rainton's P2P LA2A chassis "original style" discussion thread

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Potato Cakes

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forgotteng said:
My BOM says 10uf 450V can I get confirmation on this?

This is from the BOM v0.1 that Martin provided. In the original UA schematic C5 is also 0.1[uF]. There may be another version of which I am not aware.

Thanks!

Paul
 

forgotteng

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Potato Cakes said:
This is from the BOM v0.1 that Martin provided. In the original UA schematic C5 is also 0.1[uF]. There may be another version of which I am not aware.

Thanks!

Paul
Here is a picture of both of them side by side. This is the cap that was on the Mouser list.
 

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Potato Cakes

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I am an idiot.

My tired brain got this confused with another project. I will edit the previous posts as a tribute to my shame........
 

Potato Cakes

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The Mundorf site says the shorter lead is connected the outer foil, but I don't know if this is the same as the shorter lead being (-) polarity as it would on an electrolytic.

http://www.mundorf.com/en/?category=hifi&menu=caps_audio&content=mcap_evo_silvergold.oil

Thanks!

Paul
 

scott2000

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Potato Cakes said:
The Mundorf site says the shorter lead is connected the outer foil, but I don't know if this is the same as the shorter lead being (-) polarity as it would on an electrolytic.

http://www.mundorf.com/en/?category=hifi&menu=caps_audio&content=mcap_evo_silvergold.oil

Thanks!

Paul

That's non polar so not technically???or technically yes...lol .... This has been discussed before here somewhere.....here's a video... //////3minutes in he describes this......

https://www.youtube.com/watch?v=BnR_DLd1PDI
 

forgotteng

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Ok, so I got everything together and fired it up. No shorts and no blown fuses. It passes a ik tone but the gain knob doesn't work. It is full out volume and no change when I adjust R1. Any thoughts?
 

rainton

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forgotteng said:
Ok, so I got everything together and fired it up. No shorts and no blown fuses. It passes a ik tone but the gain knob doesn't work. It is full out volume and no change when I adjust R1. Any thoughts?

Check if the shield of the wire connected to pin 1 of R1 is properly connected ground via pin6 of the T4 socket.
If there's no ground connection, the attenuator won't work and pass through the signal at full volume...
 

forgotteng

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rainton said:
Check if the shield of the wire connected to pin 1 of R1 is properly connected ground via pin6 of the T4 socket.
If there's no ground connection, the attenuator won't work and pass through the signal at full volume...

I believe it is hooked up properly
 

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ilfungo

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Hi
I don't know if is this the problem, but pin 8 and 1 of T4B need to be connected...
 

ilfungo

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I've build mine from this layout
on T4B there is a connection between 1 and 8...
 

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forgotteng

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ilfungo said:
I've build mine from this layout
on T4B there is a connection between 1 and 8...
I see. that looks a little different than the analog vibes layout. I wonder if It would do any damage to connect 1 and 8. @rainton, any ideas?
 

kosi

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it looks different, but it's the same. pin 1 has to be connected to ground, in your case, to pin 8.
 

forgotteng

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So I connected pin 1 to pin 8 on the T4. I ended up with a loud 60 cycle hum that was not effected by any of the gain controls. I disconnected pin 1 to pin 8 and the 60 cycle is still there.
 

rainton

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Sorry guys,
I'm on vacation with my family at the moment, so there's not too much time to hang out online ;)

First - ilfungo and kosi are right - pin 1 & 8 of the T4 should be connected. It's barely visible in the wiring layout, because I missed to add a drop-shadow to this jumper (like I did for all other connections to make them easier to follow)

BUT can someone check wether the Kenetek T4s are already jumped internally? Because I remember I just built an LA2A for the step by step guide following my wiring layout (also to see if there were any mistakes) and I also forgot to jumper pin 1 and pin 8 of the T4 at first (I fooled myself for the exact same reason as mentioned above) and the unit still worked flawlessly...

However, these pins - wether they are jumpered or not, shouldn't have anything to do with what you're experiencing forgotteng.
Because this jumper would only affect the T4 itself, but the unit should still work even with T4 disconnected.
You won't be able to compress of course, so the peak reduction pot would do nothing, but the gain pot should work equally as well. Without the T4 the LA2A still is an awesome line amp ;)

I would even suggest to unplug the T4 cell until the rest of the unit works.

So the fact, that the unit passes audio at full level, can only mean that something about the gain pot R1 is wrong.
Either the pot is broken, the wire is broken (respectively the wire shield), or both is working  correctly and the pot still has no ground connection which would point towards a cold solder joint.

All of this should be pretty easy to find out. From your pics it looks like everything is wired up correctly (even though it would be better to have a shot of the entire unit as well.)

But even though it looks like everything's hooked up correctly - in terms of electronics measuring is always better than believing ;)

So, take a multimeter, set it to measuring for continuity, connect one probe to chassis ground and place the other probe on all spots that are supposed to be connected to ground. Also check the resistance the meter shows. It should be below 0.5 ohms.
Also check both ends of the shielded wire (including the shield) for continuity to make sure the wire is alright.
Since you have signal coming through at full volume I expect the audio wires to be ok - but make sure also the shield is ok, too.

If you wanna make sure the pot works disconnect the shielded wire and measure resistance between the outer pins first - and if it's ok measure between the wiper (middle pin) and pin 1/pin 3.

What I can say though - and this might also be the reason for the new problem that occurred (the ground hum) is that the solder joints look very dull. This is a sign for heating up the joints way too long. (they should be really shiny). This can lead to cold solder joints which means, even though everything looks as if it was connected as it should be, it's probably not.

The fact that you only added & removed a jumper between pin 1 & 8 and ended up with a 60Hz hum kind of strengthens my theory. It could be the ground connection was weak in the first place and by soldering and desoldering the jumper it got lost completely -> hum big time.

If you wanna rework the solder joints - take a little bit of fresh solder, place it right there at the joints and heaten it all up with your soldering iron just until everything melts together, and then quickly remove the iron...

And as mentioned before, remove the T4 until everything works as expected if you haven't already done so...

Don't worry, I'm pretty sure your unit will work eventually ;)
Martin
 

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