Klark Teknik KT-2A

[AUDIO FREQ]

Maybe one of the pots on the bottom of the picture

 

[mattenylander]

Did you find if those were it?

I haven’t actually had the time to test it yet, hopefully I can give it a try this weekend. I reached out to Klark teknik but they couldn’t provide me with a schematic or which capacitors was wich.

Do you happen to have a picture of the PCB underneath as well?
Would be interesting to see if it’s possible to follow the trails.

 

[DanKoVO]

The red one at the bottom (22nf) and the two yellow ones above it (100 nf) are directly in the signal path. The two yellow ones next to your thumb are in the sidechain, no point in changing these IMO.

Is this what you ended up using for your mods? Mouser Cart

 

[Tubetec]

If the KT2A is anything like the the EQPKT , theres a ton of out of band garbage between 50-100khz from the SMPS , I use 192khz sample rate with REW to look at the output ,
I'm doing a linear off board psu for mine ,

 

[living sounds]

Is this what you ended up using for your mods? Mouser Cart

I used what I had around, mostly Solen Fast, but I think in one of them I used a WIMA cap or two.

 

[living sounds]

If the KT2A is anything like the the EQPKT , theres a ton of out of band garbage between 50-100khz from the SMPS , I use 192khz sample rate with REW to look at the output ,
I'm doing a linear off board psu for mine ,

I did look at it with the scope and found some but not so much out of band SMPS garbage. Still have the linear PSU on the to do list, but without a schematic of the KT2A it's not so much fun with these high voltages...

 

[Tubetec]

Ive been able to look a bit closer at the ht regulator circuit used in the EQP,
both 12ax7 and 12au7 HT rails are derived are after it ,

There doesnt seem to be any regulators on the KT-2 main board so most likely there on the PSU pcb ,
you should be able to check the supply voltages at the 5 pin molex in the middle of the board then you can estimate the total currents .

 

[living sounds]

Ive been able to look a bit closer at the ht regulator circuit used in the EQP,
both 12ax7 and 12au7 HT rails are derived are after it ,

There doesnt seem to be any regulators on the KT-2 main board so most likely there on the PSU pcb ,
you should be able to check the supply voltages at the 5 pin molex in the middle of the board then you can estimate the total currents .

Yes, I'm pretty sure that the main HT voltage goes through an RC filter on the PSU PCB and then to the audio PCB. But there are other voltages. I already got zapped once poking around at that board.

 

[Tubetec]

I always add extra insulation to the + multimeter probe tip , so as to reduce the possibility of an inadvertant short while probing around ,
It also good practice to crock clip the - lead to ground ,
now your probing single handed , again in the case of inadvertant contact with high voltage , you minimise the chance of current flowing across the chest .

be safe ,dont be sorry .

 

[shabtek]

xfmr is designed AND engineered in UK...sowter winding plan? but where is it made?


I know it is just a label stuck to the tin for those who care...

Mastering lab mod if you know what's up

 

[Tubetec]

Its probably been a very long time since anything Midas had transformers in it , thats not to say they dont have the in house knowledge to design one themselves and have it produced in China .

The screening can on the EQP input transformer is very thin , less than 1mm , Im not sure how to determine if its mumetal or not . The input circuit also has a 2x 10k:1k attenuation network pre transformer so as what ever you drive it with doesnt see too low a load .
Maybe that upsets the EQ circuit drive .

 

[DanKoVO]

I just finished up the mod using the parts from my Mouser cart. Sounds great! For a few bucks it was worth it to me. Especially after investing in a Kenetek and old RCA's.

This took about 1 hour from start to finish for anyone interested. For someone without ADD it may go quicker! The trickiest part was solder-sucking after removing the original components. Had to be careful not to burn the board and went slow and steady using braided copper along with a sucker.

 

[living sounds]

I just finished up the mod using the parts from my Mouser cart. Sounds great! For a few bucks it was worth it to me. Especially after investing in a Kenetek and old RCA's.

This took about 1 hour from start to finish for anyone interested. For someone without ADD it may go quicker! The trickiest part was solder-sucking after removing the original components. Had to be careful not to burn the board and went slow and steady using braided copper along with a sucker.

It looks like you kept the big yellow 10uf cap before the output trafo. I thought that was one of the worst offenders.

 

[DanKoVO]

It's the Nichicon replacement from my mouser cart. I swapped one big yellow one for another!

I did run into a problem while recording tonight. All was fine then an hour in the sound got distorted and it stopped compressing. Still passing audio, gain works, no compression. Will need to troubleshoot that since the opto cell is new, and I wouldn't think the mods could cause that specific issue.

 

[living sounds]

Ive been able to look a bit closer at the ht regulator circuit used in the EQP,
both 12ax7 and 12au7 HT rails are derived are after it ,

There doesnt seem to be any regulators on the KT-2 main board so most likely there on the PSU pcb ,
you should be able to check the supply voltages at the 5 pin molex in the middle of the board then you can estimate the total currents .

Here's an inexpensive high voltage PSU and trafo, I wonder if these would be of use to pimp the KT2A. Mosfet filters on the PSU and 40mA output. 280V DC derrived from 265V AC, should be close enough to the nominal 275V DC:

https://fyfaudio.com/products/diy-t...-dc200v-dc200v-dc280v-dc280v?VariantsId=11281

https://fyfaudio.com/products/50w-t...-for-m7-tube-mm-phono-amplifier-265v-63v-126v

 

[rock soderstrom]

I just bought a used KT-2A, at that price I couldn't say no. I want to experiment with it and build my own T4 cells, just for fun.

Anyway, has anyone tried an ECC99 instead of the 12BH7? The ECC99 needs 100mA more current per triode system, does the KT-2A PSU get very warm when running? Otherwise the tubes are pin-compatible, the ECC99 is slightly more current-potent and also has slightly more gain.

I'm just curious and will try it out (I am still waiting for the parcel), as I have some ECC99s and have had very good experiences with them elsewhere, including as a replacement for 12BH7s. The ECC99 is also not unattractive in pricing.

Edit: Probably a brain fart, the ECC99 ist taller than the 12BH7, i guess this will not work in a 2HU box. This is probably only possible if you turn the KT-2A into a convertible and operate it without the top.

 

[beatnik]

12BH7-A from JJ is shorter than standard 12BH7.

 

[rock soderstrom]

12BH7-A from JJ is shorter than standard 12BH7.

Okay, I also remembered the usual 12BH7 being taller. The JJ seems to be more the size of a 12AU7.

 

[JohnX]

I’m preparing to do some of the suggested mods to my 2A-KT.
1 - Replace Opto attenuator - Kenetec T4B on the way. Arrives Saturday.
2 - Replace 1 12AX7 at V2 (farthest left): I have a JJ E83CC to try for now.
3 - Replace EL84: also have a JJEL84
4 - Replace 12BH7: have a NOS Sylvania we bought for a guitar amp but never used.

I may swap out these tubes for some older NOS at some point, but I think these should still be an upgrade.

Those all seem fairly simple, but I’ve got a few questions about this:
5 - Replace what is traditionally described in this thread as the “big yellow capacitor” C8? (thread #28, 55, 59, 117) I have circled what I am assuming to be the correct one in one of the photos. It is labeled on top 104J400 - the only reason I’m not sure whether the one I have circled is correct is because the value that I read in this thread to replace it with appears to be slightly different: 10uf/250v (thread #95)
Have I circled the correct capacitor to replace?
Should I replace with higher quality 10uf/250v OR did I miss the correct value in this thread?


Before I can remove and replace that capacitor, I will have to remove the PCB. I have noticed that there is a yellowish adhesive on a few of the connectors that are attached to the PCB. I have attached some screenshots. Is there any special handling that I should be utilizing when “breaking that seal”?

​

 

[Script]

That stuff is some kind of hot glue. If it doesn't come loose easily with a chopstick or screwdriver, could always pre-heat it a bit with a hot gun.

As for capacitor value, is the one in question sitting in the audio path? If so, it's likely to be about frequency response.