Hi Andrej! Oh, I like your design plenty. But it is far beyond the budget for this amplifier.
Well, I'm not sure exactly what this means, but I could certainly manage to assemble an extremely compact design.
I'm absolutely clueless on that one. Would you mind illustrating more?
As seen on the MooseFet, ferrite beads were use to help promote stability and they are available so tiny as to barely encircle one leg of IRF510. Would you want to employ something like that in your design? Well, I'm asking because I don't know.
There is ~52vdc available. For less than that, there's regs.
Well, I do happen to have one of the fastest of the chip amplifiers set in triple parallel, meaning that any signals in the Mhz will really freak it out, since stability tolerances are slimmer.
It actually has an excess of speed that maybe you could help me trim? The feedback divider of the original single chip amp had 2.7k/114k, but the new triple parallel has 3.3k/100k, which is less gain. Quick! Guess what I'm saying from the figures because my explanation sure won't be any good.
Okay, since the new amp doesn't need as much speed as the old amp, there exists some value picofareds cap to put between the + and - inputs to just about level out the difference in the amount of capacity for gain versus the (lesser) amount that has actually been used. As a bonus, the new amp won't get as nervous about out of band signals. I tried to calculate the cap value, but you know that instant kind of pain from eating ice cream too fast? Well, I got that. And I got 56p. No idea why. Is it right?
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You could also put some pF in parallel with the LM1875 feedback resistors (between Out and -In). You can probably just experiment with those. But there are equations...
He is right. Put the gate stopper resistors RIGHT up to the pins. Did you know that the same thing goes for the -In pins of chipamps and opamps, usually? You don't want ANY stray inductance, there. Otherwise, tiny little resonant tank circuits can be formed and you can get very high frequency ringing, or in some cases maybe even oscillation. So both feedback and series input resistors should be RIGHT at the -In pin. If there is no series input resistor for -In, but there is a conductor to it, then ADD a small-ish series resistor, right at the pin.
He is right. Put the gate stopper resistors RIGHT up to the pins. Did you know that the same thing goes for the -In pins of chipamps and opamps, usually? You don't want ANY stray inductance, there. Otherwise, tiny little resonant tank circuits can be formed and you can get very high frequency ringing, or in some cases maybe even oscillation. So both feedback and series input resistors should be RIGHT at the -In pin. If there is no series input resistor for -In, but there is a conductor to it, then ADD a small-ish series resistor, right at the pin.
Beads as stoppers work great in switching circuits that don't mind
inductance causing a little overshoot. And where ringing after the
fact exceeds the frequency to become resistive and lossy. And the
closed loop rolls off at a far different, much lower frequency than
the signal of interest.
I don't think they have a place in the closed loop of an audio circuit.
Even a small inductance can make a closed loop become unstable.
And not at high enough frequency to trigger a useful loss... This sort
of loop is different because it closes at higher frequency the signal
of interest.
Its fine to use them as low pass output filter after the loop is closed.
Thanks Ken!
I do have some more questions:
What are some recommendable models brands for the jfets in your schematic?
What is a good brand of IRF510? I ask because local availability is china clone and would rather order a good part.
Is 24v via adjustable regulator okay? Or would you like to see some other method?
Which of the resistors need to be greater spec than 1/4w carbon film?
What does the schematic look like with the added stoppers and bypass caps?
P.S.
The sample is still too small, with only 3:
DRV134 (control sample)
OP275 by Iam44
Jfet Phase Inverter by Kenpeter
?
?
I need at last 5 samples so that my judgement can be more accurate.
At this point, and saying it bluntly goes like this: The miniature (re-scaled for home) LM1875 disco amp needs to get its job done, compete head to head for output power (no significant difference in power output at same % distortion, not noisy brags) with BPA200 driving 4 ohm speakers, and beat it on sound quality when both are at near full blast. As for sound better, well, that's here at the phase inverter, simply because it is the input.
So, I need 2 more phase inverters to compare.
I'm not against a non-expensive vacuum tube phase inverter if it can run on 52vdc (amp power), or other low cost solution. Although tubes can have higher distortion, there's simply no telling which phase inverter will win its contest of peers via providing the missing audio effect that the power amp cannot do. Caveat: Must not reduce the high gain amp to a mid-fi with noise at the input. Unfortunately, I'm not accustomed to building with tubes, so would need some guidance.
And then one more to go. . .
I do have some more questions:
What are some recommendable models brands for the jfets in your schematic?
What is a good brand of IRF510? I ask because local availability is china clone and would rather order a good part.
Is 24v via adjustable regulator okay? Or would you like to see some other method?
Which of the resistors need to be greater spec than 1/4w carbon film?
What does the schematic look like with the added stoppers and bypass caps?
P.S.
The sample is still too small, with only 3:
DRV134 (control sample)
OP275 by Iam44
Jfet Phase Inverter by Kenpeter
?
?
I need at last 5 samples so that my judgement can be more accurate.
At this point, and saying it bluntly goes like this: The miniature (re-scaled for home) LM1875 disco amp needs to get its job done, compete head to head for output power (no significant difference in power output at same % distortion, not noisy brags) with BPA200 driving 4 ohm speakers, and beat it on sound quality when both are at near full blast. As for sound better, well, that's here at the phase inverter, simply because it is the input.
So, I need 2 more phase inverters to compare.
I'm not against a non-expensive vacuum tube phase inverter if it can run on 52vdc (amp power), or other low cost solution. Although tubes can have higher distortion, there's simply no telling which phase inverter will win its contest of peers via providing the missing audio effect that the power amp cannot do. Caveat: Must not reduce the high gain amp to a mid-fi with noise at the input. Unfortunately, I'm not accustomed to building with tubes, so would need some guidance.
And then one more to go. . .
It would be interesting to try something like these, except with phase inverter function added: Discrete Buffer for chip amp.
Scrolling down to jfet. . .
In the case of the Jfet example, there was a lot less variance with results and no endless experimentation mandated. That looks encouraging. It is conveniently split rail (this is economically within the range of regulators from amp power). Can phase inverter function be added to it?
Scrolling down to jfet. . .
In the case of the Jfet example, there was a lot less variance with results and no endless experimentation mandated. That looks encouraging. It is conveniently split rail (this is economically within the range of regulators from amp power). Can phase inverter function be added to it?
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... and finnaly we meet. That is exactly what I proposed you in post #15. Double j-fet buffer with the best inverter in front. I see you are not very experienced by this, so I suggest that forum members vote and decide instead of you. I vote for SSA trafo inverter+buffer. Have a nice day.
I see the post #15 as a fourth sample, don't you see it as a relevant one.
You'd be surprised how cheap are line transformers these days.
Regards Andrej
... and finnaly we meet. That is exactly what I proposed you in post #15. Double j-fet buffer with the best inverter in front. I see you are not very experienced by this, so I suggest that forum members vote and decide instead of you. I vote for SSA trafo inverter+buffer. Have a nice day.
Of course you're probably right. Therefore, please find the $10~20 input transformer.
I could only find $80 to $120, and that wasn't suited to the budget.
Your design theme itself is obviously correct--a really lovely input regardless of the output devices, is much more sensible than the opposite.
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You will have to calculate every possible cost in a equation: PCB, some of the fancy parts other members suggested, time, etc.
By design from post #15 you can do it immediately in the best P2P audiophile manner, like the great companies do it. So you save time, two PCB's etc. And you won't have any noise-buzz issues when you use transformers it is the most elegant way of doing it in your case.
Energy to drive your bridged amp input is only double of one input driving, so you can pick the right input/output impedance transformer in this case you can even omitt j-fet buffers. At the end you have only two transformers cost. There are many producers not only Lundahl, search the net ...
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Edcor can probably do you the transformer on the cheap.
But I still don't get why one channel entirely N, and the
other entirely P? Feature looks leftover from before you
had given up on making a jfet phase splitter and threw
a transformer at the problem.
If we use transformer to split, why do we want JFETs
afterward? Its just reintroducing DC offset we have to
get rid of with caps or another transformer. Put your
jfet up front if you are determined that a transformer
is the way to go... It only needs one jfet with primary
winding under the source...
Lets make it complicated for no reason... I agree with
your last statement that transformers alone without
additional buffer is the surest way to avoid problems.
I don't see any reason that simple wouldn't work.
But I still don't get why one channel entirely N, and the
other entirely P? Feature looks leftover from before you
had given up on making a jfet phase splitter and threw
a transformer at the problem.
If we use transformer to split, why do we want JFETs
afterward? Its just reintroducing DC offset we have to
get rid of with caps or another transformer. Put your
jfet up front if you are determined that a transformer
is the way to go... It only needs one jfet with primary
winding under the source...
Lets make it complicated for no reason... I agree with
your last statement that transformers alone without
additional buffer is the surest way to avoid problems.
I don't see any reason that simple wouldn't work.
looks to me like good 'phase splitter' transformers are generally very expencive
I guess the reason is high demands on 'especially good balanced' transformer design
and there is the signal/power level to consider
I guess too low level signal isn't really good to drive a transformer
and higher level signal demands interstage sized phase splitter
I admit to be a bit confused about it
I guess the reason is high demands on 'especially good balanced' transformer design
and there is the signal/power level to consider
I guess too low level signal isn't really good to drive a transformer
and higher level signal demands interstage sized phase splitter
I admit to be a bit confused about it
I've found that transformer bandwidth can be extended by
deliberately mismatching the input and output impedance...
I got a Stromberg Carlson 2Henry : 2Henry that supossedly
was only telephone transformer rated for 600ohm : 600ohm
use over a narrow band of voice only... 400Hz-4KHz I think.
But I found it surprisingly flat when I drove it from a source
that was lower than 600 ohms, and loaded it with a target
greater than 600ohms... At line level, went the full 9 yards
and sounded really good....
We talking a transformer I mighta spent like dollafitty....
So I got a whole bag of em... But I'm now thinking these
are nothing special, the magic was impedance mismatch.
Not trying for maximum power transfer, don't care about
transmission line theory where the wires might be long
enough to worry about reflections... 600 ohm matching
at line levels only makes the bandwidth perform poorly.
They are capable of much more when we cast aside the
irrelevant concerns of telephone use.
600:600 telephone transformers are abundant surplus...
I would try that before spending real money...
-------
As for the FET splitter, I think the IRF510 might have
been an overkill choice. VN2222A is a smaller MOSFET,
and less capacitance, but still do the job. You might
could even use this for all three FETs...
deliberately mismatching the input and output impedance...
I got a Stromberg Carlson 2Henry : 2Henry that supossedly
was only telephone transformer rated for 600ohm : 600ohm
use over a narrow band of voice only... 400Hz-4KHz I think.
But I found it surprisingly flat when I drove it from a source
that was lower than 600 ohms, and loaded it with a target
greater than 600ohms... At line level, went the full 9 yards
and sounded really good....
We talking a transformer I mighta spent like dollafitty....
So I got a whole bag of em... But I'm now thinking these
are nothing special, the magic was impedance mismatch.
Not trying for maximum power transfer, don't care about
transmission line theory where the wires might be long
enough to worry about reflections... 600 ohm matching
at line levels only makes the bandwidth perform poorly.
They are capable of much more when we cast aside the
irrelevant concerns of telephone use.
600:600 telephone transformers are abundant surplus...
I would try that before spending real money...
-------
As for the FET splitter, I think the IRF510 might have
been an overkill choice. VN2222A is a smaller MOSFET,
and less capacitance, but still do the job. You might
could even use this for all three FETs...
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And ...
... now you know how my leftovers solving the imaginary problems.
Because I simply didn't like how only N or P fet's schematics looked. Our work here must be treated like a work of art, just like a great paintings and that's how I look to our DIY love affair.
Maybe you could try the dual OP275 "inverter-follower" differential line driver circuit that's shown in Figure 6-54, which is in the downloadable PDF of chapter 6 at ADI - Analog Dialogue | Op Amp Applications Handbook . (Of course, other opamps could be used, instead of the OP275.)
You could also look at the topology in Fig 6-96 (and 6-120, for future reference).
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It is splitting 360 degrees of phase into 2 180 degrees out so the 360 is getting split into two. I have always heard it called phase splitting for 31 years+.
Moosefet pre amp, is that a pre amp with antlers ? lol
Can't quite understand a few of things in your description:
"OP275 as a bridge amp itself" - What does this mean?
"equipped with common mode feedback" - What does this mean?
"driving a 2 channel power amp" - Feedback can't be for two channels at once...
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