impedance with it. Output impedance would vary. First keep in mind that the output impedance given in the datasheet assumes the transformer is being driven from a 50 ohm source impedance. So output impedance will be higher for higher source impedances.

It will also vary depending on the position of the attenuator. If we assume a 50 ohm source impedance, and the output impedance of the transformer is 3.36k, which is the parallel combination of the transformer's raw output impedance in parallel with the 20k load impedance, that means that the raw output impedance of the transformer is about 4k ohms. So the worst case output impedance will be about 6k ohms when the attenuator is at about 60% of its resistance value.

hope this makes mroe sense

It deos. 

se

[darkmoebius]

No, it wouldn't work too well that way, but I thought you were thinking of using the Aikido after the TVC rather than ahead of it. That'd still give you a lot of excess gain, but you wouldn't have to worry about saturating the TVC.

Yeah, I thought about that, but it seems to be an inefficient solution. Reducing an already weak signal and then boosting it up multiple times beyond the original is asking for artifacts.

I'd rather start with sources of nearly equal, but sufficient output/headroom, and attentuate that signal going to the output amps. (provided your buffer is unity gain)

As for the phono stage, see if you can find out what its output impedance is. If it's reasonably low, say 100 ohms or so, what you could do is use say a 150 x 4 line output trannie wired 1:2. That would give you about 6dB more from your phono stage

I emailed Gram Slee about the output impedence, but he was a little circumspect in his answer:

"The Era Gold can drive down to 600 Ohms, but it won't give you the volume you're after if 1.5 V is required. You need a line stage such as an active preamp after it to do that. A passive will reduce your volume further. A battery preamp shouldn't be necessary as the Era Gold does it using a mains supply and has a gain of nearly 1,000 (due to RIAA EQ) at mains frequencies. Thus a preamp with a gain of 2 or 3 would have to be atrocious if it added hum or mains noise modulations."

I've always thought that much of what people have liked about TVCs has had less to do with their acting as a volume control than their simply being a transformer.

Now, there you go, ruining a great conversation by injecting some common sense     

You know, having had TVC's for 2-3 years and closely following the evolution since Thorsten L. first proposed the idea on Audio Asylum 5-6 years ago, I have never, ever, seen anyone mention that basic observation. Go figure

Would a line transformer load the source the same way TVC's do at low frequencies? Stevens & Billington have a table on their website that shows their TX-102 input impedence at 1kHz rising from 1.28M@-22dB to 2.5M@-46dB. I'm guessing that it is even higher at lower frequencies. That must really "take the load" off a sources output stage.

I think this has a lot to do with why many of us prefer the sound of TVC's - low level listening has a much more full body and bass to it. Of course, the polar opposite happens at extremely high levels of volume. Guess you can't have it all.

Would you be up to buying a second pair of them?

Hell, no!(joking)  Of course, I was going to spend a similar amount of money on Aikido PCB's, tubes, etc.  anyway.

Reason I ask is because the design has evolved a bit since the original. It's now fully balanced, push-pull using a Gilson source follower and has about 6dB of voltage gain.

Now, that's what I'm talking about!! 

That's actually why I bought the Jensen 11P4's in the first place. I wanted to run 30-40' balanced cables around my living room wall to my amps next to the speakers on the other side of the room. Balanced out from the TVC to the Jensens at my SET amp's inputs.

I like the new design, much more elegant. Drop Q2/Q3 2SA1837's and R2/R3 8 ohm 1/2 watts for a tranni.

Reason I asked about getting a second pair is that the 1:2 input trannie is made up of two trannies (which gives you the voltage gain). That's not an absolute requirement however. You could use a single transformer and a pair of 10k attenuators and let those form a virtual center tap.

Not sure I follow that completely. The input transformer in the new diagram is actually two identical transformers connected together?

Then, what is that on the buffer's output?  A choke? Or, just the secondary(or primary if turned backwards) of the second tranni?

Would I still use the JT-11P4-1's or hould I buy different models from Jensen(or whoever)?

Regarding sources, I've toyed with the idea of putting SE to balanced x-formers in their chassis, but that can get expensive. Of course, this hobby is expensive anyway.

Anyway, I like the idea of your new preamp.

[Steve Eddy]

Yeah, I thought about that, but it seems to be an inefficient solution. Reducing an already weak signal and then boosting it up multiple times beyond the original is asking for artifacts.

I'd rather start with sources of nearly equal, but sufficient output/headroom, and attentuate that signal going to the output amps. (provided your buffer is unity gain)

Agreed.

I emailed Gram Slee about the output impedence, but he was a little circumspect in his answer:

"The Era Gold can drive down to 600 Ohms, but it won't give you the volume you're after if 1.5 V is required. You need a line stage such as an active preamp after it to do that. A passive will reduce your volume further. A battery preamp shouldn't be necessary as the Era Gold does it using a mains supply and has a gain of nearly 1,000 (due to RIAA EQ) at mains frequencies. Thus a preamp with a gain of 2 or 3 would have to be atrocious if it added hum or mains noise modulations."

Yeah, that certainly wasn't a lot of help.

That it can drive a 600 ohm load would indicate the output impedance is on the lowish side. But unless you can confirm that it's not much more than 100 ohms or so I'd he hesitant to recommend using a 1:2 output trannie.

Now, there you go, ruining a great conversation by injecting some common sense     

You know, having had TVC's for 2-3 years and closely following the evolution since Thorsten L. first proposed the idea on Audio Asylum 5-6 years ago, I have never, ever, seen anyone mention that basic observation. Go figure

Well I guess it wouldn't quite be in the best interest of those pushing TVCs.

There's no question though that when having to drive a line a TVC will have an advantage over a resistive attenuator or a trasnformer coupled resistive attenuator.

Would a line transformer load the source the same way TVC's do at low frequencies? Stevens & Billington have a table on their website that shows their TX-102 input impedence at 1kHz rising from 1.28M@-22dB to 2.5M@-46dB. I'm guessing that it is even higher at lower frequencies. That must really "take the load" off a sources output stage.

The reason the TVC does this is because each position has a different turns ratio and a transformer reflects impedances as the square of the turns ratio. A fixed line transformer coupled to a passive attenuator has a single turns ratio and would present the same load to the source regardless of the position of the attenuator.

I think this has a lot to do with why many of us prefer the sound of TVC's - low level listening has a much more full body and bass to it. Of course, the polar opposite happens at extremely high levels of volume. Guess you can't have it all.

Oh yeah? Says who?

Now, that's what I'm talking about!! 

That's actually why I bought the Jensen 11P4's in the first place. I wanted to run 30-40' balanced cables around my living room wall to my amps next to the speakers on the other side of the room. Balanced out from the TVC to the Jensens at my SET amp's inputs.

Jeeebus! 30-40 FEET!? Sure you can't optimize your equipment placement a little better than that?

If you're going to be running 30-40 feet of interconnect, I'd recommend getting a second pair of those Jensens for no other reason than to fit them to the inputs of your amps.

Not sure I follow that completely. The input transformer in the new diagram is actually two identical transformers connected together?

Yes. As I said, it's a basic schematic.

The primaries are wired in antiphase parallel (i.e. the positive lead of one transformer primary connects to the negative lead of the other and vice versa) and the seconaries are wired antiphase series (i.e. the positive lead of each secondary form the two outputs and the negative leads are tied together as the center tap).

Then, what is that on the buffer's output?  A choke? Or, just the secondary(or primary if turned backwards) of the second tranni?

Well, there are three transformers total. Two input trannies wired together at the input, and the center tapped choke made from a single quadfilar output trannie.

Perhaps this will make it more clear for you:



Ideally I want to have a custom choke made for it as I'm simply using the wiring resistance of the output trannie to self-bias the JFETs and I'd like to have a bit more resistance. With the resistance as low as it is, the idle current for the JFETs is pretty close to their Idss and I'm not able to get the maximum voltage swing. But even so, it still works very well with the output trannies.

Would I still use the JT-11P4-1's or hould I buy different models from Jensen(or whoever)?

Oh no, the Jensens are just fine. I like the 11P4-1s as they have a slight amount of voltage gain and don't have the 2-3dB insertion loss that a 1:1 has. I've been trying to talk CineMag into making a similar transformer.

Also, unless you want that additional 6dB or so of voltage gain, you can just use one per channel rather than two.

Regarding sources, I've toyed with the idea of putting SE to balanced x-formers in their chassis, but that can get expensive. Of course, this hobby is expensive anyway.

True.

Though if you're going to be feeding your single-ended outputs into an input transformer, whether a TVC or something like EPH or the new Gilson follower, I really don't think there's any need to add output transformers to them. Cool thing about good quality input trannies, and unlike active balanced inputs, is that they can give you excellent common-mode noise rejection even when they're being driven from a wholly unbalanced source.

And as much of a fan of transformers that I am, I haven't found transformer/transformer interfaces to offer much benefit and have come to prefer them staggered between active stages, whether unbalanced or balanced. Though in the case of your phono preamp, a 1:2 output trannie would give the benefit of providing a bit more voltage gain.

Anyway, I like the idea of your new preamp.

T'anks!

se

[darkmoebius]

Jeeebus! 30-40 FEET!? Sure you can't optimize your equipment placement a little better than that?

Yeah, it's a quite a goal. The biggest roadblock is the cost of good balanced cables that long. As I said, it's a goal.

My room is 15'x20' with speakers along the short wall. I'd like to get the equipment rack and turntable as far away from my subwoofers as possible. Not to mention, across the room would place everything much closer to my lazy ass on the couch. Jumping up and sprinting across the room to flip LP's is a pain. This was it would only be two steps.

I'm having a pair of gigantic rear-loaded cornerhorns made in a few months (and I mean BIG) that will use vintage 15" RCA LC-1C coaxial drivers designed by Dr. harry Olsen back in 50's. The cornerhorns are supposed to 94dB sensitive at 26Hz. (see the design and cabinets here). Crazy frequency response.  Anyway, I want to get my turntable as far away from them as possible.

Well, there are three transformers total. Two input trannies wired together at the input, and the center tapped choke made from a single quadfilar output trannie.

As the beer commerical says "Brilliant!!" Ok,  get it now with the new diagram. Man, that's one elegant design - so clean & simple. Probably hides a lot of serious thinking underneath, though.

Ideally I want to have a custom choke made for it as I'm simply using the wiring resistance of the output trannie to self-bias the JFETs and I'd like to have a bit more resistance.

Might be worth waiting for then, unless I can find a nice, affordable pair of output trans for the mean time.

I like the 11P4-1s as they have a slight amount of voltage gain and don't have the 2-3dB insertion loss that a 1:1 has. I've been trying to talk CineMag into making a similar transformer...Also, unless you want that additional 6dB or so of voltage gain, you can just use one per channel rather than two.

Perhaps, I'll try it with the single JT's first and see how it goes, then if I need a little extra get more. Jensen's HQ is actually 40 miles from my house. Of course, 40 miles in Los Angeles can take 30 minutes or 3 hours depending on day and time of it.

But, I think 3V out of my dac and a 0.7V input sensitivity should do nicely.

Though in the case of your phono preamp, a 1:2 output trannie would give the benefit of providing a bit more voltage gain.

I've decided to get a new one anyway, so I don't think the boost will be needed. Maybe a used one of George Wright's tubed beauties.

One last question about the new diagram, I assume that it requires stereo attentuators for each channel or a quad deck for both.

[Steve Eddy]

Yeah, it's a quite a goal. The biggest roadblock is the cost of good balanced cables that long. As I said, it's a goal.

My room is 15'x20' with speakers along the short wall. I'd like to get the equipment rack and turntable as far away from my subwoofers as possible. Not to mention, across the room would place everything much closer to my lazy ass on the couch. Jumping up and sprinting across the room to flip LP's is a pain. This was it would only be two steps.

Ok, but why not go with longer speaker cables, or perhaps split the difference between speaker cables and interconnects? Just seems to me there's gotta be a better way than 30-40 foot interconnects.

I'm having a pair of gigantic rear-loaded cornerhorns made in a few months (and I mean BIG) that will use vintage 15" RCA LC-1C coaxial drivers designed by Dr. harry Olsen back in 50's. The cornerhorns are supposed to 94dB sensitive at 26Hz. (see the design and cabinets here). Crazy frequency response.  Anyway, I want to get my turntable as far away from them as possible.

Coolness!

Yeah, I saw those in the newsletter when it first came out. Too cool that Bill was able to get his hands on those hand written plans by Olsen himself.

By the way, you when you say "and I mean BIG" do you mean they'll be larger than the one in the plans?

As the beer commerical says "Brilliant!!" Ok,  get it now with the new diagram. Man, that's one elegant design - so clean & simple. Probably hides a lot of serious thinking underneath, though.

Well I have to give credit where credit is due here. The inspiration came from Susan Parker's work with her Zeus amplifiers and a 1978 patent by Warren Gilson. The main difference between the two is that Susan uses output transformers and Gilson used a center tapped choke so that the output is driven straight from the sources. I tried both and preferred the latter.

Might be worth waiting for then, unless I can find a nice, affordable pair of output trans for the mean time.

I'm using the CineMag CMOQ-1H which I think were only about $45 each. I could be wrong and that price could be for the 50% nickel version. But give CineMag a call and see what they want for the CMOQ1, 2, and 4. Any of them will work.

Perhaps, I'll try it with the single JT's first and see how it goes, then if I need a little extra get more.

That'll work.

Jensen's HQ is actually 40 miles from my house. Of course, 40 miles in Los Angeles can take 30 minutes or 3 hours depending on day and time of it.

Hehe. True. CineMag's in sort of the same neck of the woods in Canoga Park.

But, I think 3V out of my dac and a 0.7V input sensitivity should do nicely.

I think so too.

I've decided to get a new one anyway, so I don't think the boost will be needed. Maybe a used one of George Wright's tubed beauties.

Ah, ok. Any idea what the output impedance is?

One last question about the new diagram, I assume that it requires stereo attentuators for each channel or a quad deck for both.

That's correct.

If you're going to use a single JT per channel, each one would need to be 10k and if you're going to use two per channel, they each need to be 40k if you want to keep the same input impedance.

se

[darkmoebius]

Just seems to me there's gotta be a better way than 30-40 foot interconnects.

Well, I could put my rack mid-wall between the speakers, but that's no challenge, is that?   Actually, that's most likely how things will end up.

By the way, you when you say "and I mean BIG" do you mean they'll be larger than the one in the plans?

No, they'll be to the exact dimensions. No need to ad-lib on the good Dr's plans, he did know a thing or two about audio.

I've tracked down a pair of the LC-1C's that someone is interested in selling. They aren't in perfect condition, some of the conical radiators on the cone are dented. Although, Bill assured me it won't make a noticable difference. One thing for sure, they aren't cheap.

Well I have to give credit where credit is due here. The inspiration came from Susan Parker's work with her Zeus amplifiers and a 1978 patent by Warren Gilson.

I remember when she started that inspiring thread, really cool idea. I followed it really closely early on - came very close to building some, but I decided to upgrade other parts of my system instead.

I'll check with CineMag on those chokes Monday or Tuesday.

When it comes to phono preamps, what sort of upper output impedence would be best? You mentioned earlier that an output "of not much more than 100 ohms" wouldn't work so well with the 1:2 transfo.

[Steve Eddy]

No, they'll be to the exact dimensions. No need to ad-lib on the good Dr's plans, he did know a thing or two about audio.

True enough. Just that when you said "and I mean BIG" I'm thinking something on the order of the Jensen Imperials. Or a Tannoy Westminster or something.

I've tracked down a pair of the LC-1C's that someone is interested in selling. They aren't in perfect condition, some of the conical radiators on the cone are dented. Although, Bill assured me it won't make a noticable difference. One thing for sure, they aren't cheap.

They're sure not. You can thank the Japanese for that.

Speaking of Japan, did you see that JBL/Tokyo photo essay a while back?

I remember when she started that inspiring thread, really cool idea. I followed it really closely early on - came very close to building some, but I decided to upgrade other parts of my system instead.

Yeah, though she sure had her detractors early on.

I'll check with CineMag on those chokes Monday or Tuesday.

Chokes? You ask them about chokes and they're not going to know what you're talking about. They're line output transformers. I just wired them up to work as a center tapped choke.

When it comes to phono preamps, what sort of upper output impedence would be best? You mentioned earlier that an output "of not much more than 100 ohms" wouldn't work so well with the 1:2 transfo.

Yeah, because a 1:2 stepup increases the output impedance by a factor of four. But if you're going to get a new phono preamp that has sufficient output for you that you don't need any additional gain then that's not a concern. So I'd recommend no more than 600 ohms if possible. 1k as the absolute max.

As source impedance increases, it reduces your low frequency response and increases low frequency distortion.

se

[darkmoebius]

I woke with several questions I should have asked at the beginning of this thread, in reference to the difference of "drive" or "dynamic tension" between most passive and actives:

1. Why doesn't the resistive pot in most active preamps cause the same HF rolloff/source loading problems as resistive passives?
2. Is it the following 12-15dB gain in actives that provides the sense of "drive" and "dynamic tension"?
3. Is it the active stage, period that provides that sense?
4. Would a unity gain buffer with high input impedance/low output impedance before a TVC add the active sense?

Just that when you said "and I mean BIG" I'm thinking something on the order of the Jensen Imperials. Or a Tannoy Westminster or something.

Thank God, I don't have to go that big! I'm on thin ice around here to downsize as it is. I've agreed to just one main system and am hoping the corner horns will get back a lot of the living room real estate my current setup is hogging. Currently, 30% or more of the room is taken up with my IM-Bens + dual subwoofers. But, these RCA's will really have to kick ass in all areas, not just bass, to outperform the Cain & Cains.

Speaking of Japan, did you see that JBL/Tokyo photo essay a while back?

Yep, someone should arrange vacation packages/tours for things like that.  I applaud the Japanese's fanaticism and dedication, but damned if they don't make it expensive for the rest of us.

Yeah, though she sure had her detractors early on.

There were a lot of "experts" who were dead-set that it couldn't work without every really thinking it through or trying. Susan did a great job of maintaining composure, I'm not sure many men could have done that without getting personal. She calmly tried to answer all questions and provide masurements.

re: phono impedance -

So I'd recommend no more than 600 ohms if possible. 1k as the absolute max.

Man, I was looking at phonos last night, that's a tough requirement. Most I could find were in the 1k to 2k impedance range, if they provide the number at all. Seems like only the really best have real low output impedance.  I can afford ~$1,200 new or used.

No input impedance spec:
Art Audio Vinyl One - no spec
Eastern Electric MiniMax - no spec
Dynavector DV PHA-200 - no spec
EAR 834P - no spec
JA Michell Delphini Pro - no spec
Juicy Music Xtreme - no spec
Sutherland PHD - no specs at all
Whest PhonoStage .20 - no spec

Low outout impedence:
Art Audio Vinyl Reference - 200 0hms
Audio Research PH-3 - 200 ohms/30V(?)
Audio Research PH-5 - 200 ohms/50V(?)
Herron Audio VTPH-1 - 500 ohms
Pass labs Aleph Ono - 300 Balanced/Single-ended
Trichord Diablo - 33 ohms


Oddly,

[Steve Eddy]

I woke with several questions I should have asked at the beginning of this thread, in reference to the difference of "drive" or "dynamic tension" between most passive and actives:

1. Why doesn't the resistive pot in most active preamps cause the same HF rolloff/source loading problems as resistive passives?
2. Is it the following 12-15dB gain in actives that provides the sense of "drive" and "dynamic tension"?
3. Is it the active stage, period that provides that sense?
4. Would a unity gain buffer with high input impedance/low output impedance before a TVC add the active sense?

Not sure I can say with any confidence exactly what's responsible for sense of "drive" and "dynamic tension." Keep in mind that I'm really not much of a "detail" sort of listener. I just go by the whole experience, the "gestalt" if you will, without trying to break it down into bits and pieces. I've never found any particular need for that and I'm afraid that if I did, I might end up hopelessly neurotic about audio as all too many have already become.

But to answer your question about high frequency rolloff, the problem, or rather the potential problem when you're talking about a separate, "passive preamp" in the form of a simple pot or resistive attenuator is the capacitance of the cable used to connect it with the power amp or whatever else you may be connecting it to.

The shunt capacitance of the cable forms a low pass filter. The cutoff frequency will depend on both the capacitance of the cable and the source impedance that's driving the cable. For a given capcitance, the higher the source impedance the lower the cutoff frequency. Similarly for a given source impedance, the greater the capacitance the lower the cutoff frequency.

The pot in an active preamp isn't driving significant lengths of cable and its assicated capacitance.

Thank God, I don't have to go that big! I'm on thin ice around here to downsize as it is. I've agreed to just one main system and am hoping the corner horns will get back a lot of the living room real estate my current setup is hogging. Currently, 30% or more of the room is taken up with my IM-Bens + dual subwoofers. But, these RCA's will really have to kick ass in all areas, not just bass, to outperform the Cain & Cains.

Yeah, that may be a rather tall order. Hope it works out for you!

Yep, someone should arrange vacation packages/tours for things like that.  I applaud the Japanese's fanaticism and dedication, but damned if they don't make it expensive for the rest of us.

Yeah. Back in the 70s and 80s the Japanese made out like bandits literally buying up tons vintage American gear that at the time was either being sold for next to nothing or simply being thrown out.

There were a lot of "experts" who were dead-set that it couldn't work without every really thinking it through or trying. Susan did a great job of maintaining composure, I'm not sure many men could have done that without getting personal. She calmly tried to answer all questions and provide masurements.

Yes, she more than held her own and went above and beyond the call of duty there.

Man, I was looking at phonos last night, that's a tough requirement. Most I could find were in the 1k to 2k impedance range, if they provide the number at all. Seems like only the really best have real low output impedance.  I can afford ~$1,200 new or used.

Yeah, sadly 1k to 2k is to be expected from most of the tube based gear.

I was always a bit puzzled by the tube guys shrieking in horror at the mention of so much as a 10k load. And they'd simply faint at the thought of a 600 ohm load. I found it somewhat amusing that tube gear was supposed to be so great, yet somehow it couldn't manage what a 25 cent opamp could do.

Then I got to thinking about the days before transistors. Professional audio equipment used tubes exclusively, yet 600 ohm loads were commonplace in professional audio. So one day I asked how on earth the professional gear was able to manage this.

The answer?

Transformers!

So it's not tubes that are the problem, but rather the anemic, limp-wristed designs that have become the status quo. Much easier and cheaper to use an RC coupled output than a transformer coupled output. And with 100k and higher load impedances being commonplace, there's little incentive for the status quo to change.

se

[darkmoebius]

While looking around for alternative phono preamps, I suddenly came to the realization that there is no reasonable way to make my TVC work with a range of phono cartridges(even w/ an active stage).

S&B states:

The limit of the input voltage to the TX-102 depends upon the exact frequency and also the source impedance. For a source impedance of 600 Ohm and the unity gain connection a maximum level of +20dbu (7.75V RMS) is permissible above 40Hz before distortion becomes problematic, at 20Hz +14dbu (3.875V RMS) are permissible.

My GS Era has +41.5dB gain and the EXP stepup has +24dB.

Output of my cartridges(needed gain to get to 2V):
Grado "The Statement" - 0.50mV (72dB)
Denon DL-103D         - 0.25mV (78dB)
Cartridge Man MM3     - 4.00mV (54dB)

So, my EXP steup + GS Era Gold = 65.5dB gain leaving me -6.5dB & -12.5dB short of what I need for the Grado and Denon. The Cartridge Man actually has +11.5dB too much gain(7.5V) with those two and -12.5dB with just the Era Gold.

That means I would be attentuating 0.47V/0.60V signals for all ~4mV/5mV MM cartridges out there with just the Era's 41.5dB. With 0.25/0.5mV MC cartridges and the full 65.5dB gain, I would be attenuating 0.47/0.94V signals.

If I added a +12.5dB Aikido stage before the TVC, I would be in overloading territory(3.9V) with 0.5mV MC carts due to the TVC's 3.875V RMS limit at 20Hz. I'd assume dynamic peaks could easily overshoot that mark.

Am I right?

What is the input level limit for the Jensen transformers? The spec sheet says the maximum 20Hz input level is +16dB, but I don't what the base voltage they are working from. Could your preamp handle the 3.9V max input?

[Steve Eddy]

Yeah, it could handle 3.9 volts. By the way, dBu is referenced to 0.775 volts, so to convert a dBu figure to volts, it's 0.775 x 10^(dBu/20). S0 16dBu would be about 4.9 volts.

Anyway, I'm not sure I'd worry too much about the S&B. You're assuming that any 20Hz content on the source material will be there at full peak level. Other than perhaps some test records, I think that will be a pretty rare occurrance.

se

[darkmoebius]

Yeah, it could handle 3.9 volts...I'm not sure I'd worry too much about the S&B.

Then, it looks like we've got a nice preamp shootout in the makings - straight TVC vs. Aikido TVC vs. Buffered transfo VC.

[Steve Eddy]

Then, it looks like we've got a nice preamp shootout in the makings - straight TVC vs. Aikido TVC vs. Buffered transfo VC.

A three-way, eh? That'll make for some rather nasty crossfire. 

se