Amp/Preamp Asylum

Looking for a new Amp or Preamp? If you're after tubes, post over here.

Return to Amp/Preamp Asylum

Balanced Output from Preamp to Amp

198.179.173.2
Posted on October 27, 2009 at 13:31:29
milpai
Audiophile

Posts: 350
Location: California
Joined: August 21, 2005
 Hi,
Can somebody please let me know if it would make sense to make a balanced connection between a preamp and a power amp, despite not having balanced connections between source and preamp? Any advantages or disadvantages? I am researching for an amp to match with my TVC that has balanced and unbalanced outputs. But I do not have a CDP with balanced connections. So will it make any difference if I connect my TVC and power amp using balanced connections?
I understand from some threads that people feel that single-ended (unbalanced?) is more musical than Balanced connections.

Thanks

RE: Balanced Output from Preamp to Amp, posted on October 29, 2009 at 07:12:51
milpai
Audiophile

Posts: 350
Location: California
Joined: August 21, 2005
 Thanks guys. The Promitheus user manual states that the TVC is a truly balances design. So I guess, it might as well be worth going balanced from TVC to power amp. I would not be using ICs greater than 3 feet.

RE: Balanced Output from Preamp to Amp, posted on October 28, 2009 at 09:17:29
SimonTJU
Audiophile

Posts: 2395
Joined: February 4, 2001
 If your preamp is truly balanced then as AW described its worth to utilize this capability.

If its not so - still you will improve your sound gain provided that:

a) your power amp has, at least, truly balanced input

AND

b) you use long interconnects and/or your have a hum/noise in upstream to power amplifier components/cables

Otherwise, you will not gain at all or more probably will loose a bit.

Regards
Simon

It depends totally..., posted on October 27, 2009 at 16:40:11
Allen Wright
Manufacturer

Posts: 4737
Location: Schaffhausen
Joined: January 31, 2002
 ...on how the device that does the conversion from unbalanced to balanced actually does it.

With no data on your TVC, I cannot even guess. With a proper differential balanced preamp, it will take your unbalanced CD player signal and convert it accurately to a balanced signal, but unless it is a differential preamp(rare) it may well mess it up.

Some preamps that claim to be balanced, such as the very expensive FM Acoustics, are not balanced at all, but have a balanced to unbalanced stage at the signal input to convert to unbalanced internally, where all processing is done, and then they convert back to balanced at the outputs.

This is so far from KISS it makes no sense, and if your equipment is so configured, then I say it's best to stay unbalanced all the way.

More info?

Regards, Allen

RE: It depends totally..., posted on October 27, 2009 at 19:41:58
Kat Rand
 I did not know a differential pre-amp would change unbalanced to balanced; I guess it unlikely ARC pre-amps are differential pre-amp?

I do not think going from an unbalanced to a balanced would mess it up, just not do much at all. I have one system balanced from CD to Pre-amp- to power amp, then DVD and VHS and tuner to RCA on pre-amp, I see no problem with this other than it not being full balanced.

RE: It depends totally..., posted on October 28, 2009 at 16:04:53
KnobSpinner
Audiophile

Posts: 13
Location: Rural Washington State
Joined: August 13, 2009



I have an ARC LS-22 That is fully balanced. The schematic clearly shows this. A single ended signal is converted to balanced in the first stage.
I'll try to post. This schematic is for one channel only.
(Worshiping at the Universal Music Altar)
RE: Wow., posted on October 29, 2009 at 08:42:35
Ralph
Manufacturer

Posts: 1157
Location: Minnesota
Joined: April 24, 2002
Contributor
  Since: April 1, 2002
 Yikes! I knew ARC was conservative, but this amazes me! There are a lot of missed bets in this design...

Now now Ralph..., posted on October 29, 2009 at 16:22:13
Allen Wright
Manufacturer

Posts: 4737
Location: Schaffhausen
Joined: January 31, 2002
 ...you and I know this, but don't upset the ARC owners who believe their gear is state of the art.

Regards, Allen

RE: Now now Ralph..., posted on October 30, 2009 at 10:46:37
KnobSpinner
Audiophile

Posts: 13
Location: Rural Washington State
Joined: August 13, 2009
 Could you explain?
(Worshiping at the Universal Music Altar)
RE: OK., posted on October 30, 2009 at 12:20:57
Ralph
Manufacturer

Posts: 1157
Location: Minnesota
Joined: April 24, 2002
Contributor
  Since: April 1, 2002
 That circuit could be executed with half of the tubes that are in it. The second half of the circuit is doing nothing of benefit to the sound- the first half is a primitive differential amplifier driving a set of cathode followers. So you already have impedance matching enough to drive any power amp that the unit drives now. But then they added *another* stage of gain (that is *not* differential at all) that they didn't need and another set of cathode followers.

It perplexes me why the second stage of gain is not also a differential amp, unless there is an error in the schematic. If the schematic is right, the only thing generating opposite phases is the initial stage of gain. Since the circuit is zero feedback, minor tube differences can alter the gain of the two halves downstream. Unless you have carefully matched tubes, the resulting output would not really be what I would call balanced, even though the outputs would be 180 degrees out of phase. It would far more elegant at the very least to have made the 2nd gain stage differential also, virtually eliminating this problem, and they could have done that with less parts than are in there right now (if the schematic is correct, that is).

If it were me, I would have seen to some sort of constant current source for the first differential amp, and had no second gain stage at all (and its attendant cathode followers). This would have reduced distortion and increased gain (of that stage), while also reducing noise.

The schematic indicates that at the time, they didn't have much experience with differential amplifiers, and so amongst other things compromised the performance of said due to arc-over concerns during warmup, something easily avoided. Seriously, there are enough issues here that I question what they were thinking, Sure, it probably did not sound too bad, but for a lower cost it could have measured and sounded a **lot** better!

My comments are similar., posted on October 30, 2009 at 15:19:32
Allen Wright
Manufacturer

Posts: 4737
Location: Schaffhausen
Joined: January 31, 2002
 The first stage, a differential gain stage, is OK.

The second stage, a cathode follower, has NO practical purpose at all, except to lower the resolution of the overall unit.

The third stage, a non differential stage has negative gain (!!!) becaue it's cthode R's are much larger than the anode Rs. never ever seen that before.

The forth stage is a cathode follower - needed to get good drive into the cable, but they use a plain jane "Miss Piggy" CF, without even a constant current source as the cathode load.

It could have been done with just the input stage, with it's gain reduced to what's needed, and the output cathode follower - and would have sounded a LOT better.

Some modifier should do this and get it singing!

Regards, Allen

RE: My comments are similar., posted on November 2, 2009 at 11:12:29
KnobSpinner
Audiophile

Posts: 13
Location: Rural Washington State
Joined: August 13, 2009
 Allen, Ralph,

Thanks for your informative reply. As to the accuracy of the schematic I posted, could have errors,of course. I am not anywhere as knowlegeable as you two are about amplifier design. The last time I did a vacuum tube design was in 1969. And that was a power supply for avionics test equipment for United Airlines.

I find your comments about mods for this amp really interesting. I think I will contact ARC and dicuss this w/them.

The bottom line though, this preamp sounds really great. I have two different amp/speakers combos I use this preamp with and they both sound great. Really a "You are there" presentation.

I have seen lots of critisism for ARC designs on the web. The only problem is that they sound great! I have heard lots of ARC based systems in the last 30 years. The two things they all have in common is first class build quality, and drop dead sound quality.

I just have a hard time beleiving that a company that uses such second class designs is used so much by first class speaker designers to show case their products at the big shows. I saw the Wilson speakers room at T.H.E.Show a few years ago. Using all ARC equipment. I would think that they could have any electronics they could want (considering what they get for their speakers).

I think ARC bashing is just a popular bandwagon on the 'net. Sorry, I don't mean to insult anyone, but to me, ARC is top drawer.


(Worshiping at the Universal Music Altar)
RE: bashing, posted on November 3, 2009 at 10:40:46
Ralph
Manufacturer

Posts: 1157
Location: Minnesota
Joined: April 24, 2002
Contributor
  Since: April 1, 2002
 I've stayed away from ARC bashing, not the least of which I know those guys (they are a great bunch, and they are here in town). Like I said, I'm sure it sounds fine, it just that a lot of bets were missed that could have had it sounding better, perhaps even better than their flagship of that time.

Both Allen and I have been making fully differential line sections a lot longer than ARC, and my criticisms of this circuit stem from that experience. I have to assume that the schematic is in error, but even if it is, there are a lot of simple ways to improve that 'you are there' quality that you refer to.

I'll give you an example. See those 500 ohm resistors in the cathode circuit of the first stage? Replace them with wire jumpers, and remove the little caps associated (this is assuming that the tube is **not** a 12AX7, if it is you can't do this, also, don't do this if you don't have technical experience). This will increase the differential effect, lowering distortion and slightly increasing gain. You will hear it as being more transparent and smoother sounding, with more impact. Tip of the iceberg here...

Certainly they are well built..., posted on November 2, 2009 at 12:53:30
Allen Wright
Manufacturer

Posts: 4737
Location: Schaffhausen
Joined: January 31, 2002
 ...but when you hear somthing without ARC's design compromises, you will only then know what we are complaining about.

It's good, just a pity it's not great.

Regards, Allen

Page processed in 0.047 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2009, Audio Asylum, all rights reserved ] [ Go Green ] [ Take5 ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]