Need help with Giesberts HEXFET AMP - Page 3 - 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 7th October 2005, 02:17 PM   #21
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Quote:
Originally posted by amplifierguru
Hi Zimo,

Notwithstanding all the suggestions made to date, partticularly those from Ilimzn, the circuit has a flaw!

R10, R14 need to be linked out for the compensation on the first stage load to work!

Cheers,
greg
How so, don't the RC's effectively short any differential current in the collectors of the LTPs, hence no AC component to the bases of the VAS? OTOH, I'm not myself today with the mother in law of all colds, am I missing something?
  Reply With Quote
Old 10th October 2005, 10:45 AM   #22
Zimo is offline Zimo  Finland
diyAudio Member
 
Join Date: Oct 2004
Send a message via AIM to Zimo Send a message via MSN to Zimo Send a message via Yahoo to Zimo
I turned my amp on yesterday!

It works now (again)

I didnīt change those 2.2nF caps to 2.7nF original but however I took the risk.. So it seems really that the biggest problem here was those IRFxxxN pairs. I havenīt measured it yet with a scope, but now listened it about three hours. Sounds great

Bias current was easily increased to more than 500mA with those changed resistor values. So high value is not necessary so I left it to about 200mA. DC offset is about +-3mV per channel, so quite good indeed (It could be easily adjusted to -+1mV if you put there 10- or 20-turn trimmer.)

My DC protection circuits seems not to working yet.. I tested it with 1.5VDC but it didnīt took speakers off, but left one cuts speaker when it gets warmer.. (The layout is design of my so the problem can be there)

So there is few "bugs" left that Iīll have to repair

But anyway Thanks for anyone of you (specially to ilimzn), IRFP models were the real key to solve the problems.

Iīll tell you more info when I measure amp with scope and generator.

See you soon.

Simo
  Reply With Quote
Old 11th October 2005, 02:02 AM   #23
Account Disabled
 
Join Date: Aug 2004
Location: Earth
Hi Ilimzn,

I think your cold has got hold!

..."How so, don't the RC's effectively short any differential current in the collectors of the LTPs, hence no AC component to the bases of the VAS? "...

Looking at the upper half, the output from the first stage is single ended not differential - the voltage across R9, not R9 and R10. So the compensation should be across R9 to the rail. Since there is no output from R10 to the next stage the easiest way of ensuring the comp (R3 series C3) is across R9 is to link out R10. The compensation as it stands would be fine for a differential output from the first stage but the 1.2K of R10 adds to R3 = 1K247 rendering it ineffective.

This is also why the cct is insensitive to C3 at 2n2 or 2n7 - or 1n or 10n!! It's not doing anything.

Hope that helps.

Cheers,
greg
  Reply With Quote
Old 12th October 2005, 01:29 AM   #24
Zimo is offline Zimo  Finland
diyAudio Member
 
Join Date: Oct 2004
Send a message via AIM to Zimo Send a message via MSN to Zimo Send a message via Yahoo to Zimo
I got my DC protection circuits work!

The problem was that the chematic had changed places of two resistors. However now it cuts speakers of when +-0.8VDC is running in the output. And the temperature problem is also gone.

Thanks for your explanation amplifierguru

I canīt understand your "fix", since when you took R10 off the T2 collector is not connected to +35VDC anymore? and I think I canīt work without that... or can it?

Anyway I changed C3 and C4 to their original values. Since I canīt measure the difference anyway I have to just trust that it cuts now differentialpairs frequency at 6.5MHz.

Quote:
Originally posted by amplifierguru

Looking at the upper half, the output from the first stage is single ended not differential
I found this explanation based on Elektors original release.

"RC networks from the R3/C3 and R4/C4 decrease the bandwidth of differential amplifiers and power amplifier in the 6.5MHZ. Resistors R11-12-15-16 function as local feedback in the differential amplifiers improving the linearity. The differential amplifiers are supplied with constant current from current sources T5 and T6."
  Reply With Quote
Old 12th October 2005, 01:47 AM   #25
Account Disabled
 
Join Date: Aug 2004
Location: Earth
Hi Zimo,

I was not clear explaining! When I said -

..."R10, R14 need to be linked out for the compensation on the first stage load to work!"

I should have emphasized LINK! R10 and R14 need to be shorted. As it is it has < 6 dB effect so almost any C can be used there or pull it out. But it's presence is intended to form a pole at fp=1/(2*pi*R9*C3) and a zero at fz=1(2*pi*R3C3) but this zero is currently at fz=1/(2*pi*(R3+R10)C3 which is the same as fp because R3<<R10= R9. So C3 just parallels R9 and R10 at Fp with little effect.
The amp will not function if you pull out R10 and R14. LINK them out.

Hope that's clearer.

Cheers,
Greg
  Reply With Quote
Old 23rd November 2005, 12:54 PM   #26
diyAudio Member
 
Join Date: Nov 2003
Location: Maastricht
Zimo, I was browsing your website and saw you own a Yamaha CA-1010. I have a CA-1000 in my junkbox, you don't happen to have any schematics of the 1010?
  Reply With Quote
Old 23rd November 2005, 01:09 PM   #27
Zimo is offline Zimo  Finland
diyAudio Member
 
Join Date: Oct 2004
Send a message via AIM to Zimo Send a message via MSN to Zimo Send a message via Yahoo to Zimo
Glad to see that someone else have also great old Yammies

Yes I have schematics to CA-1010 and as far as I know CA-1000 has nearly the same interiors, so I quess they will fit to your one also.

I just got a scanner and will scan those as soon as I can. Just give me your email address and I will send those pictures to you

Iīll try to make a PDF to compress that a little if I can. (havenīt done before)

BTW what is the problem with your amp? Mine had a collapsed transistor which driver relays and It cut the speaker relay, when the transistor warmed. Not a bad problem but so hard to find (this seems to be a usual problem with 70īs Yamahas)

Cheers!

Simo
  Reply With Quote
Old 23rd November 2005, 01:52 PM   #28
diyAudio Member
 
Join Date: Mar 2004
Location: Krakow
Quote:
Originally posted by Zimo
I got my DC protection circuits work!
[....]

Hej Zimo!
thank you for your posts,
and all of you that sent yours advices!
I burned ~15 pairs 540/9540 during messing with this circuit...
Could you send real-working schematic with measured voltages of your prototype?
__________________
regards, Pawel
  Reply With Quote
Old 24th November 2005, 12:31 AM   #29
Rick NL is offline Rick NL  Netherlands
diyAudio Member
 
Join Date: Sep 2003
Location: Gouda
Hi Guys,
This amps seems to be sensitive.
A few things.
Your data refer to 540/9540 and the PSupply on 2 x 30 VAC 2 x 43 VDC. This may be too much for these rather small devices. The original Hexfet used 2 x 25 VAC and the IGBT 2 x 30 VAC.

In the July-Aug 2002 Elektor a revision to get better stability from both versions was published.
Place 27 nF paralel to R31
Place a resistor of 20k between collector of T8 and mass
Place a resistor of 20k between collector of T9 and mass
Replace R20 by 1k8
Replace R17 and R18 by 390 Ohms
Replace R3 and R4 by 33 Ohms (same sort of effect as jumpering R10 and R14?)
According to Elektor this should improve the stability and the performance.

Hope you can use this information

Rick
__________________
After all it's the music
  Reply With Quote
Old 24th November 2005, 01:09 AM   #30
Account Disabled
 
Join Date: Aug 2004
Location: Earth
Hi Rick NL,

"Replace R3 and R4 by 33 Ohms (same sort of effect as jumpering R10 and R14?)
According to Elektor this should improve the stability and the performance."

C3,4 create a pole with R9,13 at 50KHz (with R10,14 linked out)
and a zero at 1.2MHz with the 47R for R3,4. A change to 33R will only take that zero to 1.6MHz. But the original pole cannot occur because R10,14 get in the way STILL. They need to be jumpered.

Cheers,
greg
  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
HEXFET amp - please help me fix it. raise0 Solid State 69 29th April 2010 06:06 AM
Ton Giesberts - High-End Power Amp velicko Elektor 2 7th November 2007 03:38 AM
HEXFET amp silverchris Solid State 9 31st October 2006 04:38 PM
3rd generiation HEXFET vs. 5th generation HEXFET DarkOne Solid State 3 12th April 2002 08:51 PM
HexFet 60 Ychnaval Solid State 4 10th December 2001 08:16 AM


New To Site? Need Help?

All times are GMT. The time now is 05:58 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2