Valve Itch phono - Page 14

Salas · 24th April 2011, 05:25 PM

You should be getting around 350V with solid state bridge and 260VAC Tx. Is it sagging on constant current draw? What is the value of R1 on the SSHV and the voltage drop on it, also what is put between the two PSU capacitors that drops 20 further Volt? 280VDC still will operate the phono within bounds. 20V drop across reg is ample.

Ground the sink in the final box and use proper fuse on primary and AC mains ground to chassis, don't skip any safety wiring. Insulators may always breakdown in the long run.

To have the SSHV in the same box with the phono circuit is absolutely recommended. The heaters PSUs may or may not be near.

woodturner-fran · 24th April 2011, 06:11 PM

I have 470R 5W between the 2 PS caps (220uF-470R-220uF) and I get the 20V drop right there. R1 is 47R and I get ~1.8V drop across it.

Tx gives me 260VAC unloaded, ~252VAC loaded, ~320VDC after the diodes (UF4007) and 300 at the second PS cap.

Maybe I should drop that 470R a bit.....

************************************

Both chassis will be grounded.........

(like the new avatar Salas!)

Salas · 24th April 2011, 06:23 PM

You have 38mA CCS, pretty good for supplying the phono and leaving enough to massage the reg for good Zo. Since the Tx sags a bit indeed, go 100R between filter capacitors only. The reg will reject the ripple while the R element between caps will still take the edge off the pulses.

woodturner-fran · 24th April 2011, 07:53 PM

So I dropped it back to to 100R and gained another 10-12V or so. Should be able to run about 290VDC B+ now.

Thanks for the help and guidance.

Fran

woodturner-fran · 12:20 AM

While waiting for parts to arrive, I have the 2 chassis almost ready to go. One is recycled from a preamp, the other is a scrap instrument case. Another hour or 2 and the chassis work should be done..... which is great since chassis work is the bane of any DIYers life....

Another question:

Is there any good reason why I shouldn't add another set of RCA jacks and wire them directly to the circuit, by passing the step up transformers?

Lastly, I remembered I had a link kept for how to load MC carts following a step up Tx... http://www.kandkaudio.com/mccartsetup.html

Fran

Salas · 26th April 2011, 06:21 AM

If there is no noise picked up by adding those extra inputs, there is no other reason why not.

Salas · 26th April 2011, 08:24 AM

Quote:

Originally Posted by woodturner-fran

Lastly, I remembered I had a link kept for how to load MC carts following a step up Tx... K & K Audio - Moving Coil Cartridge Step-up Transformers

Fran

All well theoretically, but there can be a couple of practical catches that I have referred before in this thread for this particular input stage at least. It is possible that some SUTs combinations will show more THD when loaded heavier than 47K on this one. Also showing less multiplication ratio than unloaded nominal. To the contrary the more than necessary reflected primary load impedance for the 12 Ohm coil cart did not show signs of tonal thinness. Bottom line is, try 47K alone to compare too in your final set up.

bappe · 26th April 2011, 01:43 PM

Hi Salas,

Nice project!
I have one comment on your circuit and the use of the LL9206 Tx. Since this is a transformer with a continous amorphous core it absolutely hates DC, even if it is small. One should nver put any dc on any of its windings, and if it is done one must demagnetize the core afterwords. With zero bias there is a fair chance of dc in the secondary and this must be avoided to give the 9206 a fair chance to its stuff.

BR,
Anders

Salas · 26th April 2011, 02:43 PM

Good reminder. There was a Dynavector SUT on the second build shown too. Those were just available. Had no problems with the first one, but it may get pressed at a point if some tube will age and pump up Ig.

woodturner-fran · 26th April 2011, 07:57 PM

See the sch in the pic below:

He ties gnd on the primary side to gnd on the secondary. Salas, I note you didn't do this in your schematics, although there was some discussion about it back a little. Both version of yours are working fine? No need to follow that common gnd?

Made more progress tonight. The transformer box is done, next up is the umbilical from phono box to transformer box. Then I can start on the circuit itself - thanks to the arrival of some nice matched caps from Poros Island......

We will see which is most IMF-affected postal service... I'm already guessing it is the Irish one!

Fran

26th April 2011, 12:16 AM	#135
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	While waiting for parts to arrive, I have the 2 chassis almost ready to go. One is recycled from a preamp, the other is a scrap instrument case. Another hour or 2 and the chassis work should be done..... which is great since chassis work is the bane of any DIYers life.... Another question: Is there any good reason why I shouldn't add another set of RCA jacks and wire them directly to the circuit, by passing the step up transformers? Lastly, I remembered I had a link kept for how to load MC carts following a step up Tx... http://www.kandkaudio.com/mccartsetup.html Fran Last edited by woodturner-fran; 26th April 2011 at 12:20 AM.

26th April 2011, 01:43 PM	#138
bappe diyAudio Member Join Date: Sep 2002 Location: Furulund, SWEDEN	LL9206 and possible grid current Hi Salas, Nice project! I have one comment on your circuit and the use of the LL9206 Tx. Since this is a transformer with a continous amorphous core it absolutely hates DC, even if it is small. One should nver put any dc on any of its windings, and if it is done one must demagnetize the core afterwords. With zero bias there is a fair chance of dc in the secondary and this must be avoided to give the 9206 a fair chance to its stuff. BR, Anders

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24th April 2011, 05:25 PM	#131
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	You should be getting around 350V with solid state bridge and 260VAC Tx. Is it sagging on constant current draw? What is the value of R1 on the SSHV and the voltage drop on it, also what is put between the two PSU capacitors that drops 20 further Volt? 280VDC still will operate the phono within bounds. 20V drop across reg is ample. Ground the sink in the final box and use proper fuse on primary and AC mains ground to chassis, don't skip any safety wiring. Insulators may always breakdown in the long run. To have the SSHV in the same box with the phono circuit is absolutely recommended. The heaters PSUs may or may not be near.

24th April 2011, 06:11 PM	#132
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	I have 470R 5W between the 2 PS caps (220uF-470R-220uF) and I get the 20V drop right there. R1 is 47R and I get ~1.8V drop across it. Tx gives me 260VAC unloaded, ~252VAC loaded, ~320VDC after the diodes (UF4007) and 300 at the second PS cap. Maybe I should drop that 470R a bit..... ************************************ Both chassis will be grounded......... (like the new avatar Salas!)

24th April 2011, 06:23 PM	#133
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	You have 38mA CCS, pretty good for supplying the phono and leaving enough to massage the reg for good Zo. Since the Tx sags a bit indeed, go 100R between filter capacitors only. The reg will reject the ripple while the R element between caps will still take the edge off the pulses.

24th April 2011, 07:53 PM	#134
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	So I dropped it back to to 100R and gained another 10-12V or so. Should be able to run about 290VDC B+ now. Thanks for the help and guidance. Fran

26th April 2011, 06:21 AM	#136
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	If there is no noise picked up by adding those extra inputs, there is no other reason why not.

26th April 2011, 02:43 PM	#139
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Good reminder. There was a Dynavector SUT on the second build shown too. Those were just available. Had no problems with the first one, but it may get pressed at a point if some tube will age and pump up Ig.

26th April 2011, 07:57 PM	#140
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	See the sch in the pic below: He ties gnd on the primary side to gnd on the secondary. Salas, I note you didn't do this in your schematics, although there was some discussion about it back a little. Both version of yours are working fine? No need to follow that common gnd? Made more progress tonight. The transformer box is done, next up is the umbilical from phono box to transformer box. Then I can start on the circuit itself - thanks to the arrival of some nice matched caps from Poros Island...... We will see which is most IMF-affected postal service... I'm already guessing it is the Irish one! Fran