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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 19th September 2016, 12:09 PM   #111
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Noise floor pics with the volume pot at max. Even with power cords surrounding, a mains earthing lead to the preamp's chassis can do a decent job of chasing some hum field gremlins though. Long lead and going around through the bench PSU's route to mains is poor practice nonetheless. But at -121dB 50 HZ hum and -132dB 100HZ buzz maybe just passable for an open test build on a bench using no shielded coax signal wiring and a silly simple non battery PSU
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Old 19th September 2016, 03:40 PM   #112
Bonsai is offline Bonsai  Europe
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What sound card are you using Salas?
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Old 19th September 2016, 03:49 PM   #113
massimo is online now massimo  Italy
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Quote:
Originally Posted by Salas View Post
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.
Thank you for the extra time, Salas.
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Old 19th September 2016, 04:03 PM   #114
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
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Originally Posted by Bonsai View Post
What sound card are you using Salas?
EMU Tracker Pre (its a compact variation of the 0404 in essence). It never had proper drivers beyond WIN XP though. Hence I use it only with a second hand notebook on XP.
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Old 19th September 2016, 04:12 PM   #115
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by massimo View Post
Thank you for the extra time, Salas.
The slim ones were around 8mA Idss when the fat ones are around 6mA Idss (at 10V). The slim ones were closer to one another between channels. The slim ones tend to have less Vgs (off). Given all those differences I can only see very small differentiations in measured THD. The circuit staging of bias and other parameters prevail over small Yfs and Ciss Crss differences at set point.

When you want different enough result try matched K170s. While matched K117s are behaving like the uPAs. LSK389 is interesting because it gives the more Yfs but has different THD trend than the K170s. Has less pF than those. The pads for uPA take one Toshiba looking forward and one looking the other way. Those DGS-SGD pins are printed on the silkscreen for no confusion.
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Old 25th September 2016, 01:24 PM   #116
JimT is offline JimT  Canada
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Looking forward to this.

I am starting to put some parts together and of course I have a question. It looks like I can use matched 2SK117's in place of the uPA68HA's. As I have a bunch of these it would be great to be able to use them, but if you recommend I buy some uPA68HA's I will do that. Please note that my 2SK117's are GR grade. I tried to figure this out but can not find a data sheet for the uPA68HA's.

Thanks
Jim
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Old 25th September 2016, 02:34 PM   #117
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
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Originally Posted by JimT View Post
Looking forward to this.

I am starting to put some parts together and of course I have a question. It looks like I can use matched 2SK117's in place of the uPA68HA's. As I have a bunch of these it would be great to be able to use them, but if you recommend I buy some uPA68HA's I will do that. Please note that my 2SK117's are GR grade. I tried to figure this out but can not find a data sheet for the uPA68HA's.

Thanks
Jim
Hi Jim! I know its difficult to find comprehensive uPA data so I had posted its best datasheet in reply #25

2SK117s >3mA idss are usable and alright. GR range covers that also. I had measured with such and they compare very nicely to uPA. When same idss they look close enough on the tracer too. Beta tester had built a pre on matrix board with those (face to face bonded) as well.

News are I had finished with the minor practical stuff so I completed with Crt the little corrections on the protoboards. Added MKP2 C5 frame, corrected the silkscreen orientation of Qa, fixed correctly mirroring pads of VR1s orientations, added alternative SMD1206 pads for Cb Cc, added output bleeder resistors to DCSTB. Now they are V1.02 and sent over to Tea.

I gave my finished Pre, PSU, & I-Select modules to Michael yesterday (the first beta tester that I had to meet in months) since he has some expertise with perspex front panel manipulation and he had originally wanted to box mine up too in the end using a cheap chassis. He uses his matrix build for long time now listening with overhauled Eminent Technology LFT8s and he also made a copy for his friend Chris who listens with vintage IRS Gamma. They usually employ DIY CFA amps and have very good TT rigs etc. I gave him an empty V1.0 proto-board to finish his build nicer looking too. He is seldom in posting here though.

I will write a BOM and few construction tips at a point. Its your job to lobby Tea for a near future GB though because I don't do organizing stuff myself ever. Too attentive a thing for me

If you will like it we will possibly make separate channel boards higher rails hotrod version some time too. No worries.
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Old 25th September 2016, 05:55 PM   #118
Marra is offline Marra  United Kingdom
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Salas DCG3 preamp (line & headphone)
Count me in if a GB goes ahead.
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Old 25th September 2016, 07:04 PM   #119
JimT is offline JimT  Canada
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Great news Salas. Seems I was reading too fast to spot the link, I was overly excited. I have been looking at building a pre and almost dug out the old tube collection to search for 6V6's. Will build it some day, but the new pre has just the right gain, drives headphones and I know the design, PCB and Group Buy will all be excellent.

PS:
Sorry but I will wait patiently for TeaBag's GB or at least bear my anxiety quietly. Don't want to distract him from getting things ready!!!

Thanks to you, CRT and TeaBag. A great team.

Jim
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Old 25th September 2016, 07:26 PM   #120
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Alright What headphones you got?
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