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 Post subject: Newbie
PostPosted: 26 Apr 2017, 08:09 
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Joined: 26 Apr 2017, 08:01
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Hi everyone!! Although I've been using tube bass amps fo a good while, I'm new to tube audio. My friend that built my tube bass amp( 4x KT-120's) ( 3x 12AX-7's) He's building me a tube power amp converted from a baldwin organ amp. I want to buy a tube pre, My question is why on a lot of pre's do they only have 2 knobs? Are some volume and a tone??


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 Post subject: Re: Newbie
PostPosted: 28 Apr 2017, 15:01 
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Joined: 01 Jun 2013, 09:05
Posts: 598
JRBASS wrote:
Hi everyone!! Although I've been using tube bass amps fo a good while, I'm new to tube audio. My friend that built my tube bass amp( 4x KT-120's) ( 3x 12AX-7's) He's building me a tube power amp converted from a baldwin organ amp. I want to buy a tube pre, My question is why on a lot of pre's do they only have 2 knobs? Are some volume and a tone??


Standard practice,

on audiophile preamps is to have Two volume controls one for left and one for right channel.
The reason for this is it eliminated the need for a balance pot which in audiophile circles adds distortion.
This can also be done with a duel concentric pot often used by pioneer equipment.

Tone is not normally used or if provided has the ability to be removed from the signal path.

There is a lot more to this however that's the simple answer.
The audiophile argument is also that it changes the loading on cables and frequency response particularly on non driven cables eg passive preamps etc. The idea is cables have capacitance and linked to resistance loading can cause a notch filter.
An example is oscilloscope probes adjustment for square wave response.

link:
https://www.picotech.com/library/applic ... ope-probes

Anyway that's the general audiophile belief..


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M. Gregg

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 Post subject: Re: Newbie
PostPosted: 28 Apr 2017, 15:25 
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Many years ago,

This was investigated in HIFI world magazine I believe they did a project passive preamp with some sort of compensation.
Better to look at other things.. :D
Passive vs powered pre-amps etc and so it goes on.. anyway its of topic ref the question.

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M. Gregg

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 Post subject: Re: Newbie
PostPosted: 28 Apr 2017, 17:57 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I have both kinds and personally feel that the active ones better suit my equipment. I am a believer in less is more in audio gear...but this is one exception. My designs are based around a normal input impedance of around 100K. At that level most passive controls ought not have much effect. However my listening experience differs from that. My sense is that the passive controls have a greater influence on the signal being fed to the power amps due to loading, capacitive or other effects and seem to alter the sound subtly. A well executed line stage will present a nearly constant impedance to the amps and seems to be a better solution to me. YMMV.

Good listening
Bruce

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 Post subject: Re: Newbie
PostPosted: 29 Apr 2017, 03:37 
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Hi Bruce,

Again just my thoughts.
I was surprised many years ago with audiophile cables, the pronounced effect changing from one type to another seemed to have.
Then the realisation that wires seem to "use" or need power, which is obvious really when you think they have a capacitance and resistance.
OK in high frequencies you can get severe signal loss with the wrong wire, which is nothing new.
However I also find "driving" the cables with a pre-amp seems to reduce the effect.
Then again this should be no surprise when you look at TV antenna amplifiers.
Its the trade off of circuit distortion vs cable distortion and passive pre-amps. :D

In the past the argument of having separate pre and power amps vs combined.
(If its combined do you have an audio cable, and does it need a screen etc)

Its a PITA really, dual volume controls. I must admit I can't think of a time except in a car when I use a balance control.
So I make sure the channels are as close as possible with gain and just use a dual pot.
Or I use dual volume controls on the pre and a single dual master on the power.
I always add a master volume to all power amps, then at least you can use them on their own.
Dual power amps with single masters also gives balance.
As you say YMMV.

Regards
M. Gregg

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 Post subject: Re: Newbie
PostPosted: 29 Apr 2017, 12:02 
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Hi, yes the issue of controls is one that will have as many answers as individuals using them. My system has a relay based stereo digital ladder control for volume. Input selection is also by relay control. That is it. I will not say I'm a purist, but I prefer as few things in the signal path as makes sense. There is no balance control, tone controls or filters. All these things can be useful, but only in two situations IMO. First if you have deficient source material. Scratch filters and tone controls may be beneficial. I just refuse to listen to poor copies and will replace it if I really want to hear it. BTW most stuff is now pretty clean. I buy a lot of used bargain bin LPs and after a good cleaning about 75% are just fine. The others go into the don't listen to cabinet. The second case for controls is if your system is deficient in some way. This can be either because of the equipment itself or the room it is located in. Controls can help. If the gear is deficient I replace it. That is one area I will not tolerate. If the gear causes problems in the reproduction of the source material it goes away. Call me a snob if you want, but that is what I do. The problem with rooms however is not so easily solved and indeed not so easy to identify. Knowing that the music doesn't sound right and what is causing it is not simple. I use a calibrated mic and PC with spectrum analysis (by 1/6 octave) software to test the room. No room will ever be truly flat in response with no reflections or nulls. But you can minimize them. I have various reflectors, absorbers and careful placement of the speakers etc in my room. If you don't have the capability (most won't), or the materials to fix room issues then tone controls and balance controls can improve the listening experience. A band aid, but IMO better than nothing. Unfortunately this leads to another of my pet peeves. Many folks set tone controls to highly un-natural levels. It boils down to personal preference. If someone likes chest crushing bass on soft vocal music...OK. Not my thing. I much prefer to hear as much of the artist's intent as comes through in the media I am using. it will certainly not be the "real" thing, but as close as I can get it.

Jumping off my :soapbox:

Good listening
Bruce

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 Post subject: Re: Newbie
PostPosted: 29 Apr 2017, 20:43 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
IME, fitting the speakers to the room can eliminate the need for tone controls or EQ's all together. Tone controlsEQ's don't compensate for a bad setup.

Too many times people are putting big speakers in small rooms or bookshelves in rooms the sq. footage of my whole house!

Once the system is matched for the room, use any controls to compensate for a poor recording.... not poor equipment ;)

:2c:

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 Post subject: Re: Newbie
PostPosted: 02 May 2017, 19:26 
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Joined: 29 Apr 2017, 15:14
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your question was, " why on a lot of pres, there are only two knbs? are some volume and tone?.......I have observed that, daily in my research on diy preamps.
and usually regard them as somewhat incomplete.but you are quite right, one
is volume, and the other tone, but that is hardly the components of a preamp, such
as it is, a pre amp must have, as an iclusive part of its design, ... an input selector
bass, treble and volume controls, at the very least.any preamp that lack these
important features, places the user, with the inability to select the features of
the music, that suits him best, since we are all different types of the same species
our listening preferences differ, as well, so, any preamp built with only a volume
and tone control, is only suitable for our listening pleasure, at the barest minimum.


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