Need orientation with tweaking a TASCAM MF-P01 - Page 2 - 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 3rd August 2012, 12:47 PM   #11
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The 470K actually biases the FET. Without a resistor here the FET input would be undefined at DC and so the voltage would be unpredictable and "roam" around. No DC current flows in the resistor but its vital it's there.

A 1uf ceramic is OK for the input but not perhaps the best choice quality wise. A film or polyester type would normally be used. That said the ceramic will work just fine.

The 470K resistor at the output needs to be on the other side of the cap. This always ensures the output is at zero volts DC.

The 22uf cap. An ordinary electroylitic is fine here because the AC signal changes equally on both sides of the cap and so the cap always sees 0 volts DC across it.

A practical point is that any minute DC offset at the opamp output could be "either way" (although unlikely there will be any with a FET opamp). So when the preamp is built and working and with NO signal measure the DC voltage across the 22uf cap. It should be no more than a mv or so and for perfection the cap should be orientated to alighn with the offset.
Attached Images
File Type: jpg Capture.JPG (72.3 KB, 15 views)
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 3rd August 2012, 02:35 PM   #12
diyAudio Member
 
Join Date: Jul 2012
Ok, very clear.

I understood the mission of C2, so in this case I can remove it because Im using FETs...
What I feared is a DC offset coming from the other side connected to my OA Output, but... there is no sense in that point of course jaja

Then what I see is that I can remove R5 also and happily! cause when output is disconnected, the AO output current travels through R2 and R3 making the same function as R5... (the output will be tied to ground even without R5)
  Reply With Quote
Old 3rd August 2012, 05:09 PM   #13
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The FET opamp will give zero volts DC output so C2/R5 can be ommitted.

(having them present makes the design "universal" in that it would work under any scenario... if you know the conditions and what it connects to then they can be safely left out)

The opamp output is at a low impedance and settles to zero volts irrespective of R5 and irrespective of the values of the feedback network (although the feedback network determines the operating point... if that makes sense). Even a resistor from opamp output to either the plus or the minus rail would not alter the output voltage away from zero by even a mv (as long as the resistor didn't cause the opamp maximum specified output current to be exceeded).
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 9th August 2012, 02:55 PM   #14
diyAudio Member
 
Join Date: Jul 2012
Ok, its done... and works like a charm!!

Thank's Mooly it has been a very nice talk, I could make it and works better than the bipolar transistor of the main line output of the machine, because at 0dB (Attenuation of the fader) the signal is compressed and clips, while my TL081 +6V/-6V does not
So the differences viewed in SoundForge drops that this preamplifier is better than nothing inside the machine.. I recommend to anyone who has one of this old-school "thing" to build this one.

For that I have included the final schematic and the photo of the case...
I hope to be usefull for anyone making preamplifiers or even better for tweaking this old model of TASCAM
(Price of the components around 25 euros)

Best regards
Attached Images
File Type: jpg IMG_0195.jpg (514.3 KB, 8 views)
Attached Files
File Type: pdf TASCAM MF-P01 4ch Hack.pdf (76.3 KB, 3 views)
  Reply With Quote
Old 9th August 2012, 02:59 PM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Really nice job, it looks great... well done.

I'm pleased it all worked out.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 9th August 2012, 03:05 PM   #16
diyAudio Member
 
Join Date: Jul 2012
in action
Attached Images
File Type: jpg TASCAM MF-P01 4ch Hack in action.jpg (815.5 KB, 5 views)
  Reply With Quote
Old 9th August 2012, 03:08 PM   #17
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Excellent
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  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
Tascam CD200 john dozier Digital Source 7 23rd June 2011 04:45 PM
Tascam M-06ST Ivn Francisco Solid State 1 27th October 2010 06:38 PM
MF Citation12 - MF gate resistor value NVD33 Pass Labs 14 21st September 2010 07:30 PM
Tascam 688? Riker Analogue Source 0 3rd September 2007 10:08 PM
Tascam 32 akersa Analogue Source 0 22nd June 2003 03:10 PM


New To Site? Need Help?

All times are GMT. The time now is 10:01 AM.


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