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Old 17th April 2012, 08:16 PM   #121
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Quote:
Originally Posted by Joachim Gerhard View Post
I build the super simple version of post one. It worked right away. I made some additions and changes. I run it on plus-minus 35V with 500 Ohm resistors instead of trimmers. I runs quite hot that way but i can stilll toutch the cooling profile so it must be around 55° Celsius.
I added a low pass filter at 3MHz -3dB. This amp is very fast and with the filter the square wave is clean. I have cap multipliers in the PSU. That way the amp is dead quiet on my 95dB sensitive speakers.
The sound is a bit lighter then with my power buffer ( see MPP ). By adjusting the gain in the preamp and using a warmer sounding cable i got it going. I have to listen more but the amp is very transparent.
Hi Joachim long time no "see"

Hey, first post worked right away, very nice to hear the news hehe, like that.

OK, what to do to make it more heavier, definitely something on bias and low spectrum linearization. Diodes 1N4148 forward voltage reach threshold potential of input Vbe quite fast, few mA of forward current is enough. But we want a little more current here to make diode potential more stable, independent of feedback current modulation. So solutions are two:
- using diodes with lower forward voltage characteristic than 1N4148 and feed them with more current to get to the right potential to bias input pair - brutal current force will make +0,65V and -0,65V potential much more stable
- logically more uF of elcos parallel to diodes would help to maintain stable DC potential too, also AC current transfer frequency characteristic would go down substantially

To resume, try to use Schottky diodes BAS70 or similar instead 1N4148, you will have to bias them with much more forward current to get just the right bias potential for the inputs. Secondly try to higher elcos to 4700uF each, bass response should improve. Also you can experiment to decouple diodes with film caps 1uF or 0,1uF.

The main aim with all this measures is to make +/-0,65 V DC potential as stable as possible. I am very curious what the results would be, regards Andrej
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Old 17th April 2012, 08:57 PM   #122
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Sure, i just build it as is to study it. What do you think to replace the 1kOhm resistors with CCS“s ? Gives more open loop gain but stability has to be watched.
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Old 17th April 2012, 09:32 PM   #123
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When Josie come home
So good
She“s the pride of the neighborhood
She“s the raw flame
The live wire
She prayes like a Roman
With her eyes on fire
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Old 17th April 2012, 09:38 PM   #124
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Quote:
Originally Posted by Joachim Gerhard View Post
Sure, i just build it as is to study it. What do you think to replace the 1kOhm resistors with CCS“s ? Gives more open loop gain but stability has to be watched.
In a simple design as TSSA is, each and every part must tend to its theoretical maximum for the role in the design.

Yes CCSs would definitely be much better choice in this position than resistors, certainly.

Before CCS you can try quick&dirty test from schematic attached, just to be sure this is the right direction to go.

This simple circuit will completely eliminate feedback current influence. Sound check with this test bench will also tell you more.
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Old 17th April 2012, 09:42 PM   #125
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later

it does sound as is so interesting that i need to listen more to get the full measure

there is some hardness that makes me sad but dynamics are imense

it is a rough ride but exiting


it has tremendoes speed and resolution
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Old 17th April 2012, 09:54 PM   #126
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Quote:
Originally Posted by Joachim Gerhard View Post
When Josie come home
So good
She“s the pride of the neighborhood
She“s the raw flame
The live wire
She prayes like a Roman
With her eyes on fire




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Old 17th April 2012, 10:55 PM   #127
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Try :
Joe Sample
"Rainbow Seeker"
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Old 17th April 2012, 11:17 PM   #128
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According latest LC advises on empty space and trace length...
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Old 18th April 2012, 01:18 AM   #129
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According latest LC advises on empty space and trace length...
Nice progress Idefixes. As this is single layer PCB it's understandable that you're playing inside limited options. Wire jumpers sometimes are just not enough, space optimization in this kind of PCB depends only on designer's ingenuity. You're getting close to the limits, but still some more room for improvement.

Also the output's emitter resistors should be different, MPC71, 0,22 ohm/5W, non-inductive should find place here. 10 ohm zobel resistor should be 2 W, much smaller than the present one.

TLP627 area is to crowded and too close to screw. Move BF245B + resistor to the other side and put blue LED in the middle position near the input. It's always nice to maintain symmetry from the sch to the PCB as well.

Input BJTs should be closer with pins since their flats will be glued together.

Orientation of the IR LEDs should maintain their serial position as on sch, no brainer when installing the parts and soldering.

I still see separated crowded building blocks from sch like islands, not spreading enough across the empty areas. When and if you will relax that blocks, tracks will automatically be shorter, individual parts will find more space around them. Yeah PITA job I know.
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Last edited by Lazy Cat; 18th April 2012 at 01:22 AM.
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Old 18th April 2012, 07:22 AM   #130
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Hi LC, Thanks one more time for new advices, i will rework. I would conserve PC length at 150mm as there is a 150x200 standart board. For MCP i must look on ebay as i couldn't find those brand on conventionnels store even internet stores. It's quite normal you can identify "crowded building blocks from sch like islands" as i split it into blocs. I will see if i been able to relax that blocs.

Could you give me the Voltage reating for 100µ, 1mF and 2.2mf to see if i could gain more space to adjust to real needing size?

Marc
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