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PostPosted: 13 May 2020, 12:30 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thanks Bruce. I see that 38 and 47k in parallel give 21.05 but I have 22k , is this ok?


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PostPosted: 13 May 2020, 14:34 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, That will do fine, just remember to change it if you ever change cartridges.

Good listening
Bruce

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PostPosted: 13 May 2020, 19:00 
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Joined: 14 Feb 2010, 13:13
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Location: Lisbon, Portugal
A small pcb with resistors combinations and dip switch would be nice :)


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PostPosted: 14 May 2020, 07:31 
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Joined: 27 May 2013, 02:51
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Location: Sheffield, UK
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: 14 May 2020, 21:26 
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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

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PostPosted: 16 May 2020, 13:33 
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Location: Athens-Greece
Hi, I recall again the issue of MC transformers, specifically the LL1678. I will use the 1:8 due to 300 ohms cartridge. I am still confused with transformers connection. There are two in lines , two out and one that seems to be connection to chassis. But in the diagram I see one line; should I connectthe second in and out to grounding line? Pls help me since I have not much experience and I do not want to damage the transformers.
Thank you


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PostPosted: 16 May 2020, 13:51 
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One channel output is on 9(+) - 10(-), the other one is on 16(+) - 15(-)

Inputs are 1(+) - 4(-), the other is 8(+) and 5(-)

Pins 13 and 14 are CAN and CORE grounds if needed @gofar99 have you tried this?

http://www.lundahl.se/wp-content/uploads/datasheets/1678.pdf

This is what I understand from this file.


Go for it! :)

Miguel


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PostPosted: 16 May 2020, 14:38 
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So one transformer is needed? i have 2!


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PostPosted: 16 May 2020, 14:45 
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Location: Lisbon, Portugal
dimitris1811 wrote:
So one transformer is needed? i have 2!


It depends of the ratio you need, because you can series the winding according to your needs, thus consuming one entire transformer for the channel.

I don´t know these, I just had some free time and searched for you.

I hope i´m right!


Cheers,

Miguel

P.S. - I just realized there is only one core, so you need one transformer per channel!


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PostPosted: 16 May 2020, 16:05 
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Hi, There are multiple sets of windings on each transformer. Yes you need one transformer for each channel. In the PDF file use either set up A or set up C. A is 1 to 8 ratio and C is 1 to 16. With A you get less "gain" but a wider range of possible loadings ( I posted that a little while ago). The max is nearly 400 ohms when feeding a typical 47K ohm phono input stage. With C you get more gain, but fewer choices for loading. Max is about 180 ohms. The reason for the different settings is that low output moving coil cartridges have outputs from about 0.1 millivolt to about 0.5 millivolts. The lower ones are also nearly always ones with very low impedances and require the most step up to match the typical phono preamp input. The ones with higher outputs tend to need less step up and usually have higher impedances. The cartridge impedance is an internal value of it that indicates the AC resistance of the coils in it. You can not measure this with a typical meter as it will only show the dc resistance. To fully understand how these as well as other transformers work you might google it. There are many sources that to varying degrees explain the operation. There is pretty good info on the K&K audio site. BTW, the transformers are fairly robust when used with cartridges and you are unlikely to harm one. You might wire it in a way that it won't work, but I really can't see how one could be damaged ....

Good listening
Bruce

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