Nielsio said:
I believe so, and the favourable reactions I've
so far are most promising. Thank you for your
kind remarks.
It's kinda funny that the JLTi ends up as a
subject in DIY discussion forum when it isn't
a DIY product.
It's only that it uses an element familiar
to some DIY-selfers. But so does other commercial
products as well. After all, audio is made up of
many diverse bits, DIY or otherwise. It's all about
how you combine them. It's cooking!
But having said that, I would like pass on some
of my ideas (discoveries?) and let's see how it is
received. I want this contribution to be very well
thought out and presented. It may take about two
weeks as I may want to include actual measurements.
This will be a comprehensive presentation.
At least I have accomplished something others have
not done yet, combining tubes and the 'gainclone'
IC. The idea has been spoken about it, but has
anyone actually done it?
Personally I love the results - it works beautifully!
Thorsten sent me an email saying that he had
suggested it in a November post (another forum) and
gave me the link. But I had already started this well
before then.
Here is the URL he sent me:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=9348
I didn't follow his suggestion of making the
'gainclone' behave more like an SET or adding 2nd
harmonic warmth. I trusted my instincts and went
for the cleanest possible signal path, the Tube
Buffer I use is very low distortion and very wide
bandwidth. Actually hugely wider than the IC, which
led to a problem I had to solve.
Another absolutely important aspect of the Tube Buffer
is the power supply solution I came up with. I also
the same idea for the optional Phono Stage, so have
a look, it the third illustration down on the page:
http://members.ozemail.com.au/~joeras/jlti_phono.htm
The main difference here is that the +15V/-15V is +55V/-55V
for the Tube stage.
Regards
Joe
Serow said:
Hi Eric
Please be patient. You will be happy to know that
I have already started preparing diagrams and
circuits.
There will two designs presented, one can be
easily adapted to current GCs, it requires a
number of values altered and a few additional
components. Also a change to either 10K Log Pot
OR 25 Log Pot. The original 50K Lin Pot will be
discarded.
The SECOND design will be far more ambitious. This
will be a simplified version of the JLTi. This is
for the SERIOUS constructor!
YES, A DIY HYBRID TUBE GC.
But the power supply solutions to the tube front-
end will need to be filled in by the DIY-selfer.
The +35V & -35V supply can be done using a small
25V-0-25V 30VA tx, toroidals should be available,
and same 1000uF/35V caps as using by the GC chip.
This will give us a very well filtered but unregu-
lated supply. If the constructor wants to regulate
this... go ahead with whatever solution you can or
want to come up with.
Also a 6.3V 330mA supply will be required for the
filament.
The choice of tube (suggestion) will be the same
as the JLTi, the Sovtek 'Relector' 6922, as this
tube will work at the low (no high-tension here)
voltages used.
Hope that has got your appetite up.
I'm looking at two weeks, hang in there.
Regards
Joe
Hi Guys
Check this out:
Yes, actual component values will be supplied.
This is the simplified JLTi for the DIY mafioso...
Promise!
Joe
Check this out:
An externally hosted image should be here but it was not working when we last tested it.
Yes, actual component values will be supplied.
This is the simplified JLTi for the DIY mafioso...
Promise!
Joe
Was just testing if my signature works, but I can't delete the message.
Well, guess I have to say something smart now.
Ok, I've got one:
Why is it that the exact grounding is never included in the schematics? Especially when it seems to matter so much.
Not everyone here is a Kuei, a Peter or a Joe.
Well, guess I have to say something smart now.
Ok, I've got one:
Why is it that the exact grounding is never included in the schematics? Especially when it seems to matter so much.
Not everyone here is a Kuei, a Peter or a Joe.
Our feet on the ground
Originally posted by Nielsio
"Why is it that the exact grounding is never included in the schematics? Especially when it seems to matter so much."
=============================================
...Because, then everyone would be able to build a nice sounding equipment
Regards
George
Originally posted by Nielsio
"Why is it that the exact grounding is never included in the schematics? Especially when it seems to matter so much."
=============================================
...Because, then everyone would be able to build a nice sounding equipment
Regards
George
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!'
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!'
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?
----------------------------------------------
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?
AKSA said:
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
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:
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.
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/~joeras/tubes_&__the_gainclones.htm
Using a Unity Gain Buffer (i.e. no gain or gain = 1) looks like this:
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:
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:
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.
Caption: Normal looking 320KHz.
Caption: 330KHz, that’s right, only 10KHz higher. Notice the jump in amplitude.
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...
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:
An externally hosted image should be here but it was not working when we last tested it.
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.
An externally hosted image should be here but it was not working when we last tested it.
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/~joeras/tubes_&__the_gainclones.htm
Using a Unity Gain Buffer (i.e. no gain or gain = 1) looks like this:
An externally hosted image should be here but it was not working when we last tested it.
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:
An externally hosted image should be here but it was not working when we last tested it.
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:
An externally hosted image should be here but it was not working when we last tested it.
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.
An externally hosted image should be here but it was not working when we last tested it.
Caption: Normal looking 320KHz.
An externally hosted image should be here but it was not working when we last tested it.
Caption: 330KHz, that’s right, only 10KHz higher. Notice the jump in amplitude.
An externally hosted image should be here but it was not working when we last tested it.
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...
... Continuation of Part One:
This is the NS data sheet gain vs. phase response:
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.
This is the NS data sheet gain vs. phase response:
An externally hosted image should be here but it was not working when we last tested it.
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.
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?
).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?
millwood said:
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.
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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