D-LA2A Support Thread

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Hey everyone,
Just finished wiring up my build. The only thing i cant figure out is how to wire up the pilot lamp jewel light thing i've got for the front. I think I read somewhere about hooking it up to the heaters. But wasn't sure if that means hook it up to the left AND right heater, or left OR right.

Thanks!
 
charlievela said:
Hey everyone,
Just finished wiring up my build. The only thing i cant figure out is how to wire up the pilot lamp jewel light thing i've got for the front. I think I read somewhere about hooking it up to the heaters. But wasn't sure if that means hook it up to the left AND right heater, or left OR right.

Thanks!
Click to expand...

Take the current from the heaters of one channel (black-black or brown-brown).
 
The right channel seems to be working just fine.

The left Chanel isn't compressing unless I have the PR knob fully turned up. And it's not so much compressing as distorting the signal.
I've swapped tubes and optos as well as the PR molex but that doesn't seem to be the issue.

When I have the stereo link enabled with a test tone applied to the broken channel, I'm seeing the correct amount of gain reduction at corresponding settings of the knob. So, if I had signal going through the working channel and was seeing 5db of reduction when the pot was at "6", having the link enabled with a signal running through the broken channel and a pot setting of "6" shows 5db reduction on the working channel but not on the broken channel.

The broken (left) channel gain knob works normally, except when I turn it all the way up with no signal running, I can hear a high frequency modulation in the tubes that isn't present in the right. But the meter seems to track the output just fine, and goes to zero when I flip it to display GR.

Any suggestions for trouble shooting?
 
charlievela said:
The right channel seems to be working just fine.

The left Chanel isn't compressing unless I have the PR knob fully turned up. And it's not so much compressing as distorting the signal.
I've swapped tubes and optos as well as the PR molex but that doesn't seem to be the issue.

When I have the stereo link enabled with a test tone applied to the broken channel, I'm seeing the correct amount of gain reduction at corresponding settings of the knob. So, if I had signal going through the working channel and was seeing 5db of reduction when the pot was at "6", having the link enabled with a signal running through the broken channel and a pot setting of "6" shows 5db reduction on the working channel but not on the broken channel.

The broken (left) channel gain knob works normally, except when I turn it all the way up with no signal running, I can hear a high frequency modulation in the tubes that isn't present in the right. But the meter seems to track the output just fine, and goes to zero when I flip it to display GR.

Any suggestions for trouble shooting?
Click to expand...

try to switch Left and right transformers wires, maybe one of them has an issue
 
Tried swapping transformers and no change. Also tried solder wicking around the molex connectors on the pcb and reflowing. Checked continuity on all my heaters and they're good.  I saw that some folks earlier in the thread had a similar issue. Any word on solutions?
 
charlievela said:
Tried swapping transformers and no change. Also tried solder wicking around the molex connectors on the pcb and reflowing. Checked continuity on all my heaters and they're good.  I saw that some folks earlier in the thread had a similar issue. Any word on solutions?
Click to expand...

try swapping peak reduction pots...
 
charlievela said:
I've tried that as well when I double checked the Peak reduction molex
Click to expand...

Follow your signal from the Input, and you will see when there is  a difference between the two channels.  You have to lacalize it
 
Okay,

Finally got almost all the pieces together for this guy. Including original input and output transformers, Kenetek slow cells, and about 10 JAN 5751's to choose from. Hopefully this will be an okay tube replacement for the 12AX7 for V1. Apparently inbetween a 12AY7 and 12AX7 in gain.

Questions

Any ideas as far as mounting the UTC's inside the case? I guess a strip of metal would do with some 90 degree legs. Do input and output have to be a suitable distance from one another or anything else (outside of the obvious power transformer)

Also, I wonder if someone has wired up a switch for selecting between fast and slow T4 cells? (I plan to get a fast set in the future, and hopefully use this for some mastering as well) Does anybody have any info as far as how exactly I would wire up something like this, where to mount the extra T4's, and how far they can be from the board etc?

 
Was sent the wrong tube, but wondering the if it's okay to use 6AQ5 without the A for controlled heater warmup?
 
Hello folks,
I'm seeking some advice here for a DLA2A board. I bought this mostly stuffed from another forum member. He used carbon comp resistors. I realize values are a little lower tolerance in that regard, and also because I'm measuring them in circuit. But I wanted to check every resistor just to make sure they're not drastically off, and that L and R channels are pretty close.

The following are my measurements IN circuit, but without tubes/transformers/T4. Just the circuit board. Some values that perhaps look fishy in comparison with one another or in comparison to the intended value out of circuit  are:  R111, R112, R117, R119, R126, R128 Can someone please look at these and advise me?

As for matching my channels, I bought matched tubes  and T4 cells, so I want to make sure I can get the two channels to match and I'm wondering if some of those following resistors will compromise my ability to do this.

Schematic              In Circuit Value
Value                              L ch/Rch

R105 68K=              75.6K /73.4K
R106 68K=              74.2K/75.5K
R107 2.7K=                2.7K/2.7K
R109 220K=            228K/227.5K
R110 1.5K=          1.51K/1.48K
R111 68K=          23.9K/24.2K
R112 470K=        482K/496K
R113 220K=        228K/224K
R114 2.7K=          2.73K/2.65K
R115 470K=        487K/489K
R116 68K=            74K/75K
GS101 1K=        1.05K/1.07K
R117 10K=          11.2K/12.5K
R118 1K=          1.07K/1.05K
R119 470K=      487K/494K
R120 1K=        1.06K/1.05K
GS102 1K=      1.06K/1.06K
R121 100K=    106K/108K
R122 33K=      23.4K/23.7K
R126 330K=    304K/340K
R127 10K=      11.38K/11.5K
R128 470K=    494K/488K
R129 4.7K=            5K/5K
R130 47K=      48.7K/50.4K
R131 1K=          1.1K/1.03K
R132 1K=            1.1K/1.05K
R133 220K=    230.2K/228.2K
R134 10K=        10K/10K
R135 220K=      223K/221K
R136 470R=    482R/476R
R138 22K=        26.4K/28.8K
 
Well... looks like quite a few are at or beyond 10% off the spec value.
The LA2A does have a stereo trimmer to balance the channels but the actual gain reduction is handled by a voltage divider between R106 (sound) and R127 (meter). If you bought matched T4Bs you probably should put a well matched, high quality resistor in there at a minimum (and pay the extra $0.13 or whatever they cost..)

Not only is the spec'd R value important - i.e. most people use 1% tolerance resistors vs the 10% tolerance it seems like your board uses - but the temperature coefficient is important. You want the resistor to maintain it's correct value even as it heats up (with all the light bulbs (tubes) in there giving off heat).

So if you want it to be well matched between channels go ahead and put in 1% metal film resistors.
Tube gear is pretty forgiving so it would probably sound great and operate in a healthy way the way it is though
 
Hey,

Thanks! They are off that much, though, being measured IN circuit, which changes them a bit. I'm more concerned actually about L and R channel matches. I'd pull them all as there are not that many, but so far my experience has been it's pretty easy to lift pads on this board.

I'll heed your R106 and R127 advice though.
 

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