Lightspeed Attenuator a new passive preamp - Page 112 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 19th January 2008, 02:50 AM   #1111
diyAudio Member
 
Join Date: Feb 2005
Default Increase Zin of amp

Excuse me for butting in with a slightly off-topic question -

The Zin of the F3 (ZV9, etc) power amp is only 10K and I'm using a buffer after the L'speed to make it function (remarkably well) but, as George has said, this is not ideal.

Can this input Z be increased to 100K without an input buffer stage?

I have also found that TL431's benefit from simple noise filters in CCS situations.

Thank you George for your design and years of development.

... James
__________________
... jh
  Reply With Quote
Old 19th January 2008, 03:02 AM   #1112
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Hi James, Nelsons amps are not the norm input wise, his earlier Threshold Stasis could be increased easily, via the input resistor (also fet input), I've done a couple of them without having dc offset problems, but the F3 is a different beast.
I know he reads this Lightspeed thread as I've had comunications with him, he is very interested in the Lightspeed progress, so maybe he will reply to this question better than I, if not in a couple of days I will ask him to contribute.


Cheers George
Attached Images
File Type: jpg f3.jpg (59.4 KB, 1907 views)
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote
Old 19th January 2008, 03:51 AM   #1113
diyAudio Member
 
Join Date: Feb 2005
Thanks George - much appreciated

... jh
__________________
... jh
  Reply With Quote
Old 19th January 2008, 04:27 AM   #1114
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Default Re: Increase Zin of amp

Quote:
Originally posted by jameshillj
The Zin of the F3 (ZV9, etc) power amp is only 10K and I'm using a buffer after the L'speed to make it function (remarkably well) but, as George has said, this is not ideal.

Can this input Z be increased to 100K without an input buffer stage?
In a word, no.

You will need a buffer. If you can't come up with one, I do have
a nice 100K input JFET circuit scheduled for publication early this
year.
  Reply With Quote
Old 19th January 2008, 05:20 AM   #1115
diyAudio Member
 
Join Date: Feb 2005
Default increased Zin for F3

Thank you, Nelson -
And for all your designs, publications and "shared time" over the years - will look forward to this one, too.

Currently using a fairly standard k170, j74 cct with shunt supplies that works fairly well but "sucks out" some of the dynamics (unlike the NS10 cct) - could be better, no doubt.

L'speed has a different sound to the X2.5, especially with the NOS dac.

Both F3 amp and preamp are working perfectly and do like silver IC's.

Regards ... James
__________________
... jh
  Reply With Quote
Old 19th January 2008, 08:33 PM   #1116
diyAudio Member
 
Join Date: Dec 2002
Location: Houston
Quote:
Originally posted by pietjers
Tolu:

This is the CCS version I designed. See post #1001 for details. I use it as a volume control of a tube amplifier (so not as a passive pre-amp). The attenuation range of the version with the fixed resistor is about 60dB. But as you can read in post #1001 the design leaves much room to suit your specific needs.

Peter

Click the image to open in full size.

Peter,
I want to build a version of your CCS to test. My setup has mono controls, about 125K log pots, parallel tracks from a stereo 250K Alpha.
Looking at your circuit, the main change is a single LDR per circuit. I think the value of R2 and R4 needs to be doubled. Would the voltage reference also need to be increased.
I should have some TL-431 2.5 volte references, but also some LM329DZ, Low noise, but 6.95 volt refferences. Would a reference this high be usable?
My power supply is a raw 17 volts. Now how tracking regs dropping to 12 volts and then down to 5. This can be changed to any supply voltage from 14 volts down.
I would ask this offline, but your email is not enabled.

Thanks in advance
George
__________________
Cheapest is bestest
  Reply With Quote
Old 20th January 2008, 08:34 AM   #1117
diyAudio Member
 
pietjers's Avatar
 
Join Date: Oct 2006
Panelhead George,

The 250k pots and TL431 are just fine! The other references are too high.
Let me explain how to calculate the range of the CCS. Its VERY simple.
First you need to calculate the voltage at the emitter of T1, T2 (Ve). For 3-pin references such as TL341 and TLV431 this is very simple because these ICs maintain Vref at their ref pin, so Ve=Vref. For two pin references you will have to subtract the Vbe of the transistor from the voltage of the reference. Because the base current is very small, 0.5V per p-n junction is a good value to calculate with. So subtract 0.5V for a normal transistor and 1V for a darlington.
Now divide the Ve by the resistance between the emitter and the anode of the reference, and you have the current of the CCS. For Imax (the maximum current) of the CCS I take 10 mA. First calculate R2 and then calculate the range of the CCS.

Formulas for TL431 / TLV431:
R2 = Vref / Imax
Imin = Vref / (P1 + R2)

Formulas for two pin references (such as LM336-2.5, LM285BYZ-1.2, etc.)
R2 = (Vref Vbe) / Imax
Imin = (Vref Vbe) / (P1 + R2)

So with a TL431, a 250k pot and a Imax of 10 mA:
R2 = 2.495 / 0.01 = 249.5 Ohm
Imin = 2.495 / (250k + 249.5) = 10 uA
This will give a LDR resistance range of approximately 50 Ohm to 20 kOhm.

Peter
  Reply With Quote
Old 22nd January 2008, 06:03 PM   #1118
diyAudio Member
 
theophile's Avatar
 
Join Date: Sep 2006
Location: Sunshine Coast Queensland Australia
Default New Lightspeed owner.

Living in Australia,I decided to take a punt on George's little creation.
I've never met George,but it turns out I surfed on George's turf for a few years('72-'76).
From the time I sent George the money,to the day I received the Light speed,was almost lightspeed in itself.I think George bumped me up the list a bit.
My system is comprised of a collection of some great sounding vintage components.Japanese,Solid State.Awesome sounding.
My phono stage is brand new(Simaudio Moon LP5.3) and my speakers are diy activated Altec Valencias.
The Lightspeed was inserted into the system as a substitute for an EchoWars modified Kenwood 700C preamp.
First-up I had to turn-up the input level for my active crossover,since unlike the 700C,the LS doesn't provide any gain.
The initial listening impressions were very favourable for the LS.In my system the EW 700C wipes the floor with the other new(Transcendent Sound Grounded Grid)and Vintage preamps(High quality Japanese Solid State)that I have.
The LS initially sounded on a par with the EW 700C.However further use of the unit has elevated it above the 700C.
They both sound cut from the same cloth.Wonderful dynamics,richly harmonic,great openness and spaciousness,well defined imagery.great focus,natural tonality,great rhythm pace and timing and a general sense of being 'unprocessed'.
Both extremely musical,and musically involving.
It's like the LS takes all the individual qualities of the EW 700C,and extends each parameter a further step or two.
Very nice indeed.
I may incur the wrath of George(insert the sensation of the ground shaking here),and admit that I have inserted a Burson Audio Buffer stage after the Lightspeed to no apparent ill effect.
I'll try taking the Burson out of the loop again,to test it's contribution.
So far it's a big thumbs-up from me for the Lightspeed.As long as you have high output sources(no vintage tuners,cassette decks),and your impedances aren't contrary, it's a very,very nice sounding unit.
Thanks George.
  Reply With Quote
Old 23rd January 2008, 10:58 AM   #1119
majkisk is offline majkisk  Macedonia
diyAudio Member
 
Join Date: Jan 2008
Please could anyone can tell me (maybe Georgehifi)can I find lightspeed attenuator in some kind kit form.
  Reply With Quote
Old 23rd January 2008, 11:33 AM   #1120
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Quote:
Originally posted by majkisk
Please could anyone can tell me (maybe Georgehifi)can I find lightspeed attenuator in some kind kit form.

As yet no, one day maybe.
But I can see a problem already with the 4 x matched NSL-32SR2S, I could send them out matched in a kit, then a heavy handed someone and soldering iron too hot will unmatch them again, yes you can change the resistance curve with too much heat from a very hot soldering iron.
The built version is 500aud which is 296euros, a kit would be around 100aud cheaper, it's the matching of the NSL-32SR2S that is the most labour intensive part of the Lightspeed Attenuator, and there's no way that part can be left to the diy'er who buys the kit.

Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  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



New To Site? Need Help?

All times are GMT. The time now is 12:48 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