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Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 17th September 2016, 07:03 PM   #101
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by AndrewT View Post
if you don't approve of source resistors then use emitter resistors in the mirror.
200r on both sides and then a 10r on Q2 side and the 22vr on the Q1 side.
This lets you dial out the offset and lets you see the balance of the LTP.

Big mirror resistors don't harm performance.
Emitter resistors in the mirror I had tried few values. 10-33-47-68-100R. Leaned to third harmonic and the DC turn on bump jumped high. I did not like it.

* They can be seen on the little blue breadboard in crop detail from the first picture of post#2
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Old 17th September 2016, 10:00 PM   #102
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switch on thump would be a problem with headphones.
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Old 17th September 2016, 11:27 PM   #103
Bonsai is offline Bonsai  Europe
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Andrew,

We are still waiting for you to publish one of your projects/designs.

No need to try to redesign Salas' pre/headphone amp. The distortion plots speak for themselves.

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Old 17th September 2016, 11:33 PM   #104
Salas is offline Salas  Greece
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He, I just found a forgotten one in the camera from the development phase. The mirror BJTs and the the second 9610 on daughter boards. There emitter resistors no more. That pic has much stuff. Slim uPA on main board, LSK170s and various Toshibas scattered around, LSK389 TO-71 lying at front left, 1uF C5 rejected at upper left. A Cosmos Tocos test pot at upper right that Tham will like, DN2540s aside left after cascoded and made not much sense, various C1s and C2s from hands on compensation trials, hey even a current regulator diode under the uPA that was evaluated for stability vs the BF looking at us over the "101" ceramic. I mean by blowing on them with the hot air station "scientifically" evaluated.
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Old 17th September 2016, 11:56 PM   #105
Salas is offline Salas  Greece
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Default Pottery

What pot to use? 10K-20K-50K-100K? OK not the extremes. Had it with 20K but how is it with 50K that's smoother for turning up and easier on sources? Well its not bad at all. Nice tone, just a bit rounder. Safer.
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Old 18th September 2016, 08:30 AM   #106
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Bonsai View Post
Andrew,

We are still waiting for you to publish one of your projects/designs.

No need to try to redesign Salas' pre/headphone amp. The distortion plots speak for themselves.

I am following this Thread with interest and was deliberately not making any comment on topology nor performance. It was looking good.
Until Salas said this:
Quote:
The LTP's tail CCS forces the units to bias at about 2.5mA Id per LTP side.
That is wrong and I felt forced to speak out and correct his error.
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Old 18th September 2016, 10:41 AM   #107
Salas is offline Salas  Greece
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When you want the LTP best balanced you set the trimmer to zero. The servo still copes fine. So simple.
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Old 18th September 2016, 01:34 PM   #108
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Quote:
Originally Posted by Salas View Post
What pot to use? 10K-20K-50K-100K? OK not the extremes. Had it with 20K but how is it with 50K that's smoother for turning up and easier on sources? Well its not bad at all. Nice tone, just a bit rounder. Safer.
Rounder in tone?
Can you describe that. I have only tried 50K. I am pleased.
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Old 18th September 2016, 04:14 PM   #109
Salas is offline Salas  Greece
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Quote:
Originally Posted by Tea-Bag View Post
Rounder in tone?
Can you describe that. I have only tried 50K. I am pleased.
Like when I was listening to Carey from Joni Mitchell's Blue in 192K FLAC with the 20K pot it was upfront and pristine but with the 50K one it came across bit less tiresome. A small difference but it could make the song passable without reaching for testing another filter from the DAC's menu. In this video the Appalachian dulcimer is sounding much softer in tone than the one in the record which is much tinnier in comparison. It won't make it soft like that, it will just put it in the recording space hanging a bit better. (https://www.youtube.com/watch?v=A1kcTjtdVE8)

Maybe it has to do with the necessarily narrower resulting bandwidth vs 20K. Then again all 20K or 50K pots won't be the same, but at least I had same cheap ones of various values. Its more of a system matching choice thing each builder has to do for himself.
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Old 18th September 2016, 04:28 PM   #110
Salas is offline Salas  Greece
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Quote:
Originally Posted by massimo View Post
Another Salas' interesting design! Thank you for sharing, it definitely deserves a try.

I have a few questions:

1. uPA68H (old, fat) or uPA68HA (new, slim)? You had the chance to test both, any prefrence?
I put the fat ones in today to answer you better. But I could not find any subjective difference. Maybe its the aural memory fainting between listening with the slims then desoldering them, soldering the others, and let warm up, but nothing striking.
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