SA-3A (LA-3A Clone) Support Thread

[rob61]

Could you post some hi rez pictures of the power transfer and IEC so I can check how that's wired?

 

[mulletchuck]

This is how I wired my unit.  I live in the States (120VAC):

IEC Neutral ->  Neutral Primary of the transformer
IEC LIVE -> Fuse -> Power Switch -> LIVE Primary of the transformer

the thread has pics of how the secondaries is wired to the board. 

If you read up on the 51X PSU build thread, there are lots of pics of how to wire up the Power Inlet, Fuse, Power Switch and Transformer Primaries.

 

[sage]

So after a few months of total bliss with my SA3A unfortunately yesterday it stopped working:

- NO compression and some disrotion in the output

We put it on the bench:

- Changed the T4bs and that is not the problem
- TP1 is good
- All voltages good as per schematics
EXCEPT for +V which i am not sure what is suppose to read - Test point 7 read 43 Volts

Both sides have the same behavior -

ANY SUGESTIONS ? I am addicted to this unit on my stereo buss... in fact i am gonna buy another kit today but in the meantime I really need to get this machine going...

Sage

 

[mulletchuck]

since both sides have the same problem, that would indicate that it is a part that both sides share, right?  So, what stuff do both sides share?  PSU?  the link switch? 

 

[sage]

well PSU seems fine or the voltages would be all wrong - also the Voltage regulators measure OK -

I will take a look at the link switch but also in mono mode it's the same thing - it barely compresses if at all - VU barely moving even with maximum compression -

I took a T4B from another unit and that is not it... I will look at the link switch I guess... but that seems strange as I said even in mono mode same behaviour -

I bought another kit yesterday but really need to get this going ASAP !!!

sage

 

[sr1200]

did you hit the board with your iron?  Maybe just a cold solder somewhere that finally fully quit.

 

[sage]

I guess the question is what voltage I should have on the +V ?

Anyone other suggestions?

Sage

 

[mulletchuck]

at that point in the circuit it's the 15VAC + 15VAC secondaries in series being rectified.  so whatever 30VAC converted to DC is what you should have.  Anyone know the equation for converting AC to DC voltages?

 

[Echo North]

at that point in the circuit it's the 15VAC + 15VAC secondaries in series being rectified.  so whatever 30VAC converted to DC is what you should have.  Anyone know the equation for converting AC to DC voltages?

The peak voltage (X 1.141 1.414) less the diode voltage drops (0.7 X 2 for full wave). 

Roughly.

 

[Spadehead]

Hi All,

Just gearing up for the build and raring to go! Ruckus, you mention on page one about posting a drill template for a collective case enclosure? I'm hoping to get one through from Dan soon and don't want to spoil the lovely front panel.....

Many thanks

Ade

 

[Spadehead]

bump...

 

[Ptownkid]

at that point in the circuit it's the 15VAC + 15VAC secondaries in series being rectified.  so whatever 30VAC converted to DC is what you should have.  Anyone know the equation for converting AC to DC voltages?

The peak voltage (X 1.141) less the diode voltage drops (0.7 X 2 for full wave). 

Roughly.

Me thinks that may be a typo....it should be X 1.414 no?

 

[Echo North]

at that point in the circuit it's the 15VAC + 15VAC secondaries in series being rectified.  so whatever 30VAC converted to DC is what you should have.  Anyone know the equation for converting AC to DC voltages?

The peak voltage (X 1.141) less the diode voltage drops (0.7 X 2 for full wave). 

Roughly.

Me thinks that may be a typo....it should be X 1.414 no?

Ah thank you!  I'll go back and correct it for the people.

Mike

 

[rainton]

I just finished my SA3A yesterday and it worked right away 
Thanks Mike for putting this project together - it was really straight forward and the compressor sounds awesome!
Also calibration was a breeze with your step by step instructions and stereo linking works flawlessly! I adjusted the HF mod to add 5db of compression
@ 15khz and despite others here finding the HF switch to be a waste of space on the faceplate I find it a great feature to have!
Since the extra compression starts smoothly above 1khz I love how this can kind of soften out the high-end a little and keeping everything up to 1khz
round and full! Makes it even more versatile to have a switch for this on the front!

In terms of noise - I haven't measured yet but even though there is an audible noise after turning up the gain more than 8 - I think I could live with it
since at that level my speaker would already be blown

The noise is not a low freq. hum - it is more somewhere between 1k and 5k. I tried rotating the power xfmr and putting a mu-metal shield between it and the pcbs but it didn't change anything.
The funny thing is that the channel that is further away from the power xfmr is even a little noisier than the one closer to the power xfmr.

I probably have to change the wiring at the XLRs for unbalanced use (since the SA3A is used on unbalanced inserts of my console only), because up to now it is still wired for balanced use.

The other thing I encountered when - with no input signal - turning the input gain all the way up to 10 and crank my speakers up a little more is a slowly oscillating low level noise...about 1 rotation a second.

It reminds me of how my soldering station sounds when it is up on temperature

So these are the only two things I would try to optimize somehow - if anybody has any idea - please let me know!



 

 

[rainton]

Ok short update,

the higher freq. noise went completely away after mounting the lid

And the the low freq. hum described above is so low that it is only audible when turning the gain up all the way to 10 and cranking up my my CRM level on the console to 3 o' clock -
which in a real live situation would either blow my woofers or my windows or both ;D

And I would actually not investigate further but I mentioned above that this low freq. hum is kind of oscillating - on both channels the same (here actually the one closer to the power xfmr is a tiny bit
louder)
Now the strange thing is that on the right channel there's also some kind of clicking noise - like a sweep hand of a clock...(no I didn't forget my watch in the case while building it )

Like I said it is only audible at extremely loud levels but I have never heard anything like this in one of my units.
I recorded it (SA3A Gain @10) and amplified it in the DAW by 25db so you can clearly hear it - if anyone knows what this could be - I'm all ears for any suggestions!

The clicking appears only on the right channel

Here's a link to the files:
right channel: https://dl.dropboxusercontent.com/u/43915944/Right%20Channel.mp3
left channel: https://dl.dropboxusercontent.com/u/43915944/Left%20Channel.mp3

 

[sharpeleven]

sounds exactly like a watch... Actually it's pretty spot on at 1 cycle per second. You said you didn't leave your watch inside  but maybe you have it next to youf on the table? I know my Swatch produces all sorts of noises in equipment, eg I cannot play guitar wearing it as it will as the clicks will be picked up loud and clear. Or maybe you have mounted it in a rack next to a unit that has a built-in timekeeper? Just a thought...

 

[rainton]

sounds exactly like a watch... Actually it's pretty spot on at 1 cycle per second. You said you didn't leave your watch inside  but maybe you have it next to youf on the table? I know my Swatch produces all sorts of noises in equipment, eg I cannot play guitar wearing it as it will as the clicks will be picked up loud and clear. Or maybe you have mounted it in a rack next to a unit that has a built-in timekeeper? Just a thought...

The thing is - I don't even own a watch
And in my racks: below the SA3A is a tube-preamp and above is a Tube-Vitalizer...

On the left channel the hum also has its cycles - but only on the right channel there's that clicking sound added to the cycling hum. Could it be a faulty relays  or anything?

I mean I worked with the unit a couple of weeks now and in a real world scenario you neither hear  a hum nor a clicking since it is only audible when the gain is set to "10" - but still I think it is not supposed to be like that and I'm a little worried there's some part in the unit that is causing it (like a relays or something)

 

[Spadehead]

Quick couple of questions guys....

I have just finished putting everything together and am waiting to power her up - I just have some niggling questions about the power supply.

I am wiring for 230V in the UK.
I have the Grey and Violet primary leads from the power transformer soldered together and isolated.
Blue from the tranny primary goes directly to neutral on the IEC inlet.
Live from the IEC goes straight to the power switch on the front - top position.
Middle position on the front power switch goes back to the brown cable from the power tranny.

So far so right (Ithink...?)

Next I have the 0V molex header terminal (J16) from the power section of the primary board wired directly to star ground, meeting the ground from the IEC. I have also individually earthed the XLR inputs and outputs on both channels.

Confusion is centred around the power secondaries going to S1S and S2F. A while back someone said these should be black and yellow respectively from the tranny's secondary wires.

I just had a look at the Triad data sheet that came with the tranny and at the bottom it says BLK to ORG and RED to YEL for Parallel. Should I be putting black AND orange together at S1S and red AND yellow together at S2F?

Apologies if this is obvious but I've spent a lot of time with this build and don't really want to blow it, or me for that matter, up when I power it up!!

Best wishes

Spadehead  8)

 

[atticmike]

Is a 50 VA power transformer gonna work with 15V? Or is that too much? 25 VA rather recommended?

 

[atticmike]

Also 2N5089 and 2N3417 are out of stock and nowhere attainable, any substitute?