Dear Routhan,
I am not suggesting that any amp is good or bad. In my opinion all amps are essentially good, as you rightly mention some are better than others.
I do know of the LM4702 as we receive early samples of newly developed semiconductors and we got some of LM4702C in TO-3 11 pin package around the middle of 2005.
I have a few left over samples, but I have never used one myself. Maybe one day I will find something to do with them.
I guess I am old school and I love doing things the hard way, that to me is more fun than building something off a data sheet, because if I design it, I can truly claim that it is mine, after all it is a hobby.
If you love your LM4702 based amp then, that is excellent, I cannot comment.
I was merely suggesting that we may be frigthening our friend away instead of helping him.
In my reply I said nothing about any amplifier/chip or otherwise. I am concerned that you attack me for thinking that I may not like what you like only because I said nothing.
If you care to look in previous discussions I suggested he looks at Marks chip amp site.
You do not say which chip you use (A,B or C) or your operating voltage, but I am sure National Semiconductors would be pleased that you have improved their THD by two orders of magnitude.
The quoted THD + N is only 0.005% by no means a magical figure at all.
I am not suggesting that any amp is good or bad. In my opinion all amps are essentially good, as you rightly mention some are better than others.
I do know of the LM4702 as we receive early samples of newly developed semiconductors and we got some of LM4702C in TO-3 11 pin package around the middle of 2005.
I have a few left over samples, but I have never used one myself. Maybe one day I will find something to do with them.
I guess I am old school and I love doing things the hard way, that to me is more fun than building something off a data sheet, because if I design it, I can truly claim that it is mine, after all it is a hobby.
If you love your LM4702 based amp then, that is excellent, I cannot comment.
I was merely suggesting that we may be frigthening our friend away instead of helping him.
In my reply I said nothing about any amplifier/chip or otherwise. I am concerned that you attack me for thinking that I may not like what you like only because I said nothing.
If you care to look in previous discussions I suggested he looks at Marks chip amp site.
You do not say which chip you use (A,B or C) or your operating voltage, but I am sure National Semiconductors would be pleased that you have improved their THD by two orders of magnitude.
The quoted THD + N is only 0.005% by no means a magical figure at all.
" ... complete project with 2/3 way electronic cross-over ..."
Good thinking. I intend to do a bi-amp job on my main speakers ( http://3dotaudio.com/waterputtyexperiment.html ) ... I'll just build one 4702 into each speaker, turn the bass woofer and middie+tweeter into active crossover control (and use all those great big caps & coils for something else). I'll be trying for balanced inputs to the 4702 ...
Good thinking. I intend to do a bi-amp job on my main speakers ( http://3dotaudio.com/waterputtyexperiment.html ) ... I'll just build one 4702 into each speaker, turn the bass woofer and middie+tweeter into active crossover control (and use all those great big caps & coils for something else). I'll be trying for balanced inputs to the 4702 ...
Dear Nico Ras,
I am not attacking you in any means. My point is that none of them offered a clear solution, but when I offered a simple solution I was accused of coming to conclusion on somebody's behalf. I am afraid that with all the endless discussions floating on the thread we might not give Prorm a simple practical solution as one of the choice as it happens in all high-level discussions.
Hi FastEddy,
I don't have the PCB designs, I've bought my PCBs from www.chip-pcb.cn. Each PCB costs $6 a peace and complete kit costs $32 and shipping starts at $20. The PCBs are double sided and are professional. Please search the chipAmps threads for LM4702 somebody called harvardian also built an 8-channel amp with this kit.
-Routhun
I am not attacking you in any means. My point is that none of them offered a clear solution, but when I offered a simple solution I was accused of coming to conclusion on somebody's behalf. I am afraid that with all the endless discussions floating on the thread we might not give Prorm a simple practical solution as one of the choice as it happens in all high-level discussions.
Hi FastEddy,
I don't have the PCB designs, I've bought my PCBs from www.chip-pcb.cn. Each PCB costs $6 a peace and complete kit costs $32 and shipping starts at $20. The PCBs are double sided and are professional. Please search the chipAmps threads for LM4702 somebody called harvardian also built an 8-channel amp with this kit.
-Routhun
Hi Routhan,
This is a page from their data sheet. I do not see erata anywhere. Besides, this is also with no load. Add a load and see how this value drops on any distrotion analyser.
But I don't quote anything, this is from National. If you look at the graphs a little further, then you also see mpre revealing things not just numbers.
Maybe their appnotes have a different specification. If that is the case I doubt if either are correct. I do not always believe what I read. Put it on test and see if this is really the case after the addition of some other components in a real environment driving non resistive loads at elevated temperatures with ripple on the power supply and noisy non lab environments. The results may be far from perfect.
Anyway as you may notice - FastEddy is suggesting a little project and I am keen regardless if THD is 1% or 1 micro%, if it sound good then this is a starting place.
If after I build one, and I don't like it, it goes to the dustbin and I have learned something. Maybe, I also like it and rave about it.
Kind regards
Nico
This is a page from their data sheet. I do not see erata anywhere. Besides, this is also with no load. Add a load and see how this value drops on any distrotion analyser.
But I don't quote anything, this is from National. If you look at the graphs a little further, then you also see mpre revealing things not just numbers.
Maybe their appnotes have a different specification. If that is the case I doubt if either are correct. I do not always believe what I read. Put it on test and see if this is really the case after the addition of some other components in a real environment driving non resistive loads at elevated temperatures with ripple on the power supply and noisy non lab environments. The results may be far from perfect.
Anyway as you may notice - FastEddy is suggesting a little project and I am keen regardless if THD is 1% or 1 micro%, if it sound good then this is a starting place.
If after I build one, and I don't like it, it goes to the dustbin and I have learned something. Maybe, I also like it and rave about it.
Kind regards
Nico
Attachments
All: if this complete kit from www.chip-pcb.cn is worthwhile what I will do, get one or two kits for my projects. http://www.chip-pcb.cn/images/47021.gif & http://www.chip-pcb.cn/images/47026.gif & http://www.chip-pcb.cn/images/47027.gif ... looks pretty good and will fit into my speakers just fine (for bi-amping). This appears to conform to National's PCB layout and looks like all I have to add is the '4702B chip, their or my PS & transformer ... and of course a case or chassis to wrap it in ...
Anyone ever dealt with www.chip-pcb.cn ???
Anyone ever dealt with www.chip-pcb.cn ???
Fast Eddy,
I and another member called Harvardian bought the kits from this place. Kit and shipping charges are reasonable. They ship it from China and it takes between 1-2 weeks to receive the kit after they ship it. Only complaint is the heatsink they give is in-adequate for that kit, you may want to replace it with bigger heat sink to keep the temperature down.
Routhun
I and another member called Harvardian bought the kits from this place. Kit and shipping charges are reasonable. They ship it from China and it takes between 1-2 weeks to receive the kit after they ship it. Only complaint is the heatsink they give is in-adequate for that kit, you may want to replace it with bigger heat sink to keep the temperature down.
Routhun
routhun: " ... They ship it from China and it takes between 1-2 weeks to receive the kit after they ship it. Only complaint is the heatsink they give is in-adequate for that kit, you may want to replace it with bigger heat sink to keep the temperature down. ..."
That's the kind of feedback that I like: " ... only one complaint ..."
(Wondering: picture #1 at http://www.chip-pcb.cn/7300/4702e.htm indicates that there are two trim pots on the board. I would guess that this is bias adjustments. My guess that proper bias adjustments while under output load (no input) might reduce the heat question .... No?)
Thanks
All: end of suggestions for a new thread for LM4702x project(s). I'll be ordering a couple of these for a tryout ... if no joy, then I might suggest (re)starting a thread ...
That's the kind of feedback that I like: " ... only one complaint ..."
(Wondering: picture #1 at http://www.chip-pcb.cn/7300/4702e.htm indicates that there are two trim pots on the board. I would guess that this is bias adjustments. My guess that proper bias adjustments while under output load (no input) might reduce the heat question .... No?)
Thanks
All: end of suggestions for a new thread for LM4702x project(s). I'll be ordering a couple of these for a tryout ... if no joy, then I might suggest (re)starting a thread ...
About LM4702 and the Applications of useing it.
hi
A little rave about LM4702 from National mentioned here.
It is a 150/200 Volt output devices driver
for easy make of powerful amplifier.
If it will do for Hifi like they say, may depend on HOW you use it.
There is an application, for download:
Application Note 1490 LM4702 Power Amplifier
See this PDF: http://www.national.com/an/AN/AN-1490.pdf
Here is this AN-1490 Schematic.
Se my attachment.
I say, there has to be many ways to use this chip better!
If only LM4702 has got 50% of the things they say it has,
it might be possible to make quite a good and powerful amp.
And use some better circuit than this app note.
For example replace those Output Darlingtons with some other transistors,
that we, the audio people, more frequently use (read: in 95% of all our designs)
Regards
lineup
hi
An externally hosted image should be here but it was not working when we last tested it.
A little rave about LM4702 from National mentioned here.
It is a 150/200 Volt output devices driver
for easy make of powerful amplifier.
If it will do for Hifi like they say, may depend on HOW you use it.
There is an application, for download:
Application Note 1490 LM4702 Power Amplifier
See this PDF: http://www.national.com/an/AN/AN-1490.pdf
Here is this AN-1490 Schematic.
Se my attachment.
I say, there has to be many ways to use this chip better!
If only LM4702 has got 50% of the things they say it has,
it might be possible to make quite a good and powerful amp.
And use some better circuit than this app note.
For example replace those Output Darlingtons with some other transistors,
that we, the audio people, more frequently use (read: in 95% of all our designs)
Regards
lineup
Attachments
Hi,
re that 4702 schematic.
What does Cb2 &Cb4 do (across the Vbe multiplier base to collector)
Any thoughts on why they suggest such high values for the global NFB and input R & C?
Why is Csn1 & 2 set to 20nF (Zobel)?
The rest of the Thiel seems to have been thought about rather than the usual 10r etc.
I agree, dump the integrated Darlingtons and go discrete.
re that 4702 schematic.
What does Cb2 &Cb4 do (across the Vbe multiplier base to collector)
Any thoughts on why they suggest such high values for the global NFB and input R & C?
Why is Csn1 & 2 set to 20nF (Zobel)?
The rest of the Thiel seems to have been thought about rather than the usual 10r etc.
I agree, dump the integrated Darlingtons and go discrete.
Lineup: " ... For example replace those Output Darlingtons with some other transistors,
that we, the audio people, more frequently use ..."
I agree.
... I was hoping to find some way to use the LM4702B to drive complimentary pairs of power MOSFETs ( "Complementary Dual Differential Cascoded Topology running in Class AB" )
... and I would want XLR balanced inputs for a speaker bi-amp, speaker bi-amp would reduce concerns about cross talk between the two channels (the any cross talk being just another part of the signal component, filtered by the crossovers)
... and the circuit board could also have the facilities for "active" crossovers (passive components on the board, active components as used in the design.
... Also wondering if there will be a mono-block, single channel version, I know a mono-block would find a market in lab equipment & industrial control as well as improve any crosstalk questions.
that we, the audio people, more frequently use ..."
I agree.
... I was hoping to find some way to use the LM4702B to drive complimentary pairs of power MOSFETs ( "Complementary Dual Differential Cascoded Topology running in Class AB" )
... and I would want XLR balanced inputs for a speaker bi-amp, speaker bi-amp would reduce concerns about cross talk between the two channels (the any cross talk being just another part of the signal component, filtered by the crossovers)
... and the circuit board could also have the facilities for "active" crossovers (passive components on the board, active components as used in the design.
... Also wondering if there will be a mono-block, single channel version, I know a mono-block would find a market in lab equipment & industrial control as well as improve any crosstalk questions.
FastEddy said:
Such a MOSFET driving use of LM4702 might be very possible.
I can't say for sure, as I haven't studied LM4702 enough.
Reading both datasheet and that application note more closely
may answer some questions.
I have a slight remembering of a topic with LM4702 project
but it may as well be some similar chip they used.
LM4702 is not the only of this type.
And I also do not know anything about which of these type chips
may have the best qualities.
What do they cost?
My hope with my post,
was mainly to inspire some members to try this chip
in a different and maybe more optimal circuit.
This is a good project in Chip Amps forum,
for more flexible and more creative amplifiers
than with LM1875 LM3875 LM3886.
(Nothing bad from me about those - they are all good amps for many people).
Each topic/project needs one or two DRIVING FORCES
to become alive and stay alive to finally give some good result.
Hope one of those of our 'good leaders of projects' would get interested enough
to give LM4702 a good try out.
Regards
lineup
Lineup: " ... My hope with my post, was mainly to inspire some members to try this chip in a different and maybe more optimal circuit. ..."
Yes, exactly ... a more optimizal curcuit. I know that National did quite a bit of work with this, although a single NS engineer appears to be the lead. NS engineer Mark Brasfield wrote this in May 2006: http://www.national.com/an/AN/AN-1490.pdf and he apparently tried to optimise with the darlington output stages, MN2488 & MP1620 (US$3 each or less) ... which would follow the National philosophy of "if the part has a cheaper equal, use the cheaper device and tweak it ..." or words to this effect.
Those of us who are after the best possible specs and best possible sound usually say "hang the costs of a few transistors, use the best ..." or words to that effect.
Yes, exactly ... a more optimizal curcuit. I know that National did quite a bit of work with this, although a single NS engineer appears to be the lead. NS engineer Mark Brasfield wrote this in May 2006: http://www.national.com/an/AN/AN-1490.pdf and he apparently tried to optimise with the darlington output stages, MN2488 & MP1620 (US$3 each or less) ... which would follow the National philosophy of "if the part has a cheaper equal, use the cheaper device and tweak it ..." or words to this effect.
Those of us who are after the best possible specs and best possible sound usually say "hang the costs of a few transistors, use the best ..." or words to that effect.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.