Stereomour II 45 Conversion - Anyone Do It Yet?

[maryc27182]

Also, tip of the hat to this thread which helped me when I was looking for 45s: https://www.diyaudio.com/forums/tubes-valves/120611-hashimoto-wonderful-45-a.html

[Deke609]

Thanks so much, Mary. That's really helpful.  I'm guessing those supports help cut down on vibration/microphonics.  I will keep my eye out for similarly constructed tubes.

cheers,

Derek

[Deke609]

 I decided to go with a pair of the EML 45B's.  My second SII kit has shipped from BH and should arrive shortly.

I no longer plan to build dual 45 Stereomour monoblocks - at least not this year. For now I will keep one SII as a 2A3 and the other as a 45, modded to take full advantage of the 45B tube's higher power output capacity.

Order of operations:

(1) Get new SII up and running in stock 2A3 configuration with all 3 upgrades - albeit with a larger chassis to accommodate bigger iron in the future. I'm thinking a 12" x 12" copper chassis. Or maybe even 14 x 14.

(2) Convert to standard 45, burn in and compare with the 2A3 version.  The EML 45B's are stated to be compatible with standard 45 amps.

(3) Replace the PT, OTs and chokes and make other necessary modifications to run the 45Bs to get somewhere between 3.5 and 4.5 wpc. Since Kaiju iron is not available, I am leaning towards Lundahl transformers and chokes.  The EML webpage for the 45B has some recommended operating points for various Lundahl OTs: http://www.emissionlabs.com/datasheets/EML45B.htm  It looks like I have 3 options that will give me my desired output wattage.

I welcome any thoughts/input on which iron to go with. The amp will be used with my Audeze LCD4 headphones. On my current SII 2A3 I listen with the OT's configured for 16 Ohms. Damping really isn't a factor b/c the LCD4 has  200 Ohm input impedance and completely flat plot of impedance against frequency.  And they like a lot of power.  One of the main things I'm looking for with the 45 conversion is greater bass extension. 

The biggest question I have is whether the SR upgrade and the DCF upgrade can be modded to work with the 45B amp at the wattages I want. PB indicated that the SR and DCF will work with a standard 45 amp, but what about at double the standard wattage output? Is this doable? It would be great if I could use the BH boards and only need to swap out some components.  I hope to use the build as an opportunity to learn more about how these circuits actually operate. I learned some of the basics building a "Nickel Wonder" preamp that PB suggested - which I realize is incredibly simple in comparison to an SII.  I think the prospect of having a powerful 45B SII amp will motivate me to take my learning up a notch. But any guidance that BH can provide on the build will be most appreciated! 

Of course, one suggestion might be to just get a Kaiju. I hope to do so later in the year, but will pair the Kaiju with Jaegers. 

cheers and many thanks in advance,

Derek

[Doc B.]

I welcome any thoughts/input on which iron to go with.

Sure, since you plan on a bigger chassis the all nickel MQ EXO-050s I have for sale will rock with 45s. Look for plate chokes in the 50H range to go with them.

https://bottlehead.com/smf/index.php?topic=11296.0

[Paul Birkeland]

(1) Get new SII up and running in stock 2A3 configuration with all 3 upgrades - albeit with a larger chassis to accommodate bigger iron in the future. I'm thinking a 12" x 12" copper chassis. Or maybe even 14 x 14.

The 12x12 is probably just enough extra room. 

(3) Replace the PT

This would be a really, really bad idea.  You can basically throw away the DC filament supply, SR driver supply, and stock power supply.  If you go any get something from Hammond, it will probably hum and annoy you.  Then you'll have to figure everything else out from scratch.  While we are normally very helpful on this forum, if you need help we will just tell you to put the stock transformer back in.

OTs and chokes and make other necessary modifications to run the 45Bs to get somewhere between 3.5 and 4.5 wpc.

Well, if you want to do that, you are probably better off with a Kaiju and Doc B's 5K nickel output transformers, then add an appropriate filament transformer to heat the EML tubes.

The amp will be used with my Audeze LCD4 headphones. On my current SII 2A3 I listen with the OT's configured for 16 Ohms. Damping really isn't a factor b/c the LCD4 has  200 Ohm input impedance and completely flat plot of impedance against frequency.  And they like a lot of power.  One of the main things I'm looking for with the 45 conversion is greater bass extension. 

I would just go with the normal 45.  The extra power will be barely audible, and seems a little silly on headphones. 

The biggest question I have is whether the SR upgrade and the DCF upgrade can be modded to work with the 45B amp at the wattages I want. PB indicated that the SR and DCF will work with a standard 45 amp, but what about at double the standard wattage output?

The driver and DC filament supply won't care about that, but when you toss the power transformer, you kind of have to toss the rest of the amp.

Is this doable? It would be great if I could use the BH boards and only need to swap out some components.  I hope to use the build as an opportunity to learn more about how these circuits actually operate. I learned some of the basics building a "Nickel Wonder" preamp that PB suggested - which I realize is incredibly simple in comparison to an SII.  I think the prospect of having a powerful 45B SII amp will motivate me to take my learning up a notch. But any guidance that BH can provide on the build will be most appreciated! 

I do understand what you're after, and I can tell you (from experience) that the amount of fine tuning that we had to do to get the DC filament supply on the Stereomour II to work properly was a little crazy.  There is no other power transformer from any other manufacturer that I have seen that will give you the AC voltage you need to get that module to work. 

Of course, one suggestion might be to just get a Kaiju. I hope to do so later in the year, but will pair the Kaiju with Jaegers. 

Yes, a Kaiju with the DC filament board (which is regulated, and a fair improvement over the design in the SMR2) would be the way to go.  You'll also be able to use lots of different 300Bs from various manufacturers. 

[Deke609]

Hmm. Looks like I jumped the gun in getting the 45Bs. I had naively assumed that everything in the SII could simply be "scaled up" to accommodate the greater power output.

But there's still hope that the conversion to 45s will work with the LCD4. I got a good bump in perceived loudness when I added the BeePre in front of my SII . Even when really rocking out, I have the coarse attenuator set at -9dB on the SII with the BeePre fully open.  If I understand this right, every doubling of power yields about a 3dB increase in volume.  So going from 3.5Wpc with the 2A3 config to 2Wpc with 45 should result in less than a 3 dB drop in volume?  Do I have that right?  If so, I think that should be ok - but it will mean running the SII a little closer to fully open.  On the upside, the 45Bs should last forever if only asked to put out 2W.

cheers and thanks,

Derek

[Deke609]

@PB - What about keeping the PT and OTs, but swapping in different after-market plate chokes?  In a different thread, PJ indicated that the PC together with the parafeed cap sets the bass extension.  If the OT-2 is only asked to handle a max of 2W with the 45 instead of 3.5W with the 2A3, I think it follows that the OT-2 should go lower in the bass before saturating - and I am guessing that this is where the greater bass extension comes from with the conversion to 45s.  Could swapping in some after-market PCs push the bass extension even further? In the same thread, you indicated that you had experimented with putting the Kaiju PCs in a Stereomour and were only down -2dB at 8Hz.

If this would work, can you tell me what specs should I look for in a plate choke?  If there are no stock PC's that fit that bill from Lundahl, Electraprint, etc., maybe I could get them custom made.

Many thanks,

Derek

[Paul Birkeland]

When you do the 45 conversion, part of that involves connecting the entire winding of the plate choke between the 45 plate and B+, which is 40H instead of the 20H in the 2A3 configuration.  This is not possible with the 2A3 because it draws more current, but the reduced current drawn by the 45 allows this connection.  This change in conjunction with changing the parallel feed capacitor will work to improve the low end frequency response.  The power bandwidth of the OT-2 doesn't seem to be the limiting factor in this situation.  If you want to go for the high power 45B, then the plate current goes back up, and you need the other connection.

The Lundahl LL2743 may work, but it's a little off in terms of the options for the air gap. The Sowter 8985 would be the most appropriate aftermarket choice, but it's 50H/40mA, so you're not gaining much over what we provide. 

It kind of sounds like what you may want to do is build the Stereomour stock, then sort out the mods to get to #45s, then do a scratch build with all aftermarket parts. 

[braubeat]

Electraprint will build custom plate chokes to whatever specs you want. I have purchased several. Jack is very knowledgeable and can advise you about what will work well with different tubes.
My favorite amp is a low power parafeed 845 with Electraprint iron throughout.

Michael

[Deke609]

It kind of sounds like what you may want to do is build the Stereomour stock, then sort out the mods to get to #45s, then do a scratch build with all aftermarket parts.

Thanks PB. Yeah, that may be road I will need to take. The problem, of course, is that there's a snowball's chance in hell that I'll be able to build an 45B amp that will sound as good as a Stereomour or Kaiju - even assuming that I learn the ton of stuff I still need to learn to even build a 45B amp from scratch. 

So I'm rethinking things again.

The 2nd Stereomour amp on its way to me presents me with another opportunity: if I build it stock, I can bridge the two SII's giving me 7 Wpc. I'd like to hear what the extra headroom might give me.  Until I added the Beepre, my SII could lose some bass slam on some tracks. Example: Rush's Tom Sawyer. It would start out with slam, but once full instrumentation kicked in, the drums became a bit muted. I thought at first that this might just be the recording, but adding the BeePre disproved that hypothesis. With the BeePre in the system, there is no noticeable loss of slam.  (Although how adding the BeePre achieves this, I haven't the foggiest: I would have thought it impossible to get more out the SII by adding a pre-amp -- if an amp can be likened to a pump with a maximum pressure output, my understanding is that you can't increase that pressure output by adding a "pre-pump"; although I guess a prepump could reduce the amount of work the second pump needs to perform to get up to full pressure -- if so, did adding the BeePre make more current available to the headphones at the same voltage output?).

Bridged SII's will give me a sense of what the dynamics of the Kaiju might be like, and whether I want the added headroom.  If Kaiju (which would also give me added bass extension) is the way to go with the LCD4, I can convert the SII's to standard 45s for a very nice 2 channel system for listening at moderate volumes.  I very much miss having speakers, but living in semi-detached house makes loud-ish listening impossible without disturbing my neighbors. 

cheers,

Derek





 

[Deke609]

Electraprint will build custom plate chokes to whatever specs you want. I have purchased several. Jack is very knowledgeable and can advise you about what will work well with different tubes.
My favorite amp is a low power parafeed 845 with Electraprint iron throughout.

Michael

Many thanks Michael.  Some custom Electraprint plate chokes for twin Stereomour 45s could be a fun and manageable project. It's good to know that you've been happy with their products.

cheers,

Derek

[Deke609]

The second SiI arrived today and I've started the assembly. I want to give the new amp a minimum of a month of burn-in before bridging the two amps.

In the meantime, I'd like to convert my original SII to 45 and listen to the EML 45Bs. Do PJ's instructions set out on the 1st page of this thread capture the first steps?

Since I will be placing a parts order with Digi-Key, are there any other values of the quoted components that I should pick up in anticipation of having to make some tweaks? Factoring in shipping costs, it will likely be cheaper for me to order a scattershot range of component values in one go than to make make a series of more targeted orders for fewer components.

Many thanks in advance,

Derek

 

[Deke609]

...

2.  The 130R/3W resistors in the power supply need to be removed and replaced with 600 ohm 5W resistors.  It may be easier to just replace the two resistors that go from the 5 lug strip by the power transformer to the other two 5 lug strips with 1.1K/10W resistors and leave the other two 130 ohm resistors where they are.  Your mileage may vary, let us know which way works best.  This change lowers the power supply voltage for the 45.

3.  The 0.15 ohm resistors need to be removed and replaced with 0.22 ohm 2W resistors (3W is fine too).  This will reduce the filament voltage to 2.5V when the 45 is plugged in (the 2A3 draws more current, so if you don't change the resistors the filament voltage will be too high).

...

The presence of the DC filament upgrade will change the value of those 0.22 ohm resistors.  If someone can report what filament voltage they are getting (DC voltage between pins 1/4) with the 45 and the DC filament supply, we can suggest  tweaks to those values.

...

I would also note that the shunt regulated driver stage might call for tweaking the power supply dropping resistors a little bit as well.  It may be that a pair of 1K/10W resistors and 2 of the 4 original 130R resistors might be a better combo in the power supply.

@PB - I have both the DCF and SR upgrades. So I'm thinking my best approach is:

(1) leave in place the two 130Rs that connect 34L/31L and 30L/27L, remove the other two 130Rs and add wire leads to their termination points to make it easier to insert different replacement values (1.1K or 1.0K 10W - any other foreseeably likely values?  E.g., 950 or 900?)

(2) order a range of values for replacing the 0.15 ohm resistors - would 0.18 - 0.25 in 0.1 increments be a safe bet? Or is their some other range you would guesstimate?

Many thanks in advance,

Derek

[Paul Birkeland]

There's no reason to expect the 1.1K value to be a problem, you shouldn't need to try different values.

Since you are going to start with AC heating on this build, the 0.15 ohm resistors in the stock build can go to about 0.25 ohms instead (2W is OK). 

When you get to the DC filament installation (which you should do dead last), you can start by installing the resistors provided, then let us know what DC voltage you see across the filament pins.  When I dialed in the kit design, I was ordering resistors in 0.02 ohm increments. 

-PB

[Deke609]

Many thanks PB - and just to clarify: I am converting my existing SII that already has the SR and DCF upgrades installed. Is that problem, or would you suggest building the new kit as a 45 from the start?

My thinking is that I'll get a quicker sense of the 45 sound with my original SII b/c the caps and other components are already burned in. And I believe the EML 45Bs come with a partial factory burn-in.