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 Post subject: Re: KT120 Oddblocks
PostPosted: 16 Dec 2018, 09:33 
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Joined: 04 Jun 2008, 20:59
Posts: 3954
Location: Arizona, USA
Hi, If I had a dollar for every time someone said it would not work, or would sound horrible or would have lots of distortion or non-linear response....I would be very wealthy. It is simple in appearance, but a carefully executed design. Yes there are some negatives....mostly that it is only possible in class A operation. Efficiency is typical of that and a consequence is that the output transformers must handle a lot of dc current. They need "wattage" ratings of about twice what is expected. I love tubes but a little "sand" in the right places makes for a great amp.

This all doesn't denigrate other designs, just I believe you will find few if any simpler to build high performance amps.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 10:04 
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Joined: 07 Mar 2017, 03:14
Posts: 102
In the oddblocks, I used Claritycap CSA (0.33 uF 630VDC) on the signal path. I can say they sound very neutral, never fatiguing (but not dull either) and are also fast caps. All of the frequency spectrum is very good top to bottom. I believe they matched good with oddblocks. Their capacitance values are also in strict limits. Good quality caps for a very low price.

Well I was thinking just using them in the prototype. But now, I'm in doubt if I should ever change them. Because, I don't know what I can get else on the board with much higher priced caps.

What caps (signal path) did you use in your oddblocks? What are your results with them?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 10:10 
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Joined: 29 Mar 2013, 20:37
Posts: 149
Location: Italy
I always use Russian PIOs when I find them. They sound the best to my tastes


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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 10:35 
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Can you elaborate?

TIJ-NIKI wrote:
I always use Russian PIOs when I find them. They sound the best to my tastes


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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 10:43 
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Joined: 22 Feb 2017, 07:55
Posts: 21
gofar99 wrote:
If I had a dollar for every time someone said it would not work, or would sound horrible or would have lots of distortion or non-linear response....I would be very wealthy


This is one area that I have a particular distaste for. It’s one thing for people with experience to offer their opinion about a design choice, however, the ones who have little or no design experience seem to be the ones who offer the strongest opinions about a design. These people are usually the ones who “read or heard...”.

I applaud Bruce for his design even though I have not built it or heard it.

I built a 2A3 amp and committed almost every “audio sin” and it turned out great (and sounds great too).

Audio Sins to be avoided:
1. Using Hammond output transformers.
2. Using an LM317 anywhere in the design. (In my case I used a 317 for a filament regulator and then committed a double sin by using another 317 for a constant current source)
3. Using a parallel 6SL7 for an input tube.

I imagine hyperbole and hearsay will always be apart of any Internet forum.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 11:20 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, There is always room for disagreement. I find the LM317HV to be quite excellent in the CCS. Lots of others agree. I believe they get a bad rap because of an article I saw about 5 years ago. It said something like they have noise....sure at about -100db. All devices do. They are quite linear in they way I used them and do not cause distortion in the amps. (distortion is under 1% at half power) I recommend that any folks that are critical of the use should build one of the amps. :smoking:

On a different answer..... I use Audyn TrueCopper Caps in mine. The PIOs are nice and neutral and are supplied in the kit amps.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 12:25 
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What attracts you to Audyn TrueCopper? Some say they sound a little thick.
What difference do you hear between a normal polyprop. cap like CSA and a copper foil cap like TrueCopper?

gofar99 wrote:
On a different answer..... I use Audyn TrueCopper Caps in mine. The PIOs are nice and neutral and are supplied in the kit amps.

Good listening
Bruce


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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Dec 2018, 13:04 
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Joined: 07 Mar 2017, 03:14
Posts: 102
On preamplifier grounding:
I'm working on a passive preamplifier. Well I read your following article.

http://diyaudioprojects.com/Technical/G ... Shielding/

You write that
"the input jacks I have found that you can connect the two input signal ground returns together (not to the chassis) using isolated jacks provided you don't run shielded cable with both ends connected together internally to the unit."

What do you do with output jack (RCA) ground returns?

Where do you connect other signal ground returns (internal)? On the bus between two input jack ground returns?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 21 Dec 2018, 11:04 
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Joined: 24 Oct 2010, 07:05
Posts: 286
ozapaydin wrote:
What do you do with output jack (RCA) ground returns?
Where do you connect other signal ground returns (internal)? On the bus between two input jack ground returns?

Quote:
Also at the input jack ground I attach a single wire from the active circuitry ground also with a low impedance wire.
...
An exception is in power output stages. The large amount of current involved can cause noise in the signal ground so I ground them separately to the input jack ground. Could you run separate ground wires from each place in the active circuitry that puts current into the ground path? Certainly, and it would be a type of "star" ground system. I find generally it unnecessary.

Bruce uses a silver (low impedance) wire so it is not important where do you connect other circuits precisely. You can connect them to "a bus" or to a central pin of any RCA input jack.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 22 Dec 2018, 20:10 
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Joined: 04 Jun 2008, 20:59
Posts: 3954
Location: Arizona, USA
True, in the power amps the exact grounding scheme I like is not mandatory. That said though, if you do it poorly the amps are not likely to be as stable and quiet. Grounding and shielding are IMO some of the most important things in any project. They are the source of the majority of problems that folks report.

Good listening
Bruce

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