DIY EAR 834p phono stage - a short evaluation/ test with those chinese PCBs

[Jessica_K]

The resistors are R13 and R16 in the part schematic. The values shown will reduce the output by 1/4 (the R13 resistor (51k)  is 1/4 of the whole resistance (R13 + R16) 198k), these values can be altered as long as the total resistance is about 200-220k.



The voltage gain of the amp is about 240 @ 1K.

so for another example if the sensitivity of your power amp is 600mV and your cartridge provides 5mV at 1khz, then the gain required 1/2 and R13 == R16 and each will be 100k

On Dan's amp, V3 is the ECC82, and that is a cathode follower that is always a gain of 1 (ish) regardless of the gain of the valve, therefore using the ECC82 there will not effect the gain of the amp.

The cathode follower is used as an impedance converter, high input impedance so as to take minimal current from gain stage and effect the RIAA and low output impedance to drive the power amp.

Robert

[Chris65]

Input sensitivity of the Stereo 20 is 125mV.

[Jessica_K]

That would require an attenuation of 1/10 (ish). R13=25K and R16=200k would do it

I think reducing the gain of the power amp would be the better option, its far more normal these days to have a line input of 1V specially if playing from CD players.

Was this amp designed for ceramic carts!!?

Robert

[Chris65]

Was this amp designed for ceramic carts!!

Designed to complement/compensate for the Leak pre-amps. From the website linked to above:
"All LEAK power amplifiers are very sensitive ~ The matching LEAK pre–amps were very poor in design and performance ~ their signal to noise S/N was >20dB worse than the power amps and the output from a pair of EF86s for each channel was 125mV so the power amps needed to have enough gain to compensate"

[spaceistheplace]

Hi James
I will do a simulation of using an ECC82 for all valves and see what the overall gain is. It may effect the RIAA will see. Otherwise is should be just a change of cathode resistor values.

Robert

I believe Thorsten's EAR mods go over this:

"Remove C5, R6 & R7, then bridge R7 with a piece of high quality wire. If you want to be sure to stop any possible tendency of oscillation in the cathode follower place a 100 Ohm carbon composite 1/4W Resistor in the R7 Position C5 and R6 remain omited. If you wish to retain an ECC83 for V3 change R9 from 68K to 120K. If you plan to change the V3 to a 12AU7/ECC82 or at least 12AT7/ECC81 leave it as is in Value." Link: http://www.goodsoundclub.com/GetPost.aspx?PostID=2052

[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