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Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Mon Jan 07, 2019 2:30 pm
by RhythMick
izzy wizzy wrote:
Mon Jan 07, 2019 2:01 pm
Look at the input grid point. That's referenced to earth and then to both the other stages star points albiet the 2nd stage shares the 0V and supply. I imagine your 2nd and 3rd stages would be referenced to the input grids as he has done with his 3rd stage.

Cheers,
Stephen
You're referring to the more detailed schematic of course. http://www.nutshellhifi.com/Karna.gif

Lynn (actually Gary Pimm did the grounding design) follows what I'd picked up as the mantra ... "though shalt have only one chassis connection, and that shall be at the input point". However the similarities start to break down. For a start he shares power supply between input valve (6H30 etc) and driver (45). But yes, the centre taps of the signal transformers are referenced back to that chassis earth connection by the input tx. His RCA input floats across the input TX primaries and so is not grounded, while he doesn't show XLR pin 1 grounded at all. Also my chassis is wooden - any exposed metal is connected to safety earth at the mains input.

My plan is ...

- 26 local star at base of cathode resistor
- XLR input pin 1 to 26 local star
(I plan to make this liftable as I'm never sure whether this makes a ground loop with the previous equipment or not)
- Input TX C/T to 26 local star
- PSU return path from 26 local star to LCLC
- heavy gauge connection to Channel Star Ground, thence to mains earth

- 71A local star at base of cathode resistor
- Interstage 1 C/T to 71A local star
- PSU return path from 71A local star to LCLC
- heavy gauge connection to Channel Star Ground, thence to mains earth

- 45 local star at base of cathode resistor
- Interstage 2 C/T to 45 local star
- PSU return path from 45 local star to LCLC
- heavy gauge connection to Channel Star Ground, thence to mains earth

The only other thing I propose on top of that will be additional tubecaps across B+ (anode centre-tap) to local star as proposed by Mike. 20uF for 26, 30uF for 71A, 47uF for 45. I have those spare and and am building in mounting points for them, I will try them once I have the amp working and stable.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Mon Jan 07, 2019 2:42 pm
by Ant
Why not just run a busbar all the way along the amp and drop off the components to the busbar?

All the amps I've built including the nuvistor phono stage have had this type of connection and all have been quiet

I tried star earthing on the phono stage and it was no more or less quiet. Simplifies things for me as I tend to lay things out exactly as the schematic shows, I have neatness ocd when it comes to amps, all right angles ect where wiring is concerned. Can't stand a rats nest and it makes things easier to fault find if something goes.

I've seen star earthing done as simply as a bolt through a metal top plate, the plate is connected to the mains earth wire and the bolt forms a turret, then everything connected to that bolt with a ring tag.

Kinda like a 2 sided pcb where one side it a ground plane

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 2:40 pm
by RhythMick
Ant wrote:
Mon Jan 07, 2019 2:42 pm
Why not just run a busbar all the way along the amp and drop off the components to the busbar?

All the amps I've built including the nuvistor phono stage have had this type of connection and all have been quiet

I tried star earthing on the phono stage and it was no more or less quiet. Simplifies things for me as I tend to lay things out exactly as the schematic shows, I have neatness ocd when it comes to amps, all right angles ect where wiring is concerned. Can't stand a rats nest and it makes things easier to fault find if something goes.

I've seen star earthing done as simply as a bolt through a metal top plate, the plate is connected to the mains earth wire and the bolt forms a turret, then everything connected to that bolt with a ring tag.

Kinda like a 2 sided pcb where one side it a ground plane
Thanks Ant - sorry wasn't ignoring that advice just busy building.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 2:44 pm
by RhythMick
Now heavily into the rebuild following the redesign. Pics for interest. Hoping I get this done by the weekend.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 2:45 pm
by RhythMick
Latest build pic.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 6:11 pm
by izzy wizzy
Is that the wiring before you cover it with the white sleeving? I like watching builds progress like this, thanks.

Do you reduce the size of your pics or the resolution or both before posting?

Cheers,
Stephen

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 7:29 pm
by RhythMick
izzy wizzy wrote:
Thu Jan 10, 2019 6:11 pm
Is that the wiring before you cover it with the white sleeving? I like watching builds progress like this, thanks.

Do you reduce the size of your pics or the resolution or both before posting?

Cheers,
Stephen
I use white shrink where needed for labelling is all. I write on it before I shrink it...

I use Lit Photo app (Android) to compress the photos before posting.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 7:53 pm
by izzy wizzy
RhythMick wrote:
Thu Jan 10, 2019 7:29 pm
I use white shrink where needed for labelling is all. I write on it before I shrink it...
Previously you had wiring that looked like white shoelaces?

Cheers,
Stephen

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Thu Jan 10, 2019 8:00 pm
by RhythMick
Ah yes the silk covered. I've left that out for now in favour of confidence with the build and wiring. At some point I'll switch the signal wiring back over to hear the difference.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Sat Jan 12, 2019 5:12 pm
by RhythMick
Well I'm a very happy chappy. Considering I stripped, redesigned and rebuilt this (greatly simplifying along the way) I'm overjoyed to report it worked first time and voltages are where I expected them to be.

There's a hum which I need to track down. However listening through that the amp sounds superb, lots of running in to do, but superb.

So... All tips and tricks for tracking down hum needed please.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Sat Jan 12, 2019 5:26 pm
by izzy wizzy
RhythMick wrote:
Sat Jan 12, 2019 5:12 pm
Well I'm a very happy chappy. Considering I stripped, redesigned and rebuilt this (greatly simplifying along the way) I'm overjoyed to report it worked first time and voltages are where I expected them to be.

There's a hum which I need to track down. However listening through that the amp sounds superb, lots of running in to do, but superb.

So... All tips and tricks for tracking down hum needed please.
Excellent. Great news!

I would track down hum like before. One stage at a time. Only run with output going and work backwards.

But first, does it hum by itself? With input shorted? Is mains earth connected? Or lifted?

Cheers,
Stephen

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Sat Jan 12, 2019 6:47 pm
by RhythMick
PSU and amp on the floor in front of the cupboard. Once all is finished both slide into the cupboard on rollers. Swapped the shoulder type valves for my favourite Cunningham Globe types, big improvement. Aside from that hum it's spectacular.
1547318687712699.jpg

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Sat Jan 12, 2019 7:47 pm
by izzy wizzy
What's the doodad on the left behind the power supply?

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Sat Jan 12, 2019 7:55 pm
by RhythMick
izzy wizzy wrote:
Sat Jan 12, 2019 7:47 pm
What's the doodad on the left behind the power supply?
It's not in circuit yet, but that will be the power distribution unit and on/off switches. LL1662 mains transformer stepping down to 230v and putting out balanced mains. On/off for heaters, b+ for phono and amp.

Re: Finished and working - 12 valve all DHT PP 26-71a-45

Posted: Sat Jan 12, 2019 10:09 pm
by RhythMick
Oh my goodness. This is SO good.

Anyone in South Yorkshire this weekend I have the house to myself (plus Geoff) and you'd be welcome to pop in for a listen.