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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 10th January 2019, 08:05 PM   #3411
jimk04 is offline jimk04  United Kingdom
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I'm sorry I don't know if that is what you said. I'm new to all this.
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Old 10th January 2019, 10:43 PM   #3412
UKToecutter is offline UKToecutter  United Kingdom
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Salas DCG3 preamp (line & headphone)
No problem.
I’m waiting for my board to arrive from the DIYAudio shop so I can only say from having read all 342 pages of this thread, that the general advice is to use 2 independent transformers. I have seen some people use a single (or in your case, two connected together) but you may suffer crosstalk using a single power supply.
My old ears probably wouldn’t tell the difference but as my children are likely to use it as well, i’m Going for the dual transformers.
Good luck with your build.
Cheers
Andy
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Old 11th January 2019, 07:14 AM   #3413
jimk04 is offline jimk04  United Kingdom
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Yes sorry probably we are at cross purposes due to my lack of understanding and incorrect terminology.

I am building a dual mono DCSTB. The two toroids I just got were only 2 wire which was my mistake.

Not wanting to buy more incorrect parts, my comment regarding 2 times trafos with 2 of the 4 wires paralleled was ambiguous. Having looked at the commonly used here Antek AS0518 along with corresponding pictures of completed builds, I now better understand how to wire 2 transformers with 4 secondary wires each...into the two dcstb supplies.

I've ordwr3d yet more toroids!

Enjoy your build too. I shall document here as it progresses.
Cheers
Jim
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Old 11th January 2019, 07:46 AM   #3414
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
The BOM in the guide document is clear

"Transformers
2x 18+18V 50VA (example AnTek AS-0518)"
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Old 11th January 2019, 07:50 AM   #3415
jimk04 is offline jimk04  United Kingdom
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Salas yes the BOM is clear, however my head isn't!
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Old 11th January 2019, 08:10 AM   #3416
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
I would suggest you list the single secondary wrong ones in the swap meet section here to recover some of the cost if you envisage no projects with a likely use for them.

You may also use one of the Talema small guys you got for exclusively powering the In-Selector board which accepts single AC secondary. That's when fully populated including its local rectification+regulation area. Its spec is for 12V AC input but its sink can take 18V AC and the large voltage drop across its 7812 chip regulator when not using its utility 12V DC output (+Vreg out) for some sub module of significant consumption.

Any unused secondary wires from the small Talema you insulate and tuck away. You just need two wires from it for single AC output.
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Old 11th January 2019, 08:14 AM   #3417
jimk04 is offline jimk04  United Kingdom
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Yes I am considering selling them or using them to power some other class d amp build that I don't really need!

I don't have an I Select but I do have one if these
£18.28 | Amplifier board Chassis signal selection switch board audio source signal switching relay band with RCA AMPLIFIERS
Amplifier board Chassis signal selection switch board audio source signal switching relay band with RCA AMPLIFIERS-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

So maybe the talema will come in for that!
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Old 11th January 2019, 08:31 AM   #3418
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Just from the photos it seems to have two rectification diodes, a 15V Zener for DCin to a TO-92 sized chip reg of 12V out most possibly. The smoothing capacitor must be upgraded to 35V (if 25V, its marginal) and the series protection resistor to the Zener must take the dissipation of 18V-0-18V AC instead of 12V-0-12V AC which the kit has midway spec for (9V-15V), or modify it. If the small reg gets hot there are some top hat mini sinks for TO-92. Or power resistors can drop the AC. See it as a little practical electronics project to analyze for making it compatible and reliable for 18V-0-18V AC use.

By the way before the Mezmerize buffer preamp (introduced 10 years ago) it was not usual to see the relays DC manual switching selector principle on ebay or Ali kits
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Old 11th January 2019, 10:19 AM   #3419
jimk04 is offline jimk04  United Kingdom
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Thank you for analysing the board. I had been trying to fathom out how the power input side was configured.

I am sure that the I Select is far superior to this Ali board. I missed the last one from Tea bag and hope to get one in the next GB.
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Old 11th January 2019, 10:58 AM   #3420
Salas is offline Salas  Greece
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It surely has better quality signal relays and more inputs (as many you like up to six) or more options like a power output and sitting an Alps directly vs that AliX example which has no input wiring but it also fixes the panel work. I-Select BOM is more expensive on the other hand. You may accomplish the input switching job with various solutions that better suit your needs, no question about that. Ranging from a straight mechanical signal switch to a sophisticated remote controlled board with an LCD colour screen. Its up to a builder's aspiration.
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