Perfect Nordic...interesting that i am painting an enclosure with the same colour you
are using.
Was a mix...the colour i have made mixing materials...it has a corrugated, not flat, not shining finishment.
I like it, your enclosure...it is perfect.
My paint is not finished.... two coatings more will be needed and them a varnish will be used (not a brigth varnish)
regards,
Carlos
are using.
Was a mix...the colour i have made mixing materials...it has a corrugated, not flat, not shining finishment.
I like it, your enclosure...it is perfect.
My paint is not finished.... two coatings more will be needed and them a varnish will be used (not a brigth varnish)
regards,
Carlos
Attachments
Looking good, Nordic.
Lovely vintage look, reminds me of old guitar-amps and tube-gear.
The hammertone you're referring to, is it like this (this is the grey variety) ? We call it hamerslag overhere.
Gives a very nice rugged look
Keeping my fingers crossed for your wisdom-tooth
Best regards,
Klaas
Lovely vintage look, reminds me of old guitar-amps and tube-gear.
The hammertone you're referring to, is it like this (this is the grey variety) ? We call it hamerslag overhere.
Gives a very nice rugged look
Keeping my fingers crossed for your wisdom-tooth
Best regards,
Klaas
Mine Dx case had the painting material prepared by myself
Old style...alike Leonardo Da Vinci.... mixing oils and colours....had that white material we use to cover holes into the wall.... oils, colours and brush heating the surface.
It is nice to make.
Under, you can see the waterproof gray paint.... two more layers and a non brigth varnish will be used.
I will produce details in black...and some knobs will be placed...it will result fine.
regards,
Carlos
Old style...alike Leonardo Da Vinci.... mixing oils and colours....had that white material we use to cover holes into the wall.... oils, colours and brush heating the surface.
It is nice to make.
Under, you can see the waterproof gray paint.... two more layers and a non brigth varnish will be used.
I will produce details in black...and some knobs will be placed...it will result fine.
regards,
Carlos
Attachments
The colour is alike the forum blue colour...sundown is creating some redish
colour that is not natural.
here is the detail.... the surface was heated by a brush while not completelly dried...to produce that type of surface.
This paint resulted "rock solid".... old style man!
regards,
Carlos
colour that is not natural.
here is the detail.... the surface was heated by a brush while not completelly dried...to produce that type of surface.
This paint resulted "rock solid".... old style man!
regards,
Carlos
Attachments
The home page is beeing updated related Dx amplifier adjustments
Because VBE multiplier turn standard, some adjustments will need revision.
The bias trimpot must be adjusted to 700 ohms .
The offset trimpot must be adjusted to 7400 ohms.
Multiturn trimpot will be very helpfull.
The instructions will produce 80 to 110 miliamperes of stand by bias current...idle current....but you may find a better operation point to your transistors tweaking this current to lower values...listening to low level music and searching for quality.
Nordic and Klaas found that 80 to 110 miliamperes is a little bit big compared with their adjustments.
Of course the standard adjustment will work...but if you want to tune it to the best possible performance...use your ears and make small adjustments....and do that will very small volume, also keep those 10 ohms resistances in series with the supplies, because of safety reasons, during your low volume adjustments.
Finally.... after "fine tuning"...remove the resistances.
The amplifier cannot distort when playing very low volume music.
regards,
Carlos
Because VBE multiplier turn standard, some adjustments will need revision.
The bias trimpot must be adjusted to 700 ohms .
The offset trimpot must be adjusted to 7400 ohms.
Multiturn trimpot will be very helpfull.
The instructions will produce 80 to 110 miliamperes of stand by bias current...idle current....but you may find a better operation point to your transistors tweaking this current to lower values...listening to low level music and searching for quality.
Nordic and Klaas found that 80 to 110 miliamperes is a little bit big compared with their adjustments.
Of course the standard adjustment will work...but if you want to tune it to the best possible performance...use your ears and make small adjustments....and do that will very small volume, also keep those 10 ohms resistances in series with the supplies, because of safety reasons, during your low volume adjustments.
Finally.... after "fine tuning"...remove the resistances.
The amplifier cannot distort when playing very low volume music.
regards,
Carlos
The adjustment section, into the home page, will be updated following this text.
Adjusting the bias, and trimming DC offset
Follow the steps below to adjust bias and trim the DC offset.
Note: The test points A, B, C, D and E are shown on schematic and PCB layout.
Step
1 ........... Ensure the power is off and filter capacitors are fully discharged.
2............ Install a 10 ohms (5 watt or higher) protective resistor in series with each of the supply rails—see diagram below.
3 ........... Install a wire or low ohm resistor to short the input.
4 ........... Ensure there is no load on the output (i.e. no speakers connected).
5............
Set your multimeter to the resistance range.
6 ............ Set the bias trimpot (VR2) to 770 ohms PCB – Top View).
7 ............ Set the offset trimpot (VR1) to 7400 ohms (between test points D and E—see PCB – Top View).
8 ............ Set your multimeter to the 2V DC range.
9 ........... Install two multimeters connected across each of the protective resistors—see diagram below.
We are measuring the voltage that develops across the protective resistors when a current flows. Because of the zener diode, Z1, the bias current in the positive rail will be just a bit higher, about 10 milliamps, than the negative rail.
10.......... Turn the power on.
11.......... Adjust the bias (VR2) to between 800 and 1,100 millivolts (0,8 and 1,1 volts) on each rail.
Remember the positive rail will read slightly higher (about 100 millivolts) than the negative rail.
12 .......... Set your multimeter to the 200mV DC range.
13 ......... Install a DC voltmeter between the speaker output and star ground—see diagram below.
14.......... Adjust DC offset (VR1).
Initially try for a DC offset of less than 3 millivolts.
The maximum allowable is 20 millivolts.
15 ......... Return and check the bias, adjust it again.
16 ......... Re-adjust your DC offset to a voltage lower than 3 millivolts.
The voltage there must be stable, not fluctuating.
17 ......... Once more check your bias and adjust if needed.
18 ......... Return to check the offset for the last time. It should be under 3 millivolts.
19 Remove the 10 ohm protective resistors.
20 ......... Repeat the setup for the second amp.
21.......... Connect your audio source and speakers.
22 .......... Now enjoy the romantic sound
regards,
Carlos
Adjusting the bias, and trimming DC offset
Follow the steps below to adjust bias and trim the DC offset.
Note: The test points A, B, C, D and E are shown on schematic and PCB layout.
Step
1 ........... Ensure the power is off and filter capacitors are fully discharged.
2............ Install a 10 ohms (5 watt or higher) protective resistor in series with each of the supply rails—see diagram below.
3 ........... Install a wire or low ohm resistor to short the input.
4 ........... Ensure there is no load on the output (i.e. no speakers connected).
5............
Set your multimeter to the resistance range.
6 ............ Set the bias trimpot (VR2) to 770 ohms PCB – Top View).
7 ............ Set the offset trimpot (VR1) to 7400 ohms (between test points D and E—see PCB – Top View).
8 ............ Set your multimeter to the 2V DC range.
9 ........... Install two multimeters connected across each of the protective resistors—see diagram below.
We are measuring the voltage that develops across the protective resistors when a current flows. Because of the zener diode, Z1, the bias current in the positive rail will be just a bit higher, about 10 milliamps, than the negative rail.
10.......... Turn the power on.
11.......... Adjust the bias (VR2) to between 800 and 1,100 millivolts (0,8 and 1,1 volts) on each rail.
Remember the positive rail will read slightly higher (about 100 millivolts) than the negative rail.
12 .......... Set your multimeter to the 200mV DC range.
13 ......... Install a DC voltmeter between the speaker output and star ground—see diagram below.
14.......... Adjust DC offset (VR1).
Initially try for a DC offset of less than 3 millivolts.
The maximum allowable is 20 millivolts.
15 ......... Return and check the bias, adjust it again.
16 ......... Re-adjust your DC offset to a voltage lower than 3 millivolts.
The voltage there must be stable, not fluctuating.
17 ......... Once more check your bias and adjust if needed.
18 ......... Return to check the offset for the last time. It should be under 3 millivolts.
19 Remove the 10 ohm protective resistors.
20 ......... Repeat the setup for the second amp.
21.......... Connect your audio source and speakers.
22 .......... Now enjoy the romantic sound
regards,
Carlos
After following the standard adjustment instructions...
You will have from 80 to 110 miliamps of current...of idle current...stand by current.
This is not so good...it is safer, as people will not make mistakes...the "tuning" depends of some "ears" and knowledge.
But, fine tuning the bias will result better.
How to fine tune:
Keep the rail resistances there...already made your adjusted to 800 to 1100 milivolts measured over 10 ohms resistances.
Now, remove the input short and inject audio.... low volume audio...very low power.... only the needed to listen.... the speaker may be very near your ears...than go reducing your bias...reduce volume to zero and check the stand by bias.... remember to keep the resistances, the protective ones, in place....
Increase the volume to really low audio level...the amplifier may produce some miliwatts of output and the DC readings will be crazy because of consumption.... go reducing till you find distortions..because underbiased.... transistors will be cutting.... will be alternating "on" and "off"...audio will be strange...then turn your adjustment to the other direction.... now increasing till you have no distortions....this may be the optimized point.
Now remove the protective resistances and be happy...your rail current will be around 60 miliamperes to positive rails and 50 milimaperes to negative rails (not exactly, depends from your circuit and transistors..this is only a reference).
Now be happy man...sonics will be optimized...amplifier will run cooler.
If my informations, those instructions i am finishing to type, was considered confused, or complicated...than...."please"...do not even try if you are not experienced enougth...keep the standard current (the one offered as suggestions) and he happy too.
700 ohms to the bias trimpot will work if your colector to emitter resistance, into the VBE multiplier, is 2000 ohms.... this adjustment (700 ohms as starting point) will not be good if your base to colector resistance, into the VBE multiplier, is 1K8 or 2K2.
Also, the offset 7400 ohms suggested will work when using 35 volts positive and 35 volts negative...and this is only a reference to start adjustments...do not expect to have the amplifier adjusted to high precision fixing 7400 ohms...this is starting point only.
Bias fine tune, will work, ONLY, if your audio power is very small...only the minimum needed volume to drive a small speaker or a headphone..... adjusting using normal volume...or something alike 1 watt of audio will not work.
regards,
Carlos
You will have from 80 to 110 miliamps of current...of idle current...stand by current.
This is not so good...it is safer, as people will not make mistakes...the "tuning" depends of some "ears" and knowledge.
But, fine tuning the bias will result better.
How to fine tune:
Keep the rail resistances there...already made your adjusted to 800 to 1100 milivolts measured over 10 ohms resistances.
Now, remove the input short and inject audio.... low volume audio...very low power.... only the needed to listen.... the speaker may be very near your ears...than go reducing your bias...reduce volume to zero and check the stand by bias.... remember to keep the resistances, the protective ones, in place....
Increase the volume to really low audio level...the amplifier may produce some miliwatts of output and the DC readings will be crazy because of consumption.... go reducing till you find distortions..because underbiased.... transistors will be cutting.... will be alternating "on" and "off"...audio will be strange...then turn your adjustment to the other direction.... now increasing till you have no distortions....this may be the optimized point.
Now remove the protective resistances and be happy...your rail current will be around 60 miliamperes to positive rails and 50 milimaperes to negative rails (not exactly, depends from your circuit and transistors..this is only a reference).
Now be happy man...sonics will be optimized...amplifier will run cooler.
If my informations, those instructions i am finishing to type, was considered confused, or complicated...than...."please"...do not even try if you are not experienced enougth...keep the standard current (the one offered as suggestions) and he happy too.
700 ohms to the bias trimpot will work if your colector to emitter resistance, into the VBE multiplier, is 2000 ohms.... this adjustment (700 ohms as starting point) will not be good if your base to colector resistance, into the VBE multiplier, is 1K8 or 2K2.
Also, the offset 7400 ohms suggested will work when using 35 volts positive and 35 volts negative...and this is only a reference to start adjustments...do not expect to have the amplifier adjusted to high precision fixing 7400 ohms...this is starting point only.
Bias fine tune, will work, ONLY, if your audio power is very small...only the minimum needed volume to drive a small speaker or a headphone..... adjusting using normal volume...or something alike 1 watt of audio will not work.
regards,
Carlos
Hi Destroyer,
should this say collector to base resistance?
BTW,
I like your choice of Vbe resistor values. It keeps the resistor currents up at a sensible level. Many use resistors that are far too high a value and reduce resistor currents to less than a few hundreds of uA. Aim for a mA or more. Even better, aim for about 10% of the VAS current to flow through the resistors (this can be varied with the gain of the Vbe transistor).
Yes Andrew, colector to base.... this is the rigth position for them.
Yes..... here is the schematic.
Those resistances choice was made by Michael Bittner, our MikeB...my first schematic used 18K from Base to Colector...was working..but not so good as this one suggested by Michael.
This one is tracking perfectly the increasings of heat.
Carlos
Yes..... here is the schematic.
Those resistances choice was made by Michael Bittner, our MikeB...my first schematic used 18K from Base to Colector...was working..but not so good as this one suggested by Michael.
This one is tracking perfectly the increasings of heat.
Carlos
Attachments
Hi,
The transistor in the Vbe multiplier is an active device that monitors the the voltage across the BE resistor and adjusts the CE voltage to keep the current near constant.
As this is an active system it can suffer instability.
Borrowing from RF practice where they use resistor strings regularly. They arrange that any tapped off current that may vary with duty to always be below 10% of the resistor string current.
If we adopt a similar strategy for the Vbe multplier, then the resistor string current should be 10times the base current being tapped off and sent into the NPN Vbe multiplier.
If we assume that the gain of the transistor is about 100times, then the resistor current will be about 9% of the total VAS current.
Let's assume the VAS current is 17mA and hFE at this current is 100. Then base current is about 170uA.
The resistor string current should exceed 10times 170uA or >1.7mA. The resulting transistor collector current is then about 15.3mA and emitter current about 15.5mA and base current about 0.17mA.
A BE resistor (the pot) = 390r will pass a current that is in the ballpark to meet the 10times the base current and in turn be about 10% of the VAS current.
Note that the minimum resistor current is closely related to the chosen transistor gain. Use a low gain medium power device or a MPSA42 and the base will pull a much larger current risking instability. But easily cured, just reduce the resistor values a bit more for low gain transistors. Conversely high gain Vbe can use higher value resistors.
The transistor in the Vbe multiplier is an active device that monitors the the voltage across the BE resistor and adjusts the CE voltage to keep the current near constant.
As this is an active system it can suffer instability.
Borrowing from RF practice where they use resistor strings regularly. They arrange that any tapped off current that may vary with duty to always be below 10% of the resistor string current.
If we adopt a similar strategy for the Vbe multplier, then the resistor string current should be 10times the base current being tapped off and sent into the NPN Vbe multiplier.
If we assume that the gain of the transistor is about 100times, then the resistor current will be about 9% of the total VAS current.
Let's assume the VAS current is 17mA and hFE at this current is 100. Then base current is about 170uA.
The resistor string current should exceed 10times 170uA or >1.7mA. The resulting transistor collector current is then about 15.3mA and emitter current about 15.5mA and base current about 0.17mA.
A BE resistor (the pot) = 390r will pass a current that is in the ballpark to meet the 10times the base current and in turn be about 10% of the VAS current.
Note that the minimum resistor current is closely related to the chosen transistor gain. Use a low gain medium power device or a MPSA42 and the base will pull a much larger current risking instability. But easily cured, just reduce the resistor values a bit more for low gain transistors. Conversely high gain Vbe can use higher value resistors.
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