What causes an amp to have a narrow soundstage?

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glynnw

What causes an amp to have a narrow soundstage?
« on: 4 Dec 2017, 11:05 pm »
I just picked up another 2A3 amp and the soundstage is very narrow.  I use a Chesky test track to test this.  Normally the guy starts in the middle, then is halfway between center and right speaker, then at right speaker,  then outside the right speaker -  same for left.  With this amp when he should be at the right speaker he is just at the midway point.  Same for left.  Using all the range of the balance control on my Tortuga passive pre I cannot get some images that are considerably off center to move to the center where I like them.  I figure it must be some form of crosstalk.  Any ideas out there?

FullRangeMan

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Re: What causes an amp to have a narrow soundstage?
« Reply #1 on: 4 Dec 2017, 11:28 pm »
What causes an amp to have a narrow soundstage?
The recording or an multiple ways loudspeaker or speaker placement etc

jules

Re: What causes an amp to have a narrow soundstage?
« Reply #2 on: 5 Dec 2017, 12:25 am »
I'd suggest it could be your passive pre.

Power amp input impedance should be at least 10X pre-amp output impedance though in practice something like 50X is probably going to be better.

Without looking up the figures I can say that a system I'm using which should in theory have been ok in terms of the above ratio, didn't come alive until I inserted a burson buffer in the chain. The difference related exactly to the sound image problem you've outlined though I'd add that post buffer the system gained depth as well as width.

Doublej

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Re: What causes an amp to have a narrow soundstage?
« Reply #3 on: 5 Dec 2017, 12:27 am »
Are you saying that with one 2A3 amp the soundstage is fine and with this one it is narrow? If that is the case then the amp is either defective or needs a bias adjustment. (do these things need biasing?)

glynnw

Re: What causes an amp to have a narrow soundstage?
« Reply #4 on: 5 Dec 2017, 12:35 am »
Not the recording, speakers or placement. Soundstage has been normal with every other amp I have used and speakers have not moved - I am lazy.  As for passive pre impedence, I am using a tube buffer between the Tortuga and the amp.  I also tried a different set of 2A3 tubes - no change.  The only variable is the amp.  I will try bypassing the buffer to see if that makes a difference.
Anyone ever experienced an amp doing this?

FullRangeMan

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Re: What causes an amp to have a narrow soundstage?
« Reply #5 on: 5 Dec 2017, 01:13 am »
It could be a mismatch on the 2A3 amp OPT/speaker, the speaker impedance is benign? or swing hi & lows?

glynnw

Re: What causes an amp to have a narrow soundstage?
« Reply #6 on: 5 Dec 2017, 01:20 am »
The amp has the transformer for playing into 16 Ohm speakers.  I just put my main amp back in the system and soundstage is again normal - Passes the Chesky imaging test.  There is just something off with the new amp.  Tomorrow I'll try different speakers.  Thanks to everyone for help so far. I had the new amp custom built and it took almost a year to get it, so I really don't want to deal with asking the builder to try again - much less the cost and danger of shipping a tube amp across the country.

Rocket_Ronny

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Re: What causes an amp to have a narrow soundstage?
« Reply #7 on: 5 Dec 2017, 01:39 am »
Amps can image differently, including having different soundstage width. I don't know why, crosstalk, like you mentioned certainly can be looked at. I have switched amps and had to completely change speaker positioning. Most times though, they are the same.

Rocket Ronny

glynnw

Re: What causes an amp to have a narrow soundstage?
« Reply #8 on: 5 Dec 2017, 05:05 am »
I've been in the hobby for almost 50 years and never encountered a problem like this before.  Most amps have adequate channel separation.

ohenry

Re: What causes an amp to have a narrow soundstage?
« Reply #9 on: 5 Dec 2017, 09:28 am »
Using all the range of the balance control on my Tortuga passive pre I cannot get some images that are considerably off center to move to the center where I like them.

No defined central image often points to phase problems.  For grins, switch one of the speaker's wiring phase (either at the amp or speaker post) to see what happens.  It can be easy to make a mistake while wiring the amp and accidentally switching phase on one channel.  That can make the poor thing sound broken and could be a simple fix if it's the issue.  Good luck.  :D

belle harbor

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Re: What causes an amp to have a narrow soundstage?
« Reply #10 on: 5 Dec 2017, 01:48 pm »
Did you ask the builder if the amp performed properly prior to shipment?  Is this one of his own designs, or just a build of a published design?  I've been helping another fellow who recently took delivery of a custom build and encountered similar issues.  Strange coincidence.

A number of questions come to mind which can be answered if I can see the schematic.  Do you have a copy you can post?  And, are you comfortable with taking voltage measurements under the chassis?

Where are you located?

glynnw

Re: What causes an amp to have a narrow soundstage?
« Reply #11 on: 5 Dec 2017, 05:49 pm »
This morning the first thing I did was disconnect one speaker at a time, thinking if there was serious crosstalk I would still hear sound from the disconnected speaker.  But not at all - dead silence when disconnected.  Next I reversed 1 of the speaker leads and that didn't solve the problem.  However, instead of the weird  disembodied voice in the sky I usually get when some wires are crossed, I got a super wide soundstage but the vocals were not centered - they, too, were spread across the soundstage.  But it was clear, not the distorted sound I usually get when doing this.  And I have to say, now that I have put a pair of TJ meshplates in it, the sound quality is as good as I have ever heard in my system.  Lush female vocals from Jane Monheit, and on another recording I could hear (slightly) the snare wires vibrating against the drum head.  Truly lovely sound, so it will be worth it for me to get this fixed.  I don't know if it is from a standard design or unique to the builder and I have yet to discuss this problem with him. I want to listen for a couple of days and then call him and discuss it in detail.  My first desire is to send it back and let him work on the issue, but we shall see what transpires.  And I am willing to take live voltage readings (yes, I have a death wish apparently), but not at this time.  Maybe in a couple of days. I have built several Bottlehead kits and on the first couple I just plugged them in and hoped for the best and they always worked.  But I finally built a stand to hold them upside down so I would not have a shakey playing field and that helped a lot.  If it comes down to my doing voltage checks I will build a similar stand before getting into it.  I live in Shreveport, Louisiana.  One more odd occurrence.  I hooked the amp directly to my DAC using a couple of EVS attenuators that Ric Schultz built 17 years ago - one of my prized and most useful possessions - I will own them 'til I die.  When I played the track I use for left and right checks, the voice barely moved on the right side and the "I am now standing beyond the right speaker" track the voice was still inside the right speaker and to the rear.  The left channel had the voice move a little to the left and the "standing beyond left speaker" voice was huge and way to left of speaker.  So the 2 channels are acting differently.  I am open to new comments, but I think any actions will have to be later in the week after I get a chance to talk to the builder.  But man, it is playing now and the quality is to die for.

simoon

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Re: What causes an amp to have a narrow soundstage?
« Reply #12 on: 5 Dec 2017, 06:12 pm »
Deleting post.

gregfisk

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Re: What causes an amp to have a narrow soundstage?
« Reply #13 on: 7 Dec 2017, 03:29 am »
I had an amp that had a mono switch on it in the back. Once, the switch got flipped without me knowing it. What you describe is exactly what I experienced and what my speakers were doing. You probably don't have a mono switch but I thought I would bring this up anyway.

Good Luck,

Greg