VSSA Through-Hole Version by Jason - Page 38 - diyAudio
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Old 3rd April 2014, 01:31 PM   #371
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Quote:
Originally Posted by Gooniman View Post
Hi Jason. Did you decided which SMPS to use with the VASS.
Almost finish the boards, so I believe I will need some type of power to set up and test the boards.
Can you recommend a inexpensive table top power supply for testing.
Will post some pictures later..
Hi Cesar,

I have actually not yet settled on a firm recommendation. I'm actually biting the bullet and getting a few different ones and can give better impressions when I have units on hand. Despite my current issue with a Connexelectronic SMPS500R that is being sent back, for the price get one of their SMPS300RE units in the +/-36V output. I suggest using the vendor HiFimeDIY out of the US warehouse. Links:

HiFimeDIY US Store
SMPS300RE +-36V (dual voltage) 110V Power Supply

For testing and initial set-up I actually recommend using a plain vanilla linear supply if you can, at about the final output voltage you are planning on using. That way you can use a 'bulb limiter' (a must for any DIY'er) and a variac (nice to have but not essential) to help with fault finding and reduce the chance that an error will result in damaged parts.

For that a smallish ~100VA 26-0-26 (centre tapped or dual secondary, from 24V to 26V per tap or winding) transformer, mains fuse, switch, bridge rectifier, filter capacitors (smallish, maybe ~4700F @50V), bleeder resistors and output fuses would make for a nice little 'bench supply' that can be used for testing other things later on. Put all that in a cheap project box with binding posts to connect to the projects needing power. The bulb limiter is an add-on the feed the small linear supply.

If you just want to get one supply and do the testing off the final supply then I suggest initial power-up be with a pair of 1/4W 100Ω resistors in the supply lines. If all is good then initial set-up can be done with a couple of 5W 10Ω resistors be put in-line with the +/- supply lines at. Final verification is done on an unlimited supply. Let me know when you are fully ready and we will walk through some initial set-up.

I know you have been studying the photos but the very first thing is a careful check of your work. Look for missed solder joints, joints that are shorted together (solder bridges), incorrect components / values, etc. one satisfied all looks good we will pre-set the adjusters before we power up for the first time.
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Old 4th April 2014, 02:57 AM   #372
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Default Suggested Set-Up Sequence

Hopefully this will assist with setting up the boards for those who aren't familiar with the VSSA already.

This is easiest with more than one multimeter and test leads with small alligator clips if you have them. It can be done 'fully manual' with one meter and regular leads if need be. Just make sure you are slow and careful with set-up to avoid shorting something out with a slipped test lead tip.

Please Note: If properly pre-set VR1 and VR3 won't need large adjustments. If you feel like you are turning them too much, you probably are. Stop! Power off and start over. An anecdote; I had one test lead on a test module that wasn't in good contact when measuring the VAS current resulting in a false reading. It resulted in me turning the adjusters too low and popping the VBE and a 100Ω gate stopper. No major damage, but still a repair all the same.
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Old 4th April 2014, 05:45 AM   #373
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Very helpfull Jason but one question does the input need to be shorted for the offset measurement?
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Old 4th April 2014, 12:48 PM   #374
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Originally Posted by meanman1964 View Post
Very helpfull Jason but one question does the input need to be shorted for the offset measurement?
It certainly can't hurt to short the input, but it doesn't float either with the 100kΩ across the input. I haven't seen any significant difference either way, just don't attach any cables to the input before they are tuned.
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Old 4th April 2014, 07:51 PM   #375
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Quote:
Originally Posted by meanman1964 View Post
Very helpfull Jason but one question does the input need to be shorted for the offset measurement?
Yes, whether the input is DC or AC coupled, shorted input simulates source's (preamp) low output Z and zero output DC. Also prevents unwanted EMI signals to enter sensitive input among measuring phase, while holding the amp in very steady condition.

DC coupled input transfers source's (preamp) output DC offset with gain 1 (AC coupled GNFB) or full gain (DC coupled GNFB) to the output. In this sort of connection any other than zero input DC calibration condition (shorted input) would cause certain output DC offset when zero DC source would be connected.

AC coupled input cuts source's (preamp) output DC offset influence completely. Now the source of output DC offset is the amp's input stage unsymmetry, driven by thermal changes practically in all stages.
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Old 5th April 2014, 06:44 AM   #376
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Boards are soldered now adjusting have ordered some special clips for that
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File Type: png 8463_GRIP_TEST.png (14.0 KB, 279 views)

Last edited by meanman1964; 5th April 2014 at 06:47 AM.
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Old 5th April 2014, 02:24 PM   #377
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That is the type of clip I like for this kind of work.
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Old 5th April 2014, 03:23 PM   #378
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Those are the same as on my Peak Atlas tetser
I can order a few more if you like
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Old 5th April 2014, 03:41 PM   #379
Rick G is offline Rick G  United States
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Meanman1964,
Where did you find those clips. i need a few more myself.

Rick
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Old 5th April 2014, 03:43 PM   #380
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Audiophonics.fr
Very usefull gadget and tool
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