much less crazy idea - Page 8 - diyAudio
 much less crazy idea
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 3rd July 2002, 11:25 AM #106 diyAudio Member   Join Date: Oct 2000 Location: Sweden ehh? I'm not completly sure what you mean If I increase the value of R6 to 1k1. I will get 0,75V across Q4. /Freddie
 3rd July 2002, 11:26 AM #107 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada also, it would be a good idea to add a current mirror to your long tailed pair, it'll achieve proper balance upon application of power and improve distortion and linearity figures... To see the mirror, just peek at my diagram on this post, you'll see it... It's quite easy to implement and I don't believe it requires any modification of the curcuit mathwise or currentwise...
 3rd July 2002, 11:29 AM #108 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada okay, sorry for my bad description of the current thing... you must reduce the value of R7 to compensate for the voltage drop accross the 47 ohm resistors essentially, the current through the curcuit will stay the same, but the voltage drop accross R7 will be less and the voltage accross R6 will stay the same... say, for example you have 2mA flowing down your LTP, thus R7 drops 1.12 volts and that's that, but say you add the 47 ohm resistors, and you want .5 volts accross them, then R7 must only drop only .62 volts and thus be reduced to 310 ohms respectively to remain at the same current. but this is only an example since .62 volts is much too little accross R7... You'd basically want between 3 and 4 mA flowing down so each side of the LTP gets between 1.5 and 2 mA to idle at and there's enough voltage drop accross R7 to keep the current sink transistor happy at all times... i hope this explains a little better
 3rd July 2002, 11:38 AM #109 diyAudio Member     Join Date: Oct 2001 Location: Denmark There are some parameters you want to have right first. To minimize DC-offset you should set the idle current to a optimum level. So in the VAS stage you want a idlecurrent ~9.5mA. At this current the voltage drop across R9, R10 would be ~51V(R9 and R10 should be .5W resistors). => R40 * 9.5mA = ~.95V across R40. => .95V+.65V = 1.6V Idle current in Q1 => 1.6V/R6 => 1.6V/560R = ~2.86mA. At this point your current through Q3 should be 2*2.86mA => R7 = ~250R. This is not an optimum value for MPSA06. Use 2N5550/5551 instead. With MPSA06 the optimum idlecurrent would be around 30mA where the HFE curve is flat. With 2N5550/5551 2.86mA is perfect. It is faster and the Cob (the capacitance between C-B) is lower than with MPSA06. Sonny
 3rd July 2002, 11:42 AM #110 diyAudio Member   Join Date: Oct 2000 Location: Sweden Sonny, Thanks a lot for the detalied reply. /Freddie
 3rd July 2002, 12:04 PM #111 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada shoot, I was thinking that you wanted to compensate for addition of tail resistors, i must be tired, but what sonny just described is, of course, correct, so never mind my babble there. But it would still be an interesting idea to add a current mirror...
 3rd July 2002, 12:07 PM #112 diyAudio Member     Join Date: Oct 2001 Location: Denmark It's okay to babble!!! Current mirror is a nice thing to add... Some like it .. some don't .. I do like them. Sonny
 3rd July 2002, 12:10 PM #113 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada Well, I know it's okay to babble, but I hate it when I get real into detail without first thinking clearly what I was getting into detail about... Anyhow, yes, a current source is a nice addition, but not a requirement, kind of like an opinion basically
diyAudio Member

Join Date: Oct 2000
Location: Sweden
Final version?

Here it is once again.

BTW: Is the value of R11 and R12 critical.

Thanks again Sonny.

Duo, I won't add a current mirror. Lower distorsion does not always mean better sound, and I don't want to make this amp more complicated either. For example I like the sound of my BoZ preamp better, than my OPA604 based preamp. Guess which one has got the lowest distorsion

/Freddie
Attached Images
 p3a-mod.gif (19.7 KB, 412 views)

 3rd July 2002, 12:17 PM #115 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada Yeah, like I said, just an opinion, if you're trying to keep it simple, I agree, it's a good way to go about things for sure Also, I believe I read on Rod Elliot's pages that R11 and 12 arent very critical, but let sonny make a proper point of that cause he probably has more experience with compound pairs And i'd also have to agree that lower distortion doesn't always have to do with better sound. I 've seen some pretty high distortion numbers that meant nothing when you listened to the amp
 3rd July 2002, 12:25 PM #116 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada also, thanks to info from sonny, I'll change my input trannies to 2n5550 and 5551, the've got perfect specs
diyAudio Member

Join Date: Jun 2002
hmmm, i was just thinking, i didn't work out my resistors properly, can you give me some pointers for biasing the vas in here sonny, it would be much appreciated!
Attached Images
 theend.jpg (70.3 KB, 394 views)

diyAudio Member

Join Date: Oct 2001
Location: Denmark
Quote:
 Originally posted by Duo also, thanks to info from sonny, I'll change my input trannies to 2n5550 and 5551, the've got perfect specs

uhhmmmm!!! 2N5550/5551 is npn, The complementary pair is 2n5401 - PNP.

First find the datasheet on the fairchild BJT's in the VAS stage. Then i will get back later.

Freddie and Duo : R11 and R12 will form a pole with Cob in the output.
Also : Try figure out wich idle current you will have in the drivers and output in the compound outputstage.

Sonny

 3rd July 2002, 02:14 PM #119 diyAudio Member     Join Date: Jun 2002 Location: Victoria, BC, Canada okay, well, the current in my OT's is variable, but I'm having trouble with the current mirror... have I got the VAS connected properly?? It doesn't seem like it'll bias properly will it?
 3rd July 2002, 02:41 PM #120 diyAudio Member     Join Date: Oct 2001 Location: Denmark The current through the driver pairs in the compound outputstage will not change that much. Only a few mA's. Replace R21 and R20 with 100R instead of 27R. There can easely be 20mV difference in the VBE of to identical BJT's With 100R a mismatch of 20mV will give a mismatch of 200uA. With 27R this will be 1mA! KSD401 should at least be HFE class Y not to load your current mirror to hard. Have you checked the pin combination on the new BJT's?. Are you sim or building it? You should have something around 390mV across R20 and R21 @100R.?? Sonny

 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 OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post ak_47_boy Digital Source 2 7th February 2009 05:38 AM mazeroth Solid State 13 8th January 2005 06:20 PM Nysan Solid State 6 15th April 2004 01:10 PM mekanoplastik Everything Else 12 6th January 2003 12:28 AM

 New To Site? Need Help?

All times are GMT. The time now is 10:30 AM.