All things LA2a related

[mushy]

+1 for the Allied. 

Should we have a party to celebrate the 100th page of the LA2a thread?

 

[millzners]

Thanks guys, I had a feeling some of these parts are grossly over-priced.  My next cost reduction will be in sourcing Cinemag xfo's instead of Sowter -- that could save over $70 depending on what they quote me with shipping.

Edit:

Also I just found this, obviously once I stopped looking for this information b/c you guys answered it, I stumbled upon it:

http://www.groupdiy.com/index.php?topic=26376.msg314502#msg314502

From our esteemed LA2A Guru SSLTech:

The Allied has no split/dual primary, so it's 110/120V only, the Hammond has 100/110/120/200/210/220/230/240 as primary voltage options. It's also rated VERY slightly higher in terms of VA, but if you're building a US-Only LA-2a, the Allied is the less-expensive option, of that there is NO doubt!

They're perfectly quiet, both mechanically and -in the completed unit- electrically. I also believe that they're manufactured by Hammond to the same standard as the 369JX, but made as a volume batch using a slightly shorter body, and with only 110V/120V primary windings,

they were the standard power transformer for the BLOO LA-2a's, and the Hammonds were supplied only for those kits going overseas, at extra charge IIRC. The quality is the same for both.

Keith

 

[regularjohn]

My next cost reduction will be in sourcing Cinemag xfo's instead of Sowter -- that could save over $70 depending on what they quote me with shipping.

Which cinemag's are you looking at?
Just curious because I've always used the sowter - and although they sound amazing - they are really pricey.  And the way exchange rates are going they're not getting any cheaper!

 

[millzners]

My next cost reduction will be in sourcing Cinemag xfo's instead of Sowter -- that could save over $70 depending on what they quote me with shipping.

Which cinemag's are you looking at?
Just curious because I've always used the sowter - and although they sound amazing - they are really pricey.  And the way exchange rates are going they're not getting any cheaper!

That in and of itself is a little complicated -- so I'm hoping the guy I emailed at Cinemag is helpful (I've read that he is).

From another thread I found somewhere on this board:

CMLI-15/15B  15k:15k Input (1:1)

CM-9589   10K : 600   Output (4:1)

Now this begs the question, did whoever I copied and pasted these two parts from know what they were doing, and are these the easiest options to implement into a P2P design.  Because the one thing I don't want to do is save myself some money and then spend countless hours trying to figure out how to modify the circuit to fit these things.  

What I do know is that these things don't match the basic specs the Sowters I found which are supposedly direct replacements for the original xfo's:

1009 Teletronix LA-2A 1968 Input transformer 600 ohm to 50K input transformer ratio 1:9
1010 15K/600 LA-2A 1968 15K/600 Line op 15k to 600 ohms output transformer Ratio 5:1.

Studioelectronics.biz offers that same Cinemag input xfo for "LA2A clones"...  But they charge $70 which I believe is significantly marked up (everything on that site is outrageously expensive!)

So obviously there's a big difference there on the impedances, and that could mean those parts won't work as exact replacements.  But they supposedly sound good and you can get these two for around $120 instead of $170 plus international shipping of something that weighs 10 pounds.  

Anyway I'll post something when I hear back from Cinemag.  If anyone has used Cinemags before it'd be nice to hear how it went.

 

[Kingston]

I have tested the CM-9589 in LA2A build (the 50/50 steel/nickel version, not the high-nickel one). It's one of the finest 4:1 step down output transformers in the world. You simply cannot go wrong. The impedance difference between 4:1 and 5:1 in this circuit is completely negligible. Think of it as 3dB of "free gain" for the 4:1 version.

Hey, it'll even work brilliant as LA2A input! (wired reverse of course)

No modifications needed in circuit whatsoever. Just read Cinemag datasheets for correct 600 ohm termination and wiring.

I know some sites and documents recommend 15k:15k and 10k/10k line level input transformers for LA2A. I personally wouldn't do this. It completely defeats the purpose of LA2A as a line level amp, or as a medium gain mic preamp. It also makes it difficult to really exploit (read:slam) the compressor. Don't be a pussy and install at least 1:4 input.

bury the needle

 

[millzners]

I have tested the CM-9589 in LA2A build (the 50/50 steel/nickel version, not the high-nickel one). It's one of the finest 4:1 step down output transformers in the world. You simply cannot go wrong. The impedance difference between 4:1 and 5:1 in this circuit is completely negligible. Think of it as 3dB of "free gain" for the 4:1 version.

Hey, it'll even work brilliant as LA2A input! (wired reverse of course)

No modifications needed in circuit whatsoever. Just read Cinemag datasheets for correct 600 ohm termination and wiring.

I know some sites and documents recommend 15k:15k and 10k/10k line level input transformers for LA2A. I personally wouldn't do this. It completely defeats the purpose of LA2A as a line level amp, or as a medium gain mic preamp. It also makes it difficult to really exploit (read:slam) the compressor. Don't be a pussy and install at least 1:4 input.

bury the needle

Thank you for your advice, that's awesome to hear the 4:1 is worth it:  I'm sold...  I agree the 1:1 input doesn't really make sense, and I plan on using the thing as a medium gain preamp often, maybe even incorporating the preamp switch to bypass some of the resistors like someone did in their LA2A last week or so.

The other Cinemag options on the input, besides the 1:4 CM-9589, is:

CMMI-8C 150, 600 : 10K which would give me the same ratio if wired for 600, but it's meant to be a mic input (probably doesn't make any difference).

The more intriguing option is the  CMQEE-3440A  37.5,150,600 : 50K, which would give the same ratio and impedance as the Sowters and UTC models...  That I think, besides the fact that I'm not sure how expensive it is, seems like the best option.

Thanks again for your advice!

 

[Kingston]

CMMI-8C 150, 600 : 10K which would give me the same ratio if wired for 600, but it's meant to be a mic input (probably doesn't make any difference).

The more intriguing option is the  CMQEE-3440A  37.5,150,600 : 50K, which would give the same ratio and impedance as the Sowters and UTC models...  That I think, besides the fact that I'm not sure how expensive it is, seems like the best option.

Be careful when substituting the input transformer with a mic input model. Keep in mind LA2A is line level unit first and foremost. Mic inputs generally won't take line level gracefully. Many will crap out (nasty clip) at standard mixdown levels and input pad is the last thing you want in LA2A.

The input should handle at least +10dBu gracefully. Notice +15dBu spec of the Sowters, it's there for a good reason. Check the transformer datasheets. None of the Cinemag mic input models are well suited for this task.

That said, CM-9589 will also work very well as LA2A input, even if it's not exactly marketed for that kind of tasks. I've tested it as input transformer, just not in this exact circuit, but very similar anyway. It has high (actually extreme) level handling capability, and flat frequency response. No distortion to mention.

 

[mushy]

I'd hesitate to use 600/50k on the input. Even with 600/10k I couldn't bring my knobs past 1 and had to do the 12AY7 mod. Even still, I have enough gain to run medium level mics through it.  I certainly have no problem burying the needle. Just my 2 cents. 

 

[millzners]

CMMI-8C 150, 600 : 10K which would give me the same ratio if wired for 600, but it's meant to be a mic input (probably doesn't make any difference).

The more intriguing option is the  CMQEE-3440A  37.5,150,600 : 50K, which would give the same ratio and impedance as the Sowters and UTC models...  That I think, besides the fact that I'm not sure how expensive it is, seems like the best option.

Be careful when substituting the input transformer with a mic input model. Keep in mind LA2A is line level unit first and foremost. Mic inputs generally won't take line level gracefully. Many will crap out (nasty clip) at standard mixdown levels and input pad is the last thing you want in LA2A.

The input should handle at least +10dBu gracefully. Notice +15dBu spec of the Sowters, it's there for a good reason. Check the transformer datasheets. None of the Cinemag mic input models are well suited for this task.

That said, CM-9589 will also work very well as LA2A input, even if it's not exactly marketed for that kind of tasks. I've tested it as input transformer, just not in this exact circuit, but very similar anyway. It has high (actually extreme) level handling capability, and flat frequency response. No distortion to mention.

Thanks again for everyone's advice on this topic.  I'm honestly torn on the topic of the input xfo.  I'm definitely sold on the CM-9589 output, and I know for sure I want to use Cinemags and stay to around 1:4 or less on the input ratio b/c I've read how little use that gain knob gets otherwise.  I'd prefer to have that gain knob up to around 5 or 6 most of the time to get those tubes working, but having never owned one of these things maybe that's wishful thinking...

I guess I've got some things to think about here...  Great stuff.

Other than this touch choice, I'm also looking into a Drip T4B instead of the StudioElectronics.biz reissue b/c I'm trying to cut costs for this initial build understanding that at some point I can always upgrade to a reissue or a vintage T4B.  Plus I'm convinced that website is gouging people.

By going with the allied power xfo, the cinemag input/output xfo's, and the drip T4B the cost can be reduced by around $250.  That makes the dream of building two of these puppies a lot more attainable. 

 

[regularjohn]

Nothing against David Kulka, he's a brilliant tech and knows his **** inside and out.  But I agree with you, the prices at StudioElectronics are absolutely outrageous! I'd never buy from there unless it was the ONLY place open at midnight and I had crazy mad munchies, you know what I mean! 
Seriously, $26 for the 1M zero adjust pot for the LA2A??!!!!  Are you kidding???!!!!  Get it from Digikey for $8.  And the 25K pot with switch that you use for the attack on an 1176, he's got for $35, when you can get it from mouser for $3.  It's highway robbery!

Yeah man, go with the Drip T4.  I'd pick it over an NOS T4 any day.  Not just because of the price, but because the electroluminescent material degrades over time (who knows how old those NOS T4's are), and also because Drip has painstakingly high standards of production.

 

[Kingston]

looking into a Drip T4B instead of the StudioElectronics.biz reissue b/c I'm trying to cut costs for this initial build understanding that at some point I can always upgrade to a reissue or a vintage T4B.

this one is easy: go with the dripelectronics t4b. Reissue would be no upgrade, more like degrade. Drip has all things T4B perfected to such precision I would be worried with T4B by anyone else. Search this forum for the exact breakdown of what happened. I seem to recall there is a direct link in META...

I guess you are not the first one to fall into the trap of "it has to be better when it's more expensive"

 

[emrr]

I'd prefer to have that gain knob up to around 5 or 6 most of the time to get those tubes working, but having never owned one of these things maybe that's wishful thinking...

Find my posts in this thread about actual dB gain for various popular ratios, and think about that. 

"getting those tubes working" has nothing to do with the position of the knob, the tubes don't care where the knob is, so long as the input voltage is sufficient to drive the output to at least unity.    The importance of the position of the knob is mostly in the user's mind.  When the knob is almost entirely off, there may be some issues with ability to fine tune levels, and you will begin to hear some HF roll-off. 

 

[millzners]

Nothing against David Kulka, he's a brilliant tech and knows his **** inside and out.  But I agree with you, the prices at StudioElectronics are absolutely outrageous! I'd never buy from there unless it was the ONLY place open at midnight and I had crazy mad munchies, you know what I mean! 

Yeah, my favorite was I found this old thread about the topic, maybe not even on this forum...  Anyway, somebody came to the guy's defense like "look, it's not like he's got a permanent auction on ebay with a stupid buy it now price, he's not doing this for the money"  Yeah well, now he does have a permanent auction; and his buy it now price for the NOS T4B is $185 for a part he payed $60 for 5 years ago.  Nothing against a good businesman, but he's even marking up Cinemag's $30 from where you can get them directly from Cinemag.

Anyway, I had a good feeling about Drip and I did read over that very old thread he did about how much work he put into matching the exact response of the old device.  I should have taken the hint early on but there is this stupid tendancy to just assume more expensive = better. 

Find my posts in this thread about actual dB gain for various popular ratios, and think about that. 

"getting those tubes working" has nothing to do with the position of the knob, the tubes don't care where the knob is, so long as the input voltage is sufficient to drive the output to at least unity.    The importance of the position of the knob is mostly in the user's mind.  When the knob is almost entirely off, there may be some issues with ability to fine tune levels, and you will begin to hear some HF roll-off.

Thank you for addressing this misconception, I still have a lot to learn about tube amplifiers as they don't teach you anything about them in school -- just op amps and transistors.  The tendancy is to believe tubes are magical -- anyway I'm going back to the posts you made.

 

[emrr]

I think David's prices represent a desire to not sell parts unless it's really worth his time to do so.  If I were running a repair shop, and spent all my time selling individual repair parts, I probably wouldn't get much repair work done.  The prices are probably meant to discourage most from buying, but you know, if you have to.....

But, I don't know this.  No reason to complain about it, just buy elsewhere if you like. 

 

[sircletus]

Anyone think the Hammond 369JX could deliver enough current to power two LA-2As?  I'm considering cramming two into a single box.  How do I figure out approximate current draw for the B+ of an LA-2A (or any other tube device for that matter) anyway?  I've just been adding up maximum plate current draw according to tube spec sheets, adding about 10% margin and going from there:

1 x 12AX7 = 2.4mA (1.2mA current per triode)
1 x 12AX7 = 2.4mA (")
1 x 12BH7A = 23mA (11.5mA per triode)
1 x 6AQ5 = 30mA max plate current

Total = 57.8 mA for a single LA-2A.

Using that "logic," the Hammond could supply enough current for a single unit, but the Allied that many people are using couldn't, as it's rated 500V @ 40mA.

 

[mushy]

Check the D-LA2a thread.

 

[Biasrocks]

Using that "logic," the Hammond could supply enough current for a single unit, but the Allied that many people are using couldn't, as it's rated 500V @ 40mA.

The original LA2 Triad PT was rated for 500V @ 40mA.

Mark

 

[regularjohn]

Using that "logic," the Hammond could supply enough current for a single unit, but the Allied that many people are using couldn't, as it's rated 500V @ 40mA.

I'm pretty sure your calculations aren't correct.  I've used the Allied for four different LA2A's and all sound and work fantastic!  And I've never had any issues with the power trafo even getting noticeably hot, as it would if it were being overworked.

 

[sircletus]

I've used the Allied for four different LA2A's and all sound and work fantastic!  And I've never had any issues with the power trafo even getting noticeably hot, as it would if it were being overworked.

Right.  That's exactly my point.  Obviously 40mA is enough current for an LA-2A, so how exactly do I measure the actual current drawn by an LA-2A?  I have one in front of me, I just don't know how to measure the current, or the best way to spec a power trafo for any given project.  Off to another thread, I suppose!

 

[sircletus]

Figured it out, never mind.