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Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 11th December 2019, 03:11 PM   #4281
Salas is online now Salas  Greece
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Salas DCG3 preamp (line & headphone)
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Originally Posted by bubba177 View Post
Salas, got my 10k TKD pot installed. Used a 3.01k resistor, didn’t have any 2.2k. Overall impressions? I once described this preamp as a “ window on the world”, well somebody just found the windex ! Blacker backgrounds, smoother, but the bass, clean, airy, articulate and musical all the way down to dc. THE best bass I have ever heard in my 67 years on the planet. My hat is off to you Salas ! Bravo ! I have different bc327-40 to try next, will check back in later. Mark
Congratulations. You are welcome.
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Old 11th December 2019, 03:26 PM   #4282
Salas is online now Salas  Greece
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Originally Posted by alexkosha View Post
I did find out that this is all in my analyzer setup cables. Salas mentioned that once when we discussed cheap RCA to TRS adapters. Tried several other homemade cables with these cheap ¼ TRS adapters with mostly same results. Some are more noisy than the others, but all have same picks at the same exact points as on my image during loop test.
Besides good termination contacts, when there is interference star quad is best. But it has double the capacitance.

Star-quad microphone cable demonstration
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Old 11th December 2019, 04:11 PM   #4283
Salas is online now Salas  Greece
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This is the cable from the video. Canare L-4E6ES. I mainly use it for umbilical between PSU and MC phono boxes. For signal at home its better to avoid the highly capacitive star quad cables if there is not a specific interference source crossing the interconnections that you can hear with normal ones.
In the photo there is also a switching DC to DC bipolar converter board I once made. I used it for powering a differential input chip phono I designed for lab play. In collaboration with a plug style switching adapter so it could be remotely placed on the wall. Thus no transformer and no AC power cabling near the audio circuit.
Goal was to avoid any mains related magnetic field interference around such a high gain & low input signal circuit with the least of expenditure and space.
And I did. No hum spikes for 62dB 1kHz gain. But there was a gotcha. The SMPS noise generated beyond the audio spectrum came back integrated and more than doubled the audible hiss. Weak sound in lower frequencies too. Fail.
Just like when you don't use the 20MHz limit button on a few hundred MHz scope and its line is fatter than a slower cheaper scope. Because noise appears over bandwidth and comes back integrated as a total mV number. The wider the bandwidth the more there is. It can be low per Hz but when the Hz are many it adds up.
Moral of the story is you win some you lose some. Something working great in a specific area isn't necessarily great in all areas.

*Because of RIAA curve there is 40dB gain difference from 20Hz-20kHz. As reflected in the plot's grass tilt. So hum frequencies are even more promoted to be picked in a phono.

*I used UBiB in the end to avoid the hiss and the weak SQ.
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Old 11th December 2019, 06:50 PM   #4284
orelli is offline orelli  Italy
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Hi Salas, I want build the DCSTB with J113 in the range 10-20mA.
Have I to change the value of R1 (33R) or not?
Thanks
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Old 11th December 2019, 07:12 PM   #4285
Salas is online now Salas  Greece
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Yes, but you have to experiment on a breadboard first. You got to find R1 value that drops those averagely high IDSS JFETs down to 5mA. Like in post #452 but with 10VDC. You may also differentiate R1 for individual J113s if you don't have four with same mA result for same R1.
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Old 11th December 2019, 08:47 PM   #4286
orelli is offline orelli  Italy
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If pf1502 is below 10mA, and J113 from 10 to 20mA, R1 become higher in value.
I'm correct?
let's me know.
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Old 11th December 2019, 08:53 PM   #4287
Salas is online now Salas  Greece
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Yes, the higher the Idss the higher the R1 for same Id (5mA).
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Old 11th December 2019, 08:55 PM   #4288
orelli is offline orelli  Italy
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Thank you very much
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Old Yesterday, 01:26 AM   #4289
alexkosha is offline alexkosha  United States
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by Salas View Post
Canare L-4E6ES.
I used it for powering a differential input chip phono I designed for lab play.
*I used UBiB in the end to avoid the hiss and the weak SQ.
Sorry for deviation from the main subject of that thread, but it is very interesting presentation on YouTube and useful info. Thank you for that link. I also use umbilical cord made of quad star cable on my 2 FSP phonos, but I use industrial type Belden made (# 1172A B591000) cable. I did not get an issues with 60Hz magnetic pickup on my phonos yet (I did not measured.. ), but I have AM pick up issue by cable that connects my arm to my phono. I use Cardas Wire 4 x 33awg cable designed for tunearms and it is about 1m long. That is probably wrong cable type for that purpose and I would be glad if your can advise for a better one. I do not have a DIN on arm side and it is soldered directly to the arm wires inside of arm column. Other side is RCAs gong to phono with GND.
Very interesting DC-DC device to isolate magnetic pickup, but it is 24V out with CT and probably impossible to use it on our FSP running 50V.
It might be possible to use +24V and -24V and let it to float?
My just arrived Mogami cables are quite and I see no picks at low frequencies at all. Totally flat there and I’ll attache ARTA images soon.
About my 2nd just upgraded with Khozmo DCG3, I’m planing long listening session during coming weekend and some “golden ear” friends will come.
So, lets see what would be the impression and consensus, if any….

P.S. As far as I remember, it was an attempt to change regulator on FSP PCB for UBIB. Is it still in plan-list?

Last edited by alexkosha; Yesterday at 01:31 AM.
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Old Yesterday, 10:40 AM   #4290
Salas is online now Salas  Greece
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Use RF bead or 1uH mini coil in the signal entry point of the phono board to try kill AM. The tonearm maybe needs chassis GND could be a reason.
Don't use SMPS in a phono, the example was to show you may avoid hum field with such when no AC cables are around too but their hundreds kHz switching noise can come back as hiss especially in high gain circuits. Because SMPS small hum field benefit was mentioned in the video. Then again all the adapters he used to demonstrate strong interference were SMPS too. There could be very good ones well filtered and screened suited for line level. Like the one in the pro DAC he showed.

Still enough people tend to prefer L-Adapter linear stabilizer for instance when replacing SMPS bricks even in non interference problematic gear anyway.

That DC/DC in my example came handy to convert a single rail SMPS adapter in a specific situation. Wouldn't be there if the wall adapter was delivering +/- to start with. There is variety.

Nice that you solved the hum susceptible test cables problem.

P.S. Not only that but also trying to make sensitivity selection easier with DIP switches than configuring it by changing some parts. Its under development. A phono only test board is ready for now so to can connect it with regular UBiB and see how they behave together.
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