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Old 3rd January 2013, 08:48 AM   #31
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I'll post some scope shots tomorrow. I would have posted them sooner, but I'm almost embarrassed to post them, kind of makes me look like I'm crazy. They won't be pretty, and they are guaranteed to make me look like a fool, or someone who likes distorted sound. But I'll do it anyway. I should print a disclaimer on the pictures "it sounds better than it appears".


I would love to post the preamp schematic, if it were only that easy. I reverse engineered this.3
schematic, and that's the simple part of the amp, the preamp has way more components than the power amp section, despite it not even having a phono stage. I have once copied the amp circuit and tried it, and it sounds much different than the original. I think they designed them to work together. Since there's so many people interested, I'll reverse engineer the preamp too. It's not fair to just give people only half an amp.


I wonder how the condition of the components in the amp changes the sound quality. Several capacitors in the amp are over-voltaged from the factory. Like in the preamp there's a 25v 1000uf with 33 volts on it. Alot are 25v with 27 volts on them. No circuit fault, they just put too low of voltage caps in several places of the amp. I'm kind of amazed, it seems if a cap has seen too high of voltage since day one, then it's okay with it, like it becomes used to the voltage. I know all about the volt rating of caps and would never purposely do that to a circuit, it's literally playing with fire. In the amp the cap has alot of resistance in front of it, like 1K, so if it shorted, nothing would explode. I think it's for the tape amp section. It's worth noting this amp has nothing to to with the tape recorder, that has a separate chassis.

I wonder if I could post a sound clip somehow?


Keith
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Old 3rd January 2013, 08:51 AM   #32
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by repair guy View Post
I'll post some scope shots tomorrow. I would have posted them sooner, but I'm almost embarrassed to post them, kind of makes me look like I'm crazy. They won't be pretty, and they are guaranteed to make me look like a fool, or someone who likes distorted sound. But I'll do it anyway. I should print a disclaimer on the pictures "it sounds better than it appears".
Not at all. I post many many scope shots on here to get a point across. Even sussed out how to attach video clips (without youtube )

A sound clip probably wouldn't reveal much tbh because its not the same as hearing it in situ driving the real speakers.

I would suggest trying around 1Khz and 10Khz square wave tests at around a couple of volts peak to peak output into 8 ohms.
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Old 3rd January 2013, 09:57 AM   #33
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Quote:
Originally Posted by Mooly View Post
A sound clip probably wouldn't reveal much tbh because its not the same as hearing it in situ driving the real speakers.
Well, a sound clip can give you a good indication of the system.
Here is an example: Voxative Acoustic, KR Audio, Gregitek, highend electronics - YouTube
Play it in HD mode.
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Old 3rd January 2013, 10:04 AM   #34
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Default It is not promising into the simulator.

to me this is enough...biasing is wrong...i had to tweak a lot, fourier analises result in a tragedy......3.5 volts in the output..too much sensitive in the input...well...i give up about this one.

But i do like to listen...set a movie camera and make a recording..then post it in Youtube.

You see...it is possible to make reasonable recordings if you use 1 watt and 1 meter from the speaker....have to use matresses and all absorbing material around...it is not that easy..also have to enter a digital processor to remove noise from the recording....hissing noise.

Camera was Kodak Playfull Ze1, one meter distance and microphone sensitivity reduced to the maximum i could.... a fifty dollar camera did this job..imagine a good one what can do.

Dx Super A - MKII - good sound with poor speaker - YouTube

regards,

Carlos
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Last edited by destroyer X; 3rd January 2013 at 10:31 AM.
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Old 3rd January 2013, 11:04 AM   #35
oshifis is offline oshifis  Hungary
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Remember the once infamous Sugden A48? Another "tube sound" from a (technically) poor design...
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Old 3rd January 2013, 12:35 PM   #36
wahab is offline wahab  Algeria
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So called tube sound come from the upper power device being current
base starved at high output power while the negative side can supply
enough current thanks to the VAS not being current limited , hence
the circuit will clip assymmetricaly , firstly on the positive side of the signal
wich will in principle induce high level even harmonics.

I guess that overall it is the sound of a poorly behaving tube amp......
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Old 3rd January 2013, 01:26 PM   #37
Mooly is offline Mooly  United Kingdom
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This is the distortion plot at 1 watt into 8 ohms in Ltspice.
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Old 3rd January 2013, 03:48 PM   #38
cotdt is offline cotdt  United States
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Quote:
Originally Posted by Mooly View Post
This is the distortion plot at 1 watt into 8 ohms in Ltspice.
No wonder it is said to sound so sweet! It has relatively high levels of monotonically decreasing harmonic distortion. This creates a "fat" sound like certain classic tubes ie 6SN7.
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Old 3rd January 2013, 10:36 PM   #39
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Default Sound tests, recording with digital camera, if good camera

can show you quality..... this is the best sound i have found in the internet

This one is Class D, but has error correction, a kind of digital negative feedback applied.

This one beat mine amplifiers.... or matches, as i have no KEF speaker to test together my ones..but this one is really awesome.... I use to say that i gonna eat my amplifier if you find another one able to beat it..... i will have to say this exception.... this NAD together this KEF is one exception.

Listen the quality.... we can perceive quality easy..even if recording is not that good.

You see audio does not scratch as a demo published from some tube amplifiers that sounded very bad in my opinion.

NAD C390DD.... this one is hard to beat.

KEF LS50 SPEAKERS - YouTube

http://www.youtube.com/watch?v=8jA9zOr-1e0

regards,

Carlos
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Last edited by destroyer X; 3rd January 2013 at 10:48 PM.
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Old 10th January 2013, 01:32 PM   #40
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Quote:
Originally Posted by destroyer X View Post
can show you quality..... this is the best sound i have found in the internet

This one is Class D, but has error correction, a kind of digital negative feedback applied.

This one beat mine amplifiers.... or matches, as i have no KEF speaker to test together my ones..but this one is really awesome.... I use to say that i gonna eat my amplifier if you find another one able to beat it..... i will have to say this exception.... this NAD together this KEF is one exception.

Listen the quality.... we can perceive quality easy..even if recording is not that good.

You see audio does not scratch as a demo published from some tube amplifiers that sounded very bad in my opinion.

NAD C390DD.... this one is hard to beat.

KEF LS50 SPEAKERS - YouTube

Audio Advisor - NAD C 390DD Direct Digital DAC Amplifier - YouTube

regards,

Carlos
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