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PostPosted: 17 May 2020, 08:57 
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Joined: 01 Feb 2015, 13:41
Posts: 160
Location: Athens-Greece
Thank you very much for your responses. I think that I approach the end, however still some gray areas. I attach the schematics and transformer data sheet to be specific, As you see transformer has two input lines 3 and 7 and two output 10 and 16. Meanwhile, we see that 13 and 14 are going to chassis or grounding; since there is no grounding line in schematics I assume chassis which will probably be the shielding.
Reading the note above (from LL1678 datasheet) "grounding reference" is required in case of MC cartridge. Thus, following should be answered:

1. Since one line in schematics only, should I use one coil eg 3-10 or 7-16 or a series connection as mentioned in the forum eg in 3-10-7-16 out? OR 3-10 according to schematics and 7-16 to grounding?
2. 13-14 are going to chassis or to grounding?
3. Last what is the grounding reference for MC?

Has anybody used this with MC cartridges and LL1678s? What connection was it used?

Thank you to everybody


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PostPosted: 17 May 2020, 11:26 
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Joined: 04 Jun 2008, 20:59
Posts: 4166
Location: Arizona, USA
Hi, Look at the wiring configurations in the data sheet. The X+ is is the hot input and X+ on the output side the hot output. The plain Xs are the signal grounds in both cases. All the connections with dots are tied together. The ones that do not have dots just pass over. For 16 to 1 (version C) , Yes you need grounds. Pins 7,8,16 are signal grounds. Often the case and core (13,14) go to the same place. 3 and 4 are connected together and are the input signal. 1,2,5,6 are tied together but don't attach to anything else. 9 and 15 are tied together and do attach to anything else. 10 is the output signal.

BTW this is a commonly used transformer and works quite well for its cost (many can cost up to $1000 each). The choice on connections is up to the user based on the cartridge. Most use the 16 to 1 ratio, but it can do 8 to 1 and 32 to 1. See the data sheet for the pin connections. For normal use ...use only A,C or E. The others are not recommended by the manufacturer even though they would seem to work. I suspect frequency response problems with them.

Make sure the transformers are well away from power transformers and chokes. They will pick up hum easily. I like to put mine in external steel enclosures connected to the preamp and cartridge with RCA cables with a chassis ground connection. Separate the left and right channels including the signal and case/core grounds and attach the external ground wire to the steel chassis. A wire from the turntable to the transformer enclosure then another from the enclosure to the actual preamp chassis. If you build them inside the preamp, allow that you might have to shift the power transformer around (tilt, angle, location) so that it won't induce hum into the step up transformers. You could also move them around ,or both.

Grounding and bonding is not a simple task. It looks that way, but done incorrectly it can ruin a good project.

Good listening
Bruce

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PostPosted: 17 May 2020, 13:13 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thank you. I will do it


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PostPosted: 22 May 2020, 09:02 
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Joined: 27 May 2013, 02:51
Posts: 34
Location: Sheffield, UK
Hi,

I finished wiring up the new PSU with a toroidal transformer. (this one: https://sklep.toroidy.pl/en_US/p/TSTA-0 ... -tubes/636 ).

I used the 13V windings for the heaters and that seems to be regulating well with the LT1085. The transformer puts out 14.6AC and after rectifying that is at 18DC. I put a 500R pot and 820R resistor on the adjust pin of the LT1085 and have tuned it to12.7V. It runs at about 40C.

For the plate current, there is 220AC which rectifies to 260DC. The LR8K4 seem to handle that fine, again with pots on the adjust pin these run at about 40C with 220V output.

To raise the ground on the heaters, I changed the pair of resistors in the April schematic from 100R to 200R each as suggested by Bruce. The strange thing is that the ground have been lifted to 200V! I have the same divider resistors as in the schematic (220K to one of the LR8K4 outputs and 100K to the plate ground). I checked everything over several times and cannot find my mistake. Do you have any suggestions? Can I run it with the heater ground that high? Should I try lowering the 100K to 50K?

Thanks for any advice.



gofar99 wrote:
Hi, You should not need to change them except for the ones on the regulator and the 100 ohms I would change to 200 ohms. Depending on your transformer just rectifying a 12 volt winding may or may not provide enough headroom for the regulator to work. You may find a simple resistor in the 0-3 ohm range sufficient to make the voltage right. It will dissipate some power so it needs to be probably a 5 watt one or larger. You can calculate the rating when you know what value is needed. The big question is why change to 12 volts? the tubes run equally fine with 6.

Good listening
Bruce


henryyyy wrote:
Hi,
I'm upgrading the psu on a groovewatt I built a while ago with a toroidal transformer. I want to use 12.6v on the heaters and intend to adapt the circuit Bruce made in April of this year (pg69). My question is: Other than changing the adjust resistor on the regulator, do I need to change the 100R, 100K and 220K resistors that raise the ground voltage?
Thanks!
Henry


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PostPosted: 22 May 2020, 12:06 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, No, The H-C rating is 200, but my experience is that over time that goes down. 100-125 is about max IMO. So you need to find out why the 100K is not seeing the ground.

Good listening
Bruce

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PostPosted: 22 May 2020, 12:49 
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Joined: 27 May 2013, 02:51
Posts: 34
Location: Sheffield, UK
OK. It just doesn't make sense - it should be simple circuit. I'll desolder and reassemble. Thanks again!


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PostPosted: 23 May 2020, 11:44 
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Joined: 27 May 2013, 02:51
Posts: 34
Location: Sheffield, UK
Hi, it turns out that when I moved the heater wiring to 12.7v, I managed to connect the plate supply to pin 9 so that was lifting the heaters to 200V. I have corrected that and tried out the Groovewatt and it sounds great. I'm really pleased with the Toroidy transformer and would recommend them to anyone in Europe. Thanks again!


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