New Here: Just Ordered Stereomour!

[Paul Joppa]

Within the range I talked of (half to twice the "theoretical" value) it's hard to predict what value will work best in a given system. The reason is the interaction of the cap and plate choke with the speaker's impedance, which in most cases fluctuates quite a lot in the deep bass. I can generalize - tighter, cleaner, but not as deep bass with the smaller cap - but I can't be confident that's what you'll hear in your room with your speakers.

As usual, I recommend you build it stock first, then experiment with different caps if you are interested.  The difference between 2.5uF and 3.3uF will be small; the difference between a Solen and a Mundorf may well be larger, subjectively at least.

Here's what I'd do if I wanted to get a lot of information: I'd build it stock, and give it at least 100 hours of music to be sure the cap is broken in and my ears have become accustomed to the sound of this amp. Then I'd swap in the Mundorf, again for at least 100 hours. Then I'd add the Solens back, in parallel with the Mundorf, and try to hear the effect of the larger capacitance. The capacitance effects will be mostly in the deep bass, while the capacitor sonic differences would likely be throughout the audio band and especially in the treble. Based on the results of those trials, I'd choose the one I liked the best, or decide what other things to try.

 

[Grainger49]

I would make the suggestion that you experiment with cheaper caps of different values first.  Then when you zero in on the value that reaponds best invest in the high dollar caps.  I'm a fan of Obbligato Film and Oil caps, their cheapest.  You could use a hand full of those to decide on the value then go to the Mundorfs.

 

[Thoburn]

Thanks Paul and Grainger49 for the excellent advice on the caps.

 

[InfernoSTi]

Well, I want to give a big "THANK YOU" to Bottlehead for their Stereomour kit!

Excellent instructions, an easy build, and 30 feet of wire!  I put mine together after work Wednesday, Thursday, Friday, and quite a bit on Saturday and Sunday. 

My resistance checks were all spot on and my voltage checks were tolerable (but not as close as I would have liked...more on this in a bit).  Since everything was within 15% and there wasn't any "magic smoke" released, so I plugged in my OB Hawthorne Duets and oh WOW!!! 

Rich, smooth, music with amazing detail, special placement/soundstage, silky highs, and buttery mids.  Everything I want in a tube amp!!!  And I can't wait until it breaks in a bit (I'm typing after about 30 minutes of operation on the stock tubes).  My hum is only 0.28 mA on the right channel and 0.33 mA on the left channel.

So my only worry is that a four of my readings are right on the edge of acceptable (the vast majority of reading are either spot on or within 6-7%).  However, I have a handful that are 10-15%, so I figure I'd ask folk's opinions to see if I should worry (or just grab an adult beverage and listen to some music and stop nit picking!).  I need to mention that my mains VAC measures 123 VAC (not the test 119VAC).

Here are the handful of high readings (just the big ones, not the 6-7% readings):

Terminal    Expected    Actual  Variance %

T2            230            207        -10%
T14          230            194        -15%

OA            230            207        -10%
OB            230            194        -15%

Should I worry?  It is on the ragged edge but everything sounds WONDERFUL!!!!

Thanks a bunch!
John

 

[Paul Joppa]

You got NO PROBLEM.

It's a good illustration of the complexity of making good tests. The points you identify are the driver plate voltage. Because the driver is running under fixed bias, this point will vary more like 20% or even 30% - 2 or 3 times the variation expected at more stable points. This is because of variations in individual tubes. It's just too confusing to try to say this in the manual.

If you look at the schematic, you'll see that my theoretical values for these points were 200 volts. The actual first production unit measurements were 230 volts, so that's what is in the manual - we use real measurements rather than theory. Your measurements are much closer to the theoretical value, which is based on the published tube curves, so I think you have just validated my theoretical calculations - thanks!

:^)

 

[InfernoSTi]

You got NO PROBLEM.

Thank you for the quick reply, Paul.  And your answer is music to my ears!  I didn't think the Stereomour could sound this good and have a problem!  

It's a good illustration of the complexity of making good tests. The points you identify are the driver plate voltage. Because the driver is running under fixed bias, this point will vary more like 20% or even 30% - 2 or 3 times the variation expected at more stable points. This is because of variations in individual tubes. It's just too confusing to try to say this in the manual.

If you look at the schematic, you'll see that my theoretical values for these points were 200 volts. The actual first production unit measurements were 230 volts, so that's what is in the manual - we use real measurements rather than theory.

I appreciate the detailed background, and I'm certain others will too.  This starts to help me understand the what and the why (and gives me a place to start looking for more info on the topic).

Your measurements are much closer to the theoretical value, which is based on the published tube curves, so I think you have just validated my theoretical calculations - thanks!

That's what we are here for, Paul. You just keep dreaming up great designs and we will keep proving them up in practice!  

Cheers!  John

 

 

[InfernoSTi]

I have about 60+ hours on the Stereomour now and I wanted to post what I believe will become a very familiar posting as more folks build the Stereomour: the first few hours were really sweet but then I hit about 40 hours of "tightness" in the music.  At about 50+ hours, the sweetness started coming back and in a serious way!

The bloom on this amp is distinctively noticeable.  However, I don't feel there was only one area that was more notable; it is generally across the board.  That being said, what caught my attention first were the cymbals; I had one of those "hey wow, that sounds really nice, I need to pay attention" moments. 

I assume the burn-in can be noticeable for a few more hours, say 100+, but after that I assume it will settle into a nice, steady state where I can roll a few tubes and such and not worry that changes in sound are burn-in, rather than due to the changed tubes?

John

 

[Grainger49]

John,

The labeling you did under the chassis will be good when you went to tweak.  Not to mention it can help you find your way through the circuit.  I'm experienced but label everything.

The Solen Parafeed caps will be 98% settled out in 100 hours.  More expensive, and often better sounding, caps take longer.  I am burning in Teflon caps for 3 weeks now to get rid of the hard and congested days.

I have the first generation Paramours, two little "mono blocks."  And I am very happy with the sound.  I am as sure as you that anyone with appropriate speakers will love the Stereomour.

 

[InfernoSTi]

Grainger,

Thank you!  It is great to hear that you still enjoy your Paramours...that is the real test of sound quality if you still have them!

The labeling felt a bit odd writing on a beautiful blank chassis but it was a great help while building.  I hadn't thought about it, but it will help down the road, too.

Thanks for the info on the Solen's.  I think I will be rolling different tubes over the weekend just because I can't wait any longer!  I have to confess I have already swapped in a JJ 12AT7 and it was a really nice tube.  It has a signature that is pleasing to my ear. I will be trying some old RCA 2A3s and JJ 2A3-40s, as well as some NOS 12AT7s (a few of the classics). 

I have also ordered some Auricap 3.3uF caps to swap out with the Solen's at some point.  Based on the postings, that seems like a popular swap for a (relatively) small price.

I can attest that Hawthorne Audio + Stereomour = Heavenly sounds!!!  I am really loving the Stereomour's signature coming through the HA's!

John

 

[Grainger49]

There is a thing I say, and often, about expensive caps.  They are like seasoning.  I might like cinnamon you might like nutmeg.  At the cost of some caps, over $100 each, you can be horribly disappointed with the wrong ones. 

To heap insult upon injury the more expensive the capacitor the longer it takes to get to the final sound it will produce.  The more expensive Black Gates, Mundorfs, V-Caps and any Teflon cap can take weeks to come to rest as far as the sound goes.  Less patient men may not get there.

Tell us more about the Hawthorne Audio Duets, I'm not familiar with them.

 

[InfernoSTi]

Grainger,

I understand what you are saying about caps: I think I'll focus more on tube rolling than cap rolling for a while.   I'm not certain you can really learn an amp until you have lived with it in a static state for some time.  One needs to be comfortable that you can hear subtleties and that just takes time.

Thank you for asking about the Hawthorne's.  These are an open baffle speaker that is purpose designed as such. The Hawthorne's are rated at 96db and are designed with low watt SET amps in mind.  They are often set up with either a single driver/tweeter combo or as a "duet" with an additional bass augmenter speaker or even as a "trio" with two additional bass augmenters.  Some recent experiments with five 10" bass augmenters has yielded very fast, detailed, and musical bass response for the handful of brave souls who have tried this set up.  Everyone tries their own baffle design and configuration.  Mine is a "1015 Duet" style.  I use a narrow top of the baffle to keep a fast mid and upper range, while I have a wider bottom to aid in bass response (with OB, you can "tune" the sound by the baffle shape/size).

My current setup is a 1" compression driver center firing through the cone section of a 10" mid-woofer.  This gives the benefits of both a crossover speaker (letting each driver handle the range it is good at) and the pinpoint detail of a full range speaker due to the unique configuration of the compression tweeter.  I also have 15" bass augmenters that I am bi-amping in true stereo with two Rythmik plate amps with a special OB "shelf" design.  I'm not an expert on the specifics but Rythmik worked hard to develop an OB version of their Servo plate amp.  Having these in stereo really adds to the imaging, particularly on drums and such.    

Front showing 10" and 15" drivers (CD tweeter center mounted in the cone of the 10"):

Back showing 10" and 15" drivers (CD tweeter center mounted in the cone of the 10") and remote crossover:

in the left and right background, you can see the two plate amps:

Basically, I drive the compression tweeter and 10" mid-woofer with my SET amp and send a split signal via RCAs to each of my two Rythmik amps.  The idea is to maximize each of the strengths of the components to have as few compromises as possible.  There doesn't seem to be an end to how far folks can take this (and I'm just in the beginning of my OB journey).  The sound is a very present, highly detailed quality with lots of 3D soundstage.  Moving the speakers a bit can adjust the dipole delay to create more/less depth, which is really fun!

Here is a professional review of a set of Hawthorne "Duet" speakers:
http://www.positive-feedback.com/Issue31/hawthorne.htm

Hope that helps!

John

 

[Grainger49]

Wow, I got it now.  I have heard several open baffle designs, not this one.  Some were hits some misses.  I like the idea of the concentric drivers.  It would have to be a better arrangement, phase wise, than a design with all the drivers mounted to the front baffle.

 

[InfernoSTi]

Wow, I got it now.  I have heard several open baffle designs, not this one.  Some were hits some misses.  I like the idea of the concentric drivers.  It would have to be a better arrangement, phase wise, than all mounted to the front baffle.

Everyone is trying to find that "just right" sound for what they enjoy.  For me, these are the direction that "does it" for me. I get lost in the music in a way that I have never before.

Now about that Stereomour: tonight I put in the JJ 2A3-40s and JJ 12AT7.  I think I'm going to have a hard time rolling tubes as these seem to have the signature I love!  They are fast, detailed, and have crisp yet soft extended highs.  This amp with these tubes is blowing me away listening to Dire Straits "Dire Straits" on the new Japanese SACD.  I hate that I sound like a hyperbolist but I'm loving the Stereomour!

I have to give a plug to Eurotubes for their great price on the 2A3-40 ($210/matched pair)...thanks Bob!

https://ssl.eurotubes.com/cart/index.php?page=product_details&category_id=3&product_id=2A3-40-2

John

 

[InfernoSTi]

I just finished up a satin black case for my Stereomour. I had already painted the bell housing satin black.  Normally I do a wood stain but I asked Jeanine what she thought might be nice and she thought it would look good in black...I think she was right! 

John

 

[2wo]

I think she is right too. Pure classic...John

 

[InfernoSTi]

Thanks, John, you are right, the Stereomour is well suited for a classic look.

I have been itching to do a cap upgrade and finally did one last night and I'm really pleased with the results.  First, I took out the two 3.3uF Solen caps and replaced them with Auricaps in a "super cap" configuration consisting of the base 3.3uF Auricap bypassed with 0.33uF and 0.022uF Auricaps. Second, I bypassed the 0.1uF coupling caps with 0.022uF Auricap caps.

The improvements did have a very nice affect on the sound quality of the Stereomour 2A3: the overall clarity increased (i'm not sure if this is a tonal improvement or if the soundstage is being better handled, or perhaps both), the extension of the upper end was improved (cymbals have a longer "splash" decay), and the width and placement of the soundstage increased (minor improvements).

As I said, I'm very happy with the results which didn't change the overall sound of the amp as much as make things I liked about the amp a bit better!

This isn't the greatest photo as you can only see three of the four new caps, but it shows the general idea:

Thanks, John

 

[InfernoSTi]

Just thought I'd post an update: I've recently hooked up my Rega P1 with an Ortofon Blue cartridge and play it through my 2A3 and my Hawthorne Audio OB speakers (to which I've added a second pair of 15" giving four 15" woofers total plus the two 10" mids and the two compression horns).  Wow!  What a great combo for the price...lots of midrange bloom and just enough upper end extension/decay to sound great...and the bass is effortless bi-amping with two Rythmik amps plus the Stereomour 2A3.  Lovely with Dire Straits, Van Morrison, Dr. John, etc.

John

 

[InfernoSTi]

I've recently switched out the Auricaps for Mundorf Silver/Oil caps in the parafeed and coupling cap spots. 

 

I used the 2.7uF and 0.1uF caps, respectively.  They are significantly larger than the Auricaps but locating them was easy with the 0.1uF going below and in front and the 2.7uF going above and centered (a "hanging" cap location). 

The improvement is dramatic and well worth the $200 for the four caps.  Silky smooth upper end, detail across the entire range (the texture of the instruments is much more present, as well as the sound stage being smoother while maintaining detailed separation of instruments).  Finally, their is a more dynamic presence to the music (the bass sounds punchier and the horns have a more biting leading edge, for example).  The tone, texture, and dynamic nature of these caps is really a treat.  It makes listening very direct and creates a strong emotional connection to the music.  I couldn't be happier! 

I have to give credit to Ed (ebag4) for trying these out first and telling me how great they sounded to him....thank you, Ed!

John

 

[ebag4]

Hi John,
I am glad to hear you are enjoying the Mundorfs.  I have to tell you that those cute little caps are not big, these are big:

And I thought you were from Texas?? ;-D

Best,
Ed

 

[jrebman]

John,

Glad to hear you're enjoying the sio caps.  I can only imagine that setup you have sounds terrific.

Ed, are those the ampohm aluminum/poly/oil caps?  I've got a pair of those in 3.9 uF size for my stereomour though I may end up going with those in my FPIII+ and use something a bit smaller in the stereomour seeing aas the bass with the v-2s isn't going to be an issue.

Of course they may not fit nicely in the foreplay, so who knows.

-- Jim