First Budgie Preamplifier Post

arduino based linestage using 12B4 tubes

Re: First Budgie Preamplifier Post

Postby Shannon Parks » Tue Jul 29, 2014 10:43 am

Auricle wrote:The IRremote library seems to be missing from budgiesketchv0_05.zip.

I was able to download IRremote library from https://github.com/shirriff/Arduino-IRremote. After that, I was able to successfully install the library and Verify/Compile budgiesketchv0_05.


Fixed - left the filename the same. Thanks, Auricle.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3761
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Re: First Budgie Preamplifier Post

Postby Auricle » Tue Jul 29, 2014 6:25 pm

This was a Rev A addition to the circuit that helps the relay's coil to collapse faster. So when power is disconnected the mute circuit works much faster with much less of a thump. I'll look into my schematics and update the drawing on the site. D14 is located near RL3 and D7.

A nice web write up on the theory:
http://jumperone.com/2011/10/using-relays/


Very clever! Thanks for the reference.

Regards,
Auricle
Auricle
 
Posts: 37
Joined: Mon Jul 28, 2014 1:22 pm
Location: Vancouver BC Canada

Re: First Budgie Preamplifier Post

Postby Shannon Parks » Wed Jul 30, 2014 6:35 am

You can see from the schematic that pin A6 is monitoring the 24V supply voltage. It's actually using two voltage dividers: one from the filaments which cut it to 12V and then another resistive divider (1/3). This gets monitored all the time, and when it dips a certain percentage it engages the Mute relay immediately. With zener in there, it works OK.

I could have used the on/off switch as a standby switch (eg going into standby via Mute hold or IR Standby is silent) but I didn't want the Budgie running all the time - wanted a true hard off. I experimented with a nice isolated opto relay, but a feature one wants in a muting circuit is to work (be closed) in an OFF state. With the opto relay, I had a high impedance line running to the power amp that was noisy whenever the Budgie was turned off. So that's a reason physical relays are handy at outputs. P-channel JFETs could also be used at the output, but they are becoming less available (particularly the lowest RDS ones).

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3761
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Re: First Budgie Preamplifier Post

Postby Auricle » Mon Aug 04, 2014 4:33 pm

This gets monitored all the time, and when it dips a certain percentage it engages the Mute relay immediately. With zener in there, it works OK.


I could see from the article you cited that addition of the zener to the flyback cct could improve response time, in the order of 10ms. I couldn't see how this would be significant if the voltage were checked only every 2 seconds. Comments in setup.h say:

    vinCheck monitors our 24V supply from a tap off the filament supply.
    We monitor this voltage every two seconds in our void main() and see
    if it has dipped by 2%

From budgisketch.ino, it seems that the voltage is checked a lot more often; line voltage variations are tracked once every 2 sec. Should work well as long as nobody presses a pushbutton during a brownout ;-)

I never would have anticipated that initial heater current might cause the power supply to current-limit or fold-back. You are very insightful, Shannon, or once or twice bitten ;-)

You say of cycling the 24V in setup.h:

    //this stutter lets the filaments preheat some before fully engaging 24V
    //it is meant as a inrush current technique to prevent PS fromfoldback

Does this technique rely on some current limiting in the power supply?

Respectfully - comments in either VolumeUp() or VolumeDown() don't appear to correspond to code. The magic of cut & paste?

I may have to buy a PCB from you - the preamp is ever more interesting.

Best regards,
Auricle
Auricle
 
Posts: 37
Joined: Mon Jul 28, 2014 1:22 pm
Location: Vancouver BC Canada

Re: First Budgie Preamplifier Post

Postby Shannon Parks » Tue Aug 05, 2014 5:14 am

Auricle wrote:I could see from the article you cited that addition of the zener to the flyback cct could improve response time, in the order of 10ms. I couldn't see how this would be significant if the voltage were checked only every 2 seconds. Comments in setup.h say:

Code: Select all
//vinCheck monitors our 24V supply from a tap off the filament supply.
//We monitor this voltage every two seconds in our void main() and see
//if it has dipped by 2%


From budgisketch.ino, it seems that the voltage is checked a lot more often; line voltage variations are tracked once every 2 sec. Should work well as long as nobody presses a pushbutton during a brownout ;-)


The main loop in setup.h is checking pin BROWNOUT (A6) for a "turn off event" in microseconds (haven't done a calculation) - it uses the variable monitored24Vsupply. It's comparing that voltage to vinCheck (our reference compare voltage) which does get updated every 2 seconds. Originally I had vinCheck just initialize once at startup, but the load changes on the supply as the filaments warm up, so I switched to checking every 2 seconds. Figured a warmed up supply and varying AC mains might effect it as well, hence the slowly updating vinCheck reference value. Also it looks like I've adjusted the code to look for a 1% difference. I think I was able to get this close once I added the slowly updating vinCheck code, and it gains us shutdown speed.

Interesting note: once you flip off the power switch, we still have many milliseconds of useful processing time. The shutdown circuit gets processed immediately, the micro does nothing (a one second delay prevents a command that could screw up eeprom) and then we wait for the relay to slowly disengage.

Auricle wrote:I never would have anticipated that initial heater current might cause the power supply to current-limit or fold-back. You are very insightful, Shannon, or once or twice bitten ;-)

You say of cycling the 24V in setup.h:

Code: Select all
//this stutter lets the filaments preheat some before fully engaging 24V
//it is meant as a inrush current technique to prevent PS from foldback


Does this technique rely on some current limiting in the power supply?


Twice bitten! I've seen this on my old 12B4 DIY Budgie linestage and also while prototyping this one. All these switching power supplies have very handy foldback current limiting. So a 1A rated supply will go into foldback if the supply hits >1A - i.e. it will then try every 500ms or some value forever thereafter to see if the overload condition is gone. So without the code a supply may work, or hiccup a couple times, or hiccup indefinitely. I just have the relay hit the filaments with some startup pulses to ease the current load at startup. Alternate methods would be to use a larger rated power supply, but this just wastes money and power. 12B4s filaments are just tough initial loads. On my original DIY Budgie linestage, for instance, I've been having people use CL50s in series with them (R31?).

Auricle wrote:Respectfully - comments in either VolumeUp() or VolumeDown() don't appear to correspond to code. The magic of cut & paste?


Remarks for VolumeDown are correct, but swap the polarity in my VolumeUp remarks (as in code). I call the SN75441ONE "H-bridge". The motor driver IC takes all the complexity out of the code work. You just toggle the polarity of the two inputs and enable as long as you want.

Code: Select all
void VolumeDown() {
  digitalWrite(VOL_1A, LOW); // set leg 1 of the H-bridge low
  digitalWrite(VOL_2A, HIGH); // set leg 2 of the H-bridge high
  digitalWrite(VOL_EN, HIGH); // turns motor on
  volumeMillis = millis();
  volumeOn = 1;

} /*VolumeDown*/


Auricle wrote:I may have to buy a PCB from you - the preamp is ever more interesting.


Thanks, Auricle!

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3761
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Re: First Budgie Preamplifier Post

Postby Freecrowder » Mon Feb 09, 2015 11:17 am

This is my first post to this site. I hope this is the proper place for my question. I have been reading about the pre and it sounds very exciting. I would be interested in integrating it into an existing tube pre. Has anyone tried that? I would like to only use the input switching and the remote volume function. I would assume I could use it without the gain stage and connecting with shielded cable for in and out to my Preamp. Or have you thought about offering a board that would function as described?
Freecrowder
 
Posts: 1
Joined: Mon Feb 09, 2015 10:33 am

Re: First Budgie Preamplifier Post

Postby Shannon Parks » Tue Feb 10, 2015 5:44 am

Freecrowder wrote:This is my first post to this site. I hope this is the proper place for my question. I have been reading about the pre and it sounds very exciting. I would be interested in integrating it into an existing tube pre. Has anyone tried that? I would like to only use the input switching and the remote volume function. I would assume I could use it without the gain stage and connecting with shielded cable for in and out to my Preamp.


It could probably be hacked and modded to do just that. But I think a buffer would still be required for a good design. Just hack it up with a unity gain stage with your favorite op amp in there.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3761
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Previous

Return to budgie preamplifier

Who is online

Users browsing this forum: No registered users and 1 guest