A tube headphone amplifier using 6080

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Heh was just back here to post the L-R, R-L remark :green:

Yes, the likelihood of the examiners finding the +20 year prior art these days is slim. I would task the forum with keeping the eyes peeled and being vocal if one of the semi manufacturers attempts a patent.
 
Just to clarify in case I'm not following your driver's internal logic

Left = (L-R)
Right = (R-L)
sleeve/common = -(L+R)

Your sleeve/common appears to be +(L+R) which fed into the minus earspeaker terminal would result in Left= +L-L-R-R for -2R rather than +2L. So L&R flipped sides and polarity.

JR
 
Now, if you put a variable pot in the middle (sum) channel you would get a variable stereo base expander for a cost of one pot...
 
[quote author="Wavebourn"]Now, if you put a variable pot in the middle (sum) channel you would get a variable stereo base expander for a cost of one pot...[/quote]

If merchandising some mojo for thousands of dollars you might want it to sound different... My original design was for monitoring while tracking so I went for same, just louder.

JR
 
If it agrees with the math, I guess. I'm too lazy to look inside 1240s.

I used opamps with real (to-220) power transistors in mine so I had some serious drive capability even into low Z cans.

JR
 
EDIT before hitting send, (composed before seeing mediatech's latest, but here it is):

Suppose we already have L and R signals that swing about rail-to-rail. Then this scheme doesn't help us, if we want to assure we never clip.

Why?

Well, take the two cases of L = R (even for a moment) and L = -R (again however briefly).

When L = R call the signal C. We drive our third wire with -2C---but wait---that overloads. So we have to drive with -2C/2 = -C. Meanwhile our L-R and R-L drives are each zero (C-C). The net can drive for each is just C, no different than we would have if the third wire were grounded.

When L = -R call that signal D and its inversion -D. We drive our third wire with -(D-D) = 0, meaning it is effectively grounded. Meanwhile wires one and two are driven with D-(-D) or 2D on the left and -D - D or -2D on the right. But this clips so once again we have to cut each by 6dB, so our net can drives are once again just what they would have been before resorting to this scheme.

What one could do: Use a crossover on each of right and left, do the scheme for low frequencies and not for high frequencies. Then one could realize the advantage of bridge drive and the approach towards ~6dB of bass enhancement, at the frequencies where localization is relatively unimportant. That is, at low frequencies we drive wires one and two with (L+R)/2 and wire three with -(L+R)/2, but at higher frequencies (L-R)/2, (R-L)/2, and -(L+R)/2, respectively. (EDIT so come to think of it only the wires one and two need the crossover treatment).

What would hang us here a bit would be some pathological bass mix that would undo our assumptions about monaural bass.
 
[quote author="mediatechnology"]A few housekeeping bits after a long, hot ride:

Three:
JohnR: Seems like this would have advantages for the following signal correlations:

L+R (mono) becomes 2(L+R)
L or R becomes either 2L or 2R

(These above are matrix gains from double-summation. They double our drive voltage.)*

The only time we don't obtain any added drive benefit is full L-R. L-R, obtained with identical polarity-reversed inputs, produces no output on the L+R, or common, power amp output.

Now here's where I'm a bit stumped: Since there's no added voltage gain from matrixing with a full L-R correlation, will we hear this? In this condition we're driving the transducers and our ears fully differentially. So maybe not.

..[/quote]

I'm not sure I follow what you're really saying but there is a little unfortunate physics or reality involved in that we have only three channel but need 4 discrete signals to really get 2x swing for all combinations.

Indeed if we were to configure for mono only we only need 2 discrete signals and can indeed get er dun...

The matrix I suggested gives good headroom increases for true L or R signals but mono will be similar to single ended.

How much of a benefit this delivers will depend on the musical mix. It seems the envelope should be dominated by monophonic bass, and the benefit limited but in practice it does make a difference. Not 4x power, but IMO a useful difference.

JR
 
[quote author="bcarso"]EDIT before hitting send, (composed before seeing mediatech's latest, but here it is):

Suppose we already have L and R signals that swing about rail-to-rail. Then this scheme doesn't help us, if we want to assure we never clip.

Why?

Well, take the two cases of L = R (even for a moment) and L = -R (again however briefly).

When L = R call the signal C. We drive our third wire with -2C---but wait---that overloads. So we have to drive with -2C/2 = -C. Meanwhile our L-R and R-L drives are each zero (C-C). The net can drive for each is just C, no different than we would have if the third wire were grounded.

When L = -R call that signal D and its inversion -D. We drive our third wire with -(D-D) = 0, meaning it is effectively grounded. Meanwhile wires one and two are driven with D-(-D) or 2D on the left and -D - D or -2D on the right. But this clips so once again we have to cut each by 6dB, so our net can drives are once again just what they would have been before resorting to this scheme.

What one could do: Use a crossover on each of right and left, do the scheme for low frequencies and not for high frequencies. Then one could realize the advantage of bridge drive and the approach towards ~6dB of bass enhancement, at the frequencies where localization is relatively unimportant. That is, at low frequencies we drive wires one and two with (L+R)/2 and wire three with -(L+R)/2, but at higher frequencies (L-R)/2, (R-L)/2, and -(L+R)/2, respectively. (EDIT so come to think of it only the wires one and two need the crossover treatment).

What would hang us here a bit would be some pathological bass mix that would undo our assumptions about monaural bass.[/quote]

If I thought they had a schematic in the owners manual I'd try to download one,,, right now specifics of this design have gone into my memory's dead letter dept.

Staring again from scratch we can ASSume worst case for clipping on sleeve is MONO signal, so lets reduce the drive on the common sleeve to -(L+R)/2 .

This makes L drive = L-(R/2) and R= R-(L/2),

Compared to 2 circuit only grounded sleeve, this gives us 1.5X for stereo or mono signals, more than twice the power.

Headroom is a bit of a mixed bag Mono will clip on the sleeve first, left only or right only will clip on the L or R line first but at the same amplitude.

Perhaps you could game this further by making assumptions about bass being mostly mono and HF mostly stereo but then you may not get the full 1.5X if Bass isn't mono or if HF is.

With this approach only real gotcha signal is if left is 180' out of phase or opposite polarity from right in which case clipping would occur in L and R legs at 2/3rds of 1.5x or roughly the same as a stock unit.

I'll take 2x power for only 50% more circuitry.

JR
 
[quote author="JohnRoberts"]Staring again from scratch we can ASSume worst case for clipping on sleeve is MONO signal, so lets reduce the drive on the common sleeve to -(L+R)/2 .

This makes L drive = L-(R/2) and R= R-(L/2),

Compared to 2 circuit only grounded sleeve, this gives us 1.5X for stereo or mono signals, more than twice the power.

Headroom is a bit of a mixed bag Mono will clip on the sleeve first, left only or right only will clip on the L or R line first but at the same amplitude.

Perhaps you could game this further by making assumptions about bass being mostly mono and HF mostly stereo but then you may not get the full 1.5X if Bass isn't mono or if HF is.

With this approach only real gotcha signal is if left is 180' out of phase or opposite polarity from right in which case clipping would occur in L and R legs at 2/3rds of 1.5x or roughly the same as a stock unit.

I'll take 2x power for only 50% more circuitry.

JR[/quote]

Again, although it may not occur frequently, it would seem that some would still want to avoid the clipping when the signals are L-R/2 or R-L/2, although clearly that's at higher signal levels than the L-R scenario.

It would be an interesting statistical study to look at real signals that are likely encountered. I know that for some synthetic surround signals there can be a lot of bass energy nearly in reverse polarity---it's a serious challenge to the reproducing system.
 
Indeed, but if there is significant content completely out of phase the headroom collapses to just normal, so it's not worse than 1x, only equal to or better, and I submit 180' between L and R is not that common. There is also out of phase content in delay based stereo synthesis, but again not that common.

I seem to recall a Madonna (?) CD that was recalled because they did some gimmicky super stereo separation trick that wasn't mono compatible.

WRT surround, I recall years ago when the local cable would crunch the stereo from some dolby surround action movies to hard mono without pulling the effects out first. It would be amusing (not) to see a large explosion on screen with almost no report. :roll:

Sorry to hijack this thread, I only meant to mention this in passing. I especially don't need to redesign my old work.

JR
 
[quote author="mediatechnology"]>I ran some tests with my Koss PRO-1s :thumb:[/quote]

as far as level, IMO the worst-case headphone is probably the 600ohm akg k240m. (this model happens to be my personal reference) alot of cheaper headphone amps can't put out enough *voltage* to get them loud enough (can't hear squat with an i-pod or the 1/8" jack on my laptop unless you are in a silent room.) in addition to being high-Z they are not sealed, so any environmental noise gets right in. I believe they are not making them at this point but as you know these were popular studio phones and there are probably a bunch of these still in use. IMO the newer 50 ohm version sounds very different to me, more bass, different character, not as good.
 

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