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LSK pre - BAF 2013
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Old 11th January 2018, 08:13 PM   #541
Hikari1 is offline Hikari1  United States
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Attachment 655655

I did in fact add more feedback...520R/150R was as close as I could get to what you suggested. The sound is a little bit more lively now. Seems like a little less gain too? Not sure which I prefer, the original has a smoothness and silkiness I like. But I will have to listen for a while and see.

Also, while the circuit seems DC stable in a temp controlled situation it does fluctuate a bit (20mv or so) with temp changes. It probably doesn't help that my phono amp with shut regs is on top of it. I will leave the cps for now.

Still impressed. Thanks Juma.
Juma,

After playing with the feedback values I think I like 680/150R, your original values, the best. It has a smooth, airy sound I like and the widest soundstage.

I'd like to try a buffer on output. Why? Might get some more low-end dynamics and keep the airy highs without changing the feedback values. Also, might be awesome for headphones.

Do you have any recommendations?

Currently I am thinking about using the output stage from Wayne's Pass DIY headphone amp (attached) since the bias mechanism is convenient.
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Old 12th January 2018, 08:45 AM   #542
juma is offline juma  Germany
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If you want to drive headphones, it's OK.
If you just want low Zout, a simple JFET Source follower at the output would be enough, like this:
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Last edited by juma; 12th January 2018 at 08:49 AM.
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Old 14th January 2018, 03:43 AM   #543
Hikari1 is offline Hikari1  United States
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Thanks Juma. That is good info. Currently Iam playing around with coupling caps to see if I can get it where I want it without adding another stage. Believe it or not, right now I have a 100uf Silmic cap on output bypassed by a poly cap and it sounds very good. I like the original lower feedback values. But at this point it’s really more tweaking than anything.
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Old 28th January 2018, 08:22 PM   #544
eLarson is offline eLarson  United States
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Would it be worth trying something like the circuit of post #485 in a single-ended fashion?

I ask because I happen to have some LSK170s but I do not currently have any LSK74s to form the complementary side.
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Old 28th January 2018, 09:33 PM   #545
juma is offline juma  Germany
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Would it be worth trying ...
Interesting idea. I am looking forward to see your schematic.
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Old 29th January 2018, 01:32 AM   #546
eLarson is offline eLarson  United States
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Interesting idea. I am looking forward to see your schematic.
Thanks, I'll give it a shot. I'm trying to learn how to use KiCad so it might be a little bit before I get it to work.
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Old 8th February 2018, 04:30 PM   #547
Hikari1 is offline Hikari1  United States
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Juma,

After playing with the feedback values I think I like 680/150R, your original values, the best. It has a smooth, airy sound I like and the widest soundstage.

I'd like to try a buffer on output. Why? Might get some more low-end dynamics and keep the airy highs without changing the feedback values. Also, might be awesome for headphones.

Do you have any recommendations?

Currently I am thinking about using the output stage from Wayne's Pass DIY headphone amp (attached) since the bias mechanism is convenient.
So, I started to put together Juma's LSK/CM front end (very nice) + the pass optocoupler output stage. Why? I want to drive headphones AND power amps at home and Juma's front end has the sound I am looking for, spatially.

I am wondering about the feedback values. 680/150R sounds right to me...Best mix of dynamics and soundstage.

Wayne's follower uses 4.75K/1K for feedback. About the same ratio and gain. But the ground resistor loads the BJT's in Juma's stage and 1K might wrong.

Should I stick with 680/150R? Feedback will be as attached, all the way to the output of the follower stage. I am planning on mounting Juma's front end above the mosfet followers like UGS to potentially experiment with other follwers and front ends later. Fun stuff.
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File Type: jpg headphoneSCH1.jpg (195.3 KB, 484 views)
File Type: png Screen shot 2018-02-03 at 9.26.57 PM.png (12.5 KB, 477 views)
File Type: jpg IMG_1775.JPG (911.7 KB, 268 views)

Last edited by Hikari1; 8th February 2018 at 04:33 PM. Reason: add pics
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Old 9th April 2018, 07:53 PM   #548
Hikari1 is offline Hikari1  United States
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Here’s some progress.

It works. Cap coupled for now although offset seems very stable. But Iam being cautious. Boards do not bolted down until I figure out if I need the caps.

Iam going to listen for a while and see what I think.

THANK YOU JUMA!
After the first version I made of Juma's Current Mirror preamp was auditioned I decided to go back and try it again with better matched BC transistors (matched to 2% or so) and a little more attention to detail (mundorf silver solder, teflon wire, etc.). This time I used Takman metal films and omitted the pot since I was using a cap on output anyways. Hoping it sounds better than the first version but it's too early to tell. Seems a bit warmer but it's not broken in yet. I really like the sound of these preamps though.

Curiously, both versions seem to raise the DC offset on the power amp 10-20mv although they are cap coupled and they have no measurable DC on preamp output. Strange.
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Old 11th April 2018, 10:36 AM   #549
woofertester is offline woofertester  United States
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Quote:
Originally Posted by Hikari1 View Post
After the first version I made of Juma's Current Mirror preamp was auditioned I decided to go back and try it again with better matched BC transistors (matched to 2% or so) and a little more attention to detail (mundorf silver solder, teflon wire, etc.). This time I used Takman metal films and omitted the pot since I was using a cap on output anyways. Hoping it sounds better than the first version but it's too early to tell. Seems a bit warmer but it's not broken in yet. I really like the sound of these preamps though.

Curiously, both versions seem to raise the DC offset on the power amp 10-20mv although they are cap coupled and they have no measurable DC on preamp output. Strange.
Are you using a signal generator? If so, place a cap between the sig gen and your preamp and see if that solves the 20mV offset.
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Old 11th April 2018, 03:28 PM   #550
Hikari1 is offline Hikari1  United States
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Are you using a signal generator? If so, place a cap between the sig gen and your preamp and see if that solves the 20mV offset.
I do not. But I have a CD with some tone sweeps...I could use that.

Bu all my sources are cap coupled as well. It really is kind of strange.
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