I have some boards left over, please PM me for details!
I have some questons about the TGM8: the big caps are rattling if I gently knock them with my finger. Each of the caps makes a noise as if something inside was loose. For the sound: as long as I play "tidy" music everything is incredible clean and beautiful. But with complicated stuff the amp starts to become "untidy", especially when the percussionist plays fast and uses a lot of high hats and cymbals. I tried to use an external PSU to feed clean DC to the amp boards (from a nice H+F 450VA transformer), but no improvement. Even dual mono transformers (2x H+F 450VA and 2 PSUs) didn't change anything. As an example, this kind of "busy" music I mean: that recording is borderline compressed and at the limit in every respect, but can sound extremely good if the system is capable (BTW I use this recording also to test for fatigue). This track from the same CD sounds fantastic! (Of course I have the original, online compression makes this recording almost unusable)...
What else can be done?
I have some questons about the TGM8: the big caps are rattling if I gently knock them with my finger. Each of the caps makes a noise as if something inside was loose. For the sound: as long as I play "tidy" music everything is incredible clean and beautiful. But with complicated stuff the amp starts to become "untidy", especially when the percussionist plays fast and uses a lot of high hats and cymbals. I tried to use an external PSU to feed clean DC to the amp boards (from a nice H+F 450VA transformer), but no improvement. Even dual mono transformers (2x H+F 450VA and 2 PSUs) didn't change anything. As an example, this kind of "busy" music I mean: that recording is borderline compressed and at the limit in every respect, but can sound extremely good if the system is capable (BTW I use this recording also to test for fatigue). This track from the same CD sounds fantastic! (Of course I have the original, online compression makes this recording almost unusable)...
What else can be done?
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Weird, never encountered capacitors with an internal rattle (I buy only from known good vendors). Could it be as simple as the caps being close enough to each other that they are rattling against each other ?
Great to see some listening impressions and the start of your explorations. In general, I have read that problems with complex music shows up as sounding muddy if there’s too much inter-modulation distortion. I think there would have to be quite a lot more distortion from this amp to produce that kind of problem though. And I’m not sure that type of distortion would ever be described as ‘untidy’. The sound at high frequencies can be influenced by lots of things, the feedback compensation being one of them. I’ve not observed anything untoward but my hearing rolls off earlier these days, not as good as it was when I first built this amp so now there’s ‘nothing left’ by 14kHz to 15kHz.
Keep going! it’s good that you are familiar with your own system i.e. source, speakers, room etc. and will be sensitive to anything that sounds differently from what you’ve been using beforehand.
Great to see some listening impressions and the start of your explorations. In general, I have read that problems with complex music shows up as sounding muddy if there’s too much inter-modulation distortion. I think there would have to be quite a lot more distortion from this amp to produce that kind of problem though. And I’m not sure that type of distortion would ever be described as ‘untidy’. The sound at high frequencies can be influenced by lots of things, the feedback compensation being one of them. I’ve not observed anything untoward but my hearing rolls off earlier these days, not as good as it was when I first built this amp so now there’s ‘nothing left’ by 14kHz to 15kHz.
Keep going! it’s good that you are familiar with your own system i.e. source, speakers, room etc. and will be sensitive to anything that sounds differently from what you’ve been using beforehand.
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The caps are SLPX series by CDE from Mouser and don't touch each other (I checked carefully because I also coudn't believe that something inside a cap yould rattle). As for the sound: I am not sure it's related to distortion. I also experienced this with Aleph amps (a diy Aleph UP and a Aleph 5 iirc), they also sounded chaotic (but only in the lower registers) when music got complex. Many amplifiers do that, I heard it often. Noticeable also with classical music (big Orchestra), but impossible to detect with small Jazz groups or music without a certain amount of complexitity. But as soon as the listener needs to follow a lot of individual voices it makes a great difference: less listening "effort" means easier listening and better understanding of what's going on in the music. I would be interested in your opinion on that if you manage to compare the TGM8 with your TGM10 as Naim usually does well in this regard. You did mention that you preferred the TGM8 to the TGM10, but this kind of thing would be interesting to compare as well...
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To my ears the Naim 160 clone had a distinctive sound of it’s own, it has a texture, not at all like the TGM8 (clean) or any of my other amps. The Naim sound that I hear matches some of the descriptions from reviews I’ve read of their old amplifiers. To my ears, the treble on the Naim was an acquired taste and didn’t suit all the music I like. But that’s going from memory several years back now. My TGM1 has a sound of it’s own too, inspired by Hugh’s AKSA.
I can’t really comment on your question of ‘untidy‘ sound because I’ve never heard it do that. I’ve never heard the Aleph either. Maybe I would get a better sense of your impressions using your recording and similar speakers. At the present, my other amplifiers are not wired up but I’d like to put them back together sometime so I can hear the Naim clone and the latest version of TGM1. I have a new TT and a different CD player than was in my system back then.
I can’t really comment on your question of ‘untidy‘ sound because I’ve never heard it do that. I’ve never heard the Aleph either. Maybe I would get a better sense of your impressions using your recording and similar speakers. At the present, my other amplifiers are not wired up but I’d like to put them back together sometime so I can hear the Naim clone and the latest version of TGM1. I have a new TT and a different CD player than was in my system back then.
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Interesting comment on intermodulation, Bigun.
I was discussing this with a committed audiophile and EE and he thinks intermodulation is created in conventional long tailed pairs.
Many years ago I found that making up a LTP using CFPs, complementary feedback pair giving four devices for one LTP, fixed much of this intermodulation.
This shows, I think, that the operation of a LTP, where one reduces current while the other increases, giving a variation of gm, leading to distortion.
Hugh
I was discussing this with a committed audiophile and EE and he thinks intermodulation is created in conventional long tailed pairs.
Many years ago I found that making up a LTP using CFPs, complementary feedback pair giving four devices for one LTP, fixed much of this intermodulation.
This shows, I think, that the operation of a LTP, where one reduces current while the other increases, giving a variation of gm, leading to distortion.
Hugh
So the TGM10 is a 160 clone? I never heard one, and the only unregulated Naim I know well is the NAP90. I owned a 140 briefly but prefered the regulated amps. So my Naim clone is also regulated. But I agree it's not as neutral as the TGM8.
Interesting that you mention texture! I find many modern amps too smooth (not to speak of those super smooth DACs). Many instruments have texture. But if an amp adds texture that is not in the recording...
Interesting that you mention texture! I find many modern amps too smooth (not to speak of those super smooth DACs). Many instruments have texture. But if an amp adds texture that is not in the recording...
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Strictly speaking, the TGM10 amplifier was designed by reverse engineering the NAP110 and ‘fixing’ the Vbe thermal control. But no doubt you are aware that the original NAP amplifiers are basically all the same and differ by their power supplies. My first build was anywhere from the 140 to 180 depending on psu. And the sound does have a dependency on the psu details. One day I fancy reverse engineering the more modern Naim regulator, just for fun. FYI, although the TGM8 is my go-to solid state amplifier, I‘ve no self-imposed restrictions on using amps that have a sound of their own such as the Naim.
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Minimising gm variation can be achieved to some extent simply by minimising signal swing relative to the standing current/voltage headroom. Take a transistor and operate it at high voltage
indeed, as we’ve discussed before, the LTP is a building block for a Gilbert cell, a mixer, and depending on how well you decouple the power supply it can be a fundamental contribution to the sound of the amp - my TGM1 benefits from this approach.
The 'speed-up variation' for the DC protection circuitry shown in the TGM10 thread seems like a worth while modification, however I want to use my existing TGM8v5B boards as is without modification so I was thinking of simply changing the following resistors and caps, and retaining the dual colour LED section.
(numbers on the original TGM8 circuit)
R33 - 1k to 10k
R35 - 4k7 to 1k
R36 - 100k to 560k
R38 - 4k7 to 10k
C20 - 47uF to 33uF
But don't use the green LED
Don't use the 1uF 'speed up' cap
I've been simulating using the values proposed and found that the 'speed up' cap didn't contribute much so I am happy to leave it off.
My sim gives an approx DC fault trigger time of 13 ms.
My question is around the susceptibility to false triggering low signal freq. After all, an extreme low Hz, high voltage swing speaker signal starts to look like a DC fault. As Gareth explains it 'R32 samples the amplifier output and together with C16 forms a low-pass filter so that the circuit is sampling the average dc-level ' so I have been fooling around with different values here.
In my sim it looks like the circuit as suggested is great at lowish signal levels but once the speaker output at 20Hz is above 33 v peak (66 v p/p) the protection starts to trigger. At 15Hz I see triggering starting at 25 v peak. Yes I know that this is extreme output and there shouldn't be any signal below 20Hz, but it is with such low bass that the largest voltage signals will occur, particularly in home theatre situations.
So perhaps it is a non issue?
Have any builders of the TGM8 had any false triggers?
And finally, have any builders ofthe TGM8 had the protection trigger with a real live fault?
**************************************
Caveat re my sim
I know that they are only a sim, not real world.
And in my case, because all my stuff is in storage for a year and I'm house minding in the country, I don't have my desktop PC and only have a chromebook. This forces me to use a web based sim (multisim) that is pretty clunky and has a poor library. I have tried to input the models Cordell has on his site, for the transistors but I am not sure they work 100%. So please take my post above with a great big grain of salt.
....great with chips!
https://www.diyaudio.com/community/attachments/dcprotect-speedup-jpg.612241/
(numbers on the original TGM8 circuit)
R33 - 1k to 10k
R35 - 4k7 to 1k
R36 - 100k to 560k
R38 - 4k7 to 10k
C20 - 47uF to 33uF
But don't use the green LED
Don't use the 1uF 'speed up' cap
I've been simulating using the values proposed and found that the 'speed up' cap didn't contribute much so I am happy to leave it off.
My sim gives an approx DC fault trigger time of 13 ms.
My question is around the susceptibility to false triggering low signal freq. After all, an extreme low Hz, high voltage swing speaker signal starts to look like a DC fault. As Gareth explains it 'R32 samples the amplifier output and together with C16 forms a low-pass filter so that the circuit is sampling the average dc-level ' so I have been fooling around with different values here.
In my sim it looks like the circuit as suggested is great at lowish signal levels but once the speaker output at 20Hz is above 33 v peak (66 v p/p) the protection starts to trigger. At 15Hz I see triggering starting at 25 v peak. Yes I know that this is extreme output and there shouldn't be any signal below 20Hz, but it is with such low bass that the largest voltage signals will occur, particularly in home theatre situations.
So perhaps it is a non issue?
Have any builders of the TGM8 had any false triggers?
And finally, have any builders ofthe TGM8 had the protection trigger with a real live fault?
**************************************
Caveat re my sim
I know that they are only a sim, not real world.
And in my case, because all my stuff is in storage for a year and I'm house minding in the country, I don't have my desktop PC and only have a chromebook. This forces me to use a web based sim (multisim) that is pretty clunky and has a poor library. I have tried to input the models Cordell has on his site, for the transistors but I am not sure they work 100%. So please take my post above with a great big grain of salt.
....great with chips!https://www.diyaudio.com/community/attachments/dcprotect-speedup-jpg.612241/
I just tested the behaviour of my TGM8: yes, it plays stable down to 20Hz with a 2V sine input (full power with my 40V rails) into a 8R load. Below 20Hz it starts to trigger the protection circuit, at 15Hz the portection tries to switch off after a couple of seconds but goes on again, at 10Hz the portections stays permanently on. The values are as in attached diagram which shows my TGM8 as built. Question: obviously I omitted R37, is that a problem?
Attachments
Thanks JPK for checking this out for me. I can't see how the omission of R37 would effect the triggering.
One reason I was a little dubious of my own sim was that I found that leaving out the 1uF 'speed up' cap actually gave a faster trigger! ....but I can't imagine Gareth would have added it if this was actually the case. One reason I was concerned was that Rod Elliot's protection circuit works down to 5Hz and he usually knows what he's doing.
Anyhow, although a larger margin for the triggering freq at full output would be nice, that fact that it still works OK at 20Hz (and much less than that at lower output) may be good enough in the real world. So I will go ahead and use the suggested component values and suck and see. Probably never going to be an issue.
(For the record my sim was using 45v rails and C20=33uF)
Thanks again JPK ...and Gareth
One reason I was a little dubious of my own sim was that I found that leaving out the 1uF 'speed up' cap actually gave a faster trigger! ....but I can't imagine Gareth would have added it if this was actually the case. One reason I was concerned was that Rod Elliot's protection circuit works down to 5Hz and he usually knows what he's doing.
Anyhow, although a larger margin for the triggering freq at full output would be nice, that fact that it still works OK at 20Hz (and much less than that at lower output) may be good enough in the real world. So I will go ahead and use the suggested component values and suck and see. Probably never going to be an issue.
(For the record my sim was using 45v rails and C20=33uF)
Thanks again JPK ...and Gareth
What case are you using? I had the same experience with my Aleph J at high volumes and specific frequencies (exactly as you described), which made the Modushop deluxe 5U case ring like a church bell... terrible!!! I could clearly hear this from my speakers. I fixed the issue by placing the whole amp on 3 hollow ceramic cones with a very thin "wall" (can't find a better word for it.... see below). The cones were great in completely killing the ringing, plus the space / 3D improved substantially. Give it a try...
https://www.martinloganowners.com/threads/report-on-new-isolation-cones.4336/
here as well... with a great photo: https://www.stereonet.com/forums/topic/598448-ra-design-lab-isolation-footers/
Here's something I learnt re captors... the cylinder sizes are standardised; the manufacturers will not make tiny cylinder size adjustments to fit the coiled/foiled aluminium "ribbon" to fit EXACTLY into the cylinder.
In other words, you may find that for the same nominal voltage (for example 50V DC), and the capacitances of 5600uF, 6800uF and 10000uF, the cylinder size is the same. In that case, go for the 6800uF because the empty space left inside the cylinder will be populated by a rubber ring (the space will not be left empty, like with cheap Chinese ripoffs). So, the 6800 uF cap in that case will have some rubber inside to dampen mechanical oscillations.
Give it a consideration, and definitely try what I suggested above - you'll be surprised.
Another option is to use large, heavy & expensive filter capacitors... like Nichicon Gold Tune 10000uF 50V. Their special construction and "heavy and inert" dielectric will make them completely immune to vibrations.
In other words, you may find that for the same nominal voltage (for example 50V DC), and the capacitances of 5600uF, 6800uF and 10000uF, the cylinder size is the same. In that case, go for the 6800uF because the empty space left inside the cylinder will be populated by a rubber ring (the space will not be left empty, like with cheap Chinese ripoffs). So, the 6800 uF cap in that case will have some rubber inside to dampen mechanical oscillations.
Give it a consideration, and definitely try what I suggested above - you'll be surprised.
Another option is to use large, heavy & expensive filter capacitors... like Nichicon Gold Tune 10000uF 50V. Their special construction and "heavy and inert" dielectric will make them completely immune to vibrations.
Oh, I did exactly the opposite and took the largest value cap in the same size can. It has 6800uF. Might be the reason for the rattling...?
My TGM8 is still without case BTW, but thanks for the hint about the cones!
And yes: I used Mundorf 22.000uF caps offboard. In my other amps they sounded so much better than anything else...
My TGM8 is still without case BTW, but thanks for the hint about the cones!
And yes: I used Mundorf 22.000uF caps offboard. In my other amps they sounded so much better than anything else...
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My neighbour across the road has an antenna mast and once in awhile I get a chance to hear Morse Code from my speakers. Todat I dug out some C0G capacitors from my junk box to make an r.f. filter at the RCA input connectors. The mains power is already filtered. I added an RC filter both inputs with corner frequency of 200kHz. If it fails to be the solution I’ll find out when he next transmitts, if it works I’ll never know 😀
