Threshold SL10 modified - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th August 2007, 07:23 PM   #1
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Default Threshold SL10 modified

Hello,

recently I got a Threshold SL10 and was wondering why it had a loud noise on one channel using the MC input. I investigated a little bit and found this Nelson Pass designed input stage with the 8 parallel transistors. And I realized that my SL10 is not original state. There are some modifications, pls see the picture below.
Now my question is: what do you think about these modifications, are they "improvements"?

The noise thing is another theme, it was caused by a bad contact inside my MC cartridge and the DC offset on the SL10 input.

Thanks in advance
Gerhard
Attached Images
File Type: jpg sl10mod.jpg (76.9 KB, 689 views)
  Reply With Quote
Old 24th August 2007, 08:27 PM   #2
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Without knowing the actual brand/type of capacitors it's impossible to say if they are "improvements"
  Reply With Quote
Old 25th August 2007, 05:24 PM   #3
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Thanks for the quick response.

The 1uF (in place of 47uF at the collectors) is a foil type "Audiophiler KP Kondensator 1uF 250V", I suppose MKP type.
The 220uF (in place of 47uF at the bases) is an electrolytic SME 47uF 25V.
The 47K resistor in place of the 15K is a metal film type.
I enclose a picture.

Thanks
Gerhard
Attached Images
File Type: jpg mods03.jpg (58.2 KB, 584 views)
  Reply With Quote
Old 26th August 2007, 01:03 AM   #4
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
I wonder why the brand and type is essential for answering my question.

Isn't it more important that the original nominal values of the parts have been dramatically changed?



Regards,
Gerhard
  Reply With Quote
Old 26th August 2007, 12:49 PM   #5
Giaime is offline Giaime  Italy
diyAudio Member
 
Giaime's Avatar
 
Join Date: Oct 2004
Send a message via MSN to Giaime
Quote:
Originally posted by SL10User
I wonder why the brand and type is essential for answering my question.

Isn't it more important that the original nominal values of the parts have been dramatically changed?



Regards,
Gerhard
Yes, of course it is. With those mods, specifically the 1uF cap at the output, you greatly increased low cutoff frequency. Perhaps this helps with rumble noise, which I found a little bit high in the SL10 (it is a DC coupled design in MM mode), I don't know. But I think that a new, good, high quality 47uF electrolytic in place of that 1uF would be better, especially when you consider that in the original unit IIRC there were tantalum units.

A friend of mine did this (replacing all coupling tantalum, and all old electros, with new high quality electrolytics) with his SL10 and the sound greatly improved...
  Reply With Quote
Old 26th August 2007, 05:25 PM   #6
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Hi Giaime,

thanks for your reply.

That was I thought first, too, when I realized the mod with the 1uF. The original 15K was increased 3 times, I suppose for compensating the smaller capacitor. And the 4 times bigger capacitor at the bases, what effect does it have?

I cannot hear a lack of deep bass, maybe the frequency goes deep enough.
Can anyone here calculate the theoretical frequency cut off?


I think I listen a couple of days to it and then restore the original state. I'll keep you informed.

Thanks,
Gerhard
  Reply With Quote
Old 27th August 2007, 12:28 PM   #7
Giaime is offline Giaime  Italy
diyAudio Member
 
Giaime's Avatar
 
Join Date: Oct 2004
Send a message via MSN to Giaime
Quote:
Originally posted by SL10User
Can anyone here calculate the theoretical frequency cut off?
I'll see if I can without committing too many errors

Let's make a rough calculation. The stock unit has 47uF, and it sees a 15k resistor, then a 22k pot in parallel (let's forget about the 1.5k collector load for the bjts). For low settings of the volume pot, total resistance is about 9k. The -3dB frequency is about 0.4Hz.

With those mods, total resistance "seen" by the cap is about 15k, so the cutoff frequency (with 1uF cap) is ~11Hz.

Useful if you have rumble problems, absolutely: but if you haven't, I would use a larger cap, at least 10uF. Voltages in the SL10 are pretty low, so no need for 250V caps (it looks like 250V), and I bet you can find a commercial grade 10uF 63V mylar capacitor that has the same physical dimensions of that audiophile capacitor
  Reply With Quote
Old 27th August 2007, 08:47 PM   #8
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Hi Giaime,

thanks again for your kind support.

So it seems that the modifications are really well-thought, not only "improvements" following blind some "replace all electrolytics!" religions.

I'll follow your advice after hearing a few days and getting accomodated. In my opinion it sounds pretty good in the current state. Maybe it's even getting better..........

Can you imagine the sense of the 220uF? Is it also a subsonic filter function?

Cheers,
Gerhard
Attached Images
File Type: jpg cap10uf.jpg (41.6 KB, 377 views)
  Reply With Quote
Old 28th August 2007, 09:24 AM   #9
h_a is offline h_a  Europe
diyAudio Member
 
h_a's Avatar
 
Join Date: Sep 2006
Location: Graz, Austria
Well, personally I don't want -3dB at 11Hz. That means that 20 Hz is also affected, albeit less.

Sure this won't really affect audible frequencies, since I can't imagine records with 20 Hz frequencies (groove would be insanely deeply and widely cut), but as a matter of principle I won't like it.

If you have a reasonable turntable - and I'm sure you have - you don't need a rumble filter at all.

At least for me the questionable benefit of those Mundorfs is not worth the frequency trade-off. I would get a MKP with larger capacity.

On the other hand if you don't care, it seems to be nicely done, so why not stick with it?

Cheers, Hannes

EDIT: oh and I forgot: what would be the sense of adding another subsonic filter?
  Reply With Quote
Old 27th September 2007, 10:35 PM   #10
diyAudio Member
 
Join Date: Aug 2007
Send a message via AIM to SL10User Send a message via MSN to SL10User Send a message via Yahoo to SL10User
Hello all,

the green 10uF MKT sounds pretty good. As good as the (Mundorf) 1uF cap......;-))

I cannot hear a difference.

Hannes, I agree!

Thanks to all
Gerhard
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
threshold sl10 intense-tavda Pass Labs 116 1st December 2013 09:52 PM
threshold SL10 - DC output pjmont Pass Labs 11 29th February 2012 07:26 AM
threshold sl10 donadi.tv Pass Labs 1 15th February 2008 04:25 PM
Threshold sl10 fs intense-tavda Swap Meet 3 23rd December 2006 11:22 AM


New To Site? Need Help?

All times are GMT. The time now is 05:59 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2