"Russian" DLA2A

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Silvas

Well-known member
Joined
Aug 15, 2006
Messages
727
Location
Chia, Colombia
Hello !

It's been almost 2 years with my Christmas edition DLA2A. I seriously love this thing !

Recently i got a couple more PCBS which are partially stuffed now.

I've been playing with this idea in my head : Building another DLA2A, but replace the 12AX7 with 6N2P and replace the 12BH7 with (maybe) 6N6P. Obviously, heater arrangement must change (and maybe heater PT requeriments) and a small trace cutting is required on the PCB. Also, russian teflon caps for coupling, except the 10uF solen fast (it can be bypassed with a teflon one)

What do you think ?
;)

 
6N2P is 12AX7. Only pinout changes. No point in that swap. Using 6N6P is also debatable. The line amp output of LA2A is completely drenched in feedback. No one would even notice if someone replaced it with solid state alternative, it's that clean. I experimented with some tube and plate load swaps. The differences were negligible. The sound itself comes mainly from the transformers.

Changing the entire line amp would be much more interesting, remove the useless feedback loop, set up better load lines, have less gain available. but then your PCB would be useless already.

Teflon caps are MASSIVE. Consider PIO instead, if you have that silent arts PCB. I have an "all PIO" LA2A. It even has massive PIO "tub" caps as those 10uF ones. This did make a considerable difference to the sound. But it's not the lofi LA2A like your grandma used to make, the sound people are used to.
 
Kingston said:
6N2P is 12AX7. Only pinout changes. No point in that swap. Using 6N6P is also debatable. The line amp output of LA2A is completely drenched in feedback. No one would even notice if someone replaced it with solid state alternative, it's that clean. I experimented with some tube and plate load swaps. The differences were negligible. The sound itself comes mainly from the transformers.

Changing the entire line amp would be much more interesting, remove the useless feedback loop, set up better load lines, have less gain available. but then your PCB would be useless already.

Teflon caps are MASSIVE. Consider PIO instead, if you have that silent arts PCB. I have an "all PIO" LA2A. It even has massive PIO "tub" caps as those 10uF ones. This did make a considerable difference to the sound. But it's not the lofi LA2A like your grandma used to make, the sound people are used to.

I was eagerly waiting for you to chime in !

What i'm looking for is a slightly different flavor, with my new favorite russian tubes !  (cheaper too, and top quality for the price IMO)

I have to get creative to make the caps fit somewhere, but it's perfectly doable.

I remember you did a highly modified LA2A, right ? that's the one you're talking about, with the PIO's? I'm gonna search that thread and give it a read.

Thanks !

 
Hi ,
  Here's the link -  http://www.groupdiy.com/index.php?topic=39095.msg482305#msg482305

I'm about 60% into my first D-LA2A , and refer to this time and time again  ;D
 
I have to admit. I've just been jamming through mine for the last few months with a monitor in my apartment..no mixing etc...; i really really like what it does to vocals and the ambient guitar just coming thru. This unit has the drip optos.

I've thought of trying out the Keneteks for comparison. Couldn't find PIO cap's on ebay...and i did search for a little while.
This ones using 12ay7 as well.
 
audiophreak said:
Hi ,
  Here's the link -  http://www.groupdiy.com/index.php?topic=39095.msg482305#msg482305

I'm about 60% into my first D-LA2A , and refer to this time and time again  ;D

I have since gone back to the original tubes. I found some very good 12AX7's, Tungsol modern remakes, these are really really good and available in most good tube stores. They sounded better than the 6N2P's I had anyway. I have also since made it "all PIO". None of those orange drop film caps left like in the pictures, or any Arco trimmers. only PIO and silver micas now.

I went as far as removing the 4n7 cap inside the Drip T4B modules. They are in series with another 10nF (PIO) from the 6AQ5 tube plates on the PCB so completely pointless really. Removing that T4B cap made a surprising amount of difference, and could be easily picked in A/B testing under very heavy compression.

Oh, and I replaced the input volume pot with a 21-step rotary switch. The peak reduction is still a standard cheapo pot, because lets face it, those T4B's are impossible - or at least very expensive - to match.

You know how they say LA2A isn't that great for mastering and bus duties? Well I can imagine the original (lofi unit) wasn't. But it can be transformed into one. I have also been toying with the idea of building another unit with intentional lofi sound. Use as cheap/crap parts as possible, like grandma used to make. But then, grandma also had the best I/O transformers in the whole world, so that comparison isn't entirely accurate.
 
Kingston said:
audiophreak said:
Hi ,
  Here's the link -  http://www.groupdiy.com/index.php?topic=39095.msg482305#msg482305

I'm about 60% into my first D-LA2A , and refer to this time and time again  ;D

I have since gone back to the original tubes. I found some very good 12AX7's, Tungsol modern remakes, these are really really good and available in most good tube stores. They sounded better than the 6N2P's I had anyway. I have also since made it "all PIO". None of those orange drop film caps left like in the pictures, or any Arco trimmers. only PIO and silver micas now.

I went as far as removing the 4n7 cap inside the Drip T4B modules. They are in series with another 10nF (PIO) from the 6AQ5 tube plates on the PCB so completely pointless really. Removing that T4B cap made a surprising amount of difference, and could be easily picked in A/B testing under very heavy compression.

Oh, and I replaced the input volume pot with a 21-step rotary switch. The peak reduction is still a standard cheapo pot, because lets face it, those T4B's are impossible - or at least very expensive - to match.

You know how they say LA2A isn't that great for mastering and bus duties? Well I can imagine the original (lofi unit) wasn't. But it can be transformed into one. I have also been toying with the idea of building another unit with intentional lofi sound. Use as cheap/crap parts as possible, like grandma used to make. But then, grandma also had the best I/O transformers in the whole world, so that comparison isn't entirely accurate.

Great info !

Today i'm testing my current DLA2A going unbalanced in. I use it 99% of the time in studio's mixing / mastering room, so no long cable runs here. I need to check if it can play well with the aurora. I'm leaving the edcor output.

The russian PIOs are easy to find on eBay, there's a couple guys i buy tubes and stuff who have lots of them !


 
Kingston said:
Oh, and I replaced the input volume pot with a 21-step rotary switch. The peak reduction is still a standard cheapo pot, because lets face it, those T4B's are impossible - or at least very expensive - to match.

  Thanks for sharing all this great info , on the 21-step input , did you make it 25k Log with the 75k resister ?

  (  I'll be working on my " Kingston Duct " soon )  ;D 
 
audiophreak said:
Thanks for sharing all this great info , on the 21-step input.

I made a 100k log with 3dB steps. I never had an issue with La2A with too much volume or too little control resolution on the lower volume area. Here's a chart of the switch:

21-step 100k log stepper in 3dB steps
Step 1, Attenuation = 60 dB, Rx = 99900 ohms, Ry = 100 ohms, Resistor = 100 ohms. 100R
Step 2, Attenuation = 57 dB, Rx = 99859 ohms, Ry = 141 ohms, Resistor = 41 ohms. 39R
Step 3, Attenuation = 54 dB, Rx = 99800 ohms, Ry = 200 ohms, Resistor = 59 ohms. 56R
Step 4, Attenuation = 51 dB, Rx = 99718 ohms, Ry = 282 ohms, Resistor = 82 ohms. 82R
Step 5, Attenuation = 48 dB, Rx = 99602 ohms, Ry = 398 ohms, Resistor = 116 ohms. 120R
Step 6, Attenuation = 45 dB, Rx = 99438 ohms, Ry = 562 ohms, Resistor = 164 ohms. 160R
Step 7, Attenuation = 42 dB, Rx = 99206 ohms, Ry = 794 ohms, Resistor = 232 ohms. 240R
Step 8, Attenuation = 39 dB, Rx = 98878 ohms, Ry = 1122 ohms, Resistor = 328 ohms. 330R
Step 9, Attenuation = 36 dB, Rx = 98415 ohms, Ry = 1585 ohms, Resistor = 463 ohms. 470R
Step 10, Attenuation = 33 dB, Rx = 97761 ohms, Ry = 2239 ohms, Resistor = 654 ohms. 680R
Step 11, Attenuation = 30 dB, Rx = 96838 ohms, Ry = 3162 ohms, Resistor = 923 ohms. 910R
Step 12, Attenuation = 27 dB, Rx = 95533 ohms, Ry = 4467 ohms, Resistor = 1305 ohms. 1K3
Step 13, Attenuation = 24 dB, Rx = 93690 ohms, Ry = 6310 ohms, Resistor = 1843 ohms. 1K8
Step 14, Attenuation = 21 dB, Rx = 91087 ohms, Ry = 8913 ohms, Resistor = 2603 ohms. 2K7
Step 15, Attenuation = 18 dB, Rx = 87411 ohms, Ry = 12589 ohms, Resistor = 3676 ohms. 3K6
Step 16, Attenuation = 15 dB, Rx = 82217 ohms, Ry = 17783 ohms, Resistor = 5194 ohms. 5K1
Step 17, Attenuation = 12 dB, Rx = 74881 ohms, Ry = 25119 ohms, Resistor = 7336 ohms. 7K5
Step 18, Attenuation = 9 dB, Rx = 64519 ohms, Ry = 35481 ohms, Resistor = 10362 ohms. 10K
Step 19, Attenuation = 6 dB, Rx = 49881 ohms, Ry = 50119 ohms, Resistor = 14638 ohms. 15K
Step 20, Attenuation = 3 dB, Rx = 29205 ohms, Ry = 70795 ohms, Resistor = 20676 ohms. 20K
Step 21, Attenuation = 0 dB, Rx = 0 ohms, Ry = 100000 ohms, Resistor = 29205 ohms. 30K
 
Kingston said:
audiophreak said:
Thanks for sharing all this great info , on the 21-step input.

I made a 100k log with 3dB steps. I never had an issue with La2A with too much volume or too little control resolution on the lower volume area. Here's a chart of the switch:

21-step 100k log stepper in 3dB steps
Step 1, Attenuation = 60 dB, Rx = 99900 ohms, Ry = 100 ohms, Resistor = 100 ohms. 100R
Step 2, Attenuation = 57 dB, Rx = 99859 ohms, Ry = 141 ohms, Resistor = 41 ohms. 39R
Step 3, Attenuation = 54 dB, Rx = 99800 ohms, Ry = 200 ohms, Resistor = 59 ohms. 56R
Step 4, Attenuation = 51 dB, Rx = 99718 ohms, Ry = 282 ohms, Resistor = 82 ohms. 82R
Step 5, Attenuation = 48 dB, Rx = 99602 ohms, Ry = 398 ohms, Resistor = 116 ohms. 120R
Step 6, Attenuation = 45 dB, Rx = 99438 ohms, Ry = 562 ohms, Resistor = 164 ohms. 160R
Step 7, Attenuation = 42 dB, Rx = 99206 ohms, Ry = 794 ohms, Resistor = 232 ohms. 240R
Step 8, Attenuation = 39 dB, Rx = 98878 ohms, Ry = 1122 ohms, Resistor = 328 ohms. 330R
Step 9, Attenuation = 36 dB, Rx = 98415 ohms, Ry = 1585 ohms, Resistor = 463 ohms. 470R
Step 10, Attenuation = 33 dB, Rx = 97761 ohms, Ry = 2239 ohms, Resistor = 654 ohms. 680R
Step 11, Attenuation = 30 dB, Rx = 96838 ohms, Ry = 3162 ohms, Resistor = 923 ohms. 910R
Step 12, Attenuation = 27 dB, Rx = 95533 ohms, Ry = 4467 ohms, Resistor = 1305 ohms. 1K3
Step 13, Attenuation = 24 dB, Rx = 93690 ohms, Ry = 6310 ohms, Resistor = 1843 ohms. 1K8
Step 14, Attenuation = 21 dB, Rx = 91087 ohms, Ry = 8913 ohms, Resistor = 2603 ohms. 2K7
Step 15, Attenuation = 18 dB, Rx = 87411 ohms, Ry = 12589 ohms, Resistor = 3676 ohms. 3K6
Step 16, Attenuation = 15 dB, Rx = 82217 ohms, Ry = 17783 ohms, Resistor = 5194 ohms. 5K1
Step 17, Attenuation = 12 dB, Rx = 74881 ohms, Ry = 25119 ohms, Resistor = 7336 ohms. 7K5
Step 18, Attenuation = 9 dB, Rx = 64519 ohms, Ry = 35481 ohms, Resistor = 10362 ohms. 10K
Step 19, Attenuation = 6 dB, Rx = 49881 ohms, Ry = 50119 ohms, Resistor = 14638 ohms. 15K
Step 20, Attenuation = 3 dB, Rx = 29205 ohms, Ry = 70795 ohms, Resistor = 20676 ohms. 20K
Step 21, Attenuation = 0 dB, Rx = 0 ohms, Ry = 100000 ohms, Resistor = 29205 ohms. 30K

  Hi Kingston ,
                    I see you had the Sowter Transformers in yours , I've read there are a couple of choices for Sowter input and output transformers , may I ask which ones you used ?

    Thanks,
                Chip
 
1009 and 1010. I didn't really give it much thought. It said "UTC replacement" and they can both take a loud input so I just went with it. But I can see in plain sight the output is not anywhere near UTC A24 quality/complexity. It's more like edcor, simplistic. Sounds great anyway. The input is very high quality.
 
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