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

[Jessica_K]

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

[Jessica_K]

Just looked at the data sheet ECC82 has a amplification factor of 20 the ECC83 is 100. So replace 3 tubes will not work, replacing 2 out 3 will probably still be too low. Will check

Robert

[TriplePower3]

Thank you! Very tidy. How is the microphonics and noise floor? Is it crowded at the rear panel?

Seems you could have fit the tubes inside the case. Was the decision to have them peek out aesthetic?

I believe my case dimensions are identical.


John - USA

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

[Jay]

Perhaps swapping just one of the 83s for an 82 might do the trick ?

[tabarddn]

Hi Guys thanks for the suggestions on earthing I will try them next week. 

I have no problem with gain from my valve configuration of a) 1 x ECC82 PHILIPS and 2 x GE 5 STAR 5751, And I am running a Eroica M/C high output cartridge.

The sound is in another league to my battery feed upgraded Boozgound and my Micheal Dino, when you consider I have done the whole project for $230 so far, It is unbelievable value for money. 

[Jessica_K]

If all you want to do is cut the volume then changing the 220k output load resistor into two resistors as a potential divider and picking off the middle will do a good job and a much cheaper and simpler answer, for example putting a 51K to ground and 147k to the cap and tapping off centre would also give about 300mV output @ 1k, changing the ratio will change the output, and no pot to degrade the signal.

Robert

[Chris65]

Technically it would be better to have them inside.

Thorsten, I'd be interested to hear your 'technical' reasons for this?

[xdanx]

This is my diy version of EAR 834. The sound is very OK

[Jay]

Robert,  yes cutting the overall volume is the goal.
 

If all you want to do is cut the volume then changing the 220k output load resistor into two resistors as a potential divider and picking off the middle will do a good job and a much cheaper and simpler answer, for example putting a 51K to ground and 147k to the cap and tapping off centre would also give about 300mV output @ 1k, changing the ratio will change the output, and no pot to degrade the signal.

Robert

That could well be a viable solution & not having to change to much, could I prevail upon you to draw a quick wiring diagram of what value components & where to change things.

Dan, thats a very fine looking build. I see you are using an ECC 82 does it lower the output in your build.

[Chris65]

Jay, you could also look at mods to the Stereo 20 to reduce gain. Some good info here: http://www.keith-snook.info/leak-hifi.html

[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