LA2A build

[ran]

"Hai qualche suggerimento sulle migliori fotocellule da utilizzare nella replica T4?"

 

[myers1st]

Buttoned up:
View attachment 126234
View attachment 126235

Pure artwork! Getting the final parts for my p2p and will DEFO be referencing this photo. I love how insulated everything is, what size is that clear tubing for the twisted pairs? Is it heat shrink?
Prague in the 90s must have been something! I moved there in 2011 but have heard stories from friends who were there then.

 

[Mr. Moscode]

Ok @Mr. Moscode thanks for that tip. I’m already buttoned up here on this one - just finished - but will throw it in the next one!
Easy enough to swap out on this one, but at the moment, the pair I now have is going to be stereo-able, so will keep it as Sprague for the pair.
Next one, though, will be the big Mundorf. I know this sounds dolty, but I’m also loving how huge clean and chunky they look! If they sound as big, well . . .

I always go for the best sound, be sure you fall in love with that. Like with women, looks aren't everything. . . .

 

[thelivingroom]

Help me choose for C5
View attachment 124750

Your build looks awesome!

I put those Mundorfs in my D-LA2A that I just fired up for the first time this week. I also put the same model Mundorfs in C2 & C3, an Auricap XO in C1, PRP resistors throughout, and Charcroft Audio silver Mica in all the Mica spots. I also decided to spend the extra dough for matched pairs of NOS RCA black plates for V1 and the 12BH7’s. I don’t know how much of a difference it all made or not, but I’ve been listening to music through it all week while wiring up my next project and it sounds incredible! Really I was just getting bored with sourcing the same stuff from the same places, and wanted to try some parts from the hifi world.

 

[deveng]

Nice job.

I built a p2p LA2A a few years back and just love the look of the internals. So funny thing is when someone notices the unit in my rack the first thing I do is flip the front panel open to show off the beauty inside. Some appreciate it, some give me quizzical look. I truly appreciate it!

 

[timtom]

Finished the La2a build with the honeybadger pcbs. For now a diy housing...
Used Edcor In/Out, IGS Optocell. Sounds great!

 

[Nick6691]

Finished the La2a build with the honeybadger pcbs. For now a diy housing...
Used Edcor In/Out, IGS Optocell. Sounds great!

Hi Timtom
Ive also build the honeybadger pcb version with Lundahls and kenetec.
Sounds fantastic exept from huge 50hz ground hum.
What psu pcb did you use?

 

[timtom]

Hi Timtom
Ive also build the honeybadger pcb version with Lundahls and kenetec.
Sounds fantastic exept from huge 50hz ground hum.
What psu pcb did you use?

I used the honeybadger PSU but modified to be stronger...

 

[Nick6691]

I used the honeybadger PSU but modified to be stronger...

I used the high voltage PSU and having problem getting enough voltage on the heater rail.
I only reach 5,3V. Heard about the mod with the rectifier diods but I dont really get it.
Do you want to share you solution?

 

[timtom]

I got the same problem and this mod helped.

 

[Nick6691]

Thanks a lot!
Did you cut any trace lines on the underside of the pcb? Or just the mod with invert d2 and d3 and cable them back on the top side pcb?

 

[timtom]

Thanks a lot!
Did you cut any trace lines on the underside of the pcb? Or just the mod with invert d2 and d3 and cable them back on the top side pcb?

exactly like you mentioned.

 

[Nick6691]

Made the mod and I have 6.3 v on heater
But I still have a huge ground hum at 50 hz
Been chasing that hum for a while and I thought the right voltage at heater rail could fix that but no!
any help is appreciated

 

[rock soderstrom]

any help is appreciated

Are all grounds connected/referenced to each other? (B+ and heater)

50Hz hum can also be a magnetic crosstalk of the mains transformer into one of the signal transformers. Which transformers are you using? Are they shielded? Is the shield connected to ground? Play with the position and rotation of the mains transformer. Does anything change?

Photos of your setup?

 

[Nick6691]

Hi Rock, thanks for answering
As I think I have all grounds connected as should be.
B+ and heater ground goes from the 2-connector on the red pcb with green wires to the chassis where it meets with ground from IEC and power TX
The power tx is https://www.don-audio.com/g-pultec-mono-power-trafo-sec-220v-9v-5V_1
Audio transformers is LL 1922 and LL5402
I have rotated, tilted and even moved the power tx to be laying flat on the floor with no diffrence at all.
I have replaced the LM 338 sitting at the chassis with no difference. Maybe replace the other 2 regulators in the psu?
The hum is pretty massive and constant at around -35dbfs
The picture is the best I found in my phone but I can of course take more photos.

 

[rock soderstrom]

Hi Rock, thanks for answering
As I think I have all grounds connected as should be.
B+ and heater ground goes from the 2-connector on the red pcb with green wires to the chassis where it meets with ground from IEC and power TX
The power tx is https://www.don-audio.com/g-pultec-mono-power-trafo-sec-220v-9v-5V_1
Audio transformers is LL 1922 and LL5402
I have rotated, tilted and even moved the power tx to be laying flat on the floor with no diffrence at all.
I have replaced the LM 338 sitting at the chassis with no difference. Maybe replace the other 2 regulators in the psu?
The hum is pretty massive and constant at around -35dbfs
The picture is the best I found in my phone but I can of course take more photos.

Okay, then my ideas are out of the question. If the hum is actually 50Hz, it has something to do with AC, all voltages/ground problems after the rectifiers would hum at 100Hz.

In your photo above left, the AC lines from the transformer are very close to some other things. Make sure that there is no crosstalk, distance between AC and all sensitive circuit parts of the amplifier is your friend!

 

[mihi_fuchs]

@Nick6691 - maybe one thing you could check - hope i haven‘t overseen anybody else already suggesting it:

if you follow this schematic incl. the mod (
Post in thread 'LA2A build'
https://groupdiy.com/threads/la2a-build.86652/post-1166429),
you just make a full bridge rectifier from the half rectifying system of the original schematics. that gives you access to both amplitudes and therefore gives you the increase in voltage.
however, according to the pics you still have the half rectifiers from the other rails. as i don‘t know, if they are critical, that may be fine or not. however if you have the ground rails of rail 1 and 2 connected by the jumper, you still have the oszilating half rectifying system connected to the ground of your critical rail. that may make the voltage oszilate again and would oszilate with 50 hz. do you have the connection between the ground rail 1 and 2 installed?

best regards,
hope you have it figured out quite fast,
best regards,
michael

 

[Nick6691]

In your photo above left, the AC lines from the transformer are very close to some other things. Make sure that there is no crosstalk, distance between AC and all sensitive circuit parts of the amplifier is your friend

Rock, the purple and red goes to the powerswitch on the front. So it have to be there somewhere. The orange and white twisted together in 230v configuration i can of course cut shorter

Nick

 

[rock soderstrom]

Rock, the purple and red goes to the powerswitch on the front. So it have to be there somewhere. The orange and white twisted together in 230v configuration i can of course cut shorter

Yep. My suggestion was rather that you take another look at it. I've had similar problems with a power switch on the front panel (in the wrong place). I'm slowly running out of ideas...

 

[Nick6691]

@Nick6691 - maybe one thing you could check - hope i haven‘t overseen anybody else already suggesting it:

if you follow this schematic incl. the mod (
Post in thread 'LA2A build'
https://groupdiy.com/threads/la2a-build.86652/post-1166429),
you just make a full bridge rectifier from the half rectifying system of the original schematics. that gives you access to both amplitudes and therefore gives you the increase in voltage.
however, according to the pics you still have the half rectifiers from the other rails. as i don‘t know, if they are critical, that may be fine or not. however if you have the ground rails of rail 1 and 2 connected by the jumper, you still have the oszilating half rectifying system connected to the ground of your critical rail. that may make the voltage oszilate again and would oszilate with 50 hz. do you have the connection between the ground rail 1 and 2 installed?

best regards,
hope you have it figured out quite fast,
best regards,
michael

Hi Michael and thanks for your answer
I m not sure I understand it all but the hum I have I had before making the mod with the rectifier diodes. The mod gave the 6.3v at heater but the hum is still the same.
I don’t understand what you mean with: if you have the ground rails of rail 1 and 2 connected by the jumper. I don’t understand “connected by the jumper”
Ground of rail 1 and 2 goes from a 2 screw connector with green twisted wires to chassis where it meets with ground cables from iec and power tx.

Nick