Technical Assistance/Advice Thread

[Pars]

I bought a cheapie from ebay for $50

https://www.ebay.com/itm/2-in-1-Soldering-Rework-Stations-SMD-Hot-Air-Iron-Gun-Desoldering-Welder-898D/192010034886?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

Seems OK, haven't tried the iron yet (probably sucks).

[spritzer]

I have one of those and the iron is terrible... 

[Craig Sawyers]

Iron the Terrible - wasn't he a medieval Tsar 

[Mr.Sneis]

Well it turns out I only needed to expand my skillset; touched up the chip by hand with a few passes of drag soldering technique and it is in business.  Learned to not be too loosey goosey with the wick removal as well, bent some pins when I made a false move which could have been a quick job but more like an extra hour.

Edited February 14, 2018 by Mr.Sneis

[spritzer]

4 hours ago, Craig Sawyers said:

Iron the Terrible - wasn't he a medieval Tsar 

Funny enough I just watched a short documentary on Ivan and hour ago... 

[mypasswordis]

7 hours ago, Mr.Sneis said:

Well it turns out I only needed to expand my skillset; touched up the chip by hand with a few passes of drag soldering technique and it is in business.  Learned to not be too loosey goosey with the wick removal as well, bent some pins when I made a false move which could have been a quick job but more like an extra hour.

If you can listen to the DAC now, got any impressions? Also, where did you source the replacement PMD200?

[wink]

16 hours ago, spritzer said:

I have one of those and the iron is terrible... 

 

10 hours ago, Craig Sawyers said:

Iron the Terrible - wasn't he a medieval Tsar 

If you use it to spike olives, you could call it Vlad the Impaler

Edited February 15, 2018 by wink

[Mr.Sneis]

14 hours ago, mypasswordis said:

If you can listen to the DAC now, got any impressions? Also, where did you source the replacement PMD200?

It's a long story this DAC but I can try to PM you later on with impressions.

[recstar24]

Have a question regarding ground loop hum. Was able to pinpoint it to my turntable, 3 prong power cord on same duplex as my phono stage which is 2 prong. The turntable and phono is on a completely different section/wall of the room and unfortunately cannot route them to the rest of the rig plugged into my zerosurge. 

Easiest and cheapest thing to do would use a cheater plug, but would it be safe to assume that lifting the ground isn't necessarily the safest thing to do? They sell humbuster devices which appear to be small isolation transformers but are expensive. Open to ideas!

[Pars]

Can you reverse the 2 prong and see what it is like?

[recstar24]

10 minutes ago, Pars said:

Can you reverse the 2 prong and see what it is like?

Do you mean plug in the 2 prong phono cord in the other direction with the 3 prong turntable power cord and see if it changes?

[Pars]

Yes

[recstar24]

6 minutes ago, Pars said:

Yes

Not conclusive. Hum still present, but it appears it's lower in level? That could be my brain doing tricks on me, as I also noticed the hum level appears to change in the previous orientation (sometimes louder, sometimes softer). 

I can also confirm that it's 60 hz hum - I have a strobosoft tuner and just put right next to the speaker woofer; and it shows up as the pitch B 60 hz. 

[recstar24]

After looking online at all sorts of random devices/gadgets, from Jensen isolating transformers ($200) to $80 power plug hum eliminators (little devices that plug at the outlet that have diodes in between the wall and plug grounds), I figured it prudent to see if just plugging the turntable through an extension into the zerosurge that has the whole rest of the system plugged into it would eliminate the ground loop. 

Yup it did! lol. I used a generic power strip to check so I just ordered a standard extension cord (14awg 15a, matched the supplied power cord with the technics) for a few bucks. I'm sure I can probably just order a longer power cord to replace the whole darn thing as well. 

I guess sometimes it's the simplest solution that is the most ideal. 

[DronEvil]

Hi everyone, if I shouldn't be posting this here, please just let me know and I'll move it. 

I am new to ESTAT amps, but have built some stereo tube and SS amps in the past. 

I just finished building my first estat amp, a KGST, but am having some issues with the amp boards. 

PSU looks perfect. All DC outs are what I expect them to be (~350v and ~15v) and I have bias set to 580v. 

When I connected the PSU to my amp for the first time last night, I wasn't able to adjust balance/offset to any degree of success. I could get offset to around -5/+5v (but it would fluctuate) but balance was basically +50v or -500v, so I knew something was wrong. I turned it off after about an hour of trying to adjust balance/offset. 

This morning, after coffee, I noticed that I seemed to have roasted a resistor in the SAME place on both boards, so I'm thinking I've definitely done something wrong here. 

Pictures of where the resistor is are below, and I'm going through the schematic to see where that resistor is as well (as best I can working off the board and the schematic side by side). While I do that, does anyone have any advise for next troubleshooting steps? I've already gone over all my solder joints and the look fine. I also cleaned the boards with 99% isopropyl and a toothbrush after i finished soldering. I can post some more pics of the boards if you'd like to eyeball them? 

Thanks in advance for your guidance! 

[spritzer]

That is weird, are you sure those are 50K?  Can't see from the pic neither what transistors those are. 

[DronEvil]

2 hours ago, spritzer said:

That is weird, are you sure those are 50K?  Can't see from the pic neither what transistors those are. 

I actually am thinking that maybe i've got the wrong transistors in there. It is possible that the 2sc22s got mixed with my 2sk170s on my desk when i was stuffing. I don't have any more 2sc22s on hand, so gonna order a few more and then measure when they arrive. Thankfully I have a stash of the roasted resistors on hand (and they didn't explode, just got toasty, so I should be able to remove them without issue).  This project has taught me that (i think) I need to stuff then solder a single component at a time (or group of same) rather than stuffing everything and then soldering. These estat amps are way more complicated than the simple amps i've built before, but I'm enjoying the work and learning.

 

Will follow up in a couple days once my new 2sc2s arrive and I do some more troubleshooting.

[Craig Sawyers]

Although it is a massive pain in the ass, particularly with large boards, I stuff one part at a time. And then use a highlighter to cross it off on the BOM and component layout. It just saves so much grief trying to find the stuffing error, or lead you've not soldered.

Even so I've stuffed PNP's instead of NPN's recently (pulled them out the wrong tube). Took an embarrassing length of time to find that error. Fortunately low power, so nothing fried - it just failed totally to work.

[spritzer]

1 hour ago, DronEvil said:

I actually am thinking that maybe i've got the wrong transistors in there. It is possible that the 2sc22s got mixed with my 2sk170s on my desk when i was stuffing. I don't have any more 2sc22s on hand, so gonna order a few more and then measure when they arrive. Thankfully I have a stash of the roasted resistors on hand (and they didn't explode, just got toasty, so I should be able to remove them without issue).  This project has taught me that (i think) I need to stuff then solder a single component at a time (or group of same) rather than stuffing everything and then soldering. These estat amps are way more complicated than the simple amps i've built before, but I'm enjoying the work and learning.

 

Will follow up in a couple days once my new cc2s arrive and I do some more troubleshooting.

You can read what it says on the part with a magnifier of some sort.  The SOT223 parts usually have some of the real marking on them unlike smaller stuff. 

[DronEvil]

So I installed these. 

http://www.bdent.com/2sc2240bl-toshiba-audio-transistor.html 

https://www.mouser.com/ProductDetail/Xicon/273-499K-RC/?qs=sGAEpiMZZMvD44QvxK4%2FiYpTv2fSXl6f 

 

I measured the resistor and they are 49.89kohms so hopefully that's good enough (can't find any 50-51k that are 1/2w and 700v). 

 

The issue still persists. I was able to get balance/offset to ~1v on one channel (after about an hour of power on) and then balance just randomly went to -500v on its own after being stable for about 20 minutes. 

The other channel i could get offset to ~3v but balance would never go below 30v. 

The resistors started getting brown again so I turned it off.

 

 

 

Am I misunderstanding the BOM/board, and I shouldn't be using STN9360 and instead be using these 2SA1486? 

http://www.bdent.com/2sa1486-az-nec-switching-power-transistor.html 

 

[mypasswordis]

FYI when parts start letting out the magic smoke, something is wrong with the circuit... you can't just use higher rated resistors and hope nothing blows up. 

[DronEvil]

 For sure! I was just mentioning the value of the resistors because I don't think I can get exactly 50kohm parts with the heat and volt requirements, and wanted to make sure that it being ~49kohm is OK. I'm also now wondering if I actually need 51kohm based on the schematic below (R13 and R14) which I am now reviewing again. 

I'm thinking that I have a part installed wrong or a wrong part installed (rather than cold joint) since it is happening to both 50kohm resistors in both channels on both boards (which is why I was asking about the STN9360 vs the 2SA1486). When I look at the BOM, I'm not entirely sure what the color coding means. I'm wondering if since I'm using 2SC1815/2SC2440 and 2K170 (couldn't find LSK389 or either of the MPSWs) that I also need to be using 2SA1486 instead of STN9360? Based on the photos of other people's finished boards and the spec sheets of the concerned components, I wouldn't think so, but i'm not 100% positive. 

Best I can tell from the schematic my problem lies (i think) somewhere between Q2/3 and Q6/7. 

BOM 
https://docs.google.com/spreadsheets/d/14Tblo23t4EUpw9DmFts-9yiWPm0UxGmupoycTxLq7i4/edit#gid=0 

kgst.PDF

[DronEvil]

I think I may have figured it out. Looks like I had a a 2SC2240 where one of the 2SA970s should have been. I'm never gonna poke and then solder all at once ever again. Will be stuffing one component fully at a time moving forward as this was just me being a blind idiot and could have been completely avoided.  Still need to troubleshoot why I can't get balance/offset down, but no more smoking parts is a step in the right direction. Sorry for causing all the noise in here! 

Currently i've got around -300vDC between +/O and i can't really get it to move at all while adjusting balance or offset. Bias sits pretty at 580vDC. 

-o is 100-120vDC and +o is 200-20vDC

I'm getting almost exactly +/-15v & +/- 338v into the amp from the PSU, so i'm not sure what's going on quite yet. Is it possible that I broke/over-turned the trimmer pots while adjusting them too far in one direction when i had an incorrect part in the circuit? 

[spritzer]

NPN in a PNP spot will not make the amp happy so who knows what else was damaged.  I would measure everything and lift parts to check the other side for damage. 

The 2SA1486 hasn't been made for a long time now so the STN9360 is the modern replacement. 

[Pars]

I bought a TKD 2CP2500 10K from partsconnexion awhile back (when they had their 25% off sale) and just installed it yesterday and did some listening. There seems to be a channel imbalance.

Any suggestions on how to run a curve on this to compare channels? Or is it simply compare and record ohm values at individual rotations at various intervals? Would I only be interested in wiper to gnd, or do I need input to wiper values as well?