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KT120 Oddblocks
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3089
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Author:  gofar99 [ 05 Jun 2017, 09:30 ]
Post subject:  Re: KT120 Oddblocks

Hi, Actually yes. They were very similar to the Audyn True Copper Caps. I preferred the Audyns though. Just an ever so slight "flavor" difference. Hard to quantify though. If pushed to say..I would say the Jupitors were just a little softer sounding. I could live with them.

Good listening
Bruce

Author:  ozapaydin [ 05 Jun 2017, 14:15 ]
Post subject:  Re: KT120 Oddblocks

Well, I do long listening sessions. Softer sounding may be better for my ears.

Author:  ozapaydin [ 05 Jun 2017, 14:24 ]
Post subject:  Re: KT120 Oddblocks

I also plan to make a passive preamp for kt120 oddblocks. What kind of case should I prefer? Metal or wooden?
If I use metal case, how should be the case shielding and grounding?
If I use wooden case, case will not protect from EMI? Does it introduce some noise into the signal?

Author:  gofar99 [ 05 Jun 2017, 16:23 ]
Post subject:  Re: KT120 Oddblocks

Hi, A passive can work OK with the amps, just remember that the input sensitivity is about 2 volts for full output and impedance is 100K. I always put controls in metal enclosures. What you can do is use a wood case with a metal one inside it. I do somthing like that for many projects, see the photo. I make a three sided partial case. This allows for the jacks on the back to be secure to a metal chassis and on the front looks like all wood. Use circular cutouts for front mounted controls. Basically they are recessed into the wood. With nice fluted knobs it works well.
EDIT: See the second photo as well
Good listening
Bruce
Attachment:
IMG_1500b.jpg
Attachment:
Forewatt w case 2 cropb.jpg

Author:  Geek [ 05 Jun 2017, 16:38 ]
Post subject:  Re: KT120 Oddblocks

ozapaydin wrote:
I also plan to make a passive preamp for kt120 oddblocks. What kind of case should I prefer? Metal or wooden?
If I use metal case, how should be the case shielding and grounding?
If I use wooden case, case will not protect from EMI? Does it introduce some noise into the signal?


Here's a passive pre circuit for lowest noise and no ground loops...

Bruce, got another? :idea:

Author:  gofar99 [ 05 Jun 2017, 21:44 ]
Post subject:  Re: KT120 Oddblocks

Hi, I would personally use 120-150R and 0.1uf. The other values will probably work just fine though. It is possible that depending on the output cable length that a resistor ought to be in series with the pot wiper and center conductor. Something like 2K. It can help mitigate cable capacitive effects. For passive controls though I like to use something like the digital relay switched V-02. It does require 12 VAC, but is a slick device. Not cheap though at about $125. In any case use a good pot (or stepped volume control). I have had good results with ALPs blue pots. For the actual value for the control I go for a value that is above the output impedance of the main source but less than the amps input impedance. I find values of about 10-50K work well. You want to avoid loading down the source, but still be well below the input of the next stage. Usually you would like to see about a 1 to 10 ratio there. With a passive control this may not be possible.

Good listening
Bruce

Author:  ozapaydin [ 06 Jun 2017, 01:52 ]
Post subject:  Re: KT120 Oddblocks

While looking for a passive preamp, I encountered "lightspeed attenuator". It looks like an interesting idea on the paper. But, I don't know how it performs in real life. Anybody tried it before? Any impedance match problem with KT120 Oddblocks?

Author:  gofar99 [ 06 Jun 2017, 09:57 ]
Post subject:  Re: KT120 Oddblocks

Hi, Light speed controls have been around for some time. In theory they have advantages, in practice it doesn't always work that way IMO. Essentially they use a LED and photo resistive device to to control the volume. Fine. The problems occur usually in how you illuminate the light source. Any ripple or noise on the control voltage is going to affect the photo resistor. It is difficult to get a source that has no such issues. The the control voltage itself needs a means of control. This can be any number of things but when you think about ...why not use that to control the volume and skip the extra stuff in the optical section. Better yet, skip both and use a stepped control or quality pot. Zilch noise and no power needed. This is one of those cases where I think advanced technology is not better than older simple stuff.

Another option is to use a "digi-pot". Basically an IC with a built in resistor ladder network. They do tend to be low noise and are quite precise. My issue with them is that most have input voltage limits around 2 volts. This means that any source that may go over that value will actually have to be reduced before it gets to the input. I just hate to throw away good signal to noise to accomodate a component's limitations. It really gets ugly if you exceed its limits.

Good listening
Bruce

Author:  ozapaydin [ 06 Jun 2017, 13:31 ]
Post subject:  Re: KT120 Oddblocks

Bruce,
Have you tried a lightspeed with Oddblocks? What do you think about these two together? A happy marriage, maybe a quick split? What do you think really?

IMO, the idea is bright and the circuit doesn't require much investment. It deserves a try.

Author:  gofar99 [ 06 Jun 2017, 14:20 ]
Post subject:  Re: KT120 Oddblocks

Hi, only at an audio show. I was not impressed. Didn't seem any better than a good pot.

Good listening
Bruce

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