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    Building, troubleshooting and testing of these amplifiers should only be
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Kondo KSL-M77 phono preamp clone project

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#242
Rodango said:
Does anyone have a good supply of reasonably priced 12AY7/6072A tubes? I'd sure like to pick up a minimum of four and get that many reject 12AU7's out of my KSL. But the prices of them these days!

However I did go and buy an ALPS volume pot after discovering my current one wasn't doing it for me. It'll be a little while as it makes its way out of Germany.

But I do wonder about the 12AY7s. My Amperex and Mullard12AU7's sound perfectly fine to me..... will the 12AY7s sound..... better?
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I have a quartet available. Two pairs of JAN GE 6072A. Please, feel free to pm me if your are still in search for NOS 6072A tubes. 🙂
 
#243
limono said:
What current is flowing through the linestage parallel 12ay7 tubes ? I just wonder if 2W (2 x 1W parallel) are needed or 1W will be enough.
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In the original, it is 1mA in both tubes (0.5mA per tube), so the resistor sees around 140mW. Reducing the resistor to 28k as I have done in my linestage increases the total current to 4mA and power dissipation is 820mW, no problem for two 2W resistors in my case.
 
#245
Why would the original version not have the current through each of the parallel triodes at 1mA?

The presumed benefit of parallel triodes is lower output impedance but gm drops off with lower current and the benefit maybe lost.

I wonder if the whole thing about parallel triodes is also to allow the heater elevation voltages to be different between the plate and cathode followers without sharing bottles between stages or channels.

Has anybody done a listening test to compare single vs doubled-up triodes ?
 
#247
hesener said:
Some folks like the sound of the original M77 as "organic" and "soft", others think it lacks punch and is too laid-back. Whatever floats your boat 😀

In any case, after a lot of consideration, I performed an act of blasphemy and modified the original linestage, hoping Kondo-san will never find out where I live! The mod's intention is to give the linestage a little more authority and power, and it goes like this:

1. Change the plate resistor of the first tube to 56k (I used Mills WW resistors), leave the second resistor space open
2. Change the cathode resistor of the first tube to 2x 2k2
3. Change the cathode resistor of the cathode follower to 2x 56k

As shown in the photo, you will need 6x 56k/3...5W and 4x 2k2 /1W. (I usually oversize resistors in these cases to have a little more reliability). This will increase the standing current in both the gain stage and CF, lowering the output impedance and also shifting the operating point just a touch further out.

Listened to it a couple hours, and the result is subtle but there. The line stage sounds a little more "grown up", the midrange shine is still there but it is all a little less compact, more space and extension both in bass as in treble. I like it, but then I like everything I build 😀

Let me know what you think.....
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Can you help me with cap is good for M77 ? I use 6X 0,22uf MIFLEX for my preamp !
 
#248
You may want to increase the output cap of the line stage to 1uF (depends on your power amplifier....), and using good caps definitely helps. I used Jansen Silver Caps. Checked out MIFLEX and the website did not tell much about them, what kind of capacitors are they?
 
#249
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hesener said:
You may want to increase the output cap of the line stage to 1uF (depends on your power amplifier....), and using good caps definitely helps. I used Jansen Silver Caps. Checked out MIFLEX and the website did not tell much about them, what kind of capacitors are they?
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Hi

I use MIFLEX Copper Foil Paper / Polypropylene in Oil Cap ! My amp is Jadis JA30 monoblok with KT-88 +lundahl output transformer ! I have have normal bass now ! All tube on my Kondo is 12AY7 JJ matchat. With tube recomed you ?

Many thanks
hesener said:
You may want to increase the output cap of the line stage to 1uF (depends on your power amplifier....), and using good caps definitely helps. I used Jansen Silver Caps. Checked out MIFLEX and the website did not tell much about them, what kind of capacitors are they?
Click to expand...
 
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#251
hesener said:
Thanks for the pictures, very nice! In my build I use the same (JJ matched) with good results.
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hesener said:
I have questions about power supply ! Use you 0.1uf on power supply ? I have 0.1uf how i must use they on my M77 ? Must i use one 0.1uf cap for each 100uf cap ? See photo please
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#252
In my build, I added 0.1uF in parallel to the electrolytic caps, and I think it was helpful but I did not check the sound before / after. So , frankly speaking , I cannot tell you if that makes a huge difference. Probably good when your power grid is noisy.
 
#259
Not an expert on tubes. I use JJ and they sound good to me. In terms of "tuning", please consider fixing the RIAA network and operate the linestage at some higher current, those two really improved the sound to my ears.... (and these fixes are described in this thread)
 
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