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If I remember, the idea was to create a star power ground at the common of the power rail caps and for the speaker 0V to return to this point.
I don't have distortion measuring equipment and so never did any measurements. I didn't find much time to play around with alternative configurations. Being lazy, as soon as I got it up and running and noticed that it sounded so darn good I just called it a day, then and there. I'm sure there's much to learn with some proper measurement which might be used to improve things. But I simply haven't found anything wanting in the sound to know where I might want to spend time and effort on improvements. There's no 'ego' in the way here, if you fella's can come up with some better way to do things which delivers better performance (e.g. better sound, reliability etc.) then I'm all for it.
My TGM7 is a fully dc-coupled throughout design with no on-board speaker protection. So to limit the potential of damaging dc current flow through a speaker I inserted a resistor in series with the trafo centre tap which isolated it from the 0V common. I didn't notice any performance benefit from this but doesn't mean it wouldn't be of help to TGM8.
I don't have distortion measuring equipment and so never did any measurements. I didn't find much time to play around with alternative configurations. Being lazy, as soon as I got it up and running and noticed that it sounded so darn good I just called it a day, then and there. I'm sure there's much to learn with some proper measurement which might be used to improve things. But I simply haven't found anything wanting in the sound to know where I might want to spend time and effort on improvements. There's no 'ego' in the way here, if you fella's can come up with some better way to do things which delivers better performance (e.g. better sound, reliability etc.) then I'm all for it.
My TGM7 is a fully dc-coupled throughout design with no on-board speaker protection. So to limit the potential of damaging dc current flow through a speaker I inserted a resistor in series with the trafo centre tap which isolated it from the 0V common. I didn't notice any performance benefit from this but doesn't mean it wouldn't be of help to TGM8.
By "Mooly amps" what do you refer to ?
How does it compare with "Bigun" TGM7 (or 8 ?).
I understand there is a negative statement about the latter, I hope this will be cleared or at least explained clearly.
Mooly amp:
My MOSFET amplifier designed for music.
https://www.diyaudio.com/forums/sol...-amplifier-designed-music-67.html#post5502137
As mentioned earlier, these are intended to be constructive comments. It seems like Bigun is taking it this way
Regarding the sound, I have kept fairly quiet about this because I was not all that happy with the sound of the TGM8. HOWEVER... I have transplanted the Mooly amp into the same chassis as the TGM8 and am no longer happy with the sound of the Mooly.
The chassis and transformers was originally a Rotel RB850. All 3 amps sound very similar when using the same chassis and transformer. The Mooly amp sounded great in another chassis and with other transformers. I think there is a pattern here. In conclusion: i would not like to pass judgement on the sound of the TGM8 until I have tried it with a different PS.
My MOSFET amplifier designed for music.
https://www.diyaudio.com/forums/sol...-amplifier-designed-music-67.html#post5502137
As mentioned earlier, these are intended to be constructive comments. It seems like Bigun is taking it this way
Regarding the sound, I have kept fairly quiet about this because I was not all that happy with the sound of the TGM8. HOWEVER... I have transplanted the Mooly amp into the same chassis as the TGM8 and am no longer happy with the sound of the Mooly.
The chassis and transformers was originally a Rotel RB850. All 3 amps sound very similar when using the same chassis and transformer. The Mooly amp sounded great in another chassis and with other transformers. I think there is a pattern here. In conclusion: i would not like to pass judgement on the sound of the TGM8 until I have tried it with a different PS.
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That's interesting !
You remind me that when I first had TGM8 working it was not in the current chassis and it was with a different PSU too. My sound memory being fickle as anybody else's but I too feel it doesn't sound quite as sweet in it's current chassis although I still have no issues with the sound. The point is, despite a good PSRR (it's high feedback afterall and with big caps on-board), the sound does depend, very slightly, on factors outside the realm of the PCB. The PSU is one factor, another is grounding, another is lead dress which in my case is severely limited by a cramped chassis. Some people think eddy currents in metal casing is another factor by the way. And I didn't even think about vibration isolation.
I have noticed this before, but in that case it was TGM1 and TGM1i and it was MUCH more noticeable - that amp sounds much better at lower power supply voltages and with an EI power transformer than it does with higher voltage rails and a big Toroidal power transformer. The smaller version also has small chokes in each power rail and 0V rail. A different amp, but the experience leads me to think about such things.
You remind me that when I first had TGM8 working it was not in the current chassis and it was with a different PSU too. My sound memory being fickle as anybody else's but I too feel it doesn't sound quite as sweet in it's current chassis although I still have no issues with the sound. The point is, despite a good PSRR (it's high feedback afterall and with big caps on-board), the sound does depend, very slightly, on factors outside the realm of the PCB. The PSU is one factor, another is grounding, another is lead dress which in my case is severely limited by a cramped chassis. Some people think eddy currents in metal casing is another factor by the way. And I didn't even think about vibration isolation.
I have noticed this before, but in that case it was TGM1 and TGM1i and it was MUCH more noticeable - that amp sounds much better at lower power supply voltages and with an EI power transformer than it does with higher voltage rails and a big Toroidal power transformer. The smaller version also has small chokes in each power rail and 0V rail. A different amp, but the experience leads me to think about such things.
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I disagree, there are many similarities between the two.
However, let's take your point that they are totally different... well that just supports my point that (maybe) the PS makes more difference than the amp board/topology.
Or to put that another way: the sound quaity you get from the TGM8 (most likely) depends a lot on the PS!
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There are many key differences between the amps and I can walk you through them if you like. Of course, any gnfb SS class AB amplifier based on the now very familiar 3 stage topology will have common characteristics (input/error amplifier -> VAS -> driver/output). Mooly's amp is a great design in my opinion, unfortunately I didn't build one to hear it but I've no doubt about the quality of the design.
Hi ! thank you very much indeed. Here the discussion gets too complex for me to understand. I was just worried about those 50 Hz residual noise even if maybe not high enough in level to be audible. For instance sometimes i feel like the amp is completely silent and then putting my ear closer to the speakers i hear some kind of hum or hiss ... that 2-3 meters aways is not audible.
There is more noise coming from the street during working hours.
I think we are more sensitive to what happens in the midrange, the voice band ... where often tubes have a great musical performance.
May be i am saying something silly but during the '70s solid state amps had tube amps as competitors ... and i think that designs from that era tried to mimick the tube sound. And many can sound musical. And often they are less complex than more recent designs that can exhibit maybe better measurements.
Thanks a lot again. I will leave the thread to the experts and try to learn something.
Kind regards, gino
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Hi, my build is close enough to silent that there’s no ‘work to do’ but I noticed it does depends on the source. When plugged directly to my Bluesound Node2i digital server, I get a dirty noise/buzz, at a very low level, generally unnoticed but if the house is quiet this noise is audible from my chair on my ~95dB speaker. On the other hand, no sound can be detected when it is plugged into my old Marantz CD player. It’s not a ground loop, the noise is not a clean 60Hz and so I believe the solution requires me to open up the Bluesound and identify the problem before it can be addressed.
Hi ! the same here. Usually the chain is quite silent without a source connected. When i connect it the worse happens. should i try to add a dac that is not causing noise and then use the optical input in the dac ? in this way the source will be electrically isolated from the audio chain.
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correct.
Please note that like many amplifiers, you may get a turn-on / turn-off noise as the speaker protection has a short delay at start up and a rapid disconnect at power down too. It shows up in simulation but I never tried without the protection to see if it is real or even if it’s audible.
Please note that like many amplifiers, you may get a turn-on / turn-off noise as the speaker protection has a short delay at start up and a rapid disconnect at power down too. It shows up in simulation but I never tried without the protection to see if it is real or even if it’s audible.
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Post #1 shows the links.
#238 & #242 - discovery of, and changes to deal with cross-conduction at v. high frequencies
#314 - fix to pcb for very first incarnation (corrected on subsequent pcb layouts)
#407 - pcb files and (a now old) bill of materials
#597 - a bill of materials for Mouser
#604 - my as-built schematic (with C3 shown wrong way around, should be installed + terminal to ground)
#632 - a comment on bias for the output (60mA) note original pcb has a silkscreen error with the bias and dc offset adjust labels swapped around
#645 - a note on correct orientation of C3 (shown wrong way on pcb silk screen)
#768 - some photos and comments on how the power devices mount under the board and the use of some TO-126 transistors with legs removed are used as 'spacers'
#772 - some photos and comments on incorporating an output inductor into the wiring
#950 - updated bill of materials (BOM) based on Digikey.ca
#994 - spice file for the amplifier
#1131 - KiCad files from 'longface54'
#238 & #242 - discovery of, and changes to deal with cross-conduction at v. high frequencies
#314 - fix to pcb for very first incarnation (corrected on subsequent pcb layouts)
#407 - pcb files and (a now old) bill of materials
#597 - a bill of materials for Mouser
#604 - my as-built schematic (with C3 shown wrong way around, should be installed + terminal to ground)
#632 - a comment on bias for the output (60mA) note original pcb has a silkscreen error with the bias and dc offset adjust labels swapped around
#645 - a note on correct orientation of C3 (shown wrong way on pcb silk screen)
#768 - some photos and comments on how the power devices mount under the board and the use of some TO-126 transistors with legs removed are used as 'spacers'
#772 - some photos and comments on incorporating an output inductor into the wiring
#950 - updated bill of materials (BOM) based on Digikey.ca
#994 - spice file for the amplifier
#1131 - KiCad files from 'longface54'