Jacek's EAR 834 build

[jacekm]

Hello,
Douk EAR834 kit from Ebay
This is my first electronics project. Pictures show the circuit boards when they arrived.



Last few weeks I was reading in this forum. Witch was very helpfull. I have tried to understand the design and especially looked at schematics. I have all components now and beginning to assembly.

Here are values of my components.


I feel quite comfortable as on one component. 15nF decoupling capacitor. It should be 10nF according to the original design. Then it's an odd capacitor that I've come across. I'm unsure if it appropriate in Audio Path. I will be grateful for all comments. Here is the link to product page.

https://www.tme.eu/gb/details/kps200-115dak/audio-polypropylene-capacitors/leclanche/

I also have bypass capacitors. More about those in the next post
Thanks for now and
Cheers //JacekM

[Jessica_K]

Hi Jacek,

A lot of builders have removed that part of the circuit. There is a sticky thread "DIY EAR 834P TRLH Phono Stage - Build Guide / Parts List" about this and other modifications put together by John (spaceistheplace) at the start of this amplifier forum.

However it is quite legitimate to build as per the schematic you have posted. The effect of this capacitor is to produce a low frequency roll off often referred as a rumble filter the use of 15nf verses 10nF is to push the roll off a little lower.

That polypropylene capacitor is suitable for the job.

It is worth investing in good quality caps that are in the signal path again in the sticky thread there is a parts list of some of the best sounding parts

Jessica

[jacekm]

Yes, I ordered components from Johns list. But was confused just when it came to this capacitor. Maybe too much red wine. I'll try the one I have.
I also went after your post and ordered Mundorf Oil caps and Kiwame resistors for input.

[coolmaster]

Yes, I ordered components from Johns list. But was confused just when it came to this capacitor.

I have a fully assembled kit here and its fitted with a Vishay BC 368 type 150nF/400V. I later substituted this with some Russian PIO of same value and 160V rating. No ill effects with either type and all seems to sound excellent. The original 834 schematic show a 0.1uf type. I think the clone could be a print error but I reckon a 15nf one would do fine and no harm done.  Its up to you to choose this 15nf value, 150nf capacitor or the 100ohm mod. I may try the 100ohm mod and gauge if I like what I may hear later on. I'm also careful when I choose to install a naturally bigger sized PIO capacitors with voltage rating nearest to 20-30% more than actual voltage seen. If its about 120V at the anode of V2, I will choose a 160-250V rated capacitor (where available to buy) to suffice its purpose. I will not choose a 400V/600V/1kV type to put there as it maybe too big to fit in that tight space. I have thrown out all the electrolytic caps for more reputable makes, uprated all the power resistors to Vishay PR03 power metal film types, thrown out all the supplied axial diodes for proper legit ones found from either Mouser, Digikey or other reputable vendors. The quality looks much higher than what was installed. All these changed the sonic quality for the better, so I seem to hear.

[jacekm]

After sniffing flux for three hours ...




Bypass capacitors.
Four oranges 0.47uF for 47uF electrolytic capacitors. The medium sizes are for tubes. The smallest is the Panasonic 1uF for 100uF electrolytic capacitors located first on the main circuit board.


Right now I'm looking at the chassis. It's a little hard to find something suitable. Any suggestions? I would prefer european supplier. Douk Audio has some on ebay. But my paypal account are shut down so ebay is not the option for me.
Cheers
//JacekM

[jacekm]

Completed my circuit board assembly. Connected everything with new tubes in place. Checked my voltages after half an hour's of heating.
The values are just to low. The filament voltage is only 5.7. Can I easily adjust it?

My tubes  and values:

[Jessica_K]

Yes you can but it would be a good idea to find out why it is so low first

There are a few reasons and should be checked
1 unpowered measure the two 0.22R resistors they could be wrong value, replace if they are else..
2 if it is possible disconnect the heater supply from the valves, power up and check the no load voltage should be about 9V. Remember that the caps will hold charge for a very long time so they will need to be discharged with a resistor of a few K, alternatively load the supply with a 3-10k resistor before powering. Voltage should be the same if it’s low the transformer may not be tapped correctly, else..
3 reconnect the supply to the heaters and measure the voltage across one of the resistors, for 1A the drop should be about 0.2V. Calculate the current I = V/R. If the current is more than an amp the check wiring for a short of some kind. Else
4. Transformer rating may not be what is required. Need 2A @ 6.3 AC this sometimes requires trappings to be connected in parallel or series

Let us know how the above goes 

Jessica

[jacekm]

Yes you can but it would be a good idea to find out why it is so low first

There are a few reasons and should be checked
1 unpowered measure the two 0.22R resistors they could be wrong value, replace if they are else..

None of my instrument can measure so low values. I am getting different readings every time.  

2 if it is possible disconnect the heater supply from the valves, power up and check the no load voltage should be about 9V. Remember that the caps will hold charge for a very long time so they will need to be discharged with a resistor of a few K, alternatively load the supply with a 3-10k resistor before powering. Voltage should be the same if it’s low the transformer may not be tapped correctly, else..

I am reading 8V with no load.

3 reconnect the supply to the heaters and measure the voltage across one of the resistors, for 1A the drop should be about 0.2V. Calculate the current I = V/R. If the current is more than an amp the check wiring for a short of some kind. Else

I am in a big trouble now. The probe slip and I shorted B + and ground on the left channel. It was like a Big Bang.
The "God thing" is that fuse did not blown . But everything is mess up now. No correct voltages whatsoever.  

I need more coffee and back to the bench (kitchen table) to check the PSU board.

4. Transformer rating may not be what is required. Need 2A @ 6.3 AC this sometimes requires trappings to be connected in parallel or series

Transformer is:
Pri:230V
Sec1: 250V 0.15A
Sec2 3.15-0-3.15 2.5A
I am getting 6.3V from the Sec2

Let us know how the above goes  

Jessica

[Firebottle]

I would reduce the value of the 20K in the HT line to bring the first two stages voltages up a bit.

[jacekm]

Now i have B+ 314V with no load and just above 700V with load.
The transistor is getting hot as soon as I turn the power on.

[coolmaster]

My transformer is a 50VA toroidal from China 115 X 2 (wired in series to 230VAC/50hz), 0-250V (actual 265VAC no load), 0-6.3VAC (actual 6.5VAC), Important matter is my incoming mains input is exactly AV regulated to precisely 230VAV. If I plug direct to mains at my place, it will hover from 235 to >240VAC, and the secondary output will naturally read a little higher.

My implementation based on AC mains exactly at 230VAC with secondary output voltage as above, 1) I purposely reduced supplied 0.22ohm power resistors to 0.1ohm/5W wirewounds, thereon output to 3 tubes would be 6.19 to 6.4VDC depending what tubes I may roll around . I done this because the phono will always be supplied at precisely 230VAC mains, no more no less.
2) If I plug direct to mains the heater voltage is sure to rise a fair bit more since its an unregulated heater supply. Should it drop to below 6V, either the transformer is lacking current capacity or the some tube heater happen to be drawing more current than specified causing further voltage drop. Under any circumstances, below 6VDC isn't normal and should be addressed.
3) On the B+ side, based on 230V input and 265VAC secondary output, I get around approx 350VDC at at the rectifier output and 285VDC after the emitter follower (output of transistor) point. For me this is perfectly acceptable. I've installed all 68V zeners instead of the recommended 3+1 (whatever). Each Zener register a voltage of about 70-71VDC. I had matched them out of a handful of them. I don't trust the supplied zeners and bought new ones from a legit source.
4) With 330k plate resistors I found the gain is on the high side. I reduced the plate resistor to 200k for V1 & V2, the rest unchanged. All are 12AX7 tubes and it will stay that. The resultant gain was very acceptable again and suit my personal taste.  
5) Lastly, my tweaking or tuning above is meant for MC mode with Cinemag Step up transformers.
P.S. I only installed bypass caps direct to the heater pins (because it was very easy) but didn't bother bypassing the B+ big caps, felt there's no harm without any. My build was completed a couple of weeks ago and been enjoying it ever since.

[Jessica_K]

None of my instrument can measure so low values. I am getting different readings every time.  

No problem as long as it is under an ohm for the pair in series

I am reading 8V with no load.

A bit low probably due to bridge voltage drop but in range

I am in a big trouble now. The probe slip and I shorted B + and ground on the left channel. It was like a Big Bang.
The "God thing" is that fuse did not blown . But everything is mess up now. No correct voltages whatsoever.  

I need more coffee and back to the bench (kitchen table) to check the PSU board.

So sorry to hear this we have all done it at some time
The transistor will be dead, no other damage is likely. You will need to replace it before doing any other tests

Transformer is:
Pri:230V
Sec1: 250V 0.15A
Sec2 3.15-0-3.15 2.5A
I am getting 6.3V from the Sec2

Sec2 in series should be good enough

If you do not already, when measuring voltage it is a good idea to use a lead with a croc clip on the “-“ side and clip it to the low side of the measurement (usually a gnd) leg of a component then can concentrate on getting the “+” on the right place, can still slip

Hope you will be up and running again soon as I do not have an answer for you for the low volts yet

Jessica

[jacekm]

No worries Jessica. Newbie mistakes. I think I've learned my lesson.
I have already ordered a replacement transistor. Also ordered some resistors and new MUR4100E diodes to replace stock ones.

Probe clips I ordered a while ago. But it's long way from china and takes a little longer than expected.

To be continued...

About large caps and high voltages. I have made one of these.

[jacekm]

Finally, I have some time to continue with the build.
What happened? Not going for the details. Live.
Anyway. I have to replace the transistor in PSU after cooking it.
I also replaced all diodes, all Zener diodes and diode bridge.
Then I changed 0.22 ohm resistors to 0.1 ohm 5W.
Now I have between 6.19 to 6.29 V on filament depending on the day.
I think that is close enough.

Then we came to B+
360V after rectifier
280V output of transistor

275V after 2k resistor
260V after 20k witch I changed to 18k
194V after 200k

80V on pin1 V1
111V on pin1 V2
275V on pin1 V3

All measured with load on.

Am I close or is there more to do to get better values?
I was thinking that maybe the transformer is causing that all voltages are a way off. Maybe i have to get a better one.

[Jessica_K]

The B+ seems good to me 280V is what I expect and the 5V drop on the 2k means the amp is taking 2.5mA again good. I cannot remember the tube voltages so cannot comment on them until I fire my PC up tomorrow but in general it seems OK. The transformer is working fine at this level

Jessica