Technical Assistance/Advice Thread

[Pars]

I believe the code is still in the diy forum thread? I attached what I have. I still have some of these and keep thinking about building one...

KG attenuator balanced code.zip

[Spychedelic Whale]

On 3/24/2019 at 3:25 PM, Pars said:

I believe the code is still in the diy forum thread? I attached what I have. I still have some of these and keep thinking about building one...

KG attenuator balanced code.zip

Thanks!

[Pars]

On 2/8/2019 at 9:46 PM, Kerry said:

Just got this tapping guide.

SHARS Self Aligning Tap Holder

I'm really happy with it and thought I'd share  

I (or actually, my wife) picked one of these up for me on Friday.

I also got a set of drill bits from them (https://www.shars.com/media/flip/2018master/mobile/index.html#p=2) the 404-2201, which I am thinking I should have gotten some better ones, maybe one of the cobalt ones, or at least the HSS 6542. Any recommendations from what you see there? I probably also don't need anything larger than 3/8", so dropping down to a 22 piece set shouldn't be an issue.

I haven't used either yet.

[Pars]

So no drill bit recommendations from Shars (catalog link in previous post)?


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[jose]

The other day I saw an ad of a tool to improve the tip of the screws and threaded rods. The tool is used with a drill and is a kind of "sharpener" for the screws.

When I cut a screw, the thread is damaged. This tool allows to touch up the damaged end giving it a conical shape. 

Does anyone know what it's called or where can I buy it?

Sorry, I have a hard time explaining. 

[Laowei]

23 hours ago, Pars said:

So no drill bit recommendations from Shars (catalog link in previous post)?


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For part time use for a hobbyist, those look perfect.

28 minutes ago, jose said:

The other day I saw an ad of a tool to improve the tip of the screws and threaded rods. The tool is used with a drill and is a kind of "sharpener" for the screws.

When I cut a screw, the thread is damaged. This tool allows to touch up the damaged end giving it a conical shape. 

Does anyone know what it's called or where can I buy it?

Sorry, I have a hard time explaining. 

When cutting or hacksawing screws to length, always first screw a hexnut past the length to be cut off and then mark the cut line on a single wrap of masking tape around the screw. The tape helps the hacksaw from walking, and after the extra length cut off, unscrewing the hexnut helps straighten the mangled threads. Cleanup with a chamfer on the end using a hand file.

[jose]

Thanks Laowei. It is a good trick.

[struts]

Quick questions regarding a voltage divider to take a 580V Stax bias line down to 520V for HE90 (I believe the spec is 500V but I remember reading a post once that @spritzer had measured a number of HEV90s and found the average to be closer to 520V).  

- I assume that the difference in bias is somehow related to differences in the membrane construction between the two, maybe the coating?  

- Is there a real risk of damaging HE90s running straight off Stax bias?  I.e. can the additional potential actually lead to the membrane making contact with the grid?  Does anybody have any practical experience of this or is this just speculation?  

- By my math a  576k coupled with a 5M to ground should do it (along with a 10M in series).  Are these the values others have used?

Grateful for any clues for the clueless.

Edited April 17, 2019 by struts

[chinsettawong]

I believe the 580V Stax bias voltage with 5M ballast resistor is safe for HE90.  I have tried the HE90 with some Stax amps in the past, and I didn't notice any problem.  However, if it will make you feel better, reducing the bias voltage to 500V and adding additional 5M ballast resistor are the way to go.

[spritzer]

Well you need to look at the system as a whole and HE90's at pro bias is a really, really bad idea.  Ideally you should go even lower down than 500V as the D/S gap in them is so small.  Well that and uneven stators but that's a known issue. 

So with the HEV90, the max voltage swing is just about 1100Vppss on a good day so they can get away with that.  Now plug this into a Carbon or a T2 and... well... that's not a good idea really.  It is so easy for the amps to overdrive the headphones so I'd personally scale down the bias even further. 

[struts]

Many thanks @spritzer.  1M/5M in the divider would take it down to 483V.  Is that the right ballpark or would you take it down even further (this is for a T2)?

Edited April 19, 2019 by struts

[spritzer]

I'd start there but it might be a good idea to go even lower. 

[Ulfar4]

Hi, I wanted to simulate srm-1 amplifier in LTSPICE to understand how it is working. But I'm not able to make it work. Maybe it is something trivial, which I do not see right now. But I'm running out of ideas. If someone point me to the problem, I'll be happy. Thanks for help.

asc.zip

[kevin gilmore]

v- is actually -370v and vref3 is -350v

take a closer look at the original schematic

 

[Ulfar4]

Thanks, now it works like charm.

[jose]

On 4/2/2019 at 9:13 PM, jose said:

The other day I saw an ad of a tool to improve the tip of the screws and threaded rods. The tool is used with a drill and is a kind of "sharpener" for the screws.

When I cut a screw, the thread is damaged. This tool allows to touch up the damaged end giving it a conical shape. 

Does anyone know what it's called or where can I buy it?

Sorry, I have a hard time explaining. 

I just found it here.

 

 

[randytsuch]

If you're in the US

https://www.amazon.com/?Jonerytime?Stainless-Deburring-External-Chamfer-Remove/dp/B07JR9QPBH/ref=asc_df_B07JR9QPBH/?tag=hyprod-20&linkCode=df0&hvadid=312003160272&hvpos=1o1&hvnetw=g&hvrand=12990877068024208839&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9030970&hvtargid=pla-571685233097&psc=1

 

Reviews are mixed, but it is cheap enough to try.

[MartinC700]

Help with a KGSSHV Carbon Issue 

I posted information on my build in the Carbon build thread, and although I eventually believed the build worked fine, I do still have one recurring fault that I cannot trace. Hoping that someone who is more of an electronics expert than I can help with tracking down the issue.

The problem only occurs when I am using a balanced input and only occurs on one channel. SE input works just fine with the amps - in grounded. With balance input one channel was distortion as well as what seems like a lower overall level. The distortion sounds like overloading and is accentuated on loud bass notes. I have checked all the input wiring and the source and it all points to something on the amp board. 

I have a DVM and a scope but am hesitant to poke around with the HV supplies connected. 

Any suggestions as to where to look for the fault? - Can troubleshooting of the input stage be done with only the +/- 15 v supply connected?

Thanks for any help.

 

[Laowei]

Maybe a cold solder joint on the PCB between the terminal block and the base pin of the input JFET?

Try reflowing the connections on the -I side that distorts.

Edited May 18, 2019 by Laowei

[MartinC700]

Thanks I will give that a try.

[mwl168]

Received an e-mail from Upscale Audio containing the article below advocating that digital cable makes a difference. 

Wonder what you all think? 

Click here for the "Bits is Bits" guide 

[Pars]

While they are correct that essentially any transmission is an analog carrier with a payload (analog or digital) on top of it, I’m not sure I buy the rest of it.


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[johnwmclean]

TAS circa 1980?

[Scgorg]

I'm really not seeing their point here, they say themselves that digital transmissions have error correction but then proceed to say unwanted radio frequency signals/electrical noise can get into the data that is transmitted if the cable is bad? Wouldn't the purpose of error correction be to avoid deviation from the original data? I'm gonna say these people are looking to sell, as businesses do. When was the last time someone complained that the bits they got at the end of a cable were different than those that entered?

[Craig Sawyers]

Serial data with an embedded clock (for example the NRZ used for SPDIF) is subject to a well known set of random and deterministic jitter mechanisms. Agilent make high end car priced gear to measure and characterise these in high speed data links - but lowly SPDIF is just as prone to these at a pedestrian data rate.

And although it is true that Red Book CD's use a robust error correction code (Cross-Interleaved Reed Solomon) a SPDIF link uses a simple checksum.

Edited August 9, 2019 by Craig Sawyers