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KG Balanced Dynahi build discussion thread


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Loving this out the balanced as its intended but because my chassis is very cramped the transformer is inducing a lot of hum. Tried removing the boards from the chassis away from the tranny and it was silent as balanced. Looking as how it is, I cannot fit a tranny can over it. Distance between tranny and the boards' reservoir caps are only a few mm apart.

I think my next project is to get another PSU board and chassis and house them separately. I guess the transformer is too OP at 160VA.

Gain with the gain resistors at 51k is just the sweet spot for me. Volume knob on my DAC pre out is about halfway for my listening volume. Can go very loud real easy with this gain setting. 

*edit:
Does anyone experience sibilance or slight roughness in the treble? I'm comparing it with my Matrix Mini-i headphone out and it sounds a little rougher in the treble region.

Edited by penmarker
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10 hours ago, penmarker said:

Loving this out the balanced as its intended but because my chassis is very cramped the transformer is inducing a lot of hum. Tried removing the boards from the chassis away from the tranny and it was silent as balanced. Looking as how it is, I cannot fit a tranny can over it. Distance between tranny and the boards' reservoir caps are only a few mm apart.

 

Can you get some grain oriented steel and wrap it around the transformer.  That's what I did with my 2 channel build in one box.  It reduced the hum to almost nothing

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Been up all night coming up with the proof of concept. Moved the transformer out into a wood tidbits box and hum disappeared completely. Monday I'll go look for a proper project box and connectors+cable for it. Very happy.

But my R channel THAT340 is also noisy like some of you. Started to develop around yesterday night. Kinda thinking about the converter boards now but the matched or buying a lot of LSJ/LSK for matching is so expensive. 

IMG_20180408_074901.jpg

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If you buy the duals in the linear devices, you can just go with what you get. The 2 devices in package are matched pretty well, and Kevin said that CCS will take care of the N-P differences you have. The ones I bought from trendsetter (LSK489/LSJ689) weren't too bad.

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Hey that is great, I guess I missed those devices.

One question, how accurate are these cheap DMMs with thermocouple type k? My Dynahi reads 55°C at the heatsink wall closest to the output devices (not the fins).

Manual says Its resolution is 1°C, and accuracy of 5% rdg + 4 dgt.

 

*Edit: added picture

IMG_20180408_085536.jpg

Edited by penmarker
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55C sounds about right (forgot what was my bias).  My Dynahi runs at about the same temp after 30 min (measured via an IR-based meter, a few degs off here and there is not a big deal).  Have you checked with Steve about where he got his tranny shieldings?  I run with Anteks and they seem to shield adequately.  Single-box saves quite a bit of space; if run two boxes, do consider umbilical resistance.     

Edited by Skooby
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Change the THAT340 for 2SK170/2SJ74. Yes, it's expensive but it's worth it and this amplifier deserves it

You have Linear on DIYAstore or you can search some member that have Toshibas.

I think that 55º is right. 

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i have been using for the input of my dynalo some 2sa1349/2cs3381,that i bought from Justin  at a very good price. Even with no matching,they are working very well

 

Yes, those would work nicely as well. Just be careful in that even though these share the same 7-pin package as the 2SJ109/2Sk389 Toshiba JFETs, they are not pin compatible. Therefore, a THAT340 adapter made for one will not work for the other.

 

2SA1349/2SC3381: BCE-ECB

2SJ109/2SK389: DGS-SGD

 

 

Sent from my iPhone using Tapatalk

 

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Thanks everyone. I decided to get a set of adapter boards from the group buy. I'll try to get my hands on all the various devices available, especially LSK489/LSJ689. Nelson Pass seem to love using 2SK170/2SJ74 in his designs so I hope those will be great too.

Minor update, yesterday during lunchtime I went to the electronics store and got some project box with the fittings and cables, etc. Rehoused my transformers for the amp and channel switcher in it. The wooden box is too soft, like balsa wood.

Still haven't drilled the front panel for the jacks and knobs. Busy moving to a new house now so will buy a bench drill after the dust settles.

IMG_20180411_050218.jpg IMG_20180411_033155.jpg

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  • 1 month later...

I prefer the FETs (170/74, 109/389 and 489/689), but it isn’t a night and day difference. The offset will be lower with them. For the 3 Dynalo minis that I built, 2 of them used 489/689 FETs and one used THAT340. I haven’t listened to them extensively, but didn’t notice huge differences. The FET boards were easier to bias and seem a bit more stable.


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Made some multi-coated front panel recently. This is a small project  @ang728  and I ran together. This is our first attempt to try multi-coated for the front panels. I don't know if this kind of finishing will start to peel off in longterm. We'll see. We are thinking making more interesting colors, too. Maybe "Hulk" green or something like that...

The blue one has tapered feet while the red one has real spiked feet. 

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