D-LA2A Support Thread

[EHOFFA007]

Thanks for the help man!
So the bench multimeter I bought off evilbay was acting wonky. In the trash it went!
Got a new meter that works and this is what is actually happening.
Power traffo totally offboard is giving me 277V ac on the mains.
when connected i'm getting the same AC voltage and 362v DC on both D1 and D2
On the right channel tube sockets,getting 350V DC
On the Left channel tube sockets getting  277v DC
I flipped the board and checked for shorts with the continuity tester=OK
Maybe a bad Cap on the left channel? What would cause the DC voltage to get knocked down?
This is my first real troubleshoot so bear with me  :

 

[alexc]

Here's my DLA2A just finished and now tweaking and listening...

Using Jensen 1:4 inputs and Carnhill 4:1 outs, Drip T4Bs and mci/triplett meters.

All good, went together easy and sounding superb. Getting familiar with it
and how it sounds compared to the other la2a style units I have.

Thanks Volker for the great pcb!

 

[baadc0de]

Here's my DLA2A just finished and now tweaking and listening...

Using Jensen 1:4 inputs and Carnhill 4:1 outs, Drip T4Bs and mci/triplett meters.

All good, went together easy and sounding superb. Getting familiar with it
and how it sounds compared to the other la2a style units I have.

Thanks Volker for the great pcb!

Looking great. This four-Vus plus reminiscent-of-La3a layout of yours is very appealing to me. It will probably serve as a main inspiration when I do my second dual unit lol. I only don't dig different VU lights. A bit distracting to me. Be sure to tell us how it compares to other LA2A-like stuff

Cheers,
B.

 

[alexc]

Thanks!

Well I have to say this is a great result - unity gain noise floor of -79dBu for the first channel
and -79dbU for the channel closest to psu traffo on my RTA which is calibrated to the dBu standard.

My Motu converter noise floor is -83dBu.

Outstandingly quiet build - equal best for the units I've built, alongside the Poorman 670.

Significantly quieter than my Drip v1 build, which came in at about -72dBu (from memory).
Massively quieter than my ADL CL1 which is around -65dBu or so. (It prolly needs caps change - it is an early one)

I'm finding those Carnhill outputs a little thicker sounding with some more crunch than the Sowter
but not a lot in it really. No question - it sounds fantastic and all works as expected.

Certainly the Carnhill 600:9600 are great in this application, especially for the price which is a lot less than Sowters.
The Jensens seem very transparent as one would expect. Can't really say there's much diff to the Sowter.
Cost a lot less tho. All in all, not much in it between them - compared to the Edcor, the Edcor is somewhat
grainier. Not a bad thing for a guitar, tho.

Well - this one is closed up now and into the studio to become a bus compressor, one of a bunch of different
ones.

Anyway - highly recommended DLA2A pcb from Silent:Arts

 

[audiophreak]

Thanks tomcat  !

    I kinda thought so, but wanted to ask here to possibly get a different perspective.  I found this article - http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm -  and found it interesting, I try to take in as many opinions as possible, then try what I feel makes science to me    ;D

from that article - " The place to use CC's is where there's big signal - plate resistors, and ideally the stage just before the phase inverter. The phase inverter would otherwise be ideal, with plate resistors carrying the highest signal voltage in the amp, but phase inverters are often enclosed in a feedback loop. The feedback minimizes the distortion  the resistor generates.  "

Hi All,
        ( quoting myself is kinda weird  ;D  )  anyway,  after reading that article, and still being a newbee    ;D  I guess my question is... would R117, 118, 113, 109, 133, 134  , be the optimum places for CC resistors ?
 
  ... if not, would someone be kind enough to make some suggestions ? 

  Thanks All

 

[herrmann]

What's the carnhill ref ?

 

[baadc0de]

Sorry if this has been addressed before, but what would be the most elegant way to have two opto cells per channel and make them individually switchable. I see in the schematic that the board connects 7 wires to the opto cell, so to switch them, I would need..?

 

[alexc]

>What's the carnhill ref ?

Carnhill VTB2291 : ungapped, 9600:600

http://www.audiomaintenance.com/acatalog/info_312.html

A fine traffo at a reasonable price - an alternative to Edcor (on the cheaper side) or Sowter (on the tres expensive side)
A little 'thicker' sounding than the Edcor ('grainier' sort of hifi) or Sowter ('clean' and hifi).

Not much in it - I could maybe tell them apart in a blind test. With a couple of tries.

Definately makes a small oep or a lundahl seem like a light, girly traffo.  

One thing tho - makes the output a little hotter. May want to mod the output pot to be a fixed resistance in series with
a smaller value pot, as has been previously suggested.

I plan to do that as well as experiment with a lower gain signal tube than the 12AX7 in position 1.

My unit has the output gain pot at "1" or "2" most of the time, instead of the more usual "3" or "4" on my other units.
Anything over 5 is like a battleship PA.

Cheers

 

[[silent:arts]]

Sorry if this has been addressed before, but what would be the most elegant way to have two opto cells per channel and make them individually switchable. I see in the schematic that the board connects 7 wires to the opto cell, so to switch them, I would need..?

Pin 2, 4, 6 and 8 are connected to ground - no need to switch them.
you only need to switch Pin 3, 5 and 7.
My guess: switching Pin 3 only should work too.

[note1: Pin 3 contains high voltage]
[note2: I haven't tested any T4B switching]

 

[Sredna]

And pin 5? 

My guess: switching Pin 3 only should work too.

Do you mean that the internal resistance of the LDRs is so large when dark
that its no problem having two T4Bs in parallel?

[note1: Pin 3 contains high voltage]

aprox. 30 Volts AC

 

[[silent:arts]]

And pin 5?  

pin 5 is overrated ;D
thanks, corrected

My guess: switching Pin 3 only should work too.

Do you mean that the internal resistance of the LDRs is so large when dark
that its no problem having two T4Bs in parallel?

yes. meter might need to be re-adjusted, audio has too much gain anyway.
but again: not tested by me

[note1: Pin 3 contains high voltage]

aprox. 30 Volts AC

like I said, high voltage 8)

 

[baadc0de]

Thanks guys.. I'll report back once I implement this scheme.

 

[drgrateful]

Hi, I am planning to use this small heatsink for the 7805:

http://www.conrad-international.com/Heatsink-for-plastic-transistor-25x15x18.htm?websale7=conrad-int&pi=188115

Will this be fine? Do I need a larger one, or maybe is it better to attach the 7805 to the case, as I have seen in some builds?

Thanks for the suggestions.

Matteo

 

[audiophreak]

Hi All,
    Just starting out on this, ordering parts, Mouser is out of stock on the relays, - would this one due ?  the only diff I see is that the max currect rating is 1A instead of 2A  

Thanks,
           Chip

EDIT :  forgot the link  :    - http://www.mouser.com/ProductDetail/Omron-Electronics/G6K-2P-DC5/?qs=sGAEpiMZZMs3UE%252bXNiFaVBrMwKMEuUpxYUmZBiw8UvA%3d

 

[Randyman...]

Same here!  I ordered these and am also curious if they will work:

http://www.mouser.com/ProductDetail/Omron/G6A-274P-ST40-US-DC5/?qs=ISjK4nnpKfFgGVuxsXPgBw%3d%3d

They have an 80ma coil current and 400ma consumption rating instead of 100ma coil current and 500ma consumption like the ones on azone's BOM - but are both 5V, seem to have the same 2A switching capability and same footprint.

Anyone know if they will work properly?

Thanks

 

[[silent:arts]]

Hi, I am planning to use this small heatsink for the 7805:

http://www.conrad-international.com/Heatsink-for-plastic-transistor-25x15x18.htm?websale7=conrad-int&pi=188115

Will this be fine? Do I need a larger one, or maybe is it better to attach the 7805 to the case, as I have seen in some builds?

it really depends on your build. might be enough for the relays only, but if you have illuminated switches and meters ...
mount the 7805 to the case (isolated!) doesn't hurt.

 

[[silent:arts]]

Just starting out on this, ordering parts, Mouser is out of stock on the relays, - would this one due ?  the only diff I see is that the max currect rating is 1A instead of 2A
- http://www.mouser.com/ProductDetail/Omron-Electronics/G6K-2P-DC5/?qs=sGAEpiMZZMs3UE%252bXNiFaVBrMwKMEuUpxYUmZBiw8UvA%3d

Chip, those have a wrong pinout

http://www.mouser.com/ProductDetail/Omron/G6A-274P-ST40-US-DC5/?qs=ISjK4nnpKfFgGVuxsXPgBw%3d%3d

Randy, they should work fine

 

[audiophreak]

Thanks [silent:arts] ,
 
      Duh.... I was looking at coil current and power consumption, pinouts were further down the spec sheet ;D

  how about this one - http://www.mouser.com/Search/ProductDetail.aspx?R=G6A-234P-ST15-US-DC5virtualkey65300000virtualkey653-G6A-234P-ST-DC5

... 30ma coil current and 150mw power consumption.

 

[[silent:arts]]

Looks good.
coil current and power consumption is a matter of your PSU transformer and what else you want to drive from the 5V rail. lesser = better, the more = hotter

max. switching current etc: we are switching line audio level ...

 

[audiophreak]

[silent:arts] Thanks so much,
                                      I have now read the whole thread, I still have a few questions, but will try and figure them out first. as you can see, still ordering parts.

    From what I have read, cant wait to hear this