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SOHA II Builders Thread - Page 28

post #406 of 1609
1/12/09 at 11:03pm
Thread Starter 
Quote:
Originally Posted by DrkRipper View Post
It is set at 100mA now, I was able to turn it up to ~120mA.


What would be involved? I have access to an oscilloscope, if needed.


It sounds good, I certainly can't hear anything that sounds wrong.

*edit* A friend of mine was anxious to review it...so there will be some listening impressions posted soon.

Thanks. 120mA is about right. And you get from 100mA to 120mA with just one turn on the pot??

In any case, if the amp sounds clean to you it's probably ok.

To check the CCSs look at the voltage across P2. It should be constant when signal is applied. If it shows significant variation the CCS is not working and either Q7 or Q8 or both are bad.
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post #407 of 1609
1/13/09 at 10:26am
Quote:
Originally Posted by wolf18t View Post
Thank Arkku, I'll check if Digikey carry them. Did you experiment with the tail current to see if it change the sound somewhat?
No, I haven't really experimented with the tail current setting, as I'm not sure of the possible benefits. It sounds good to me like it is. =)
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post #408 of 1609
1/13/09 at 1:37pm
Quote:
Originally Posted by runeight View Post
Thanks. 120mA is about right. And you get from 100mA to 120mA with just one turn on the pot??
Good I don't remember exactly, but it was less than 2 turns from the end of its travel to where I set it.

Quote:
Originally Posted by runeight View Post
In any case, if the amp sounds clean to you it's probably ok.
To check the CCSs look at the voltage across P2. It should be constant when signal is applied. If it shows significant variation the CCS is not working and either Q7 or Q8 or both are bad.
I'm back at school and don't have my tools, but I'll try to measure it.

If anyone is interested, here is my friend's review:
http://www.head-fi.org/forums/f5/soh...5/#post5287301
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post #409 of 1609
1/13/09 at 1:41pm
Quote:
Originally Posted by Beefy View Post
I believe that if the transformer is in the same case as the amp, then the case should be connected to your power earth/ground for safety. This means that signal ground should be isolated from the case to prevent ground loops that can cause hum.

If you were to put the transformer in a separate case, then the signal ground probably should be connected to the amp case.
Thanks.

Since I'm planning to put the transformer in the same case, I'll get some insulator washers.
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post #410 of 1609
1/15/09 at 12:15am
runeight, with the SOHA II is there a good rule of thumb for presetting the trimpots for a safer initial startup? At least I guess it should be important for the output stage biasing pot (avoid BJT thermal runaway).

Setting them halfway, like 5ohms for 10 ohms pots, should be safe?
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post #411 of 1609
1/15/09 at 12:21am
Thread Starter 
Quote:
Originally Posted by wolf18t View Post
runeight, with the SOHA II is there a good rule of thumb for presetting the trimpots for a safer initial startup? At least I guess it should be important for the output stage biasing pot (avoid BJT thermal runaway).

Setting them halfway, like 5ohms for 10 ohms pots, should be safe?
Good question. The way the buffer is designed it actually doesn't matter where you set them. Even at max current the O/P transistors won't burn up.

So, just pick a point on the wiper, halfway is a good place to start. It's what I did when I fired up mine the first time.

BTW, I know I designed this amp, but I really like it. Been listening to it lately.

Now if I could only afford the HD800s.
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post #412 of 1609
1/15/09 at 1:04am
Thanks! I set them all halfway.

Quote:
Originally Posted by runeight View Post
Now if I could only afford the HD800s.
Me too. And the GS-1000. And the AD-7000. And the DX-1000. Ok I'm tired, time to go to bed and dream...
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post #413 of 1609
1/15/09 at 1:47am
Quote:
Originally Posted by Hayduke View Post
Thanks.

Since I'm planning to put the transformer in the same case, I'll get some insulator washers.
What exactly are you try to isolate? Both the IEC needs to be grounded to the case and the GRD point on the PCB. The only thing that's isolated, should be the input jacks.
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post #414 of 1609
1/15/09 at 2:26am
Quote:
Originally Posted by bmwpowere36m3 View Post
What exactly are you try to isolate? Both the IEC needs to be grounded to the case and the GRD point on the PCB. The only thing that's isolated, should be the input jacks.
Yep, I was talking about the input RCAs.

Although I've been working on my BOM every night for awhile now, and I think I'm going to skip RCAs and just put a 1/8"/3.5mm phono for the input. My only sources will be USB (putting a BantamDAC inside) and modded iPods.

What is the "IEC"?

I'm rereading this thread (nearly the third time through) to get ideas of what others have done. I know you used some alternative parts. Did you list them anywhere? I started looking for it last night, but haven't found it yet. Did you use the supplied Excel BOM and save your own version? If so, wanna share?
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post #415 of 1609
1/15/09 at 2:56am
Quote:
Originally Posted by Hayduke View Post
Yep, I was talking about the input RCAs.

Although I've been working on my BOM every night for awhile now, and I think I'm going to skip RCAs and just put a 1/8"/3.5mm phono for the input. My only sources will be USB (putting a BantamDAC inside) and modded iPods.

What is the "IEC"?

I'm rereading this thread (nearly the third time through) to get ideas of what others have done. I know you used some alternative parts. Did you list them anywhere? I started looking for it last night, but haven't found it yet. Did you use the supplied Excel BOM and save your own version? If so, wanna share?
"IEC" is the Inlet Connector:


I thought I did, but here it is (attached).
LL
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post #416 of 1609
1/15/09 at 12:27pm
Is 2.21 ohm OK for R10?

I'd like to use Mouser PN 71-RN55D2R21F to keep all the resistors Vishay. The only 2.2 ohm Vishay that Mouser stocks are 1 or 2 watts

I could always tombstone one of these if the value is critical. I'm slowing gaining a pretty good understanding of the amp's schematic, but I can't tell if .01ohm in R10 will make a difference.
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post #417 of 1609
1/15/09 at 12:41pm
Thread Starter 
Quote:
Originally Posted by Hayduke View Post
Is 2.21 ohm OK for R10?

I'd like to use Mouser PN 71-RN55D2R21F to keep all the resistors Vishay. The only 2.2 ohm Vishay that Mouser stocks are 1 or 2 watts

I could always tombstone one of these if the value is critical. I'm slowing gaining a pretty good understanding of the amp's schematic, but I can't tell if .01ohm in R10 will make a difference.
Yes, you can use 2.21. The .01 is less than the 1% tolerance of the resistor itself. But the reason that this resistor is xicon is because of what you discovered about the available Vishay RN55D values. MHO is that you won't notice any difference whatsoever between the two brands used in the position in the circuit.
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post #418 of 1609
1/15/09 at 6:02pm
@bmwpowere36m3

Thanks for sharing your BOM. I had already substituted a lot of the same parts

Why did you use a DPDT for your R3P bypass? In your BOM you show the same switch for this and your heater voltage switch. Wouldn't a SPST work fine here?

I'm thinking I will use R13-603C-05 and R13-602B-05

Quote:
Originally Posted by runeight View Post
Yes, you can use 2.21. The .01 is less than the 1% tolerance of the resistor itself. But the reason that this resistor is xicon is because of what you discovered about the available Vishay RN55D values. MHO is that you won't notice any difference whatsoever between the two brands used in the position in the circuit.
Thanks Alex

I didn't think that amount would matter too much. For no good reason, I just wanna use all Vishay.

I am gonna leave R3P alone though since the only Vishay equivalent available form Mouser is this:
CP00058R200JB14

I ordered my transformer and boards today. I'll be placing a Mouser order after they get back to me about a question on some test probes. Hopefully today, maybe tomorrow.

I'm still undecided on the case though. bmwpowere36m3 has me worried about fitting the larger transformer and the DAC inside the case. The BantamDAC is pretty small though. I am going to use a 3.5mm stereo plug instead of RCAs, so that's a little less stuff on the back. Plus, I'm putting the main power switch on the front, so that will help too. Only problem is I'm putting 2 small slider switches on the back panel for the heater voltage and to bypass R3P.

I think it will all fit. I'll just have to be creative

Now that I'm ordering parts, my excitement to hear this amp jumped up a couple notches.

Thanks for sharing your design Alex. Sorry for asking so many bonehead questions hehe
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post #419 of 1609
1/15/09 at 8:46pm
Quote:
Originally Posted by Hayduke View Post
@bmwpowere36m3

Thanks for sharing your BOM. I had already substituted a lot of the same parts

Why did you use a DPDT for your R3P bypass? In your BOM you show the same switch for this and your heater voltage switch. Wouldn't a SPST work fine here?

They are two different switches, however their P/N on differs by one letter "xxMSxxxx" vs. "xxMDxxxx" and yes, the other is a SPST

Quote:
I'm thinking I will use R13-603C-05 and R13-602B-05
Those look like they'd work, seem kinda cheapy looking to me. If you like then

Quote:
Thanks Alex

I didn't think that amount would matter too much. For no good reason, I just wanna use all Vishay.

I am gonna leave R3P alone though since the only Vishay equivalent available form Mouser is this:
CP00058R200JB14
I like you wanted to use all Vishay, but it honestly wasn't worth the trouble... especially since those resistors are not that "important" and some of them are adjustable in conjunction with the trimpots, so... The replacement R3P you have listed appears to be way to big as well. Just use the BOM one.

Quote:
I ordered my transformer and boards today. I'll be placing a Mouser order after they get back to me about a question on some test probes. Hopefully today, maybe tomorrow.

I'm still undecided on the case though. bmwpowere36m3 has me worried about fitting the larger transformer and the DAC inside the case. The BantamDAC is pretty small though. I am going to use a 3.5mm stereo plug instead of RCAs, so that's a little less stuff on the back. Plus, I'm putting the main power switch on the front, so that will help too. Only problem is I'm putting 2 small slider switches on the back panel for the heater voltage and to bypass R3P.

I think it will all fit. I'll just have to be creative

Now that I'm ordering parts, my excitement to hear this amp jumped up a couple notches.

Thanks for sharing your design Alex. Sorry for asking so many bonehead questions hehe
Just draw out and dimension the amp and its components layouts. I wouldn't say you have no room, but with all that careful planning will be needed. Running the switch to the front, *might* induce some unwanted hum (maybe?) by running the power lines under the PCB.
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post #420 of 1609
1/15/09 at 9:10pm
Quote:
Originally Posted by bmwpowere36m3 View Post
They are two different switches, however their P/N on differs by one letter "xxMSxxxx" vs. "xxMDxxxx" and yes, the other is a SPST
oops missed that letter

Quote:
Those look like they'd work, seem kinda cheapy looking to me. If you like then
I want small sliders and I wanted at least ~2A. That's all I could find. Mountain switch had some I liked better, but they were only .5A. I want sliders so they don't get changed on accident. I know I would hit those toggles you used everytime I messed with the cords. While not portable, I suspect this amp will get moved around a fair amount.

If you can find a nicer slider from Mouser that will work, I'll be grateful for a link

Quote:
I like you wanted to use all Vishay, but it honestly wasn't worth the trouble... especially since those resistors are not that "important" and some of them are adjustable in conjunction with the trimpots, so... The replacement R3P you have listed appears to be way to big as well. Just use the BOM one.
I'm not using the one I linked to. I already decided to use the BOM one. I was just showing what I found as the reason why I wasn't using all Vishay.

Quote:
Just draw out and dimension the amp and its components layouts. I wouldn't say you have no room, but with all that careful planning will be needed. Running the switch to the front, *might* induce some unwanted hum (maybe?) by running the power lines under the PCB.
My plan was to put this power switch in the middle of the faceplate (between the knob and the headphone jack). I was thinking I would run the power wires down the side of the enclosure. You're right though, it had occurred to me that those long runs of wire might cause or pickup some interference. Maybe I'll get some shielding or order some shielded multi conductor wire.

Any suggestions? I'd prefer to have the power switch on the front of the amp, but I don't want to introduce any noise obviously.

I'm going to build it and have everything working before I even start any casework. My friend owns a business that has lots of metal fabrication equipment (mills, CNC machines etc). He said he can do my casework for me "no problem". Might take awhile to get it back from him, but I know his work. It will be done well.
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