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

[sr1200]

Id like to add that the paint on the chassis needs to be removed where your pots and switches go otherwise there's no ground up there.  I had a bad hum on mine until i removed the paint to allow a connection to the chassis/ground.

 

[Gary C.]

Hello.
I'm late to the party - have enjoyed reading all of your posts.
Ordered the LA2A chassis from Rainton, and it is finally Out For Delivery, after a seemingly interminable wait at Customs in New York.
Been collecting UTC transformers lately, getting prepared....

 

[Phrazemaster]

Hello.
I'm late to the party - have enjoyed reading all of your posts.
Ordered the LA2A chassis from Rainton, and it is finally Out For Delivery, after a seemingly interminable wait at Customs in New York.
Been collecting UTC transformers lately, getting prepared....

Welcome Gary! Great to have you with us!

 

[Gary C.]

Thanks for the welcome, Phrazemaster.

 

[Gary C.]

Just a heads-up for any other latecomers to this project.
I bought mine from the Don Audio website, which went smoothly, but I never saw any link to the downloads for BOM, build guide, etc.
Emailed Martin, and he responded within about a day, and sent me the link.
I would advise you purchase from his website, just to avoid any delays, as he gives you the link with your purchase.

 

[Zim]

I’m starting to source all the materials for this build - just wondering if there’s a consensus is on what wire should be used?

I saw Martin said somewhere he was going to write a separate article about stranded vs solid core wire, but haven’t been able to find it. Just read the Drip Dual Opto guide which seemed to specify solid core in a number of places.

Is there a best practice, either from a practical build or a sonic perspective?

thanks

Zim

 

[Bowie]

(edit; resolved) Quick Q for ideas. Meter is not showing gain reduction. Everything else works, output metering works, meter zeroes, and I can HEAR gain reduction working normally. But, it just doesn't move the meter. Changed the tubes and looked over the wiring half a dozen times. Sound familiar to everyone?
Edit; T4 socket backwards.

 

[Rob Flinn]

Check that you get roughly 60v across the neon bulb or zener depending on what you used.

 

[Potato Cakes]

I’m starting to source all the materials for this build - just wondering if there’s a consensus is on what wire should be used?

I saw Martin said somewhere he was going to write a separate article about stranded vs solid core wire, but haven’t been able to find it. Just read the Drip Dual Opto guide which seemed to specify solid core in a number of places.

Is there a best practice, either from a practical build or a sonic perspective?

thanks

Zim

I used all stranded wire for both of my builds. I did not have enough space with all of the wiring and components to do a solid wire ground bus. Both of mine are quiet and work great. Just make VERY sure you tightly twist your heater wires using a drill. But don't rip the leads out of the power transformer. Or you can even use a DC heater circuit instead of AC from the transformer which is what I am doing.

Thanks!

Paul

 

[Potato Cakes]

Quick Q for ideas. Meter is not showing gain reduction. Everything else works, output metering works, meter zeroes, and I can HEAR gain reduction working normally. But, it just doesn't move the meter. Changed the tubes and looked over the wiring half a dozen times. Sound familiar to everyone?

I can't remember if it has been corrected but there was wiring error on the layout that differed from the schematic. Did you see that post in this thread?

Thanks!

Paul

Edit: I posted here thinking I was on a different thread. That's twice. I need to get my brain checked.

 

[Zim]

Thanks Paul - wouldn’t know where to start when it comes to running the heaters from DC rather than AC though.

re transformers does anyone have any experience with the AMI UT24 and UT10 vs the sowters. Original UTC’s just seem crazy expensive now if they crop up Was thinking I’d go with AMI now that they’re available as single units (think you had to buy 10 minimum a few months ago), but no idea whether they’re any better or worse than the Sowters that many use for this build.

anyone tried them?

 

[Potato Cakes]

See my correction above.

 

[JMan]

Paul, any tips on how to implement a DC circuit for the heaters? I’ve got two builds (this and another comp) in the pipeline that use the typical 6.3v AC for heaters, but would prefer to convert to DC to reduce risk of hum. But I am not confident enough to know where to start with that.

 

[Potato Cakes]

I found a guy selling boards for tube heaters. I used them in my 176 builds and they work great as far a reducing noise.

https://www.ebay.com/itm/DIY-PCB-Bo...-Power-Supply-6-3VDC-from-6-3VAC/143466154635
The guy was helpful with a couple of questions I had and the ones in my 176 builds are solid.

Thanks!

Paul

 

[JMan]

I found a guy selling boards for tube heaters. I used them in my 176 builds and they work great as far a reducing noise.


The guy was helpful with a couple of questions I had and the ones in my 176 builds are solid.

Paul, that's a fantastic lead, thank you! Out of curiosity, what questions did you have? Were they to do with things that one might naturally run into when using this board, or more esoteric?

 

[Potato Cakes]

It was regarding the type of diodes being used. In the photo that were used in the original ad when I bought these boards, the diodes were TO-220 but the actual board layout was for DO-41. He didn't have picture of a completed Rev. D board at the time of the original ebay listing, hence the TO-220 question. Everything else was self-explanatory.

Thanks!

Paul

 

[Phrazemaster]

I had a question regarding the power switch. I noticed in the BOM it specifies just a SPST switch interrupting the live wire. Isn't it a better practice to use a DPST switch and take both line and neutral and interrupt them both? But this makes two AC wires to the front panel and maybe overcomplicates things...but safer, no?

Also is it best practice to use a two pole fuse AC inlet?

I'm just thinking, what if I make this thing and then pass it onto someone else who plugs it into a mains that's wired wrong...could be dangerous?

This basically goes for all these DIY projects actually.

Anyone has some thoughts?

Thanks,

Mike

 

[beatnik]

I believe the single pole switch could be dangerous if for some reason the neutral becomes live, and the user is poking inside the unit with the power cable still connected.

On paper it is more dangerous but truth is, if one doesn't know electrical safety then they shouldn't be opening things up.

In my opinion a more important safety aspect that sometimes is not addressed properly on diy builds is to make sure there is a good connection to safety earth throughout the entire chassis. On many off the shelf enclosures the grounding is often undetermined so one needs to remove paint work / anodisation or add wiring. I wish some manufacturers charged a little extra and provided parts that have been masked prior to powder coating ...

And if you are using a fuse holder not integrated in the IEC inlet, make sure it's wired in the correct polarity ! If the user tries changing the fuse with the mains cable plugged in, the live becomes exposed.

 

[Phrazemaster]

I believe the single pole switch could be dangerous if for some reason the neutral becomes live, and the user is poking inside the unit with the power cable still connected.

On paper it is more dangerous but truth is, if one doesn't know electrical safety then they shouldn't be opening things up.

In my opinion a more important safety aspect that sometimes is not addressed properly on diy builds is to make sure there is a good connection to safety earth throughout the entire chassis. On many off the shelf enclosures the grounding is often undetermined so one needs to remove paint work / anodisation or add wiring. I wish some manufacturers charged a little extra and provided parts that have been masked prior to powder coating ...

And if you are using a fuse holder not integrated in the IEC inlet, make sure it's wired in the correct polarity ! If the user tries changing the fuse with the mains cable plugged in, the live becomes exposed.

Thank you beatnik. Very informative.

 

[Phrazemaster]

Question about resistor tolerances.

I wanted to get some Allen-Bradleys for resistors. I sourced all RCR mil-spec, 5%, 1W. While some are within 5%, many are between 5%-10%.

I suppose this is expected due to age. I tried baking them for about 12 hours at 100˚ C, and they got worse! I'm disgusted as these weren't cheap.

So, many (most) are between 5-10%. Would it be ok to use these ~10% resistors for this build, when the schematic specifies 5% resistors? I feel like the designers wouldn't have specified 5% if they didn't mean it.

Thanks,

Mike