Pearl Two

buzzforb · 2013-02-25 11:34 am

It seems i am being forced into the BJt world and it is different and scary....but kinda useful it seems. I stairing at the PearlII and folded simplistic and waiting for ahah moment. Morning coffee. I tihnk you are like my little one and have your days and nights mixed up

Keep getting distracted by this monstrosity
Gotta remember ground referenced load. Is that always true of folded?

bnorrish · 2013-02-25 11:39 am

Salas said:
Try 1K trimmer connected as rheostat instead of R28 and trim for 1.5V across R6 first. Then see again with P1. Your LED is higher than 1.7V Vf most probably.
Q3 is squashed for Vce in your annotated schematic measurements. Try 15-22 Ohm R21-24 to give it breath. Your input quartet IDSS is probably higher than in the original.

Thank you for the advice. It seems like a component is dead, or other major issue vs components having higher specs, no? Loud hum at moderate volume, no music. The other channel is working with voltages very close to the bad channel - except the output between R16 and R17 - bad channel 5.7 v, good around 0. When I first started troubleshooting the voltage at this point was around 12v and maxing out P1 brought it down only to 5.7v.

buzzforb · 2013-02-25 11:45 am

Listen to Salad :devilr:

He knows what he is talking about. I knew the Fe was off a little.
By lowering R28. He will drop Vgs to Mosfet and reduce its contrubution to the output, bringing it back into balance a little better? Sorry bnorrish. Using your issue as learning opportunity.

Salas · 2013-02-25 11:51 am

Not sure there is some dead semi. A small change in the 2mA CCS dif amp spec can create a rather large DC imbalance out of P1 compensation range is possible enough. Changing from 12V at least should mean it ticks still. Trim R28 to check that out is easy to test.

Salas · 2013-02-25 12:02 pm

Zen Mod said:
and for few other things

which I don't know , at least not before first coffee

up to that task

That is why I used "mainly" so to make you drink up fast.

Can swing more also since it skips the tail CCS threshold they cram there although it takes more power and it can be slower in absolute spec due to using P type.

Salas · 2013-02-25 12:08 pm

buzzforb said:
Gotta remember ground referenced load. Is that always true of folded?

They can be upside down and rail referenced too.

bnorrish · 2013-02-25 12:22 pm

Salas said:
Not sure there is some dead semi. A small change in the 2mA CCS dif amp spec can create a rather large DC imbalance out of P1 compensation range is possible enough. Changing from 12V at least should mean it ticks still. Trim R28 to check that out is easy to test.

Thanks. I will follow your advice. Need to go to store and get a 1k. Thanks.

Salas · 2013-02-25 12:25 pm

Any other trimmer values you got around now by some chance?

bnorrish · 2013-02-25 12:33 pm

I do not. I can swing by on my way to work. Will not get to it until tonight anyways. Thanks.

Mr. dB · 2013-02-25 2:11 pm

Siberia said:
I'm assembling a new TT and when it's finished, I'm going to give a 103R a try on the RB300 arm. I think that means adding a SUT to my system too.

Do you have the optional heavy counterweight? You'll need it for the 103R on an RB300. A headshell weight/shim will help too, to get the tonearm/cartridge resonance back to a reasonable number.

Siberia · 2013-02-25 2:46 pm

Mr. dB said:
Do you have the optional heavy counterweight? You'll need it for the 103R on an RB300. A headshell weight/shim will help too, to get the tonearm/cartridge resonance back to a reasonable number.

Hello, Mr dB. I have an OL counterweight and a structural upgrade. I don't know if it's any heavier, as I never had a stock one to compare. Yes, it's said that 103R prefers heavier arms. Although, a little note, it's compliance is measured at 100Hz and there are many happy users with RB300 tonearms. It gives me a hint that it still can be a good match.

Wellerman · 2013-02-25 4:52 pm

Salas said:
That's adapting to another bias point on the fets curve and to another gm total than original though.

Here's where my lack of electronic knowledge comes in

I just followed advice from -I think- Pierre Quiroule and it worked for me. But of course I would like to know if adapting to another bias point could have any detrimental effects. More noise? How about the gain?

jhsjhs99 · 2013-02-25 5:09 pm

Is there any way to get the boards for the Pearl II? Obviously I am a few years late in the game, but I just found this place and given my system it would probably be the best place to start. Thanks.

bnorrish · 2013-02-25 5:21 pm

You can them in the Store at Pass DIY.

jhsjhs99 · 2013-02-25 5:41 pm

Thank you! I didn't realize that existed.

My wife may thank you less.

Salas · 2013-02-25 5:53 pm

Wellerman said:
Here's where my lack of electronic knowledge comes in I just followed advice from -I think- Pierre Quiroule and it worked for me. But of course I would like to know if adapting to another bias point could have any detrimental effects. More noise? How about the gain?

Surely works but at a lower Vds. When there is more Vds across those fets they are a bit more linear. Up to 8V. More starts some gate leaking.

Salas · 2013-02-25 5:54 pm

Siberia said:
Hello, Mr dB. I have an OL counterweight and a structural upgrade. I don't know if it's any heavier, as I never had a stock one to compare. Yes, it's said that 103R prefers heavier arms. Although, a little note, it's compliance is measured at 100Hz and there are many happy users with RB300 tonearms. It gives me a hint that it still can be a good match.

Its real useful for arm calc compliance is about 16. Derived by FFT resonance test on vinyl record with weighed cart and known arm and screws weight. Its coils are also about 19R not 14R. We had done some experiments among two samples in the SNJFET Riaa thread some time ago. We use ~200R-220R load.

Wellerman · 2013-02-25 6:24 pm

Salas said:
Surely works but at a lower Vds. When there is more Vds across those fets they are a bit more linear. Up to 8V. More starts some gate leaking.

Well, I don't feel like dismantling it again, so let's just hope they are linear enough at Vds of 5.3V not to have a negative effect on sound quality

bnorrish · 2013-02-25 7:21 pm

jhsjhs99 said:
Thank you! I didn't realize that existed.

My wife may thank you less.

Make sure to buy her some nice records to keep her interested. Joni Mitchell, Carole King, Cat Stevens in my case.

Siberia · 2013-02-25 7:22 pm

Salas said:
Its real useful for arm calc compliance is about 16. Derived by FFT resonance test on vinyl record with weighed cart and known arm and screws weight. Its coils are also about 19R not 14R. We had done some experiments among two samples in the SNJFET Riaa thread some time ago. We use ~200R-220R load.

Thanks. So it's moderate compliance as could have been predicted. But as always there are camps: DL_RB

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