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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 13th September 2017, 01:51 PM   #2111
Algar_emi is offline Algar_emi  Canada
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Salas DCG3 preamp (line & headphone)
Hi Salas, you recommend two 50VA transformers, at 18V sec. That's more than 1.389A (Serie) per transfo (Amgis No. L01-6384 from Digikey), per channel (in dual mono supply mode). Isn't overkill?

I would had expect this rating to be sufficien for both channel, and to use instead two transformer Avmeco TE70064, 36V, 25VA each, 0.694A (Serie) per channel, or the first 50VA model is the right one?

I have both in stock, and I want to be sure to select the correct one. Thanks
SB
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Old 13th September 2017, 03:33 PM   #2112
Salas is offline Salas  Greece
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I had used 30VA split bobbin encapsulated trafos and they went near 45C hence the 50VA recommendation. Don't know if your encapsulated toroids run cooler.

Also in full bridge the trafos have 40% less max current. The preamp as a whole pulls 20W from the wall when at 100mA bias.

Keeping in mind the above info to decide your VA. Or do a dummy load test including bridge rectification and filter caps to check temperature on the small ones.
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Old 13th September 2017, 05:45 PM   #2113
Algar_emi is offline Algar_emi  Canada
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Thanks. I'll experiment and see if the smaller VA run reasonnably warm, otherwise I'll use the 50VA. Thanks
SB
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Old 13th September 2017, 06:18 PM   #2114
PKI is offline PKI  United States
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Salas DCG3 preamp (line & headphone)
Salas I finally made a proper PSU for my muses volume control and using the preamp right after RAW outputs of Soekris dam1021 as you suggested. Oh man, sounds fantastic! Thanks :-).

Out of curiosity have you ever looked at THD at higher voltage, like 5V maybe?
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Old 13th September 2017, 08:08 PM   #2115
Salas is offline Salas  Greece
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Good news. Congrats. Post some pics also when you are able.

I ran the output voltage gamut for spot frequency THD reliable tests up to 5.66V pk-pk when the proto was finished. That is my USB audio box's 0dBFS max input. I checked that the sims followed too. High swing THD I ran only indicatively when it was on the breadboard via a divider. Full swing I had run on the scope that takes huge signal voltages just to see the waveforms shapes at max.

For the audio band THD sweeps I used voltage conditions like in the O2 tests. Half open pot noise is also involved. That amp had gone viral so there was a chance that more people would be familiar with such conditions I thought.

I also added sweeps with 32 Ohm to 600 Ohm real headphone loads, not only line level resistor loads. Those you see in post #1 are those charts I kept.

I can run a sim for you now though. You mean 5V pk-pk or RMS? Also at what output load?
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Old 13th September 2017, 08:27 PM   #2116
PKI is offline PKI  United States
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Yep 5V RMS. I am running it in to F5 with 100k input. Thanks.
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Old 13th September 2017, 08:38 PM   #2117
PKI is offline PKI  United States
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Quote:
Originally Posted by PKI View Post
Yep 5V RMS. I am running it in to F5 with 100k input. Thanks.

Was planning to just plug it for a quick test before making things clean, but can't turn off since
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Old 13th September 2017, 08:59 PM   #2118
dbis is offline dbis  United States
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Default Antek transfos

The Antek AS-0518 are back in stock! I just ordered two.
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Old 13th September 2017, 09:16 PM   #2119
Salas is offline Salas  Greece
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Quote:
Originally Posted by PKI View Post
Was planning to just plug it for a quick test before making things clean, but can't turn off since
They work well together then. No weird surprises on first test = best possible news.

Quote:
Originally Posted by PKI View Post
Yep 5V RMS. I am running it in to F5 with 100k input. Thanks.
Here's your sim result. THD for 1kHz signal at 14dBV (5VRMS) output level. 100k load + 100pF for the interconnect.
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Old 13th September 2017, 09:17 PM   #2120
Salas is offline Salas  Greece
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Quote:
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The Antek AS-0518 are back in stock! I just ordered two.
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