D-LA2A Support Thread

[BGroen]

Hello everyone,

I am almost done with my D-LA2A. I am running the first tests with tubes but without T4B. To my disappointment the left channel does not pass any sound when switched IN.
The right channel does pass sound and so I swapped input transformers, tubes and gain knob for trouble-shooting. These all seem to work fine. Further more I replaced one relay, I figured this might be the case. No result.

I have removed all tubes and disconnected the gain pot to minimize the 'search-area'.
I don't understand what I am measuring at my input transformer.

Sowter 4383 input:
                  L-channel (not working)      R-channel (working)
Brown        signal                                  signal
Pink          signal                                  no signal
Green        signal                                  signal
Blue          no signal                              signal
Gray and black no signal both channels.

If anyone has any suggestions or thoughts, that would be much appreciated!

Kind regards,
Beinte

 

[BGroen]

Front view of my hopefully soon working D-LA2A.

 

[[silent:arts]]

I don't understand what I am measuring at my input transformer.

Hi Beinte,
how are you measuring those signals?

 

[BGroen]

Hi Beinte,
how are you measuring those signals?

Hi Volker,

Thanks for your response. I have a 1kHz test signal and I am measuring with my oscilloscope.
Negative terminal at star ground. Positive terminal at one of the transformer wires. See attached image.

Kind regards, Beinte

 

[[silent:arts]]

Ok, this is fine for the transformer secondary (the blue wire).
You either have no connection from the molex to the PCB,
or a short to ground.
(Without the transformer) check for continuity to R107.
(Without the transformer) measure R105.

 

[BGroen]

Thanks for your reply Volker. R105 and R107 are fine (comparing to the working channel).
Today I checked the molex of the input XLR, and here it was.... Now it's fixed!

Pictures will follow

 

[BGroen]

Really happy with the result ! All is working fine!

 

[[silent:arts]]

Congrats  8)

 

[guitar4444]

I built this D-LA2A quite a few years back. It works really well but one thing that bothers me is that one of the tubes is really close to the power supply caps. Can somebody tell me if that changed on a later revision of the circuit board? thanks Greg

 

[audiophreak]

I built this D-LA2A quite a few years back. It works really well but one thing that bothers me is that one of the tubes is really close to the power supply caps. Can somebody tell me if that changed on a later revision of the circuit board? thanks Greg

If you built it in a 3U case , I used a 7-Pin Miniature Vacuum Tube Test Socket Adapter as a “ spacer “ socket to get that one tube away from the PSU caps per channel - worked for me

 

[[silent:arts]]

I built this D-LA2A quite a few years back. It works really well but one thing that bothers me is that one of the tubes is really close to the power supply caps. Can somebody tell me if that changed on a later revision of the circuit board? thanks Greg

There are no different revisions of this PCB, and it never changed.

 

[JW]

Can someone verify that this power transformer is okay? Looks like what I'm looking for. AS-1T250 - 100VA 250V Transformer

I've been using the Rhondo power transformer but it's blowing fuses all on it's lonesome for some reason, so I'm gonna try something else. The Rhondo has been a little loud mechanically as well, so what the heck.

 

[JW]

Sorry for the last question. I ordered this Antek AS-1T250transformer. Heavy!
I was actually asking about it without searching this thread first. But it turns out it has been used.

Can I just verify the wiring?

On the primary, both blacks connected together and both reds together for 115VAC correct?

On the secondary, one set of green and blue per heater I can see. For the B+, I'm wiring the two yellow (0V) together and connecting to the board's 0V ground. Which leaves me with the two white leads for the two 250V leads. Correct?

(I haven't been using the relays so that's not an issue)

 

[guitar4444]

If you built it in a 3U case , I used a 7-Pin Miniature Vacuum Tube Test Socket Adapter as a “ spacer “ socket to get that one tube away from the PSU caps per channel - worked for me

That's a great idea, thanks for the tip

 

[guitar4444]

There are no different revisions of this PCB, and it never changed.

Thanks for the reply. It works well anyway. I might try the spacer idea at some point

 

[snowow]

How big difference does the transformers do? Is Tab Funkenwerk the closest ones to the original?

 

[andow]

Finished my second unit recently!

This is a really nice project, thanks for making it available Volker! If you ever get around doing a revision of the PCB, there are a few things that could be improved IMO:

- Additional pads for 0V/5V to use a seperate connector for each channel.
- Seperate pads for the heater wires, or at least bigger pads on the heater pins.
- Pads for adding 600R termination (or external switch) on the output.
- Increase the distance between V4 and electrolytic capacitors.
- Trim pot for R25.
- Pads for adding an external switch or pot for RV37

 

[innercityman]

Finished my second unit recently!

This is a really nice project, thanks for making it available Volker! If you ever get around doing a revision of the PCB, there are a few things that could be improved IMO:

- Additional pads for 0V/5V to use a seperate connector for each channel.
- Seperate pads for the heater wires, or at least bigger pads on the heater pins.
- Pads for adding 600R termination (or external switch) on the output.
- Increase the distance between V4 and electrolytic capacitors.
- Trim pot for R25.
- Pads for adding an external switch or pot for RV37

Saw it on FB . I will build one too for a friend in the next weeks. Would you have a mouser cart to share if you don't mind ? It would definitely save some time for sourcing parts.

 

[Ricardus]

I'd like to have a cart for this as well.

 

[andow]

I usually have more than one project I'm working on plus a lot of parts that I already have in the workshop. So I don't think my Mouser carts will make sense to anyone else, sorry...