100W Ultimate Fidelity Amplifier

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#4,281
still4given said:
Sorry, must be my ignorance. What is CMS pads wore?
Click to expand...


No still4given me sorry for may bad english; Its means that i added cms footprint.
 

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#4,290
apexaudio

Some time ago I have made very similar marantz kind of amp. I have spent lot of time on it, measuring and listening.
I think better is to keep the caps on the predrivers than putt Miller compensation at the VAS.
I persume I know why Marantz didn't used Miller caps at the VAS, I have done some tests and please take a look how the harmonics spectrum looks like with Miller compensation VS compensation cap connected to GND.
With compensation cap ''GND'' connected , haromics spectrum, IMD products and sonics is way better.

Terry
Yes I mean the 470p cap. If all is good enough it is not required of changing it but test can be made in some free time.
 

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#4,291
sonal kunal said:
Found oscillation of Apex AX9. :headbash: It was mistake I made on layout, I connected 47pF to collector and emitter of BD139 and BD140.

I have changed 15v zener to 22v for LME49860. Love sound of this amp on my monitor speaker lots of detail in mids, NX-14 will be replaced with AX9.

Corrected Layout.

Regards
Click to expand...

Hi Sonal,

I just finished building this amp based on the files in post #4259. I have a few questions for you and Mile.

1) The amp has pretty high gain. I sii the schematic shows 22R in the NFB but your silk calls for 56R. Was this something discussed somewhere that I missed. Was gain too low with the 22R?
2) What rails are you using? I figured the reason for the AX9 was to be able to used higher rails than the A9 but I tried using +-36V rails and the amp distorts. If I lower it to about +-34V the distortion goes away. I'm wondering if maybe the VAS current is too high. I used 15V zeners and am using an LT072 for the IC.

The amp sounds fine at the lower rails. However the A9 sounds just as good, maybe better and I'm running it on +-25v rails. I have a +-36V SMPS that I want to use for this AX9. Are there some values that need to be changed?

Thanks, Terry
 
#4,292
borys said:
apexaudio

Some time ago I have made very similar marantz kind of amp. I have spent lot of time on it, measuring and listening.
I think better is to keep the caps on the predrivers than putt Miller compensation at the VAS.
I persume I know why Marantz didn't used Miller caps at the VAS, I have done some tests and please take a look how the harmonics spectrum looks like with Miller compensation VS compensation cap connected to GND.
With compensation cap ''GND'' connected , haromics spectrum, IMD products and sonics is way better.

Terry
Yes I mean the 470p cap. If all is good enough it is not required of changing it but test can be made in some free time.
Click to expand...
Yes thank you, I prefer shunt compensation better tnan miller.
Regards
 
#4,293
I let the AX9 play for a couple hours. I then hooked it back to the scope because it sounded a little funny. I'm seeing oscillation at about half volume. I have the 47p caps on the b-c of the pre-drivers. The circuit is very similar to the A9 and it is rock solid. I need some suggestions as to what to do next
 
#4,294
still4given said:
I let the AX9 play for a couple hours. I then hooked it back to the scope because it sounded a little funny. I'm seeing oscillation at about half volume. I have the 47p caps on the b-c of the pre-drivers. The circuit is very similar to the A9 and it is rock solid. I need some suggestions as to what to do next
Click to expand...

Thiele, zobel? There are three 1k feedback resistors. You should try bypass it by 4.7pF, or 10pF. Be careful as it can burst oscillations if proves wrong.
 
#4,295
apexaudio said:
Replace 100pF with 3,3nF in input RF filter.
Click to expand...

still4given said:
Hi Mile,

3n3 in input filter did nothing for the oscillation. Still there on both boards. I am wondering if any of the guys who built this amp, tested it on a scope? The sound is nice so it may not be noticed unless played loudly. Still, I think it needs to be fixed.

Thanks, Terry
Click to expand...
one changes the input filter from the test version (100pF) to the audio version (3n3F) AFTER one has sorted all and any instabilities in the amplifier.
 
#4,296
still4given said:
Hi Sonal,

I just finished building this amp based on the files in post #4259. I have a few questions for you and Mile.

1) The amp has pretty high gain. I sii the schematic shows 22R in the NFB but your silk calls for 56R. Was this something discussed somewhere that I missed. Was gain too low with the 22R?
2) What rails are you using? I figured the reason for the AX9 was to be able to used higher rails than the A9 but I tried using +-36V rails and the amp distorts. If I lower it to about +-34V the distortion goes away. I'm wondering if maybe the VAS current is too high. I used 15V zeners and am using an LT072 for the IC.

The amp sounds fine at the lower rails. However the A9 sounds just as good, maybe better and I'm running it on +-25v rails. I have a +-36V SMPS that I want to use for this AX9. Are there some values that need to be changed?

Thanks, Terry
Click to expand...

With 22R gain is to high, use 100R instead 56R if you want to reduce gain.
Increase 47pF in VAS compensation, use 100pF or 220pF...
Regards
 
#4,297
Hi Sonal,

I just finished building this amp based on the files in post #4259. I have a few questions for you and Mile.

1) The amp has pretty high gain. I sii the schematic shows 22R in the NFB but your silk calls for 56R. Was this something discussed somewhere that I missed. Was gain too low with the 22R?
2) What rails are you using? I figured the reason for the AX9 was to be able to used higher rails than the A9 but I tried using +-36V rails and the amp distorts. If I lower it to about +-34V the distortion goes away. I'm wondering if maybe the VAS current is too high. I used 15V zeners and am using an LT072 for the IC.

The amp sounds fine at the lower rails. However the A9 sounds just as good, maybe better and I'm running it on +-25v rails. I have a +-36V SMPS that I want to use for this AX9. Are there some values that need to be changed?

Thanks, Terry
Click to expand...

Like miles said 22R is for high gain, 100R for lower gain. you can choose gain best suited for you. 56R work's for my setup, preamp has very low gain.

I'm using 35v supply, I am using 22v zener for lme49860 and had to change 10k resistor to 15k. Also changed 47pf to 68pF.

I'll check with 40v and 45v supply today and report.

Regards
Sonal Kunal
 
Last edited:
#4,298
Hello guys

I know the AX-20P is not a new subject but I would like to post here the changes of this layout to turn it from AX-14P to AX-20P I'm almost done with it this take time so I will continue checking to make sure all is correct

Regards
Juan
Click to expand...

Thanks Juan for making AX-20P.

I did made 4 pair version of AX-20 for old yamaha amp. Its still running and my friend loves it.

Regards
Sonal Kunal
 

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