Klark Teknik KT-2A

[kingkorg]

So after swapping the opto cell for the kenetek and the tubes for NOS RCA, I noticed differences in the sound but nothing that truly blew me away. I could take it or leave it. But today I swapped the electrolytics for good Nichicon PM and the yellow films for wima.

WOW.

First I sat and listened to old studio takes through it. Then I just started listening to old mono jazz recordings through it. Everything is better.

At first I was amazed that it seemed to now sound exactly the same coming in as it did coming out. Then suddenly I released how fat and hefty the bass was on it post. Then I started getting ASMR. I am not kidding. I've never worked with an LA2A, but if it sounds even better than this then I am speechless.

Get rid of Jamicon's in the signal path! Those yellow polys are probably not great either.

Ryan

Which Jamicon electrolytic capacitors in the signal path are you talking about?

Have you measured frequency response and THD of the unit after replacing the parts?

Do you have before and after audio samples to share? Some technical info? You didn't go just by ear here, right? 

Did you check/re adjust bias after changing the tube?

Did you measure the noise spec of the new tube?

Can you measure attenuation curves of the stock and new opto cell and post them?

I have never in my life measured or heard (null phase test included) any difference in audio signal after changing electrolytic capacitor unless something was broken or very old. Did you measure the old electrolytic after removing it?

What makes you believe stock poly capacitor might be sounding bad?

 

[FarisElek]

I didn't measure all those things. I did run and record the same vocal, bass, and drum takes through the unit before and after and observed an eq analyzer and listened.  Before and after I ran 1k through it and measured the voltage to make sure db was the same. I didn't think to save the audiophiles, I was doing it for me.

I did not re-bias the tubes. They're the same tube type. I kept the original EL84, I believe that is the only tube that would need to be biased. I may be wrong.

For all I know the poly's are good caps. They're yellow ones of which I've never seen before, but I already had that value of WIMA's lying around. The Jamicon's are  pretty terrible in my experience and I was surprised to see them in there as I've only seen them in 80's and 90's toy keyboards. Doesn't mean that these particular Jamicon's are necessarily bad, considering I don't have experience with modern ones. These may have been selected for low impedance. Who knows?

All I have to say is based on my limited testing,  It thickened my audio signal. Maybe it was just my unit, but what was coming in was coming out noticeably thinner in the low end, even after the tube change. I'm happy with it now.

I changed out the yellow poly's as I already had those value caps (0.1uf and 0.01uf). I also changed out all the electrolytics in the signal path on main board with the tubes.  It was really easy and cost me no more than $10.

I'm going to change out the big 10uf film cap and see if I notice any change. This time I'll level match and record some audio. If it seems to me worthwhile I'll post about it.

 

[FarisElek]

Also, the classic kenetek has a slightly more natural attack and release it seems. But, I'm not exactly sure If it's worth it. Especially since the VU meter doesn't respond properly after the upgrade. The compression curve is different so I get -10db at -10db, but -4db at -5db. It's not really the end of the wotld.

I personally noticed the biggest change with the caps. This is my experience, you may or may not agree.

 

[kingkorg]

Well the reason I asked is because as far as i can tell, there aren't any electrolytics in the signal path.

I have measured my unit and it measures perfectly flat down to subsonic frequencies and even below.

So if you hear "better" low end response it could be that you either lowered high end response, or boosted low end. Or that you had a faulty unit to start with. However i am glad your unit sounds better now.

No two tubes are the same no matter the type, so i re bias them always. For example Universal Audio strongly suggests re-biasing tubes after replacing tubes in their units, you can check UA LA-610 manual for example.

In my experience almost every time someone talks about particular sonic imprint of certain unit there is a fault, or low end bump, high end cut, distinct THD character. This can be achieved with an EQ, or by tweaking of the circuit. None of which cost more than few bucks. But yes, it can be done by spending a lot more money not knowing what you've done at the end.

 

[emrr]

No two tubes are the same no matter the type, so i re bias them always. For example Universal Audio strongly suggests re-biasing tubes after replacing tubes in their units, you can check UA LA-610 manual for example

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You replace cathode resistors in cathode biased amps?    That's what you imply with the circuit in question. 

 

[kingkorg]

Yes, i actually do. Occasionally plate resistor as well.  It certainly makes more difference than swapping capacitors. At least measurable difference. 

 

[[email protected]]

So after swapping the opto cell for the kenetek and the tubes for NOS RCA, I noticed differences in the sound but nothing that truly blew me away. I could take it or leave it. But today I swapped the electrolytics for good Nichicon PM and the yellow films for wima.

WOW.

First I sat and listened to old studio takes through it. Then I just started listening to old mono jazz recordings through it. Everything is better.

At first I was amazed that it seemed to now sound exactly the same coming in as it did coming out. Then suddenly I released how fat and hefty the bass was on it post. Then I started getting ASMR. I am not kidding. I've never worked with an LA2A, but if it sounds even better than this then I am speechless.

Get rid of Jamicon's in the signal path! Those yellow polys are probably not great either.

Ryan

Hello,
I'm New on this post.
I got a KT2a and love it so much but i try to mod it as i Can. I've bought a New opto (Kenetek) that i'm waiting for.
I'm looking for global scheme cause i want to swapp capacitors for WIMA.
Do you know where i Can get this ?
Thanks for your answers.

 

[FarisElek]

There isn't a public schematic for this unit. Klark Teknik has it on lock down. You can refer to the original LA2A schematic on some of the circuit, but the labels of the semiconductors wont correspond with the Klark Teknik circuit, so you kind of have to follow the circuit to see what is what. If I were you, I'd worry more about the opto and the big cheap yellow output cap off the output transformer. I noticed some improvement in the low end from changing out the electrolyrics for high quality nichicon ones, but as mentioned by KingKorg, it may have been that one of my components was slacking, and may not have been necessary for all the caps.

You'll have to recalibrate your unit after installing the new opto and you won't be able to get the GR meter to match perfectly without changing out a resistor. I'm just living with it and keeping aware that I'm getting about 1db less GR than it says.

 

[[email protected]]

There isn't a public schematic for this unit. Klark Teknik has it on lock down. You can refer to the original LA2A schematic on some of the circuit, but the labels of the semiconductors wont correspond with the Klark Teknik circuit, so you kind of have to follow the circuit to see what is what. If I were you, I'd worry more about the opto and the big cheap yellow output cap off the output transformer. I noticed some improvement in the low end from changing out the electrolyrics for high quality nichicon ones, but as mentioned by KingKorg, it may have been that one of my components was slacking, and may not have been necessary for all the caps.

You'll have to recalibrate your unit after installing the new opto and you won't be able to get the GR meter to match perfectly without changing out a resistor. I'm just living with it and keeping aware that I'm getting about 1db less GR than it says.

Hi,
Thanks for your answer.
Ok, i keep on my mind what you said.
I'll change the Big yellow cap. Can you give me, please,the reference of cap you changed ?
For the Vumeter, i don't really Care cause i use my ears ans juste look to Vumeter for the attack of KT2a.

 

[FarisElek]

If you open the box, it's the big yellow cap on the upper left if you're looking down at the unit. It's mounted on the vertical PCB. It's very obviously the biggest capacitor in there. They used a 10uf 250v, I swapped it with a Sollen 10uf 400v. It was a tad big so I mounted it on the opposite side. It's not a polar cap. Careful not to destroy any traces when removing the old cap. Remove it carefully as with any mod.

 

[[email protected]]

Hi,
Thanks for your answer.
Ok, i keep on my mind what you said.
I'll change the Big yellow cap. Can you give me, please,the reference of cap you changed ?
For the Vumeter, i don't really Care cause i use my ears ans juste look to Vumeter for the attack of KT2a.

Are you speaking of that ?
https://rmmedia.ru/threads/134485/page-2#post-2344408

 

[FarisElek]

That link just takes me to a page. But it's the biggest yellow thing in the entire unit.  Clearly pictured in the bottom right of this picture from that site you sent.

https://rmmedia.ru/attachments/158169/

 

[[email protected]]

That link just takes me to a page. But it's the biggest yellow thing in the entire unit.  Clearly pictured in the bottom right of this picture from that site you sent.

https://rmmedia.ru/attachments/158169/

Ok, i saw. Thanks for the reference, i'll buy a Sollen cap.
I'll let you know when i'll swapp the yellow cap and the difference in sound.
I've got a EQP from KT. I want to mod it. I've swapped the Bugera walve for Mullard. The sound is better, warmer and detailled (to my ears). But the Low end is still a little bit muddy. I would like change that.
Do you know this Gear ?

 

[FarisElek]

I'm not familiar with the Klark Teknik Pultec clone. I'd reference it to a pultec schematic. It's honestly probably the transformers or the circuit itself. In that case it's not really worth upgrading further as it becomes too costly. Might as well build one.

Ryan

 

[[email protected]]

I'm not familiar with the Klark Teknik Pultec clone. I'd reference it to a pultec schematic. It's honestly probably the transformers or the circuit itself. In that case it's not really worth upgrading further as it becomes too costly. Might as well build one.

Ryan

Thank's Ryan, it's valuable advice.
So swapping the 2 or 3 films caps for WIMA won't change the sound  (for EQP ) ?
I've purchased a Solen 10uF 250V yesterday and i'm waiting for it.
I'll tell you my feelings about change

 

[FarisElek]

Thank's Ryan, it's valuable advice.
So swapping the 2 or 3 films caps for WIMA won't change the sound  (for EQP ) ?
I've purchased a Solen 10uF 250V yesterday and i'm waiting for it.
I'll tell you my feelings about change

I truly wouldn't know.  It would be best to ask on a pultec clone board which caps people think influence the sound of the low end the most and then find which caps they're talking about that correspond to your clone. For the most case the Klark Tekniks follow the same signal path and you can usually find your way around if you try hard enough. Low-end issues can be PSU related, transformer related, poor components related. Could be anything.

 

[living sounds]

I've got 2 of the KT Pultec clones, too. Changing the tubes made an even bigger difference than it made for the compressor.

 

[[email protected]]

I come back to you to keep you informed of the modifications carried out on the KT2a.  I changed the two 12Ax7 Bugera which I replaced by 2 GE 5751 for a transparent sound.  I also changed the opto for a Kenetek T4B.  so far, the added value in terms of sound is obvious.  more precise, less hazy sound and more precise compression.  then on the advice of Farek, I changed the Big yellow cap n'y a Solen 10uF 250V and there, I am super surprised.  I find that the sound is really more precise.  This is my feeling.  on the other hand, the difference compared to before, is that I can turn the reduction gain knob fully without saturating the sound.  previously, when I "pushed" the gain reduction, the sound saturated whatever the level of output gain.  Next step, I change all JAMICON components.

 

[[email protected]]

I specify that I cleaned the flux a lot on the pcb with a special cleaner.  Obviously, I did not expect clean welds on standard equipment such as the KT2a but at this point !!!

 

[[email protected]]

sorry, this is not the gain reduction potentiometer but that of the peak reduction.  Now I can fully compress the sound without saturation !!!