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 Post subject: Re: KT120 Oddblocks
PostPosted: 19 May 2018, 17:36 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, 1 watt is fine, really even a 1/2 watt is good enough. I prefer "flame proof" ones but a standard one is OK.


Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 21 May 2018, 02:43 
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Thanks.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 20 Jun 2018, 02:50 
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Hi Bruce,
If I don't remember wrong, you mentioned that you separately made ground connections of power output stages to central ground bus (preferably on the input jack). What are the grounds of output stages exactly?
KT-120 tube cathode grounds (on the outputs of LM317HVs )? B+ filter cap (10uF) ground? Output transformer secondary ground?

If you can show them on the KT120 schematic I'll appreciate it.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 21 Jun 2018, 16:18 
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Hi, I return all signal grounds to a "buss" at the input jacks. Essentially a large gauge wire between the ground lugs of all the inputs. (remember the chassis is not directly connected to this but goes to it via a type X2 capacitor and parallel resistor) I run separate ground wires from the LM317s to the buss. Other independent connections are from the the other circuityr stuff (power supply grounds and active circuit grounds). The idea is to make sure that large amounts of power are not flowing through the same conductor wires as signal grounds are. It is impossible to completely do this but the fewer sources of noise (power in the grounds) the better. When everything comes together at the inputs it seems to make for the lowest noise level and fewest chances for ground loops in the amps. A "star" ground at the input is essentially the same. I just find it more conveneient to use something like 12g copper wire to go between the things that need to ground there. A true "buss bar" would likely be even better.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 22 Jun 2018, 13:23 
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I'm planning to connect B+ filter cap (10 uF) ground to power supply ground bus. Any objection to it?

Where do you connect the output transformer secondary side ground? Directly to central ground bus (on the input jack)?

One more question. Is the connect position of power supply bus, signal ground bus and the other direct ground connections (LM317HVs, maybe opt ground) on the central ground bus important? I mean the sequence of them on the central ground bus.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 22 Jun 2018, 14:41 
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Hi, That is where it ought to go, same for the output transformer ground.

"One more question. Is the connect position of power supply bus, signal ground bus and the other direct ground connections (LM317HVs, maybe opt ground) on the central ground bus important? I mean the sequence of them on the central ground bus."

This is an excellent question. :thumbsup: Yes the sequence often does matter. All conductors have some resistance. Any time a current passes through a resistance a voltage is developed. If you have a high current source sharing a ground with a sensitive signal source it can introduce noise and sometimes hum. The complication is that both need to be at close to the some potential also to reduce noise. So the way they are arranged on a buss can alter the noise level. A really low resistance "buss" will often make the noise level from an incorrect arrangement very small and it might be insignificant. The way I like to sequence things on the buss is starting from the input signal grounds and shield ends of any shielded wires, to the small signal portions of the circuit, to the output ground (so the NFB if used has good access to the signal side) then the big signal stuff (like the cathode circuit of the output tubes) then finally the power supply ground. Remember that all this is typically in my builds on a 2-4 inch long #12 bare copper wire. The actual resistance between any point is realy quite low, but if you dump 200ma (like the cathodes) into it there will be some noise and that can end up being amplified by the voltage amplifier section. The arrangement is not as significant in low gain circuits, but can cause significant problems in high gain ones like phono preamps.

The grounding arrangement rears it angry head in a more subtle way too. I have seen folks string the ground of one part of the circuit, like the signal section to the power supply ground and then to the input jacks. Also folks using the shields of wires (inside gear, not outside between equipment) to carry the ground connection to various parts of the circuitry. This will nearly always introduce a significant amount of hum and noise.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 23 Jun 2018, 08:19 
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Which side of the central ground bus do you connect to the mains ground/chassis ground? Power supply ground bus side or signal ground bus side?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 23 Jun 2018, 16:37 
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Hi, I connect the AC mains ground to the chassis. The chassis is in turn attached to the signal ground at the buss via a type X2 capacitor and parallel resistor.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 24 Jun 2018, 02:00 
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Thank you, Bruce.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 25 Jun 2018, 10:20 
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Mr. Heran, Any thoughts on using GU50 tubes with your PP monoblocks?
Thanks


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