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-   -   Salas DCG3 preamp (line & headphone) (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone.html)

Salas 19th September 2016 12:09 PM

4 Attachment(s)
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 :D

Bonsai 19th September 2016 03:40 PM

What sound card are you using Salas?

massimo 19th September 2016 03:49 PM

Quote:

Originally Posted by Salas (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4833017.html#post4833017)
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.

Salas 19th September 2016 04:03 PM

Quote:

Originally Posted by Bonsai (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4834007.html#post4834007)
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.

Salas 19th September 2016 04:12 PM

Quote:

Originally Posted by massimo (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4834019.html#post4834019)
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.

JimT 25th September 2016 01:24 PM

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

Salas 25th September 2016 02:34 PM

2 Attachment(s)
Quote:

Originally Posted by JimT (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone-post4839545.html#post4839545)
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 :D

If you will like it we will possibly make separate channel boards higher rails hotrod version some time too. No worries. :up:

Marra 25th September 2016 05:55 PM

Count me in if a GB goes ahead.

JimT 25th September 2016 07:04 PM

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

Salas 25th September 2016 07:26 PM

Alright :) What headphones you got?


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