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October 31, 2020, 12:00:22 PM

Author Topic: Stereomour II OHM setting and bass response  (Read 177 times)

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Offline lskiii

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Stereomour II OHM setting and bass response
« on: October 08, 2020, 02:20:56 PM »
Hi Everyone,

So, I'm hoping to get guidance or feedback from folks re: the Ohm setting on my Stereomour II.  Here's some background:

My setup is Bluenode 2i > Schiit MB Bifrost > Stereomour ii to Klipsch Heresy II's (that have Crites upgraded tweeter diaphragms and upgraded x-over) w/ Klipsch sub.  I installed the DC filament upgrade, shunt upgrade and built the power cord kit.  I've not yet done any tube rolling or cap mods.

Have had everything running for about a month now and really enjoying it.  Also, really enjoyed the upgrades process - esp the shunt upgrade (it made a very audible difference in a good way).  However, in the back of my head I've been struggling with the feeling that there's a lack of bass and overall heft - especially with certain types of music.  Simple jazz combos with a guitar/bass/drums or piano/bass/drums (Bill Evans or Grant Green for ex) sound fantastic.  Very detailed, lifelike and very present.  However, classical symphonies and most rock can sometimes sound thin and the bass can sound somewhat muffled.  If i turn up the volume, I can get more heft, but then the high end tone starts to sound shrill.  I found myself contemplating an equalizer, but instead I swapped in one of my old solid state amps to see if this was all in my head.  As soon as I switched on the solid state amp, the difference was very noticeable.  I lost the presence and detail and the wide soundstage I had been enjoying with the Stereomour however I picked up all of the tight bass and overall heft that I was missing. 

I started doing some research online to see what changes I might able to make to the amp to tighten up and increase the bass response.  I began learning about about the bass impacts of damping and/or Ohm selection.  I had setup the Steremour for 8 Ohms since that is what my speakers are rated at. However, from what I read, dropping to 4 might increase damping, which should provide tighter more detailed bass.  This would be at the expense of total volume, which is fine as I've never had the desire or need to run the amp full out.  I rarely get to 75% on the volume knob.

So, I resoldered the OTs for 4 Ohms and to my pleasant surprise, the bass and heft were improved noticeably and while I did get a drop in total volume it's not meaningful.  Did it get the bass / heft to the level of my SS amp?  No, not quite -however, it's much closer and I love all of the other benefits that the Stereomour II brings in terms of realism/presence and soundstage.

If nothing else, perhaps this will help other newbies like me as it had never occurred to me to experiment with the Ohm setting.

That said - my questions are:

1. Is my understanding of the relationship between lower Ohm setting on the OTs to bass and volume correct?
2. Would it be worth trying a 2 Ohm setting?  Or, would having a 2 Ohm setting with 8 Ohm speakers be a bad thing for some reason?
3. Are there other amp mods I should try if I'm hoping to get more/tighter bass from the system?  I've heard that JJ 2A3s might help - can anyone vouch for this?  Are there cap upgrade that would make a difference?
4. In terms of the speakers, my understanding is that some folks might recommend bi-amping, but I believe that would require a significant mod to my speakers, so I'm not planning to pursue that path.  However, if there are some simple mods that folks have done with a Heresy/Stereomour combo I'd love to hear about it.

Thank you again.  I've really been loving the whole experience as it's been educational and fun (and my soldering skills continue to improve as well).

Louis

PS - including a photo of my system, in case anyone's curious...

Offline Paul Birkeland

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Re: Stereomour II OHM setting and bass response
« Reply #1 on: October 08, 2020, 03:09:43 PM »
1. Is my understanding of the relationship between lower Ohm setting on the OTs to bass and volume correct?
Yes, you have increased the damping factor of the amp by wiring it for 4 ohms and using an 8 ohm nominal speaker.
2. Would it be worth trying a 2 Ohm setting?  Or, would having a 2 Ohm setting with 8 Ohm speakers be a bad thing for some reason?
It's a cheap experiment! You can always go back.
3. Are there other amp mods I should try if I'm hoping to get more/tighter bass from the system?  I've heard that JJ 2A3s might help - can anyone vouch for this?  Are there cap upgrade that would make a difference?
I can't imagine the JJ 2A3 making a huge difference.  Oddly enough if you go through the modifications to wire for a #45, that will improve the bottom end response of the amp a bit.

4. In terms of the speakers, my understanding is that some folks might recommend bi-amping, but I believe that would require a significant mod to my speakers, so I'm not planning to pursue that path.  However, if there are some simple mods that folks have done with a Heresy/Stereomour combo I'd love to hear about it.
I wouldn't be excited to cut up a vintage pair of speakers so you can biamp. It can also be tricky to set something like that up when you have two amps with very different gain.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Tom-s

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Re: Stereomour II OHM setting and bass response
« Reply #2 on: October 10, 2020, 11:50:37 PM »
Thank you for sharing this!

I can attest that going to the full winding on the parafeed choke helped my Heresy III speakers a lot.
My setup is described here: https://forum.bottlehead.com/index.php?topic=12009.0

The Emission Labs Mesh are an upgrade in the bass performance in my SII (some say the solid to perform even better). Another old stock option with good bass is the Sylvania 2A3. I use a version with springs holding the filaments, they are very good sounding with great frequency extension compared to other NOS tubes in my collection (mostly RCA build).

I don't remember if i set up my SII for 8 or 4 ohms. Will see and if possible; change to 4;2 Ohms just to try.

Offline lskiii

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Re: Stereomour II OHM setting and bass response
« Reply #3 on: October 11, 2020, 09:17:49 AM »
Glad it was helpful!  I'll take a look at your post as well and am interested in any other tube rolling suggestions, as that's not something I've tackled yet. 

In terms of the impact of moving to 4 Ohms from 8, I've been letting that modification "soak in".  So far, I really think it was the change that I was looking for and I may just stop here.  The low end is significantly improved (certain songs I can now feel the bass impact coming from the floor in just the right subtle way) and I think I also got just a hair of high end rolloff that has eliminated any sense of fatigue. i.e. I suspect 2 Ohms might be overkill.   Also, I like to make modifications one step at a time and then take a couple of weeks to see how the change truly impacts things.    If I do every try 2 Ohms, I will report back.

Thanks!