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 Forum index » DIY Hardware and Software » Jürgen Haible designs
Interested in Tau Pipe Phaser / Flanger boards ?
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Tue May 05, 2009 1:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Jürgen,

I've finished my Tau, but have somewhat similar problems as others have had. I get audio out, but no hint of phasing.

I've built an essentially standard setup, with RCA CA3046E chips, and a MOTM power supply. All IC power pins are receiving proper voltages.

None of these controls have any effect:
- Pitch knob
- Depth knob
- Color switch
- Pitch CV
- Smooth switch
- 1V/O input

Here's what does work:
- The internal LFO must be working because the LEDs behave correctly; The Rate pot behaves as expected.
- Turning the Resonance pot alters the stereo image.
- The Phaser/Vibrato switch cuts the stereo image to mono when set to Vibrato.
- The input level pot attenuates volume as expected.

I've verified all the part values, checked for obvious faults, and checked the electrical integrity of signal paths through cables.

Where do you think my fault could lie?

Thank you so much for your time,
Kevin
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Tue May 05, 2009 2:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
Hi Jürgen,

I've finished my Tau, but have somewhat similar problems as others have had.


What ?!?

Quote:

Where do you think my fault could lie?


While it's not impossible that you have a defective component somewhere, normally, when something doesn't work, it's either mixing up a component value, wrong orientation of a component, or a soldering problem ...

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Tue May 05, 2009 3:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Fetafarmer wrote:
Hi Jürgen,

I've finished my Tau, but have somewhat similar problems as others have had.


What ?!?



I was just referring to back on page 15 of this thread, where ericcoleridge and eframp described the problems they were having.

Quote:

Quote:


Where do you think my fault could lie?


While it's not impossible that you have a defective component somewhere, normally, when something doesn't work, it's either mixing up a component value, wrong orientation of a component, or a soldering problem ...

JH.


Ok, I'll try checking everything again.

Thank you,
Kevin
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Tue May 05, 2009 11:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
jhaible wrote:
Fetafarmer wrote:
Hi Jürgen,

I've finished my Tau, but have somewhat similar problems as others have had.


What ?!?



I was just referring to back on page 15 of this thread, where ericcoleridge and eframp described the problems they were having.


Well yes, and if I rememeber correctly, that was a soldering problem!


Quote:

Ok, I'll try checking everything again.


First, check for the right supply voltage on every opamp.
Then, trace an input signal, from the input, stage by stage, and see where it disappears. Then we may have a realistic chance to find the error.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Wed May 06, 2009 4:26 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:

First, check for the right supply voltage on every opamp.
Then, trace an input signal, from the input, stage by stage, and see where it disappears. Then we may have a realistic chance to find the error.

JH.


Opamp voltages are all correct.

Tracing a signal: Everything appears fine until the very last stage before entering the All Pass Filters. Referencing jh_tau_sch_page1_signal.pdf:

Junction of C3 (1u), R9 (18k), C5 (2n2) = input signal with +15V DC offset: +10V to +20V
Junction of C4 (1u), R11 (18k), C6 (2n2) = inverted input signal with +15V DC offset: +10V to +20V

At "A" (to All Pass Filters) = +15V DC
At "B" (to All Pass Filters) = +15V DC

Thank you again,
Kevin
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Wed May 06, 2009 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
jhaible wrote:

First, check for the right supply voltage on every opamp.
Then, trace an input signal, from the input, stage by stage, and see where it disappears. Then we may have a realistic chance to find the error.

JH.


Opamp voltages are all correct.

Tracing a signal: Everything appears fine until the very last stage before entering the All Pass Filters. Referencing jh_tau_sch_page1_signal.pdf:

Junction of C3 (1u), R9 (18k), C5 (2n2) = input signal with +15V DC offset: +10V to +20V
Junction of C4 (1u), R11 (18k), C6 (2n2) = inverted input signal with +15V DC offset: +10V to +20V

At "A" (to All Pass Filters) = +15V DC
At "B" (to All Pass Filters) = +15V DC

Thank you again,
Kevin


*No* voltage should be higher than 15V. Where do you get the +20V from?
Wait ... there could be a missing GND connection to the PSU?
(We're talking about a +/-15V DC power supply, and not using the on-board regulators, right?)

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Wed May 06, 2009 10:49 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Fetafarmer wrote:
jhaible wrote:

First, check for the right supply voltage on every opamp.
Then, trace an input signal, from the input, stage by stage, and see where it disappears. Then we may have a realistic chance to find the error.

JH.


Opamp voltages are all correct.

Tracing a signal: Everything appears fine until the very last stage before entering the All Pass Filters. Referencing jh_tau_sch_page1_signal.pdf:

Junction of C3 (1u), R9 (18k), C5 (2n2) = input signal with +15V DC offset: +10V to +20V
Junction of C4 (1u), R11 (18k), C6 (2n2) = inverted input signal with +15V DC offset: +10V to +20V

At "A" (to All Pass Filters) = +15V DC
At "B" (to All Pass Filters) = +15V DC

Thank you again,
Kevin


*No* voltage should be higher than 15V. Where do you get the +20V from?
Wait ... there could be a missing GND connection to the PSU?
(We're talking about a +/-15V DC power supply, and not using the on-board regulators, right?)

JH.


Yes, this is a Power-One +/-15V DC PSU, which I've been using for years with no problems. It enters the board in exactly the same way as you detail on your website for such PSUs, except I'm only using one ground wire in the power cable running back to the supply, and not two as is usual with MOTM connectors.

Using the schematic as a reference, I just went through and probed every point to ground, and they all seem to check out. As ground, I used the PSU end of the power cable to make sure that the connection was good throughout the module.

And just to be sure, I touched up the solder connections at the junctions mentioned above, but get the same measurements nonetheless.
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Wed May 06, 2009 11:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I was thinking too short.
After the AC coupling (C3), but before the Attenuator (R9 , R13), you get such high voltages - my fault.

The interesing node is *after* the Attenuator.

With a +/-1V input signal of ca. 500Hz, what AC voltage do you get "A" and "B", and what DC voltage?
Does the DC voltage at A and B change when you sweep the Phaser manually?

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Wed May 06, 2009 12:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Ok, I was thinking too short.
After the AC coupling (C3), but before the Attenuator (R9 , R13), you get such high voltages - my fault.

The interesing node is *after* the Attenuator.

With a +/-1V input signal of ca. 500Hz, what AC voltage do you get "A" and "B", and what DC voltage?
Does the DC voltage at A and B change when you sweep the Phaser manually?

JH.


With a +/-1V input signal of ca. 500Hz,
- I have no AC voltage at "A" or "B", only +15V DC.
- If OSC_LEVEL is at minimum (fully ccw), PITCH varies the DC voltages at "A" and "B" from +15.4V (ccw) - +15.0V (cw).
- If OSC_LEVEL is at maximum (fully cw), PITCH does not affect the DC voltages at "A" and "B", they stay constant at +15.4V.

Thank you again,
Kevin
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jhaible



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Posts: 2014
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Audio files: 24

PostPosted: Wed May 06, 2009 2:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
jhaible wrote:
Ok, I was thinking too short.
After the AC coupling (C3), but before the Attenuator (R9 , R13), you get such high voltages - my fault.

The interesing node is *after* the Attenuator.

With a +/-1V input signal of ca. 500Hz, what AC voltage do you get "A" and "B", and what DC voltage?
Does the DC voltage at A and B change when you sweep the Phaser manually?

JH.


With a +/-1V input signal of ca. 500Hz,
- I have no AC voltage at "A" or "B", only +15V DC.


We're looking for something in the 10mV range here.
Just to be sure: Oscilloscope at "A", 5mV/Division, AC coupling: no signal at all?


Quote:

- If OSC_LEVEL is at minimum (fully ccw), PITCH varies the DC voltages at "A" and "B" from +15.4V (ccw) - +15.0V (cw).


What is your positive supply voltage? (Higher than 15V; 15.4V I suppose ..)

Anyway, seems the bias current thru the ladder is modulated just fine. Let's see where the signal disappears. If there is really nothing (millivolts!) at A and B, you probably have a short around the upper end of the ladder.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Wed May 06, 2009 11:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

I probably won't be back until tomorrow, so ...

if you have a small signal (millivolt range) at A and B, then check for this signal down along the Ladder, thru the instrumentation amp (back to higher levels!) and so on. Look for a fault where the signal disappears.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Fri May 08, 2009 3:00 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
I probably won't be back until tomorrow, so ...

if you have a small signal (millivolt range) at A and B, then check for this signal down along the Ladder, thru the instrumentation amp (back to higher levels!) and so on. Look for a fault where the signal disappears.

JH.


I'm still investigating. With AC coupling, I was able to find the signal (about 200mV pk-pk within the ladder when the module input is +/-5V). At the moment it seems to disappear at the output of U3B:

- pin 5 has the signal plus a DC offset; moving between +5.5V and +7V
- pin 6 has the signal moving between 0 and +4V
- pin 7 is a constant +14.6V DC

I've yet to find any shorts, faulty components, or other errors, but I'll be able to continue looking later today. Thank you again, and sorry for taking up your time with this.

Kevin
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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Fri May 08, 2009 5:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
With AC coupling, I was able to find the signal (about 200mV pk-pk within the ladder when the module input is +/-5V).


Please try with a smaller input level (use the input attenuator).
Make the tests with 40mV pk-pk in the ladder.
I doubt that heavy overdrive will cause such effect as you describe, but I want to be sure.

Quote:

At the moment it seems to disappear at the output of U3B:

- pin 5 has the signal plus a DC offset; moving between +5.5V and +7V
- pin 6 has the signal moving between 0 and +4V
- pin 7 is a constant +14.6V DC


What do you have on Pins 1 and 7 of U2 ?

Is U2 an OPA2134, or some replacement?

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Sun May 10, 2009 4:44 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Fetafarmer wrote:
With AC coupling, I was able to find the signal (about 200mV pk-pk within the ladder when the module input is +/-5V).


Please try with a smaller input level (use the input attenuator).
Make the tests with 40mV pk-pk in the ladder.
I doubt that heavy overdrive will cause such effect as you describe, but I want to be sure.


Ok, i've done that now. Also, all measurements are with Resonance at min, Pitch at mid, and all trimmers at mid position.

I get completely different readings throughout depending upon the position of OSC_LEVEL, so here are readings with that pot at maximum, then at minimum:

With OSC_LEVEL at max,
U2, pin 1: 4.9V pk-pk (+1.4V to -3.4V)
U2, pin 2: 3.6V pk-pk (+4.3V to -0.7V)
U2, pin 3: 3.5V pk-pk (+4.2V to -0.7V)
U2, pin 5: 3.3V pk-pk (+1.2V to +4.5V)
U2, pin 6: 3.4V pk-pk (+1.3V to +4.7V)
U2, pin 7: 2.4V pk-pk (+5.3 to +7.7V)

U3, pin 1: 140mV pk-pk (mean 28mV)
U3, pin 2: 108mV pk-pk (mean 26mV)
U3, pin 3: 124mV pk-pk (mean 20mV)
U3, pin 5: 2V pk-pk (+4.5 to +6.5)
U3, pin 6: 4.1V pk-pk (+3.4 to -0.6)
U3, pin 7: 600mV pk-pk (mean +14.5V)

With OSC_LEVEL at min,
U2, pin 1: 180mV pk-pk (mean -600mV)
U2, pin 2: 100mV pk-pk (mean 3V)
U2, pin 3: 120mV pk-pk (mean 2.9V)
U2, pin 5: 120mV pk-pk (mean 3.3V)
U2, pin 6: 120mV pk-pk (mean 3.3V)
U2, pin 7: 200mV pk-pk (mean +690mV)

U3, pin 1: 105mV pk-pk (mean 28mV)
U3, pin 2: 68mV pk-pk (mean 26mV)
U3, pin 3: 90mV pk-pk (mean 20mV)
U3, pin 5: 160mV pk-pk (mean +5.8V)
U3, pin 6: 120mV pk-pk (mean +1.7V)
U3, pin 7: 600mV pk-pk (mean +14.5V)

Quote:

Is U2 an OPA2134, or some replacement?


Burr-Brown OPA2134PA

What is most visible, through the ladder and beyond, appears to be the phaser notches. Hard to discern signal in the midst of all the notches and noise.
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jhaible



Joined: May 25, 2007
Posts: 2014
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Audio files: 24

PostPosted: Sun May 10, 2009 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:

With OSC_LEVEL at min,
U2, pin 1: 180mV pk-pk (mean -600mV)
U2, pin 7: 200mV pk-pk (mean +690mV)


By "mean", you mean the DC voltage?
Like:
Pin 1: -690mV ... -510mV
Pin 7: +590mV ... +790mV ?

Then I suppose the ladder gets a very unbalanced current.

With Osc Level still at ccw end, do you get a similar picture (pin 7 waymore positive than pin 1) for all different settings of the pitch potentiometer?
Or is there a range where the DC part is about the same for Pin 1 and Pin7 ?

JH

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Sun May 10, 2009 10:24 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Fetafarmer wrote:

With OSC_LEVEL at min,
U2, pin 1: 180mV pk-pk (mean -600mV)
U2, pin 7: 200mV pk-pk (mean +690mV)


By "mean", you mean the DC voltage?
Like:
Pin 1: -690mV ... -510mV
Pin 7: +590mV ... +790mV ?

Then I suppose the ladder gets a very unbalanced current.


Yes, exactly. I assume it's mathematical mean - I'm just reading it straight from the screen of my Tek TDS1002. (Deutsch = "Mittelwert")

Quote:

With Osc Level still at ccw end, do you get a similar picture (pin 7 waymore positive than pin 1) for all different settings of the pitch potentiometer?
Or is there a range where the DC part is about the same for Pin 1 and Pin7 ?

JH


Yes, with OSC_LEVEL at min, and Pitch fully cw: U2, pin1 has a -3.5V DC offset; pin 7 has +1V DC offset.
With OSC_LEVEL at min, and Pitch fully ccw: U2, pin1 has a +1.2V DC offset; pin 7 has +4.5V DC offset.

In any case, U2 pin 7 appears very noisy on the scope compared to pin 1.

Sorry that this is so difficult to nail down. Sad I tried to analyze it on my own for a while, but I simply don't have an electronics background.
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jhaible



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PostPosted: Sun May 10, 2009 11:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
jhaible wrote:
Fetafarmer wrote:

With OSC_LEVEL at min,
U2, pin 1: 180mV pk-pk (mean -600mV)
U2, pin 7: 200mV pk-pk (mean +690mV)


By "mean", you mean the DC voltage?
Like:
Pin 1: -690mV ... -510mV
Pin 7: +590mV ... +790mV ?

Then I suppose the ladder gets a very unbalanced current.


Yes, exactly. I assume it's mathematical mean - I'm just reading it straight from the screen of my Tek TDS1002. (Deutsch = "Mittelwert")

Quote:

With Osc Level still at ccw end, do you get a similar picture (pin 7 waymore positive than pin 1) for all different settings of the pitch potentiometer?
Or is there a range where the DC part is about the same for Pin 1 and Pin7 ?

JH


Yes, with OSC_LEVEL at min, and Pitch fully cw: U2, pin1 has a -3.5V DC offset; pin 7 has +1V DC offset.
With OSC_LEVEL at min, and Pitch fully ccw: U2, pin1 has a +1.2V DC offset; pin 7 has +4.5V DC offset.

In any case, U2 pin 7 appears very noisy on the scope compared to pin 1.

Sorry that this is so difficult to nail down. Sad I tried to analyze it on my own for a while, but I simply don't have an electronics background.


Noisy and unbalanced.
Maybe there's a problem with the CA3046 (3086) that is the dual current sink. Can you ceck if pin 1 and pin 5 put out roughly the same current?
(Voltmeter across R47 and R48)
http://www.jhaible.de/tau/jh_tau_sch_page3_control.pdf
Manual sweep, and all settings as before.

Also check the solder joints on pin 1, 2, 3, 4, 5 of this 3046.
Check if voltage on pin 2 is always the same as pin 4.
If you have a socket here, try another 3046.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



Joined: Jul 29, 2007
Posts: 32

PostPosted: Mon May 11, 2009 7:55 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Fetafarmer wrote:

In any case, U2 pin 7 appears very noisy on the scope compared to pin 1.



I just discovered that one of my probes has broken, and is adding noise to everything it measures. So U2 pin 7 is not, in fact, any noisier than pin 1.

Quote:

Noisy and unbalanced.
Maybe there's a problem with the CA3046 (3086) that is the dual current sink. Can you ceck if pin 1 and pin 5 put out roughly the same current?
(Voltmeter across R47 and R48)
http://www.jhaible.de/tau/jh_tau_sch_page3_control.pdf
Manual sweep, and all settings as before.


The voltage across each resistor fluctuates slightly as the internal LFO sweeps (OSC_LEVEL is still set to min):
R47: 551 to 554mV
R48: 451 to 452mV

Both resistors measure an identical resistance of 1k49.

Quote:

Also check the solder joints on pin 1, 2, 3, 4, 5 of this 3046.
Check if voltage on pin 2 is always the same as pin 4.
If you have a socket here, try another 3046.


I touched up the solder joints on this socket's pins, and also swapped the 3086 for a 3046, with no change in results. The voltage on pin 2 does always match that of pin 4.
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jhaible



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PostPosted: Mon May 11, 2009 10:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
The voltage across each resistor fluctuates slightly as the internal LFO sweeps (OSC_LEVEL is still set to min):


Could it be that you don't have a normaized jack connected to the CV input??
(http://www.jhaible.de/tau/jh_tau_sch_page5_pots.pdf)
If you haven't, it's mandatory to jumper the middle and right pin of the on-board connector!

Quote:

R47: 551 to 554mV
R48: 451 to 452mV


Looks reasonable. Current sinks seem to work.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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Fetafarmer



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Posts: 32

PostPosted: Mon May 11, 2009 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Fetafarmer wrote:
The voltage across each resistor fluctuates slightly as the internal LFO sweeps (OSC_LEVEL is still set to min):


Could it be that you don't have a normaized jack connected to the CV input??
(http://www.jhaible.de/tau/jh_tau_sch_page5_pots.pdf)
If you haven't, it's mandatory to jumper the middle and right pin of the on-board connector!


That is connected as shown.

What looks odd to me, just looking at the values around the circuit, is U3 pin 7. The signal suddenly drops there to 600mV, and acquires a +14.5V DC offset which remains constant regardless of the setting of OSC_LEVEL. Does that seem right to you?

Kevin
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jhaible



Joined: May 25, 2007
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PostPosted: Mon May 11, 2009 12:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fetafarmer wrote:
jhaible wrote:
Fetafarmer wrote:
The voltage across each resistor fluctuates slightly as the internal LFO sweeps (OSC_LEVEL is still set to min):


Could it be that you don't have a normaized jack connected to the CV input??
(http://www.jhaible.de/tau/jh_tau_sch_page5_pots.pdf)
If you haven't, it's mandatory to jumper the middle and right pin of the on-board connector!


That is connected as shown.


But then there shouldn't be any LFO modulation with Osc Level at ccw end position.

Quote:
What looks odd to me, just looking at the values around the circuit, is U3 pin 7. The signal suddenly drops there to 600mV, and acquires a +14.5V DC offset which remains constant regardless of the setting of OSC_LEVEL. Does that seem right to you?


+14.5V means it's stuck at the positive rail. Certainly not where it should be.

Even with that huge DC difference at the two outputs of U2 (1.29V), the output of U3A should only have an offset of 7V, not 14V.

JH.

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"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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JoeMorris



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PostPosted: Mon May 18, 2009 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

I have a question, as an inexperienced chap at this stuff, is the tempco resistor equivalent to a PTC or NTC thermistor? I have a 3500k 1kohm NTC thermistor, but Im not sure if Im barking up the wrong tree here.
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jhaible



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PostPosted: Mon May 18, 2009 10:26 am    Post subject: Reply with quote  Mark this post and the followings unread

JoeMorris wrote:
I have a question, as an inexperienced chap at this stuff, is the tempco resistor equivalent to a PTC or NTC thermistor? I have a 3500k 1kohm NTC thermistor, but Im not sure if Im barking up the wrong tree here.


Positive Temperature Coefficient (PTC) is what you need. But I think a lot of stuff that is sold as "PTC" isn't linear, so I avoid the term PTC alltogether.
NTC is wrong in any case.

But I would simply use an ordinary resistor. Who needs temperature compensation in a phaser ?!

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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JoeMorris



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PostPosted: Mon May 18, 2009 11:41 am    Post subject: Reply with quote  Mark this post and the followings unread

good point, i will do this. thanks.
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JoeMorris



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PostPosted: Tue May 26, 2009 7:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Another possibly silly noob question: Are metallized film capacitors like these:
http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1669202
OK for the 40 15nf caps in the Tau?
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