Sorry, I meant to say if the hum/buzz that I'm experiencing using a single supply could be related to difference in current draw when sharing supply?
My question wasn't that clear
Thanks
Do
Hi Do
Nice site, thanks for the link.
Well, calibrating the First One is one straightforward procedure, very trivial and completely the same as with VSSA amplifier.
TR1, TR2 have symmetrical influence to VAS bias current and output DC offset at the same time. The best way to calibrate these two trimmers is to observe voltage drop between TP1-TP2 or TP3-TP4, same thing - same values and output DC offset between OUT and GND pin. In both measurement positions use mV meter, TP1-TP2 or TP3-TP4 should show 120 mV (at start temp app. 22-24°C) and OUT-GND should show 0 mV when TR1, TR2 are properly calibrated.
Following upper procedure TR3 should be set in a way that the whole amp module current consumption should show 280 mA (serial A-meter to positive supply wire).
Trivial setup of properly completed calibration can be done in a matter of seconds, see attached pic meters. SMD trimmers are a little bit more sensitive than TH type because they enable 5 turns only in comparison to 10 turns of a normal type.
Enjoy, L.C.
Attachments
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No matter the listening level habits I would always recommend SMPS1200A400.
And please do not forget to use DC sense module to preserve your speaker's health if something goes wrong, highly recommended. 😉
No, First One's PSRR is higher than supply current delta in dB between the channels. Please try to isolate all four mounting holes of SMPS1200, also measure DC resistance between all functional parts of a chassis, maybe heatsinks are not in zero ohm connection to main chassis plate, etc. 😉
I ordered SMPS1200A180. You made a payment for the amplifier board and protection, have written to you in the mail, but you do not otvechat already the 2nd day.
Hi Igo, the inside dimension of my chassis is 12.5" L x 8.0" W x 3.0" H. The outside dimension of the chassis not including the front panel is 12.75" L x 14.0" W x 3.0" H.
Okay, thank you.
You should have written, but I'm waiting to send information.
Let's just order the VSSA. what is the price on the board VSSA?
I meant it in spirit, as the v1.3 mods can be directly applied to the VSSA... and probably would 🙂
Hi LC,
Could you please give me the values for TR1, TR2 and TR3 trimmers on FirstOne? I want to replace them with 14 turns trimmers for finer adjustments.
Would those one fit?
http://www.digikey.ca/product-search/en?pv23=4&FV=fff40004%2Cfff80338%2C600001%2C1140003&k=trimmer&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
Thanks
Do
Could you please give me the values for TR1, TR2 and TR3 trimmers on FirstOne? I want to replace them with 14 turns trimmers for finer adjustments.
Would those one fit?
http://www.digikey.ca/product-search/en?pv23=4&FV=fff40004%2Cfff80338%2C600001%2C1140003&k=trimmer&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
Thanks
Do
I don*t know where is the problem. I calibrated it very easy and offset was 0.1 to 0.3 mV. I used multimeter for bias mesurement and at the same time scope at output for dc.
Hi androa76,
There's absolutely no problem, I just want to waste my money because I can! 😉
It just give a little bit more maneuver when you have a 14 turns instead of a 5 turns... Instead of having 1 degre in the specific fine tuning zone, I might have 3-4 degres instead.
Ciao!
Do
There is no problem.... when you describe at one channel is 30mV and other 3mV dc. This poti is already multiturn so change to anothet one would not be solution.
You want to set it better than 0.1 mV? Why?
I yust want to help you that with 2 multimeters the setting will be easy. Without changeing Tr..
Good luck
You want to set it better than 0.1 mV? Why?
I yust want to help you that with 2 multimeters the setting will be easy. Without changeing Tr..
Good luck