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Old 13th September 2011, 12:52 PM   #101
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Did you take into account that your speakers might becausing the disturbances that you say you hear whith the higher feedback. With better speakers your low feedback might might make your speakers sound way the opposite of what you described and then youd be unhappy again. And what about your source, is this perfect, or might this be the reason for what you hear ???

There is absolutely nothing wrong with feedback except when its of too low value to be useful.

Do you know the thermal distortion amps, Lavardin, they use very high feedback, amounts Im afraid to work with but several audiophiles and several writers in the audio press tribute the highest praise for sound quality for these amps and they have won several awards, now where does this feedback question stand. This amp was stacked up against amps costing 5 times more including tube amps, the writer simply describes them as magnificent. If youd like I can mention some more high feedback amps that have recieved the highest praises and awards for sound quality.
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Old 13th September 2011, 02:16 PM   #102
dadod is offline dadod  Croatia
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Quote:
Originally Posted by homemodder View Post
Did you take into account that your speakers might becausing the disturbances that you say you hear whith the higher feedback. With better speakers your low feedback might might make your speakers sound way the opposite of what you described and then youd be unhappy again. And what about your source, is this perfect, or might this be the reason for what you hear ???

There is absolutely nothing wrong with feedback except when its of too low value to be useful.

Do you know the thermal distortion amps, Lavardin, they use very high feedback, amounts Im afraid to work with but several audiophiles and several writers in the audio press tribute the highest praise for sound quality for these amps and they have won several awards, now where does this feedback question stand. This amp was stacked up against amps costing 5 times more including tube amps, the writer simply describes them as magnificent. If youd like I can mention some more high feedback amps that have recieved the highest praises and awards for sound quality.
Sorry I can not connect that what you write with this thread. Could you bee more specific? This amp is high negative feedback type, just with similar feedback trough whole audio band? I am not against high feedback, just opposite
dado
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Old 13th September 2011, 02:29 PM   #103
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Hi Dadod

From what I understood from your post was that the high NFB was the cause for the sound you described. By putting a resistor accross the compenstion cap you are reducing the loop gain and therefore the feedback at the lower frequencies..

The rest of the post just gives an example of a very high feedback amp winning awards for sound quality which goes against the thinking that NFB is bad.

Last edited by homemodder; 13th September 2011 at 02:31 PM.
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Old 13th September 2011, 02:37 PM   #104
jcx is online now jcx  United States
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Default impressive mental gymnastics to sieze on that rather than the larger point of Putzeys

Quote:
Originally Posted by dadod View Post
After readig "The F-word or, why there is no such thing as to much feedback" by Bruno Putzeys http://www.linearaudio.net/userfiles...olume_1_BP.pdf I decided to lower VAS gain, in case if there is enough gain at 20kHz, in my next project too.
Here what Bruno says and that explain some of reasons why I like the sound more that way:

"A second step in the experiment consisted of placing a resistor across compensation capacitor C
that reduced DC gain to the same value as that at 20kHz (fig 12, trace 4). The test amplifier was of
the folded-cascode persuasion which allowed this. At this stage, loop gain has indeed been reduced
across the full audio range. I surmise that, since the amplifier’s distortion was never negligible, making
it constant across the audio band makes it fly under the psychoacoustic radar more easily.
My own subjective experience would support this. To my ears, amplifiers with the normal 20dB/decade
behaviour but whose distortion is not negligible at the end of the audio range have glassy midhighs,
a “superglue stereo image” as KK once put it and the illusion of spectacularly, unnaturally
tight and impossibly controlled bass. Some love this, and seceded into a subculture of ultra-beefy
amplifiers. I don’t and when forced to make a choice I’ll take higher but consistent distortion across
the band."
dado


so you intend from the start to build amps with audible distortion? - that would be multiple % distortion from most reports

and by assumption of that undesirable conclusion, intend to use sub optimal techniques that assure just that result ruins the whole audible range?
Do you know that most “music” has ~ 3kHz power bandwidth
Or that distortions from nonlinearities with reasonable power series representations decline as higher powers of signal level? – as Putzeys points out

you could also consider that the "AM to FM" conversion mechanism with static nonlinearities interacting with integrating loop gain aren't the only distortion mechanisms that give "rising with frequency" distortions

nonlinear C causes distortion with "flat" loop gain - and it rises with frequency with flat loop gain too

I've even simmed "flat open loop gain" over audio combined with higher order compensation (which TMC is a limited example of) - higher gain at every point in the audio band gives less distortion at every frequency where the gain is usefully higher

Bob Cordell Interview: Negative Feedback (the method shown for the sim of getting 2nd order loop gain isn't too useful in real amps - you could use 2-pole T network bridged for the same shape global loop gain response)
Attached Images
File Type: png tanh_2pole.png (56.6 KB, 311 views)

Last edited by jcx; 13th September 2011 at 02:41 PM.
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Old 13th September 2011, 07:34 PM   #105
dadod is offline dadod  Croatia
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Quote:
Originally Posted by jcx View Post
so you intend from the start to build amps with audible distortion? - that would be multiple % distortion from most reports

and by assumption of that undesirable conclusion, intend to use sub optimal techniques that assure just that result ruins the whole audible range?
Do you know that most ďmusicĒ has ~ 3kHz power bandwidth
Or that distortions from nonlinearities with reasonable power series representations decline as higher powers of signal level? Ė as Putzeys points out

you could also consider that the "AM to FM" conversion mechanism with static nonlinearities interacting with integrating loop gain aren't the only distortion mechanisms that give "rising with frequency" distortions

nonlinear C causes distortion with "flat" loop gain - and it rises with frequency with flat loop gain too

I've even simmed "flat open loop gain" over audio combined with higher order compensation (which TMC is a limited example of) - higher gain at every point in the audio band gives less distortion at every frequency where the gain is usefully higher

Bob Cordell Interview: Negative Feedback (the method shown for the sim of getting 2nd order loop gain isn't too useful in real amps - you could use 2-pole T network bridged for the same shape global loop gain response)
"I surmise that, since the amplifierís distortion was never negligible, making
it constant across the audio band makes it fly under the psychoacoustic radar more easily."

That is what Putzeys says and probably I took it wrongly. In that exsample the amp distortion was never negligible. But in the case of my amp, in my opinion, distortion was negligible without gain redution at low frequences and stayed negligible with the gain reduction. A bonus is better phase behavior, I was afraid a bit of instabillity.
At Loop Gain diagram you can see that there is more then 60dB of negative feedback.
dado
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File Type: jpg LG.jpg (228.2 KB, 292 views)
File Type: jpg FFT1kHz.jpg (159.9 KB, 277 views)
File Type: jpg FFT10kHz.jpg (157.5 KB, 267 views)
File Type: jpg FFT20kHz.jpg (157.2 KB, 257 views)
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Old 19th September 2011, 01:53 AM   #106
vac231 is offline vac231  Switzerland
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Hi all, Dado,

The best way for a beginner like me to tell if an amp gives musical results is building one... For an engineer or technical, the scheme is essential, but I presume not the last word in case of doubt. After building the JLH 80W, whose sound is already very rewarding in the stereo version, Iíd like to go further, in a double mono version this time. I donít intend to build lots of amplifiers because I've no other skills than Ohms law and there are enough to do to improve the whole system before. However I guess this is a good one, doesnít it ? Letís go, for it with your help... For me, this is a challenge.

Could you prepare, Dado, one image for a power supply and amplifier PCBs ? I could then eventually try to design a PCB from them. Iíll prepare a list of components for it, but Iím not sure what is the last version.

Thanks !

Nicola
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Old 19th September 2011, 07:20 AM   #107
dadod is offline dadod  Croatia
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Quote:
Originally Posted by vac231 View Post
Hi all, Dado,

The best way for a beginner like me to tell if an amp gives musical results is building one... For an engineer or technical, the scheme is essential, but I presume not the last word in case of doubt. After building the JLH 80W, whose sound is already very rewarding in the stereo version, Iíd like to go further, in a double mono version this time. I donít intend to build lots of amplifiers because I've no other skills than Ohms law and there are enough to do to improve the whole system before. However I guess this is a good one, doesnít it ? Letís go, for it with your help... For me, this is a challenge.

Could you prepare, Dado, one image for a power supply and amplifier PCBs ? I could then eventually try to design a PCB from them. Iíll prepare a list of components for it, but Iím not sure what is the last version.

Thanks !

Nicola
OK I will check all again as same time passed after I finished my amp. For power supply I will suggest what I used and then you can make dual mono. I'll be back soon.
dado
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Old 19th September 2011, 01:37 PM   #108
dadod is offline dadod  Croatia
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Here is last schematic and bill of materials.
dado
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File Type: jpg AUDIOWOOD.sch.jpg (178.7 KB, 153 views)
Attached Files
File Type: txt Bill of materials.txt (1.0 KB, 50 views)
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Old 19th September 2011, 02:05 PM   #109
dadod is offline dadod  Croatia
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Hi vac231,
Here are PCB layout and PCB to be used for PCB making. Mirrored one is for the photo way to produce PCB and other one is if you whant to use hot iron and laser printer method.
Please check before you start to make PCB and report all errors. Just to remember that on the PCB layout R20 is combination of NFET and resistor, I attached the photo again.
dado
Attached Images
File Type: jpg DADO-T-TMC-2pairs.LAY].jpg (220.2 KB, 151 views)
File Type: jpg NJF-CCS.jpg (33.8 KB, 88 views)
Attached Files
File Type: pdf DADO-T-TMC-2pairs.LAY]-mirror.pdf (31.1 KB, 48 views)
File Type: pdf DADO-T-TMC-2pairs.LAY].pdf (31.2 KB, 51 views)
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Old 19th September 2011, 02:09 PM   #110
dadod is offline dadod  Croatia
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Components layout.
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