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Multi tubes amps what effect does each has?
Multi tubes amps what effect does each has?
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Old 23rd February 2018, 03:58 AM   #41
raybies is offline raybies  Australia
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Distortion Graph

Here's another review of the amp and the reviewer is says this about tube rolling...
Code:
It not only made a difference but it made a huge difference, so much so as to say this was not the same amplifier any longer. That is saying quite a bit considering how well this amp, in its stock configuration, works.
Grant Fidelity A534 Tube Integrated Amplifier & CD-327A CD Player Review - Dagogo
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Old 31st March 2018, 09:48 AM   #42
DF96 is offline DF96  England
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You believe what a reviewer says?
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Old 31st March 2018, 10:11 AM   #43
waxx is offline waxx  Belgium
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Quote:
Originally Posted by raybies View Post
Distortion Graph

Here's another review of the amp and the reviewer is says this about tube rolling...
Code:
It not only made a difference but it made a huge difference, so much so as to say this was not the same amplifier any longer. That is saying quite a bit considering how well this amp, in its stock configuration, works.
Grant Fidelity A534 Tube Integrated Amplifier & CD-327A CD Player Review - Dagogo
That there is no effect on changing tubes of the same type but different brands is ********, just like saying the difference is huge. The effect of tube rolling is very subtile in my ears, and spending a lot of money for a rare NOS for that is ******** for me.

I did also try a few tubes out before i settled with the ones i have now in my amp. But they were all reasonable priced new tubes that i had laying arround but one expensive winged c EL-34 set that i lended from a tube nut to test. The winged C did sound very good, but not good enough to spend 100 a piece on compared to the Prima Luna (Shuguang) EL-34's that came with my amp and cost 25 a piece and that are also very good... Idem with other tube types (KT88 and KT120's) in this amp... At the end i did go back to the excellent stock tubes of my Prima Luna Prologue 4 as they do fit the amp very well. Idem with the driver and inverter tubes on that amp. I even ordered a spare set from the manufacturer as they are very good and cheap.

To conclude: If you got quality tubes that fit your amp, tube rolling is not relevant and won't change that much. But if you're after the last 1% and got lots of money to spend for little differences, it may do something you like...
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Old 1st April 2018, 12:47 AM   #44
raybies is offline raybies  Australia
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I've clued myself up a tiny bit on tube theory and circuit design, and I'm struggling to find a compelling technical reason why in a circuit with negative feedback, tube rolling would make any acoustic difference if the tube is within spec., and the plates support the supplied voltage/anode current... I'm guessing some tubes have a higher loss than others making them more or less efficient... like pentode vs triode.

Another aspect which shouldn't impact acoustic signature is the interelectrode capacitance... bcos it only affects very high freqs.

Even a simple mono design like Rectifier > Preamp > Final Stage the difference should be minimal unless there's difference in control grid of the tubes.

Right?

Also why aren't there amps where you can dial in the negative feedback?
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Old 1st April 2018, 01:07 AM   #45
audiowize is offline audiowize  United States
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Quote:
Originally Posted by raybies View Post
Also why aren't there amps where you can dial in the negative feedback?
Some guitar amps have this.

When you have too much NFB, stability is a problem and you may run out of gain. When you don't have enough NFB, problems like distortion, damping, and noise can creep up. If the window between these two extremes is something like 15-20dB of feedback, what actual use is the control? (in a hifi amp at least)
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Old 1st April 2018, 01:14 AM   #46
raybies is offline raybies  Australia
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Originally Posted by audiowize View Post
what actual use is the control? (in a hifi amp at least)
I'm a noob, so I could be way off on this, but NFB is just looping the signal back, if you could dial it, couldn't you also dial all the attributes of the signal?
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Old 1st April 2018, 01:17 AM   #47
audiowize is offline audiowize  United States
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I think it depends on what attributes you'd like to change. You can put tone controls in a feedback loop, but in a power amp this isn't the best plan.
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Old 1st April 2018, 02:18 PM   #48
DF96 is offline DF96  England
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Negative feedback has to be designed in or designed out, you can't just add it like salt to a meal. Every amp with variable feedback is a sign that the designer does not understand feedback and assumes that his customers don't understand it either.
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