My first DIY amplifier 20 years a go - Page 40 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 29th June 2013, 02:05 PM   #391
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Finally the Lat FET's !

In spite of all the work I have had I managed to , finally, remove the bipolar Darlingtons and replace them with Hitachi 2SK1058/2SJ162 latFET's.

I got blue smoke !!

Luckily I had used 10 ohm protection resistors in the fuse holders. They burnt up dramatically. I spent a long time trying to figure out what was happening and burnt a few more resistors ( those in the fuse holder!).
Finally while I was checking the devices it suddenly dawned on me that the LatFET pin out isn't like the IRFP MOSFET's ! I had forgotten that it was Gate Source Drain from left to right. I haven't used one in a long time ! So I had interchanged the Drain and Source leads.

I fixed that and the amp worked fine ( the devices were not damaged). The sound is very good like the bipolar version but I felt that transients like the kettle drum etc., had a bit more bite without being harsh. Voice is just as good and about deep bass I'm not certain. It does go very low and is tight but is the bipolar tighter /and a shade deeper?
I can't judge as I used the same pcb for this one. I'll have to remove the power transistors again to check this one. It has to be a level adjusted A/B comparison which I can't do now. But I like both but would build the LatFET version due to the apparent crisper transient reproduction . I am not using an input capacitor. The signal comes direct from the Bluray player via an Alps volume control. The power supply has 2x10,000uF caps per rail ( so total of 4x10,000uF )

Now I will have to build a stereo version of the bipolar and the LatFET circuit and do an A/B comparison. If I had to choose without any more testing I'd pick the LatFET version for reasons mentioned above and the fact that I needn't worry about dc bias stability.

So finally I can use my precious stock of 2SK135/2SJ50 and 2SK134/2SJ49 !
In fact I have a whole lot of plans around this module. Plenty of testing to do. It's going to be exciting !

I guess I'll also have to build a P3A also just to compare and see where each one stands in relation to each other.
Trust many others are also building this amp . I'm guessing that someone will come up with some comparisons with other amps.

I still have to try out the discrete Darlington ! Maybe I should do it now, before this board gets damaged or 'lost'!

Listening to Sade right now. Sounds very good !
__________________
AM

Last edited by ashok; 29th June 2013 at 02:08 PM.
  Reply With Quote
Old 29th June 2013, 03:39 PM   #392
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Ash,
use a mains bulb tester to power up after EVERY modification.
__________________
regards Andrew T.
  Reply With Quote
Old 29th June 2013, 05:15 PM   #393
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Nice work Ashok - I think there's a saying "after great trouble comes the truth" so some smoke along the way is a good sign maybe...

Since the FETs are easy to parallel you might try an extra pair - the bass may improve further, but you may lose some definition somewhere else.

Keep going !
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 29th June 2013, 05:36 PM   #394
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Hi Andrew,
I always think of rigging up a bulb and switch permanently as experimentation sometimes happens suddenly. But like many things it hasn't happened yet ! Maybe this time I should do this quickly. Loosing Lat FETS is a GREAT loss ! Not just the money but it's so hard for me to get them !

Bigun. Yes a parallel set of transistors might help the low end. But let me get some boards made that can accept both devices and then compare them. The LatFET really sounds super clean . Half my stock of LatFET came directly from Hitachi. Their semicon manager gave them to me when I was on a training visit. So they are quite 'old' !

Looks like holding on to 'precious' material does pay off after many years ! I have some Toshiba power FET's also. Want to compare them with Hitachi's LatFet. I was under the impression that Renesas still made LatFET's with a different number.

Cheers.

Yes, I just checked. The 2sk1056 to 1058 and 2SK222X and p channel versions are still in production today !
__________________
AM

Last edited by ashok; 29th June 2013 at 05:41 PM.
  Reply With Quote
Old 30th June 2013, 02:21 AM   #395
diyAudio Member
 
Join Date: Sep 2005
Ashok
That is good news, you compared the Darlington to LatFet in the same circuit before I did.
I hope you will test the darlington with the semiconductors I advised.
Believe me when I write it took me awhile until I managed to get the right transistors until I get the performance I do like.
Still I have no idea about the sound of your amp due to the experience I got over testing so many transistors for driver stage and for input (especially for the driver stage took me awhile, a lot of different transistors until I get the sound satisfied me).
I know how sensitive and how much influence has on the sound the different type of semiconductors.
Most of those transistor provided me a good result to but not outstanding.
With the recommended transistors I managed to get over all much better sound.
Again I hope you will test the amp with the recommended semis before you totally gave up on the bipolar power transistors.
I will test it to, I made the LatFet PC board layout a while back, I just run out of clad board. At local store a small piece used to buy for $2 now $8, it is a big rip of..
I will have to purchase some from Ebay.
Since I have many LatFet project I would be more interested to use Toshiba mosfets like 2SK1530/2SJ201..

Greetings G
  Reply With Quote
Old 30th June 2013, 05:32 PM   #396
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Hi G, You might be horrified if you know what I'm up to now !
I'm using bipolar power transistors ( 2SC5200/ 2SA1943 ) as current dumpers.
0.5 ohms in series with the current MOSFET's ( Drain) to the power supply. The bipolars connected to these resistors to turn them on ( BE) . Collectors going to the respective Source 0.22 ohms resistors.

If you ask why......The useable current capability goes up , dc stability is there and MOSFET dissipation reduced. Only way of knowing how it sounds is to build it and listen to it. Simulation wouldn't tell you that. Less expensive than two pairs of MOSFET's ! I've already rigged it up but I'm terribly sleepy and don't want to turn it on in case I missed something and get blue smoke again !

Single MOSFET pair really sounds very nice. Can't say if I will hear significant differences in mono mode.
Cheers.
__________________
AM
  Reply With Quote
Old 1st July 2013, 12:25 AM   #397
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
The close-spaced fins will do little of nothing without a fan.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 1st July 2013, 01:11 AM   #398
wahab is offline wahab  Algeria
diyAudio Member
 
Join Date: Nov 2009
Location: algeria/france
Quote:
Originally Posted by ashok View Post
In spite of all the work I have had I managed to , finally, remove the bipolar Darlingtons and replace them with Hitachi 2SK1058/2SJ162 latFET's.

I got blue smoke !!

Luckily I had used 10 ohm protection resistors in the fuse holders. They burnt up dramatically. I spent a long time trying to figure out what was happening and burnt a few more resistors ( those in the fuse holder!).
Finally while I was checking the devices it suddenly dawned on me that the LatFET pin out isn't like the IRFP MOSFET's ! I had forgotten that it was Gate Source Drain from left to right. I haven't used one in a long time ! So I had interchanged the Drain and Source leads.

I fixed that and the amp worked fine ( the devices were not damaged). The sound is very good like the bipolar version but I felt that transients like the kettle drum etc., had a bit more bite without being harsh. Voice is just as good and about deep bass I'm not certain. It does go very low and is tight but is the bipolar tighter /and a shade deeper?
I can't judge as I used the same pcb for this one. I'll have to remove the power transistors again to check this one. It has to be a level adjusted A/B comparison which I can't do now. But I like both but would build the LatFET version due to the apparent crisper transient reproduction . I am not using an input capacitor. The signal comes direct from the Bluray player via an Alps volume control. The power supply has 2x10,000uF caps per rail ( so total of 4x10,000uF )
Hi Ashok ,

If necessary you can extend the low frequency response
by increasing the two capacitors that are on the feedback path ,
the voltage at their pins is very low , less than 1V , you can use
6.3V 1000uF caps that should be of same size than 220uF/35V.

Anyway , latfets are quite forgiving..

I m doing some more sims to check if reducing distorsion
wouldnt endanger stability , if it works i ll post the results.
Attached Images
File Type: gif GABOR CFB MOD2 SCH caps.gif (12.7 KB, 195 views)
  Reply With Quote
Old 1st July 2013, 04:06 AM   #399
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Yeah I'm pretty much aware of the NFB caps and it's value. I didn't want to go larger as I don't have better types of that size. In any case it is good enough as it is. Bass is good right now. It won't audibly go any lower if the LF -3dB point goes any lower. Right now that is at about 1 Hz ! I do use low voltage caps ( 16 V ). This cap only sees the base emitter voltage plus the drop on the emitter resistor which adds up ,in my case, to under 1 volt.
The current heat sink seems pretty good with the LatFET's. I'm playing pretty loud and it's not getting too hot.

I don't expect the bipolar add-on version to tighten up the bass as it comes on only at higher voltage levels . So if the speakers back emf is the controlling factor , those bipolar's probably won't do anything for it.

I've always been curious about how it would sound and right now it's easy to rig it up. So before everything is stripped up again , it's time to make a test.

About stability. I have not used C6 and C7 as shown. I've used base collector caps of 47pF on the two drivers and everything is fine.
With the LatFET I decided to try the C6 and C7 as shown on your circuit and it oscillated badly. I've used 220 ohms at the gate.
__________________
AM

Last edited by ashok; 1st July 2013 at 04:13 AM.
  Reply With Quote
Old 1st July 2013, 09:22 AM   #400
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
The voltage across the NFB cap should be the same as the voltage across the Rin resistor.

This is: Ib (input transistor) * Rin and is typically 100mVdc to 300mVdc

High Gain Input transistors (hFE~500) and low values for Rin (20k) give very low input offset voltage. ~40mVdc.
__________________
regards Andrew T.
  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
camelot arthur dac 20 years old inertial Digital Line Level 5 22nd December 2012 10:57 AM
My best sound amplifier of these last 20 years audiodesign Solid State 22 28th August 2011 11:54 PM
new speakers after 20 years sys3 Multi-Way 5 28th May 2006 05:08 AM
Pic: 20 years old wasted on Xmas! Prune Everything Else 5 27th December 2004 11:01 AM
2N3055...supply for 20 years!! Netlist Swap Meet 5 12th June 2003 12:45 AM


New To Site? Need Help?

All times are GMT. The time now is 09:44 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