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Old 17th May 2013, 05:35 AM   #441
shaan is offline shaan  India
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Quote:
Originally Posted by PMI View Post
...has anyone in these very long VSSA/SSA threads compared the Renesas parts to anything else, be it the Alfet, or the Exicon part?
LC seem to be the only one who has built and tested latFET and BIGBT o/p stages. And his choice for the SSA is the latter. VSSA? Dunno...

I haven't used any other o/p devices for SSA/VSSA other than the Renesas pair. They are good; but the performance of a FET with 900pF of Ciss and 1ohm of on resistance depends on how robust the drive stage and feedback node are. Sound from my speaker has so far not shown any funny side of them, I expect they are driven well.

Haven't tried other o/p devices with VSSA, so making a comment will be pointless.
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Old 17th May 2013, 01:40 PM   #442
PMI is offline PMI  United States
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This is my first experience with this circuit topology (meaning almost completely symmetrical). In the past the choice of other components (drivers etc.) seemed to make more difference than output devices, assuming similar specifications.

Do you have any suggestions for any other tests I could try with a DMM and o-scope, besides what I already posted above, or something else to try with a second set of boards?
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Old 17th May 2013, 09:22 PM   #443
shaan is offline shaan  India
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I'm already at my limit of knowledge... Sorry PMI I disappointed you.

I don't own a scope. My boring posts reflect only the time spent with these amps and observation based on simple and cheap measurements, I love to share what I find to be good. Also I don't have an engineering degree. I'm an arts student, bachelor of English, and a classical traditional drummer.

Last edited by shaan; 17th May 2013 at 09:25 PM.
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Old 17th May 2013, 10:18 PM   #444
PMI is offline PMI  United States
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Originally Posted by shaan View Post
I'm already at my limit of knowledge... Sorry PMI I disappointed you.
Of course not, Shaan! What you write here is anything but that. After all, w/o you and this thread, I seriously doubt I would have built this circuit...

Besides, some of my best insights into sound have come from musicians, something I am sadly NOT! (One of them happens to be a retired professor who used to teach percussion at the local UW-Milwaukee)
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Old 18th May 2013, 03:53 AM   #445
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Quote:
Originally Posted by shaan View Post
I'm already at my limit of knowledge... Sorry PMI I disappointed you.

I don't own a scope. My boring posts reflect only the time spent with these amps and observation based on simple and cheap measurements, I love to share what I find to be good. Also I don't have an engineering degree. I'm an arts student, bachelor of English, and a classical traditional drummer.
Shaan,

When I was young I've been told that people in India have superior hearing compared to us westerners because they have quarter tones in their scales, something that is very difficult for us to hear. Since this is diyaudio your experiences with this particular circuit are much appreciated. I believe more to your ears than to any scope in this world.

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Ivan
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Old 18th May 2013, 08:57 AM   #446
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Quote:
Originally Posted by PMI View Post
This is my first experience with this circuit topology (meaning almost completely symmetrical). In the past the choice of other components (drivers etc.) seemed to make more difference than output devices, assuming similar specifications.

Do you have any suggestions for any other tests I could try with a DMM and o-scope, besides what I already posted above, or something else to try with a second set of boards?
Hi PMI,
what about if you do like I do, put your parts as post #1(no caps at B-C VAS transistor & only 4 big elcos) & see what will happen on your scope
Quote:
Originally Posted by shaan View Post

We need,
1. A digital multimeter.
2. 1R/1W x 2.
3. 22R/2W x 2.

For first time power-up solder two 22R/2W resistor to the PS rails, one end of each of them to each rail. Connect the PS to the open ends and turn on power. If nothing explodes/smokes then replace both of the 22R with 1R/1W and connect the PS again, but don't power it up instantly.

Take notes for the measurements from now on.

Set your digital meter to 'mV' and connect the probes to both ends of one of the 1R resistors. Turn on power. Check meter reading. That number shows total Quiscent current Iq.

Measure the front end plus VAS current I(f v) by probing the voltage at the ends of the 10R after the 4007 diodes.

Measure VAS current I(vas) by probing the voltage at the ends of the 10R at their emitters.

Now,

Total current= Iq
Front VAS current= I(f v)
VAS current= I(vas)

So, from aquired data we get,

Front end current= I(f v) - I(vas)

and

FET current= Iq - I(f v)

I hope this will be helpful.

shaan
Hi Shaan, thanks & I did it safely
here the result with +/-30v :
@ 22R = about 2volt & it is okay so
I change to 1R (the current quite low nothing warm)
@ 1R = 140mV (155mV) --->140mV on CH1 & 155mV on CH2
@ 10R (f v) = 99mV (89mV)
@ 10R (vas) = 63mV (56mV)
DC offset = 6mV (1mV)
When I test it input shorted to ground, not use caps at VAS transistors & no zobel at output only 8.2R resistor as load because without load I can't measure DC offset.
I will add zobel latter maybe if that cause it Click the image to open in full size.

Do you think it is all okay?
I think the voltage to low because you suggest 35v if we use 15k & not adjusted yet because only my first test
I want to prepare PSU for my PeeCeeBee then test it again with some suggestion from you all

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Last edited by JOHN BALI; 18th May 2013 at 09:01 AM.
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Old 18th May 2013, 09:22 AM   #447
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by JOHN BALI View Post
..................... at output only 8.2R resistor as load because without load I can't measure DC offset............../
This makes no sense.
DC offset at the output is measured with shorted input and open output.

You can specify a specific Rs, say 100r or 1000r, and state the output offset for this condition, but this is non standard and needs to be specified fully for us to understand.
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Old 18th May 2013, 10:16 AM   #448
naf is offline naf  Indonesia
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It's strange bli John, i could measured dc offset without load and it sould be done before conneced to speaker
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Old 18th May 2013, 10:23 AM   #449
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Quote:
Originally Posted by AndrewT View Post
This makes no sense.
DC offset at the output is measured with shorted input and open output.

You can specify a specific Rs, say 100r or 1000r, and state the output offset for this condition, but this is non standard and needs to be specified fully for us to understand.
What I mean is without any load at output DC offset not stable,
maybe oscillation that what I got there, that's why ask here.

At no load at output or open output my DMM can't read the DC offset...
With one 8R2 resistor at output my DMM reading 6mV and 1mV.
When I measured it there was no zobel on output

Quote:
Originally Posted by naf View Post
It's strange bli John, i could measured dc offset without load and it sould be done before conneced to speaker
kang Naf, with or without Zobel?
and with 22pF on VAS transistor right?
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Last edited by JOHN BALI; 18th May 2013 at 10:28 AM. Reason: Ask to Naf
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Old 18th May 2013, 03:16 PM   #450
PMI is offline PMI  United States
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@John Bali:Thanks for the tip, but.... naaah, I'll skip that test .

I tested my boards without zobel installed, with 44pF compensation caps, and with the six elcos as shown in the pics. Even with the 44 pF, I measured a maximum slew rate of around 100V/usec. Plenty for me, and I will try 22pF when I compare to the boards from the VSSA GB.

The DC offset does drift a bit with time and temperature, but only a few mV. No sign of any instability or oscillation, at least not so far.

I will repeat some of the tests when I build a second set of boards, but I consider the design as "tested" by LC and by Shaan. So, my goal is to make sure I did not "break" their circuit through some oversight on my part.
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