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SOHA II Builders Thread - Page 105

post #1561 of 1669
Quote:
Originally Posted by hyperbting View Post

Hi,

I'm building SOHA II as well.

At this moment only 2 parts cannot be found in mouser and Digi-key

They are

Metalized Polyester/Polypropylene Film Capacitor 1μ 63V

C1E, C2L, C2R, C6L, C6R

Mouser 581-BF074D0105J   Digikey 478-3367-ND

and

C4E,C5E Metalized Polyester/Polypropylene Film Capacitor 10n 63V

Mouser 581-BF014D0103JDC   Digikey 478-3373-ND

 

 

just wondering if

505-MKS02.01/63/5 http://www.mouser.com/Search/ProductDetail.aspx?R=MKS0C021000B00JSSDvirtualkey50520000virtualkey505-MKS02.01%2f63%2f5

and

505-MKS21/63/5T http://www.mouser.com/Search/ProductDetail.aspx?R=MKS2-1%2f63%2f5Tvirtualkey50520000virtualkey505-MKS21%2f63%2f5T

 

are good alternate?


 

Getting the right capacitor is not hard.

 

Capacitor type - match the type, you can use a different type than specified but you need to know what you are doing.

Capacitance - match the value, you can tweak the value a little sometimes but you need to know what you are doing.

Voltage rating - match the value, higher is fine.

Form factor - Try to match the lead type (radial or axial), lead spacing, lead diameter (smaller is fine) and package size (smaller is fine). If they don't match you would have to mount them the "creative" way which may sometimes cause instability.

post #1562 of 1669
Quote:
Originally Posted by Veiko View Post

Well, I got those BD139s off the board and they aren't broken after all.

It's going to be over a week before I can continue this project, so, any ideas are welcome meanwhile.

I couldn't get the BC550s off for now, I'll give those another try when I get back from my holidays.


I could be wrong here, since I am not familiar with the setup process (since I haven't got there yet).

 

FWIW.

 

Initially I kinda doubted the way you measure the voltage drop, I didn't say it obviously as I wasn't familiar with the process and I could well be wrong. It seemed to me the most intuitive way to measure the voltage drop across a resistor is to have both probes at both end of it. The resistor value is quite small, so the voltage drop would be small too. Thus to accurately measure it you need to have your DMM set to the low range. Could it be that you are setting your DMM at a range that is too high that it is unable to detect such a small voltage drop?

post #1563 of 1669
Quote:
Originally Posted by Navyblue View Post


I could be wrong here, since I am not familiar with the setup process (since I haven't got there yet).

 

FWIW.

 

Initially I kinda doubted the way you measure the voltage drop, I didn't say it obviously as I wasn't familiar with the process and I could well be wrong. It seemed to me the most intuitive way to measure the voltage drop across a resistor is to have both probes at both end of it. The resistor value is quite small, so the voltage drop would be small too. Thus to accurately measure it you need to have your DMM set to the low range. Could it be that you are setting your DMM at a range that is too high that it is unable to detect such a small voltage drop?



I'm quite certain I measured it correctly. With both probes at both ends of the resistor, I couldn't get a reading other than about 0. With one probe at either end and the other at ground, I measured little over -15 volts. I tried with two meters. One was at 2000mV zone and the other one has auto-range. Looks like the positive voltage isn't getting where it should.

It'd be really helpful to know where exactly on the schematic the TL+ and TL- points are. Either I have a couple of bad transistors (which I doubt now) or the positive voltage isn't getting to the transistors at all.

I feel like I could find the problem easier now that I understand little more about the buffer. If only I had the board and a DMM/scope with me now :D

post #1564 of 1669

Does both R10 exhibit the problem?

 

If you power down, measure the resistance across R10, do you get 0 ohm? And when you measure resistance from R10 to ground, do you get 0? Do you think there could be a short circuit somewhere? If there is a resistance, there should be a voltage drop?

 

Just thinking out loud here, as mentioned, if there is a real problem I doubt I could be of any help.

post #1565 of 1669

I get 2.7-3ohms across R10 depending of the DVM. And about 9k to ground. A voltage drop can only exist if there's current flow, which could be the problem here. Both ends of R10 measured -14.8V to ground if I remember correctly. And yeah, that was both resistors. I'm going to solder new transistors as soon as I have some time and see if it makes a difference.

 

I really want to know where those test points are on the schematic. That would at least tell me if there could be a problem in the PSU.


Edited by Veiko - 2/28/12 at 8:18am
post #1566 of 1669

I don't know if I understand you correctly, those test points look like the various outputs on the PS sections.

 

Btw, there is a slight chance that I would get this amp moving again. I wonder if I chose the wrong amp to build. If so I would have to finish this up and try to sell it if I can.

 

For those who have heard this amp, does it sound like solid state to you? I chose to do this so to have a different flavor than my solid state amp (Beta 22). I'd keep it if it sound different enough, but I have a feeling that I'd be better served with something like Pete Millett's Jonokuchi.

post #1567 of 1669

Thanks, I was able to confirm that.

My vote goes to get your SOHA II built asap ;) I personally can't wait to get this thing working.

 

So, I got everything together again and measured the test points. Everything fine until I decided to see if my meter would pick any AC. There was about 32 volts of AC on TL+!

Other test points measured 0V AC as they're supposed to.

Do you think my transistors (and other parts) survived that?

And where's that AC coming from? Ideas?

post #1568 of 1669

If there is indeed AC (I am doubtful actually), check the orientation of D1P-D4P.

post #1569 of 1669

Your doubts were correct, I repeated voltage checks with a scope and there was no AC. PSU works! I don't know what's wrong with my DMM.

After some troubleshooting I found a 14 volt drop across R11. No current flow in R9 and R10. P2 and R12 were fine.

I got +15V on the collectors of Q5 and Q6 but it's not getting through.

post #1570 of 1669
I couldn't sleep while thinking of my Soha and finally found the problem. J3 was jumpered. All this trouble and it was that simple. I'm going to remove the jumper tomorrow and hope I didn't destroy the board while changing parts.
post #1571 of 1669
Glad that you got it worked out. Yesterday I took out my SOHA II board and looked at it. Perhaps it's an omen that I will soon work on it. :-p
post #1572 of 1669

Relay clicks!

It also required installing the opamp. I was sure the opamps weren't supposed to be installed yet and now I feel kinda stupid biggrin.gif

Found out by studying the design on Cavalli's website.

 

Out of interest, do you have all the parts ready?

I think I soldered the everything in one night so it's not that much trouble for a fine sounding amp (hopefully).

post #1573 of 1669

I am missing the transformer, and also some caps which I want to replace from the kit (or I could just use those from the kit). I am also missing some parts for the some of the mod (the Regal mod). For others like enclosure, jacks and all that I had extra from my previous build. So I am one Mouser order away from being complete.

 

I am working on the amp now btw, I have a hard time remembering what I was doing. biggrin.gif

post #1574 of 1669

It.. It Works!!

And sounds absolutely beautiful. It's in a completely different class compared to the headphone output of my audio interface.

The noise floor, however, is quite high. I think I got 50Hz hum here. Ideas?

 

You've got to get yours built now :D

 

My SOHA II

post #1575 of 1669

I figured at least part of the problem was grounding-related. So I hit the ground-lift button of my sound card and 75% of the noise disappeared. The 25% of it still bugs me a bit tho. Still sounds like 50Hz hum.

 

EDIT: Tried with my phone, total silence, noise-wise. I guess I'll have to build a DAC next.


Edited by Veiko - 3/17/12 at 8:18am
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