Chinese PCB's for a DIY EAR 834p phono stage

[Jay]

Wow thanks guys Ill look at the links later & decide which way to do the 'step down' as it were.

Hadn't fully realised it was primarily the ST20's sensitivity.

off to work now

[Jessica_K]

Hi James,

I have removed my old post using ECC82(12AU7) tubes in V1 and V3 as I think I must have been tired last night and got my calculations wrong and also this will give the amount of gain reduction you need.

Again I have no idea what it will sound like, replacing V3 for ECC82 as far as I can see does not require any mods and I have limited the V1 replacement down to just 2 resistor value changes, I recommend 1% resistors.

Below is the full schematic, 5mV @1k gives 140mv output and < 0.5db RIAA   



Robert

[spaceistheplace]

So fuse needs to be anti surge and probably about 250mA for Europe and 500mA for US

Least that's a good start

Robert

Anti-surge is synonymous with slow blow, yes?



John - USA

[Jessica_K]

yes slow-blow / anti-surge / time delayed.... all the same thing

Robert

[Jay]

As things stand I can use the 834 pre upto about half volume i.e. 13 steps out of 23 which is ok for normal listening before the ST starts to overload, given that the ST20, Dark Grey one (still almost entirely original) (& probably needs a thorough component overhaul) is driving a pair of very big (home made clones of) JBL's, the sloping & curvy  Ti 10K.
drifting slightly Last seen & heard by many at 'Scalford' Hifi wigwam, Last year, then powered by a pair of 600w mono blocks. Sadly couldn't find anyone to add 6 more monoblocks to really make them sing
 But the St 20 does itself very proud to power these Kick Ass monsters.

What I really need to do is stop listening to it & finish all the Input wiring.

[Jessica_K]

I visited Scalford last year, wouldn't have known you from Adam LOL, If you are there this year will say hello.

I will probably get some ECC82's and see how they sound in my 834 kit, My turntable is sick at the moment so I have been without much listening of late 

Robert

[Jay]

Please do Robert,
 I was in the LH room, Hope your TT gets well soon

[TriplePower3]

Hi John,

space is ok but not much left. Hole drilling should be very exact, otherwise  signal PCB will not match inside.

Only reason for the board lifting was that I like to see the lightning of the tubes 
Technically it would be better to have them inside.
I am lucky that I had no hum or noise when I tested it.
I am still waiting for my RIAA 750kOhm resistors and Mica caps to be replaced.
After that I will let you know if I can still confirm noise-free operation.

Thorsten

Hi,

yesterday evening I swapped the Mica and the750k resistor. Now everything is fine

But damn, is that thing loud
I need to lower the output by adjusting the divider on the PCB.
On my preamp (Aikido 5687 from J.Broskie) I have used a stepped attenuator which is too loud even on the lowest step
when connecting the EAR834. 

@John
I can confirm that I got no noise or hum even when preamp volume is high with no signal.
 

[rodders]

Hi Rolf

I have the EAR834p phono preamp board and ordered the DOUK transformer as, I believe, you did from the supplier, before I hook this thing up I wanted to be sure about how to connect the transformer.  The 115v/115v input seems straightforward these would be wired together to get 230v input which I have as my mains supply. 

The 250/280v output connection to the top of the transformer on the other side, I'm guessing the output - did you pick the 250v or the 280v output to connect to the power board?

There are two sets of 6.3 and 8v connections to the bottom of the transformer on both sides rated 1.25A each side.  Did you connect only one side, i.e one 6.3v and 0v to the power board? I'm a little confused with this one, the power board is rated at 2A so I'm guessing both sets of 6.3v have to be used, or am I wrong?

Appreciate any feedback as I'm not experienced at the electronics side of things and as expected there were no instructions.
A dummies guide would be appreciated.

[Jessica_K]

Hi Rodders

Wire the 6.3V outputs in parallel ( the two 6.3V tags joined together etc)
I would wire the 250V output as higher would only be wasted in heat

Robert

[Jay]

Now that the SUT's have been wired in both channels have music.
 But,  there is HUM....but only when MC via SUT is selected.  It appears to be emanating from the SUT output to selector screens. When they (the screens) are touched the Hum mostly goes away but not entirely.
The SUT body's are connected to Star point. the purple wire is an attempt to earth the screens likewise when touched hum mostly goes away. but not when connected to earth points on (yellow wire) SUT's
None of the screens are connected to the Star Point
 ??


Meanwhile on the MM side All is bliss

[Jessica_K]

Try a wire from the star point and touch the screen with the other end see what happens

Robert

[ZZMoko]

Might also be worth checking RCA sockets are isolated from the case properly...I remember one of mine was slightly lose and caused hum if moved slightly.

[Jay]

Robert, connecting screen to Star point made no difference.
As I'm Also now getting a similar situation (Gripping between fingers) the input wires directly to the board, the hum diminishes.

David, you might well be onto something, Whilst I'm sure there were no shorts as it were at the RCA sockets. I am getting weird things from different inputs, so will investigate All the inputs & wiring

Should their be any kind of connection or continuity Test wise with the amp Off, from the chassis or Star point to the commons of the RCA input sockets?
With everything disconnected, of the 16 RCA sockets I get continuity between 5 of the commons & Star Point & no continuity on the remaining 9 ??

[spaceistheplace]

Couple of questions as I get closer here:

1. What is the ideal fuse type should I use on the IEC Outlet? Someone had mentioned .5A?

2. Transformer here has me a bit stumped.

3. Would this transformer be suitable to have switch for 230V operation? Might as well if I have the spare wires anyhow, yes?

4. Almost forgot... what kind of ratings should I be looking for in a power switch and how does that get wired up with what's below?

The transformer that they recommended for US voltage looks a bit different than any I've seen here:

If you are having trouble reading the sticker, it states: 100W, 50hz

I/P: 0Black - 115V, White 230V,  Red YELLOWGREEN

O/P: 0Black - 5V-Blue - 6.3V, Orange 8V Brown
12.V Purple 250V blue 250V green

Not sure what to make of this? Also, assuming Wite means white and "ren" means red lol....

The input I'm assuming is 1 and 2 labeled on my photo, while output to preamp would be 3 for 6.3V 4 for - 230-280 and 5 for + 230-280?

Assuming green for ground would link to the IEC ground on one end and position 6 on the photo? Should I also be attaching that to the chassis?

However, that leaves me with a lot of spare wires.

I got nowhere and don't feel very confident at this stage taking an educated guess with mains voltage..

After a prolonged exchange with douk they provided this wiring diagram.



Could some share some light on how I should be wiring this for us voltage? Seems the douk supplied transformer has more leads than I require. Wondering why they recommended me this transformer.

I also have the simpler antek toroidal mentioned earlier in this thread to see if I can fit the whole unit in one case (with the douk trans it requires 2).
Info here: http://www.antekinc.com/as-05t280-50va-280v-transformer/

And here: http://www.antekinc.com/content/AS-05T280.pdf

Am I better of using the antek? If so why and how should it be wired?

I've been told toroidal transformers are superior in most ways, yet I continue to see old style transformers on top of all the tube gear so there must be some kind of benefit besides vintage styling?

Is the 100w douk overkill for this?

This is the last leg of my journey to listening to my 834! Would be very appreciative of any insights.



John - USA