kgst

[valve5425]

Very stylish, neat build! Like your graphics.

[ang728]

1 hour ago, sorenb said:

 

nice work!

[livewire]

Well done, simple but elegant casing. Is it ventilated on top?

 

[sorenb]

15 minutes ago, livewire said:

Well done, simple but elegant casing. Is it ventilated on top?

 

There are a top cover, just waiting for the rings to arrive in order to finish it.

[mypasswordis]

Since the grounded grid/Carbon is getting all the love these days and I'm too lazy to build one from scratch, I thought why not just make a little adapter board for my KGST. Just a rough draft I whipped up in 10 minutes, will need revision. One of those revisions is Kicad suddenly deciding it didn't want to orient the 3D model headers correctly and gave a totally wrong size for the disc caps.

Edited July 29, 2017 by mypasswordis

[mwl168]

Maybe Kicad knows something we don't? 

[mtaifa]

I'm nearly done solderering my KGST. PSU is done and stable at +362v/-364v. Will be testing it today for the first time

One question, on the pot I have, an Alpha 50k, first gang is 49k, second 48k, 3rd 47k and 4th 46k. Will this be an audible problem, or will the amp design handle this?

 

[JimL]

Shouldn't be a problem.

[Pars]

 

 

Late post/comment. Once again, really digging the casework. I hadn't asked in the carbon thread (IIRC), but how is the lettering done. It doesn't look like engraved/infilled?

 

 

Sent from my iPhone using Tapatalk

 

[sorenb]

1 hour ago, Pars said:

Late post/comment. Once again, really digging the casework. I hadn't asked in the carbon thread (IIRC), but how is the lettering done. It doesn't look like engraved/infilled?

Thanks.
Digital printing from ModuShop (Text and Graphics in 600dpi)

[mtaifa]

Connected everything, fired it up, nothing is buring
I'm not able to zero out the offset, though. Balance is good, but can't get lower than around 10V on the offset. Series resistor is 1.2k, voltages are +/-355.
By using the blance pot I can get the offset to zero, but then the balance is of course screwed.

Will I have to go lower on the 1.2k?

 

[jose]

1.1k ~1.3k would be fine 

[mtaifa]

Wired in a 10k in parallell (1070k), works fine now Thanks for the quick reply!

[mtaifa]

So, turnes out I need some more help. Build is complete, and right channel is working perfectly.

Left channel is partly dead. It's mostly silent except for one small part of the pot, about 3/4 way up and for 1mm turn approx. In this small area I get hum. Also sometimes got distorted sound in this area, but now only hum.

Voltages are all good. Swapped tubes between channels, no difference.
Tried disconnecting the input from the board, gets constant hum then.
Have also replaced the 1.2kohm's on both boards with 2x 2.2k.
On the working channel the balance and offset was quick and easy to adjust. On the left channel it was way harder, it jumped a lot when turning the pots only a little, and it also seems much more erratic, jumping several volts all the time. (-5 to +5 and everything in between).

Any tips for where to start looking, or what I can measure on the boards to find the culprit?

 

[spritzer]

First thing I'd check is a cold solder joint or something like that.  Then measure the pots and see what they are doing when you turn them. 

[mtaifa]

All solder joint checked and they seem ok. Pots are doing what they are meant to do it seems, it's the same measurements on  both boards.

Attached some pics, if you have a chance to look over quickly I would really appreciate it.

If there is a bad component, how should I go about finding it? some strategic places to measure voltages, or resistance to ground or something?

[mtaifa]

False alarm!

Reassembled and everything works. I did reflow some of the joints, but they were already fine. I found a tiny bit of metal debris in the chassis, under where the board was mounted, that was probably it. Must have fallen of the board when I took it out.

 

[Pars]

Some of the tube pins look a bit devoid of solder. Looks like some flux there as well, probably clean it good.


Sent from my iPhone using Tapatalk

[spritzer]

Good that it works and I'd add some solder to the tube pins (helps take the strain when inserting tubes) and clean off the flux. 

[mtaifa]

I'm nearly done, everything assembled in the case. Everything works perfectly

Learned a lot building this. Like the fact that connecting the HV and LV transformers in series doesn't really work that well. 
And that it is a good idea to disconnect the mains before using a knife to remove some shrink tubing from the IEC socket. I was leaning both my elbows on the chassis at the time, giving me a small shock resulting in me butting the blunt end of the knife into my forehead. Made me feel real smart and special. Luckily it was only one phase to ground, and the chassis is anodized and have a pretty high resistance. 

I'm proud of this project because I actually finished it. Told myself not to start using the amp before the casework and everything else was done, unlike all the halfway done projects laying around my room. (like a DAC with no top cover etc)

Some pics: https://imgur.com/a/wnFi9 (even though it might look like it, I'm not actually a professional metal worker. Also I'm missing a lot of the right tools for the job. I think it looks half decent, though)
The chassis and some of the neutriks are from an old never-finished amp, wanted to use the side heatsinks so I extended the legs of the 10M90's  a bit.
Ordered wrong small heatsink for the PSU, had to slightly mod a larger one to fit. Powerbutton is ebay stuff, orange LED.

SQ on this thing is awesome. (007MK1). At first I was a bit dissapointed, the soundstage was kind of small, all inside my head,  but then I remembered switching opamps on my soundcard (xonar essence STX) a while back. Switched back to good old Audio-Gd disceets and everything changed. Very happy now! Next investment will probably be a balanced Audio-Gd DAC, but for a while the STX will have to do. 

I'm also very impressed by the KGSSHV Mini PSU, very stable and very cool operation only getting slightly warm after some hours of use. 
I know nothing of electronic design, but would it be easy to build a small version of this with only LV for +12V and +5V for powering the soundcard? 

Thanks to every one that has contributed to this forum for all the info and help, and especially spritzer for answering my noob questions!

[mtaifa]

Another question, is it possible to adjust the gain? I have an old turntable with built in RIAA, and the volume at max is a little low. 

[kevin gilmore]

messing with the gain probably not a great idea, decrease the resistance of the tail resistors in the front end, or increase the value of the feedback resistors.

both will require readjustment of offset and gain

[MLA]

5 hours ago, mtaifa said:

Another question, is it possible to adjust the gain? I have an old turntable with built in RIAA, and the volume at max is a little low. 

So, you are someone who actually needs a preamp  

To continue your DIY journey, this would be the time to build the KG ubal/bal board (check the thread). Gain of 2 into balanced, but can be set to taste by changing a couple of resistors. 

[mtaifa]

19 hours ago, kevin gilmore said:

messing with the gain probably not a great idea, decrease the resistance of the tail resistors in the front end, or increase the value of the feedback resistors.

both will require readjustment of offset and gain

OK, thanks. I think I will leave the gain alone. 

 

 

15 hours ago, MLA said:

So, you are someone who actually needs a preamp  

To continue your DIY journey, this would be the time to build the KG ubal/bal board (check the thread). Gain of 2 into balanced, but can be set to taste by changing a couple of resistors. 

Thanks, that looks like a fun project, I'll look into it  
I'll research the RIAA board also, maybe I can just adjust the gain there

[JoaMat]

I had to open up the KGST for adjustment since I lowered the rail voltages. Four plain old good trimmers.

My right foot for size comparison.

 

Edited May 8, 2018 by JoaMat