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Old 18th February 2011, 07:05 AM   #21
WuYit is offline WuYit  Sweden
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Hi,
can it be simpler?
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Old 18th February 2011, 06:06 PM   #22
hbc is offline hbc  United Kingdom
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Hi Ontoaba,

No particular problem with CFP, apart from occasional slight instability when using high capacitance, low inductance speaker cables, my preferred. However any amount of feedback does stuff (good and bad), so I want to be free of it as much as possible for this project. And ditto those long tailed pairs etc especially in high gain ccts.


Brief interlude, the amp is playing in the office on my good speakers as I write, so good, so good.... anyway


Hi WuYit,
yes that circuit looks simpler, but it does not drive the speaker which is what I am doing here, therefore, over all, no, probably not simpler.


Just so no confusion, here are some stripped down circuits of what I am aiming at, everything is fairly interchangeable device wise, just pick your flavour, the tube fet one would probably work as the “most minimal” if gate capacitance etc don't get in the way, all tube one will sort of work, got to love that volume control, with variable output damping as well.... mmm a bit more thought required there maybe, but it would work and I bet it would sound pretty good...
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Old 18th February 2011, 11:31 PM   #23
hbc is offline hbc  United Kingdom
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Default sulk

Grrr, I was wondering if anyone else had discovered the “2x oversampling” by inverting WS and of course they have..., I don't quite subscribe to GuidoB's friends (see below) observation of 16dB down at 20k, more like 7dB in my case, (2x nos 3.5dB). So unfair... never mind fortunately only three wires to rearrange.

I must say I had noticed it felt maybe a little rolled off, but did not measure frequency response recently, and have been just enjoying having it working, not really knowing what to expect.


Quote:
Originally Posted by guido View Post
theory:
non os : -0.8 dB at 10kHz, -3.5 dB at 20kHz.
shift -2.5 dB at 10kHz, -16 dB at 20kHz.

Somebody that knew what i was doing wrote me this (i didn't back then):

> Hi Guido,
> Your DAC would implement the equivalent of a 2-point moving > average filter, i.e. with impulse response h=[1 1]. You can read > more about those here: SAIC: Products: X-ray passenger vehicle inspection VACIS XPL
> This filter will have a lot of high frequency roll-off, -2.5dB at
> 10kHz, -16dB at 20kHz, so I am not sure what you mean
> with "high freq rollof of a true non-os dac is gone". On the
> other hand this filter has a very good time-domain response
> with no ringing, and it will reduce aliasing distortion quite
> significantly. I would think, although I have never heard one,
> that it makes a non-os DAC sound much more pleasant.
A wise man once said “there is nothing new under the sun” the more I know, the more convinced he is right. One of the joys of having ones memory erased on entry to this adventure playground I suppose.
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Old 19th February 2011, 01:59 AM   #24
ontoaba is offline ontoaba  Indonesia
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Hi, h.
Seem that your variation with MOSFET doesn't work, it has no back current to that volume pot, and only work as voltage follower. EF itself is feedback, it has little output correction through limited Vbe and its constant (or almost constant) current gain that draw current from input.

Anyway, YAC516 has 8x oversampling, but still 24bit 96kHz will do better. I have 32bit from AT&T but I don't know it is too much for audio.

May be the most significant effect is that volume pot (passive damper, I am waiting your link working, or do you have another archive?).
If you allowed small global feedback as active damper, may be there will be easier.
How about built another new with feedback that will compared to your only one. (just a thought)
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Old 22nd February 2011, 11:37 PM   #25
hbc is offline hbc  United Kingdom
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Had a brief diversion to the digital line level forum to sort out the -3.5 dB or -0.6 dB at 20kHz conceptual problem I had, the long and short of it is that my amp has an indicated 47% "THD+N" at 20kHz, and I embrace the "distortion".... This is one of the reasons I did this project, to break a few rules. Please see below distortion and amplitude measurements taken at 1 watt output recorded from my pc (ARTA m-audio) and Sound Technology 1700B distortion analyser.

see below.

Hi Ontoaba, I must point out the above diagrams are for indication of general topology rather than working circuits, the obvious mistake is the tube's cathodes are not on the same rail as the -ve output rail, but need to be at least 40 volts lower. I don't understand why you think the mosfet circuit won't work. It is a very common output configuration. You are right none of them are particularly linear, but good enough for this project.
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Old 23rd February 2011, 12:35 PM   #26
ontoaba is offline ontoaba  Indonesia
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Very big differences. There is something wrong with your SoundTech 1700, probably another failure not repaired yet. Your amplifier is not type that distorted by slowness or lags.

7% distortion and up are easily noticed by ears, <5% is OK, that you may embracing with it.

The mosfet problem isn't only that tubes operating voltages, but also the damper will not functional. All tubes one also need 5W pots.

Hi, what if using your project to also find the truth about feedback, you may find many things and noticing the differences between your mosfet and bjt circuit, and you may like my linearized EF to be used too. I have another more precise and complex version with mosfets, using single rail with switching assistant.
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Old 23rd February 2011, 10:24 PM   #27
hbc is offline hbc  United Kingdom
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Hi Ontoaba. Sound tech works fine, its "problem" is a distortion measurement bandwidth of >100kHz according to data sheet, unlike the m-audio which stops at 22kHz... My problem is what to call the distortion, because it is not really THD, may be just TD... It is a pity my site is not up, I think it is quite broken and not sure how to fix it short of moving it to a new host. yes i agree about the all tube circuit, it is a bit silly...
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Old 24th February 2011, 12:59 PM   #28
ontoaba is offline ontoaba  Indonesia
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It is strange... hmm.. let me think... ARTA work with soundcard, if the soundcard has 20KHz maximum frequency, that it will still measuring H2 at 10kHz and H2,3,4 at 5kHz and up to H20 at 1kHz. I remember with shorted tantalum that been removed from SoundTech, did you replace it with another or just remove it? may be that cap is crucial.
Low distortion figures isn't everything. I ever try to built an amp with very low distortion at resistive load, but my other amp with much higher distortion beat it.
Haa.. I remember something. How about test your soundtech with another amp.
I am also interested how ARTA using microphone configuration in L/R setup, it is worth to be tried.
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Old 14th March 2011, 01:28 PM   #29
hbc is offline hbc  United Kingdom
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Default Revised DAC stage

.
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Old 15th March 2011, 03:17 AM   #30
WuYit is offline WuYit  Sweden
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Hi,
J-FET instead of BC548 is a much better and much more elegant solution. I would use just one DAC and would omit C10/13.
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