Is it possible to use a balanced amp with SDA's?

nspindel

Ok, if you remember this thread of mine:

http://www.polkaudio.com/forums/showthread.php?t=65774

I probably made one of the dumbest statements I've ever posted online in the title of that thread - "I'm done!" HAH! Yeah right....

Since I wrote that thread, I've gotten new speakers (2B's became 1C's), all new cables (Signal all the way), a PS Audio UPC-200, and a room full of acoustic treatments. And now.... I'm about to change a whole lot more.

The only thing that's bothered me about this system is that I get a buzzing that's noticeable in between songs. The tube pre-amp has adjustable gain - at a gain of 3 the buzz is tolerable. At a gain of 10 (where the amp needs to be set for my 300ohm Senn headphones), I need to leave the room it's so loud. I returned the preamp and they sent me a new one, same problem.

So Little Tube is being extremely cool and letting me return the MKIVSE preamp for full price towards their new flagship model, which is balanced:

http://www.little-tube.com/forum/forums/thread-view.asp?tid=257&start=1

Now that's a beauty! So now I need a balanced source. Easy enough. Squeezebox digital out into the new Little Tube balanced DAC does the trick:

http://www.little-tube.com/forum/forums/thread-view.asp?tid=510&posts=11&start=1

Of course, I can't skimp on the digital out of the Squeezebox, so sent the Squeezebox back to Wayne at Bolder Cable to have him finish off the Enthusiast mod package with the digital mods. Previously I had only done the Analog mods.

Why am I so excited about balanced? Mainly for headphones, to be honest. It is simply breathtaking what a balanced headphone amp and cable can do for my Senn 650's. I demo'd a balanced amp with my cans at a head-fi meet a few years ago, and just couldn't believe what I was hearing.

Problem is, Little Tube suspects that the cause of the buzzing might actually be an impedance mismatch between the amp and the pre-amp. If that's the case, it may be time to look for a different amp. The mod's I did to the NAD 2200 sound just awesome, but if a mismatch is causing a buzz, then it will have to be replaced.

I'm not an engineer, so I'm not overly technical, but my basic understanding of balanced is that the left and right have completely isolated power supplies, and then use the 3-pole XLR connectors. Now I would think that having completely separate power supplies would mean that it is not common ground thus making it a no-no for SDA's. I could be completely wrong there, but then that's why I'm asking!

If I do need to replace my amp, then given I'm running a balanced source and pre-amp, it would of course be tempting to use a balanced amp and see what it can do for the loudspeaker side of my system. But it would need to be compatible with SDA's.

I suppose I could always build an AI-1, but that's added work...

Any thoughts? Thanks in advance.

ben62670

A balanced amp can be used with SDA's if it is common ground, or can have the grounds tied together. Have you gone through and checked every piece? have you tried cheater plugs on all the gear?

nspindel

Ah. Never realized that a balanced amp could be common ground! Just goes to show you what I know. That's why I ask ask ask!

I've tried everything, Ben. Attempting to get rid of this buzz is why I bought the PS Audio conditioner, to try the ground loop isolation. Tried cheater plugs. Tried changing all the cables. Nothing helps. Tried using tube dampers to see if maybe it's from microphonics, no go. Nothing is stopping this buzz.

Like I said, when the pre-amp gain is set to the lowest level (3), it is tolerable. But I don't want tolerable in this system. I want perfect!

Before I go buying an amp, I'm going to run this problem by the shop that mod'ed my NAD. This guy knows everything there is to know about these vintage NAD's. If it is an impedance mismatch, perhaps there's something that could be done to the amp to fix it. But I'm assuming if it is something with the amp, it wouldn't be fixable.

Wondering if (with balanced source and preamp) a balanced amp would have as dramatic an effect on my SDA's as a balanced headphone amp can have on cans? Just how much better would it get?

Got any suggestions for a balanced amp that is common ground??? Figure budget of around $1000 if necessary. I'm very open to buying used equipment.

nspindel

Parasound Halo A23 perhaps???

ben62670

The thing is some balanced amps have the balanced connector, but are actually converted to unbalanced inside. I wish I could be more help:(

F1nut

Have you tried a different source or removed your current source entirely to see if there is a problem there?

nspindel

It's definitely not the source. The buzz exists even if no source is connected to the pre-amp. If I connect the Squeezebox directly to the amp and use the digital volume control on the Squeezebox, sound is perfect. Pitch black between tracks.

It's the manufacturer of the pre-amp who is suggesting it's likely an impedance mismatch with the vintage amp. I'm completely psyched that they're giving me full credit towards the balanced pre, but they said there's a risk that this can actually make the problem even worse as it's a more powerful pre-amp.

So if given the choice between that gorgeous balanced tube pre-amp or a 20-year-old NAD, the NAD's not going to emerge on top.

heiney9

This is a common issue with tube gear. When I borrowed DKG999's Dodd pre-amp it had a buzz as well with the Marsh amp I was using. It had a much quieter buzz with the Adcom. Going balanced will help. I also used a PS Audio Qunitet power strip.....didn't really help.

How are you liking the Little Dot? I've had my eye on one for awhile as a way to mess with a tube pre on the cheap.

My brother bought Ted's BAT VK60 tube mono's. He also bought a PS Audio DAC and a BAT VK40 pre amp and a PS Audio power regeneration station. He had an electrician come in and put in not 1, but 2 dedicated circuits (one for each mono). So he has isolated power receptacles, power conditioning and pretty much fully balanced connections and he still has a very audible hum. We're still trying to track it down.

Electronics are sooooooooo much fun.

Perhaps you could give mini-review of the Little Dot.

H9

P.s. To answer your question, yes. I used my Alpeh and Adcom in balanced mode with the 1C's. I went back to single ended because running balanced cancels 2nd order harmonics (the good harmonics) and I think I like SE'd better. I'm still experimenting. I have an ever so slight buzz that can only be heard w/ my ear pressed up against the speaker and silence in the room. In balanced mode it's dead quiet. I use a power conditioner as well.

Schurkey

ben62670 wrote: »

The thing is some balanced amps have the balanced connector, but are actually converted to unbalanced inside. I wish I could be more help:(

Yeah, I was going to say that there's a difference between an amp set up for a balanced interconnect cable--and a fully balanced amp.

So far as I know, a balanced cable is nice if you have to have long cable runs. Doesn't make any effective difference on short cable runs.

Also--so far as I know--a genuine "balanced amp" is one that's been bridged. Therefore it will not be common-ground; and therefore you need SDA speakers suitable for the AI-1 style cable.

Separate power supplies means nothing in terms of common-ground; many amps have two transformers inside--L and R--but the ground side of the signal is shared. (Common ground)





Just for giggles...do your interconnect cables have continuity through the shield from one end to the other? "Directional" cables have the shield cut short so it doesn't actually connect to the second terminal.

If your cables don't have continuity through the shield, what happens if you connect a length of ordinary electrical wire between the chassis of the preamp and the power amp? 18 gauge would be plenty large enough. Use whatever you find handy--solid core, stranded, an old bare-wire coat-hanger would probably work. You wouldn't "have" to fasten the cable with a screw at each end, just make sure it touches both components somewhere on bare steel.

heiney9

Schurkey wrote: »

Yeah, I was going to say that there's a difference between an amp set up for a balanced interconnect cable--and a fully balanced amp.

So far as I know, a balanced cable is nice if you have to have long cable runs. Doesn't make any effective difference on short cable runs.

Also--so far as I know--a genuine "balanced amp" is one that's been bridged. Therefore it will not be common-ground; and therefore you need SDA speakers suitable for the AI-1 style cable.

Separate power supplies means nothing in terms of common-ground; many amps have two transformers inside--L and R--but the ground side of the signal is shared. (Common ground)





Just for giggles...do your interconnect cables have continuity through the shield from one end to the other? "Directional" cables have the shield cut short so it doesn't actually connect to the second terminal.

If your cables don't have continuity through the shield, what happens if you connect a length of ordinary electrical wire between the chassis of the preamp and the power amp? 18 gauge would be plenty large enough. Use whatever you find handy--solid core, stranded, an old bare-wire coat-hanger would probably work. You wouldn't "have" to fasten the cable with a screw at each end, just make sure it touches both components somewhere on bare steel.

Actually a "true" balanced circuit from input to output is NOT just bridged. That's a cheaper way to offer a balanced connection w/o having to actually have the entire circuit balanced. A true balanced circuit can be common ground.

Also there are 3 reasons to use XLR or balanced connections

1) is because the designer built the circuit to run as balanced and you will get slighlty lesser performance running it single ended. Many high end amps like Pass, Krell, BAT, etc. are all balanced input to output and are ment to be run that way for best performance.

2) any balanced circuit effectively eliminates 2nd order harmonics by way of it's design. Many audiophiles prefer a 2nd order harmonic (even) rather than the (odd) 3rd order harmonic......some don't. I have gone back to single ended connections for the time being

3) it can eliminate RF induced noise even for short cable runs too, not just long cable runs.

H9

nspindel

Schurkey wrote: »

Just for giggles...do your interconnect cables have continuity through the shield from one end to the other? "Directional" cables have the shield cut short so it doesn't actually connect to the second terminal.

If your cables don't have continuity through the shield, what happens if you connect a length of ordinary electrical wire between the chassis of the preamp and the power amp? 18 gauge would be plenty large enough. Use whatever you find handy--solid core, stranded, an old bare-wire coat-hanger would probably work. You wouldn't "have" to fasten the cable with a screw at each end, just make sure it touches both components somewhere on bare steel.

Yeah, already tried that one. I use Signal Analog II's, not sure about the shielding. But I already tried running a wire from the pre-amp chassis to the amp chassis. Didn't help. Should have mentioned that earlier...

nspindel

heiney9 wrote: »

2) any balanced circuit effectively eliminates 2nd order harmonics by way of it's design. Many audiophiles prefer a 2nd order harmonic (even) rather than the (odd) 3rd order harmonic......some don't. I have gone back to single ended connections for the time being

Wouldn't this effectively get rid of a lot of the "tubiness" of tube amps?

nspindel

H9, I really like the Little Dot MKIVSE a lot, especially considering their price point. Sound wise, I love it. The thing is built like a tank. Obviously I'm not happy about the buzzing I'm getting, but as is the topic of this thread, I think it's more an issue of the vintage amp I'm using. Certainly plenty of people use the LD as a preamp and don't have the problem I have. Headphones listening is really great.

The one complaint I have is that for adjusting the gain switches or the tube jumpers, they could have done a better job of making the switches and jumpers easily accessible. They're pretty deep down in the unit, and you need to access them through thin slots in the chassis. I use surgical clamps to access the jumper. But I don't really change them all that frequently. I change the switches when I alternate between headphones and speakers (but only because the Senn 650's need to be at a gain of 10, but I get too much buzz through speakers at 10, otherwise I'd just leave it set with the gain that high). I need to flip the jumper if I roll between M8100- and M8161- type tubes.

Looking forward to getting the balanced amp and giving it a whirl...

heiney9

nspindel wrote: »

Wouldn't this effectively get rid of a lot of the "tubiness" of tube amps?

Well, yes and no. Not all of it but.....I'm still experimenting with bal vs. SE connections from the pre to the amp. I have SS for both. You will still get the wonderful tube sound, but it might just be smidge less going fully balanced.

I will say.....I'd rather have no hum/buzz w/balanced connections than SE with a buzz or hum.

I only mention it as it is a fact............but I think in the end the impact is minimal, but nevertheless it's still there.

heiney9

nspindel wrote: »

H9, I really like the Little Dot MKIVSE a lot, especially considering their price point. Sound wise, I love it. The thing is built like a tank. Obviously I'm not happy about the buzzing I'm getting, but as is the topic of this thread, I think it's more an issue of the vintage amp I'm using. Certainly plenty of people use the LD as a preamp and don't have the problem I have. Headphones listening is really great.

The one complaint I have is that for adjusting the gain switches or the tube jumpers, they could have done a better job of making the switches and jumpers easily accessible. They're pretty deep down in the unit, and you need to access them through thin slots in the chassis. I use surgical clamps to access the jumper. But I don't really change them all that frequently. I change the switches when I alternate between headphones and speakers (but only because the Senn 650's need to be at a gain of 10, but I get too much buzz through speakers at 10, otherwise I'd just leave it set with the gain that high). I need to flip the jumper if I roll between M8100- and M8161- type tubes.

Looking forward to getting the balanced amp and giving it a whirl...

The look, build and the fact that it has switchable gain is what really appeals to me. I see them on ebay new from Canada for $249 the $45 shipping for the MKIV and $199 plus $45 shipping for the MKIII. Iv'e heard horror stories about the MKII getting so hot it can actually burn up some of the parts and or the PCB. The later versions seem to have better heat dissipation as LD addressed this specific fault from earlier versions.

Good luck

H9

nspindel

I don't think LD will support a unit not bought directly from them. Careful where you buy from. The SE comes with the EH 60H30Pi tubes, which sell for upwards of $75. And it has double the warranty.

nspindel

Just got off the phone with Parasound tech support. They confirmed the Halo's are definitely common ground. So that would definitely be a candidate.

Anyone know anything about the Parasound Halo A23? Have any opinions?