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

[Rénald]

Modification done, it is much quieter and much more transparent than the original version. In running for 24h.





Rénald

[terfyo]

Hi everybody and all the experts out there, i need some help with this phono preamp.
I recently completed the DIY clone version from DOUK audio and i'm facing a big problem.
Basically, the phono is working fine with my AT95E MM cart, there is sound coming out from my set up.

The issue is that there are some loud pops, which sends my Krell KSA200S into full beast mode.
These loud pops are not present, when the vinyl is not playing, it only happens when the cart is lowered and vinyl is spinning.

So, i'm wondering if the gain on the phono is too high for my set up?
Like there's an equipment mismatch somewhere?
Or if the phono itself has some problems.

Please visit the following DropBox link for the photos of the unit which I have done.
Some comments and help please!
https://www.dropbox.com/sh/adh29oaqu7uje92/AAAFM8SCEA4WmwMa99Crf-Psa?dl=0

Thanks in advance
TL

[be.audiophil]

Hi everybody and all the experts out there, i need some help with this phono preamp.
I recently completed the DIY clone version from DOUK audio and i'm facing a big problem.
Basically, the phono is working fine with my AT95E MM cart, there is sound coming out from my set up.

The issue is that there are some loud pops, which sends my Krell KSA200S into full beast mode.
These loud pops are not present, when the vinyl is not playing, it only happens when the cart is lowered and vinyl is spinning.

So, i'm wondering if the gain on the phono is too high for my set up?
Like there's an equipment mismatch somewhere?
Or if the phono itself has some problems.

Please visit the following DropBox link for the photos of the unit which I have done.
Some comments and help please!
https://www.dropbox.com/sh/adh29oaqu7uje92/AAAFM8SCEA4WmwMa99Crf-Psa?dl=0

Thanks in advance
TL

No, most probably you are facing an earthing issue and may be a cold solder joint or a contact problem with the tube in the tube socket. What can be seen on the pictures leads to some cold solder joints. You can recognize a good solder joint when the solder joint is shining. Furthermore and since the pcb is throughplated there should be solder on both sides and not only on one. Most connections on your PCB are tacked only but not soldered properly.

Most probably re-solder everything will help most.

[terfyo]

No, most probably you are facing an earthing issue and may be a cold solder joint or a contact problem with the tube in the tube socket. What can be seen on the pictures leads to some cold solder joints. You can recognize a good solder joint when the solder joint is shining. Furthermore and since the pcb is throughplated there should be solder on both sides and not only on one.

Most probably re-solder everything will help most.

For the tube sockets, I've soldered the underside of the board, nonetheless, I'll do as you have recommended.
Any other suggestions?

[terfyo]

Hi guys,

I've soldered both sides of the board as recommended by be.audiophil for all the components.
The video in the link below would give you guys a better idea of how the popping sound like.

https://www.dropbox.com/s/yr7611ny01107f5/20191125_191643.mp4?dl=0

Track : Tracy Chapman - Fast Car
First pop on right channel at 16secs.
Second pop on left channel at 23secs.
There is another pop at 26secs, probably on the left channel.

Thanks in advance for recommendations.
TL

[Jessica_K]

Do you have anything electrical that is turning on/off every few seconds such as fridge, heater etc as it could be mains bourn. Otherwise pops could be a voltage breakdown of some kind. If you eliminate mains then check all the voltages on the supplies starting at the output end (should be about 280V, the middle stage and the input stage, each should get lower (about 200V on input). Check the heater voltage both across the heater (6.3V) and heater to ground (40-50V if I remember correct). Check the cathode voltage at the last stage (about 80V). If you have another valve you can use swap it one at a time with the others and see if you have a faulty valve.

Jessica xx

[terfyo]

Do you have anything electrical that is turning on/off every few seconds such as fridge, heater etc as it could be mains bourn. Otherwise pops could be a voltage breakdown of some kind. If you eliminate mains then check all the voltages on the supplies starting at the output end (should be about 280V, the middle stage and the input stage, each should get lower (about 200V on input). Check the heater voltage both across the heater (6.3V) and heater to ground (40-50V if I remember correct). Check the cathode voltage at the last stage (about 80V). If you have another valve you can use swap it one at a time with the others and see if you have a faulty valve.

Jessica xx

Hi Jessica_K,

I highly doubt it has got to do with the mains as my entire setup is running through a balanced transformer and it has a dedicated power supply line.

I played back the record a couple of times and found that the pops happen exactly at the same spot and not just randomly popping here and there.

I did some quick read up and wonder if the loading of the cartridge might be of any issue? 47k ohm etc.
The RCA inlet plugs that I am using does not come with any loading of any kind. It's just the normal RCA female plugs. Any issues on this?

I'll take your recommendation and measure the voltages across the points which you have mentioned.

TL

Sent from my SM-N975F using T***talk

[Jessica_K]

I assume this does not happen on another phono stage or phono input to a pre-amp and thus only when going through the EAR?

I have never used a valve phono stage with a MM cart, only MC using a SUT, where my loading is a few hundred ohms max, if it is loading then adding a few hundred pf caps may help (150-220pf)

Jessica xx

[terfyo]

I assume this does not happen on another phono stage or phono input to a pre-amp and thus only when going through the EAR?

I have never used a valve phono stage with a MM cart, only MC using a SUT, where my loading is a few hundred ohms max, if it is loading then adding a few hundred pf caps may help (150-220pf)

Jessica xx

Yes. It did not happen through a solid state phono that I have previously. So I'm thinking that the phono stage has too much gain or is particularly sensitive to certain spikes in the pick up which causes an overload.

Your recommendation of adding a few hundred pf, kindly further elaborate on how to implement? Parallel or series at which location?

Thanks.
TL

Sent from my SM-N975F using T***talk

[Jessica_K]

Place the caps across the 47k input resistors one on each

Jessica xx

[terfyo]

Hi all, just a quick update on what I have done this evening.
I swapped out the cart for another cart, "hoping that my cart has a problem", but that did not solve the problem.
I have also swapped out the interconnects and that did not solve the problem as well.
I have measured the input load at the RCA, it shows 48k ohms on one side and the other at 51k ohm.

I'll probably try what Jessica has offered and swap out the tubes.

Any other ideas?

TL

[fasterbyelan]

I played back the record a couple of times and found that the pops happen exactly at the same spot and not just randomly popping here and there.

Is there any noise/pops with a differing phono amp at the same points even though they may be less obtrusive?

Valve phono amps are generally less susceptible to overload due to the higher voltages involved and I have not heard that this design suffers from this issue.  I tend to agree with Jessica in that something is breaking down when the signal from the pops gets too large (pops can contain much higher energy than the audio signal). If you have an oscilloscope you could trace the signal through the amp to determine what is going on.

[jphabc54]

I’ve been messing around with my 834 clone for the first time in a while and recently replaced the power supply with a Broskie Janus Shunt, however the Janus is running hot at about 330 VDC on the B+.

I drew up the new load line/operating point on the 12AX7 curve and it looks like it’s a bit more linear at that bias point, which I think is bearing itself out in a sound that is decidedly less “tubey” than when I had the Xuling PCB at ~285 VDC.

Any thoughts on whether I should adjust anything (load resistors, etc) for the higher B+? I’m not as concerned about exceeding the recommended max plate voltage.

(P.S. I am actually using 6N2P-EV but I think the grid/anode characteristics are close enough to the 12AX7 for this — correct me if I’m wrong).

[be.audiophil]

Hi guys,

I've soldered both sides of the board as recommended by be.audiophil for all the components.
The video in the link below would give you guys a better idea of how the popping sound like.

https://www.dropbox.com/s/yr7611ny01107f5/20191125_191643.mp4?dl=0

Track : Tracy Chapman - Fast Car
First pop on right channel at 16secs.
Second pop on left channel at 23secs.
There is another pop at 26secs, probably on the left channel.

Thanks in advance for recommendations.
TL

What happens when a different record is played?

[terfyo]

A different record player is used with the 2 carts which I've mentioned. The same thing happens..
A few different record was played to check. of course, the pops happen at different times but still, they're there.

I'll be buying some new tubes this weekend to swap out the tubes to check if the tubes have problems.

Sent from my SM-N975F using T***talk