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Old 29th March 2003, 12:43 PM   #31
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Default Apologetics and All That!

Hi Guys
Apologise for the delay, promise I will get back asap and post the info that I promised. Been very busy in making 'stock' of JLTi Tube Hybrid Amps as making a living must take precedence.

Next week-end things should start to happen.

Regards to All

Joe

PS: I was asked where the 'War is failure, not a strategy' came from. It was during an interview on a Sydney radio station, 30th January this year, by James Taylor, you know, of 'Fire And Rain' fame and brother of Livingstone Taylor (Chesky).

Hey, if I may quote myself this time: 'Make Music, Not War!'
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Old 29th March 2003, 10:41 PM   #32
Nielsio is offline Nielsio  Netherlands
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Go Joe!
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Old 13th April 2003, 10:10 AM   #33
Nielsio is offline Nielsio  Netherlands
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From Joe's site:

----------------------------------------------
The JLTI Tube Hybrid Amplifier will also, hopefully in time, be joined by another JLTi Product (same looks, using Gainclone Technology) which is code-named:

The NASSP

"Not A Surround Sound Processor"

This is not multi-channel, but it is stereo for audiophiles. A product that will produce an inaudible dispersive, delayed and diffused soundfield (not the same as soundstage, but more like an energy thing) that enhances the true naturalness of stereo. I repeat, this is not surround nor multi-channel, far simpler, less expensive and above all, an audiophile solution. Keep in touch with this web site over the next few months as development progresses. Two local Australian audiophile loudspeaker manufacturers are involved in this most exciting project.
----------------------------------------------

Rings a bell for anyone?
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Old 13th April 2003, 10:18 AM   #34
AKSA is offline AKSA  Australia
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Joe,

I wish you the very best with your product! I have followed your progress for some years from south of the Mason-Dixon, and I am very impressed.

Cheers,

Hugh
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Old 13th April 2003, 01:43 PM   #35
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Quote:
Originally posted by AKSA
Joe,

I wish you the very best with your product! I have followed your progress for some years from south of the Mason-Dixon, and I am very impressed.

Cheers,

Hugh
Thanks Hugh, that's very kind of you, I think I'm blushing... .

The stuff I promised to post here is under development, this won't be the whole JLTi revealed but will be suitable for reasonably experienced DIY'ourselfers, two variations 1) one with a tube buffer and 2) one without, just as I promised earlier.

The original Gaincard as well as the clones including the inverted ones, while having great sonic qualities and, as Stereophile mag said about the original Gaincard, great clarity. But along with that they also have a tendency towards brightness or lack of warmth. This means careful matching and also reportedly a long burn-in (or warm-up) period (some have said weeks). Both versions I will present will ameliorate that problem, a more balanced sonic quality and less critical system matching. The treble quality is definitely an improvement as I hope others will concur.

The way this is achieved in both versions (but more consistent results with the tube buffered version) relies on an interesting little trick that will be revealed in full.

I hope some of you will go ahead and build them, it will be fascinating to see the results, can't wait to hear your feedback.

Next weekend is a long Easter weekend and that will be the time. All diagrams are being prepared including a very interesting THD distortion graph that I feel goes some way to indicate why the 'Gainclone Chip' is a potentially good as it indeed can be. The proof of that is in the listening!

Again, sorry for the delay but putting food on the table comes first.

Joe
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Old 22nd April 2003, 02:55 PM   #36
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Hi to Everybody.

Here we go.

I assume some previous knowledge of IGC amps, all previously posted by others.

I don’t think anyone has done a posting of this length, depth and nature. In near future this will appear on a selected web site, but gets its premiere here.

Part One: Starts here and discusses the Tube IGC and various issues that will also affect the NON-Tube IGC version as well.

Part Two: The NON-Tube variation is discussed and what problems are caused by lack of buffer (which is what the Tube does) and how to deal with it and compromises involved.

Part Three: Power Supply and general Wiring and Earth suggestions and other related practical matters.

Part Four: This is a little open-ended at this stage. Key section using THD measurements and graphs, plus a discussion of the Lynn Olson ‘First Watt’ principle. Other things will surely come to mind. General mopping up, possible comments about parts selection.


PART ONE:

I promised two suggested versions, one with Tubes and one without.

I think I will start with the Tube IGC (Inverted Gainclone) first as it is the simpler to explain. Actually the NON-tubed version has more complications though it looks like a simpler circuit.

Let’s look at Thorsten’s original IGC:

Click the image to open in full size.

Now this is not meant to be a critique of Thorsten’s circuit perse’. Rather it is a logical starting point as it was originally for me. About a year ago I was approached by a friend with limited DIY abilities (hope he doesn’t mind me saying this) to build the above circuit. Which I did and found it surprisingly good. But I also started to examine it in more detail and was convinced that there were areas that could be looked at. For example, notice that Thorsten chose a LINEAR volume pot, not the usual log. This was actually quite clever: The pot is actually in the feedback path and results in the pot behaving more like Log. But it does not by shifting feedback and gain.

Here are the components/elements that control Volume and Feedback vs Gain, all are inter-related.

Click the image to open in full size.


Let’s assume that the source is Lo Z, such as a CD Player, typically 200 Ohm, or small low fraction of the 100K pot. Let’s assume Zero Z for simplicity. If we were to have the wiper at the top (max) then the input impedance is 100K and 10K in parallel = 9K09.

This circuit is –1.5dB at 10Hz, I would prefer it being flat to 10Hz and no more than -.5dB at 5Hz. Why? Because this is a feedback amp and I want to minimize the potential added phase shift that this causes INSIDE the loop. It has been my past experience that this improves the sound and also the sense of timing as well.

Possibly these values will cause even MORE noticeable LF roll-off with AC coupled sources, such as tube line output stages. So I would prefer the 2u2 cap be quite a lot higher value to be flat down to 10 Hertz. My calculations indicate at least 10uF. Response flat down to 10Hz would be my aim and by changing other values, only 3u3 will be needed.

Let’s look at the way feedback varies with pot changes. The gain is set by values (220K+10K)/10K = 23, or 27.2dB, – but this potential max gain (hence lowest feedback) is reduced by the pot changes. At pot max position the 100K pot is not seen because of ‘Zero Z’ source and no change in gain/feedback. Same applies when the pot is set to minimum (grounded). But what if pot is in the mid position, as this is where it is more to be when in general operation?

The basic maths shows 100K pot will become 25K (because it is ‘Zero Z’ at ground too so it’s 50K in parallel with 50K = 25K) in series with 10K, hence gain (220+10+25)/(10+25) = 7.28 or 17.2dB.

So feedback changes and in the mid-position we have 10dB MORE FEEDBACK.

Now in basic op-amp practice that ain’t supposed to matter. That’s how you set gain, so it’s perfectly legitimate to vary feedback – and with a linear pot it works to advantage, as the pot now seems to operate similarly to a Log pot. I feel sure this guided Thorsten’s mind? If not he may set me straight.

But it also means you cannot set the feedback exactly where you want it and you can’t easily reduce it. I note that the original 47 Labs Gaincard has fixed gain slightly above 30dB, so the feedback values they must have used were not the ones shown in National Semiconductors PDF data file. I believe they did this because it sounds better. But in Thorsten’s circuit the gain drops a whopping 13dB which means that typically 13dB + more feedback relative to the Gaincard.

Using a buffer is the ideal here and hence no a pot in the feedback path. For further discussion, I suggest you read my essay “Tubes & The Gainclones”:


http://members.ozemail.com.au/~joera...gainclones.htm


Using a Unity Gain Buffer (i.e. no gain or gain = 1) looks like this:

Click the image to open in full size.

Now there’s no variable feedback. Gain is now a stable 23 times or 27.2dB. But feedback value resistors should be adjusted to give gain a bit above +30dB a la Gaincard and predictable LF and HF roll-offs implemented. What could be better than using a tube here? It might well benefit the overall sound anyway. In fact my experience tell me this is a certainty. The actual output impedance, which is now inside the feedback loop, won’t be ‘Zero Z’ but in our new project about 200 Ohm. Thus the tube is inserted in both the signal path and Gainclone IC’s feedback loop.

Now we can introduce the Tubed Inverted Gainclone (not really a ‘clone’ is it? I agree with Thorsten, but hey, this is how language develops):

Here it is in all its glory:

Click the image to open in full size.

The tube I use in the JLTi amp and above, is the Sovtek ‘Reflector’ 6922. It is a current production premium tube, but I’m sure that others will have their own ideas. But a decent 6922 does work OK at the voltages shown; in fact I’ve seen circuits using 6922s operating at 24V. That’s a bit low for my comfort but always check that there is no DC on the input grid as grid current can be a problem, but not with up-to-spec 6DJ8s and less likely with 6922s. Also be aware of microphonics. The ‘Reflector’ that I use has been perfect in this regard, over a large sample, this is a good thing when you are manufacturing. Only one twin triode 6922 is needed, one half for each channel and 6.3V 360mA min regulated supply.

Now we come to another key feature:

Notice the 1n3* cap? Perhaps you have. It serves a couple of purposes, the first being that at very high frequencies it keeps the feedback path short (a la 47 Labs contention that feedback should be short but kinda difficult in a SERIES feedback situ). The second reason, in conjunction with 4K7 it becomes a low pass filter. You could say this is bandwidth limiting but there is more to it. It does tailor the HF response so that it is minus 1.25dB at 20KHz. The target response achieved by listening test is shown here:

Click the image to open in full size.

Caption: This is an actual measurement using an MLS signal of my JLTi amp.

It has been noted that the original Gaincard, while having great clarity and some have even said purity, it is known to be a little relentless in the top end (a bit hot or glary), some of which is claimed to be ameliorated by being left ‘on’ or burnt in. In the case of the December 2001 Stereophile review, even a month wasn’t quite enough. It was also suggested that it should be carefully system matched for optimum results. Keep your sources warm, or speakers? Choose your cables with care etc. (All Gainclones don’t like a lot of capacitance).

I was also able to confirm these generalizations myself, even with the Inverted Gainclone. It became a kind of quest to sort out what was happening and IF anything could be done about it. Happily I can affirm something can be done and the end result is a less critical, more balanced sound. Also, as it turns out, this is an aspect that can be tuned by the individual DIY’ourselfer.

I suspected it was a slew-rate type problem, in which case adjusting bandwidth by ear was the only way to go. But before I did I ran some HF signals through the Gainclone and found it just didn’t like any real input at above 320KHz, in fact the amp went awry as was evident on the scope.

Click the image to open in full size.

Caption: Normal looking 320KHz.


Click the image to open in full size.

Caption: 330KHz, that’s right, only 10KHz higher. Notice the jump in amplitude.


Click the image to open in full size.

Caption: 340Khz again, here magnified. Notice the markers indicate phase shift.

What’s happening? The first scope shot shows everything quite normal, but then suddenly something is triggered, the waveform literally splits, the original sine wave is still dying BUT an additional POSITIVE signal is generated too, but with phase shift and huge jump in amplitude. I cannot with my 20MHz scope decipher what’s in between but based on the time base shown being 0.2uS it has to be very high?

What is the cause? It’s surely got to be feedback vs phase problem, or in reality positive feedback. If anyone else would like to hazard a guess I’d gladly entertain it.

Part One is more than 10.000 characters, continued in next...
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Old 22nd April 2003, 02:57 PM   #37
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... Continuation of Part One:

This is the NS data sheet gain vs. phase response:

Click the image to open in full size.


Despite the limited resolution of the graph, having to guess the 90° phase shift point (you only need to go slightly beyond that to generate positive feedback), it does seem to indicate around 5-600KHz. Not sure how accurate the graph is but in situ it does seem to turn out lower than that. When feedback is not fast enough in an Opamp IC, then slew rate distortion is likely guaranteed. That is why many solid-state amp design have a passive low-pass filter (usually a full band-pass filter) right on the input stage. So in that sense what I’m doing is not new, BUT what I did was adjusting this low-pass by ear.

Now all I can say that this, it is CLEARLY born out by listening tests, whatever the theory!!!! Keep this in mind this: With the approach I’ve taken I’ve got about 18-20dB more headroom at 330KHz, so whatever is happening is being suppressed, in fact as standard there seems to be NO headroom at 330KHz.

In order for the final value to be verified further by ear, I asked a friend to take the amp for a period of time and adjust the value. No other changes were to be made except this cap value. His system has what I would call an even balance and no tendency towards either brightness or dullness. I put a 390pF cap in there first and gave him a handful of others with increasing values, one of which was the previously preferred 1n3. This value was preferred as well by my independent tester..

My suggestion is that any DIY builders should also try out different values and I would be interested in the feedback. Believe me, it does affect the final sonics and it’s one of the things that are NOW tunable for individual experimentation.

The NON-Tube version also incorporates this kind of approach, but it actually more complicated. This and other matters like keeping feedback more constant when we still have a pot directly in circuit. That will be covered in the next installment.

So we have now made real start, more to come.

THIS CONCLUDES PART ONE.
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Old 22nd April 2003, 09:01 PM   #38
fedde is offline fedde  Netherlands
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Thanx for the info !!! I can't wait for the rest... especially for part II

I think that you'll use a 1 Mohm resistor for feedback with a 50-67 k resistor on the - input. Or am I wrong !? Is the increased noise a problem with the 1M resistor?

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Old 22nd April 2003, 09:20 PM   #39
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Hi, I am new to this forum so excuse me if I ask dumb questions (and be assured that I will, ).

1st of all, what is this gainclone thing? why would be anyone interested in an ic-amp? granted, I haven't listened to one of those beasts but the datasheet doesn't look too impressive. Maybe the thing actually sounds better?

also, why use a tube-SS hybrid where the tube is upfront? I thought tubes have advantages over SS during to their soft clipping. wouldn't it be more desirable to use tubes in OPS and SS upfront, or reverse topology of what is being presented here?
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Old 22nd April 2003, 09:42 PM   #40
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Quote:
Originally posted by millwood
1st of all, what is this gainclone thing? why would be anyone interested in an ic-amp? granted, I haven't listened to one of those beasts but the datasheet doesn't look too impressive. Maybe the thing actually sounds better?
From all reports -- i've been gathering parts for Joe's version -- these things sound way better than anyone would think they have a right to on an absolute scale and in terms of bang-for-the-buck they are a big winner. Do a search on GainClone... in particular the megathread called "Not just another GainClone" will give you plenty to read.


Quote:
also, why use a tube-SS hybrid where the tube is upfront? I thought tubes have advantages over SS during to their soft clipping. wouldn't it be more desirable to use tubes in OPS and SS upfront, or reverse topology of what is being presented here?
Because it works? Joe has come up with a very elegant buffer to sort the biggest problems with the now "classic" Thor design (which the designer "napkined" up for others & never built himself -- he did get a huge ball rolling and DIY is forever indebted to him for this and many other useful bits).

dave
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