Pearl Grounding

[dmcgown]

I have just finished up a Pearl phonostage. Really very nice, I brought it over to a friends house today who has the top Klyne phonostage, and it compare quite well, especially given the price. I think he will build one for a backup for his Klyne.

Anyway, I have a question on grounding. The Rev 1 boards have the circuit and power grounds seperated out, with the option of tying them together. It is unclear whether this is the point to tie the two grounds back to chassis ground. I am getting a bit of hum, have the circuit/power grounds tied as noted, and have tried both tying the output jack ground to chassis ground, and tying the chassis ground back to the circuit/power ground tie point. There seemed to be somewhat less hum in the latter case, but it is still present.

Any suggestions on alternate grounding schemes for the phonostage would be appreciated. Again, the design sound great, if I can get this hum out, I will be one tremendously happy
camper.

P.S., if you need extra gain for a L.O. moving coil, Lundahl makes some transformers that are cheap ($38 each) but quite good. I have a pair of LL9206s built into my Pearl that work very well with my Benz Ruby.

[wuffwaff]

dmcgown,

are you shure the humm comes from the way you are grounding? Phone stages are very sensitive and don't like the neighbourhood of poweramps or power supplies. Have you moved the unit around and is there an influence on the humm you're hearing?

william

[dmcgown]

I have tried moving it around, I have a Tice powerblock close by, and the further away the unit is from that does drop the hum a bit. However, trying the unit out in my friend's system it is evident that some of the hum appears to be grounding related, since it was well away from any EMI sources.

[joe]

do you have hum with shortend inputs as well? If not, the hum would be caused by noise-pickup of your catridge or tone-arm.

[Nickolas K.]

Had a hum problem when i first fired my pearl up.
The solution was to remove the connection between ground points on the pcb of each channel and connect them separately to the common ground point between the output jacks of the pearl.
Now, if you use a separate outboard ps you can connect AC ground to its chassis but do not connect any AC ground to the chassis of the pearl itself.
Connect ps ground to the ground point between the output jacks and if the hum doesn't go away try connecting this ground point to the chassis, but as close to the output jacks as possible.You could even insert a 100R resistor between chassis and ground point to avoid any further loops.
The whole idea is to create a single grounding point as close to the output as possible and ground all elements independently to this point.
If you are not using an outboard ps, you have to connect AC ground to the chassis for safety but with the use of a thermistor like NP normally does. The rest is the same.


Good luck,
Nick

[dmcgown]

Nickolas,

Thanks for the tips! I will rework the grounds tonight. I do have AC ground to the Pearl chassis via the power umblical from my outboard supply, so I will disable that as well.

David

[dmcgown]

Just a follow-up. My hum problem ended up being an absence of a grounded connection at the input of the MC transformer. Adding a ground from the ground of the input jack to chassis ground solved the problem. Besides reducing the hum, it improved low level resolution dramatically.

The Pearl is sounding really good!

[Ren]

Originally posted by Nickolas K.
The whole idea is to create a single grounding point as close to the output as possible and ground all elements independently to this point.

Thanks for your post... I finished building my Pearl a couple weeks ago and have also had a small hum problem. I know Wayne discussed grounding in his original article, but your post clicked with me. A minor grounding change, and the Pearl is now hum-free!

I'm really impressed with the performance of this phono preamp. It's the best sounding phono section I've ever owned... very musical with plenty of detail, and imaging that continues to surprise me.

That new Ella Fitzgerald 5-LP set (the Gershwin songbook) is calling to me...

[Nickolas K.]

It's the best sounding phono section I've ever owned...

Well, i agree with you. But wait till you hear an Ono!
I lived with the pearl for a couple of months (it replaced the phono section of a Conrad-Johnson PV11).
But, a couple of weeks ago i finished my new preamp, which is also a Colburn-Pass design.
I have built an Ono-Aleph L.
It consists of 2 units:
The ps, fully dual-mono for each stage (it even has 4 tranformers) with separate passive filtering and regulation for each one of the 4 modules.
The preamp itself has 2 pcb's, phono and line section.
Input selection switch is Elma 041264.
For the stepped attenuator i used the Elma 04A2A00 with the original resistor values of the Aleph L.
Internal cabling is Belden.
The sound is very fine; refined and analytical without sounding sharp or grainy. Tonal balance is its major strength.
It took me some time to find the proper loading value for my MC7k5 but at 470 Ohms soundstaging is beyond imagination.
The only thing i haven' got used to so far, is the tight control in low bass but I suppose it's some kind of a trade-off for the pitch and definition.
If your record collection is worth it, try to build an Ono. You won't regret it.

Regards,

Nick

[Ren]

Sounds like a great idea; post some pictures.

I'm not up to building that ambitious yet... the Pearl is my first DIY project. I'm still giddy that the thing works, and I don't smell ozone when I turn it on. The fact that it sounds so good is a bonus, and a credit to Wayne & NP.

Maybe I'll try a BOSOZ next. I need to build things that have PCBs available. I assume you laid out your own PCBs for your new preamp?

Ren