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Topics - zgrav

Tech Help - Projects Page / Uber Tuber question
February 19, 2021, 07:25:35 PM
I built a working Uber Tuber from the original version when it was released.  It has a warm clean sound with very little distortion unless the incoming signal is high.    I noticed today there had been a 1.1 revision to the build doc not long after it was released, and saw that two trimmers were put in to replace the 100K resistors for the plate voltage.  The build doc suggests setting the trimmers to bias at about 12 volts, but there are comments that most of the tubes work OK over a bit wider range.

I checked the plate voltage on my board and they are both running over 17 volts using the 18 volt Dunlop power supply.   Would changing the resistors to drop the voltage to 12 change the sound from the tube to possibly add more use to the drive/cut/sat controls?  If not, is there a reason not to leave the board as-is with the higher plate voltage?

VFE Projects / VFE Bumblebee troubleshooting
November 21, 2019, 03:30:42 PM
Finished assembling this pedal and now troubleshooting an odd problem.  It is a split-rail design, and when powered I am only seeing -1.2 volts on the negative supply.  If I disconnect the negative power going to the main board, the output from the charge pump is OK on both the positive and negative outputs.  What I then see is that I am getting about 3.5 volts on the negative power traces on the main board with all of the transistors and the two ICs removed from their sockets.  Also getting the same 3.5 v on the negative circuit path when the transistors and ICs are in place.  I am looking for unwanted solder bridges but have not yet found any.  Since that is about 5.4 volts less than the positive voltage going in to the main board, does the voltage reading itself suggest any particular places or parts to check on the board?
A nice surprise to see the VFE Bumblebee listed as a new project.  I wonder if this is the first of several limited returns of older VFE pedals for MBP.
The parts list for the Pepper Spray lists Q2 as 2n3965       I used the links in the build doc to smallbear electronics to order parts that I needed, and I just realized the link was to a 2n3565 transistor (which I ordered, and have ready for the build).     I don't see the 2n3565 listed as an equivalent for the 2n3965, but is this a recommended sub for Q2?    I wanted to check since I do find an equivalent listing for the 2n3965 to be a 2n3906, which I have in my inventory. 

Can you use the Dreamtime to program all 8 slots in an eeprom (notwithstanding that you cannot play them on it)?  I have other pedals that can play all 8 slots, but they cannot program the eeprom.
Will the eeprom programmed for the 3 effect Headtrip work in the Dreamtime effect, since the Dreamtime effect can hold programming for 8 effects?  I know I can just try it and see, but I thought I would ask first since other builders may already know the answer.
Tech Help - Projects Page / HEADTRIP Voltages
February 15, 2019, 07:28:55 PM

I have assembled the Headtrip and encountered some difficulty.  Wiring and parts look OK after checking with DMM for continuity, and all voltages on the FV-1 are correct with the exception of pin 5.  According to the build doc, pin 5 should be at 3.2v.   It is soldered to the board, but according to the circuit diagram the board for that pin does not connect to anything.   On the FV-1 datasheet the pin is described as  "clip" with the explanation that it is for "clip LED output" (probably a clipping signal for an input that is too hot).  My voltage reading on that pin is in the low mV with no signal going in.  Should it really be registering 3.2v?

As for the effect, I get a clean dry signal, and some wet signal that is altered by the three pots.  But in addition to that I get a lot of weird variable high frequencies that sound like someone tuning a short wave radio.  Those sci-fi noises drown out the audio signal.   I still need to trace the audio signal with a probe to make sure a clean signal is going in to the FV-1, but I'm also thinking I might have gotten a bad FV-1 chip.  This was a purchase from an ali-baba seller so I won't be surprised if that turns out to be the case. 
Build Reports / Dreamtime build
January 15, 2019, 05:02:22 PM
No pics to post since the build is still in its white case with some masking tape for labels, but I wanted to report a successful build on the Dreamtime pedal.  I shopped carefully for the right parts, and followed the SMD soldering tips and assembly guide very closely.  The fit for the three circuit boards and jacks in the  small case is very precise, but certainly functional.  The board worked when first tested out of the box, and went into the case without any major issues.  Very nice layout on the board, and great instructions in the build docs.   I'm finishing up the assembly on the Headtrip this week, and looking forward to noodling around with both of these pedals. 
VFE Projects / Blueprint compared to Mobius Strip
August 15, 2018, 02:33:01 PM
I have built both of these VFE pedals and like them.  For the Blueprint, my pedal has a very low level of background sound -- sort of a hi-frequency harmonic  - that is present with any of the delayed signals from the PT2399.  And the pedal is otherwise very, very quiet which is the only reason I can hear the other sound.  I have changed out the memory chips and it does not seem to make a difference.  I am guessing it is part of the modulation circuit that the BP uses, since there is no similar sounds from my Mobius Strip pedal even using both of the delay channels.    Wanted to ask if anyone else has noticed this.
Nice to see that the Dragon, Pinball Tilt and Standout pedals are listed to be available in mid-July.  Maybe even a combo package for the three of them.
VFE Projects / VFE Switching board
July 01, 2018, 11:26:04 AM
I previously messed up a couple of VFE switching boards (v1) trying to remove the input/output jacks from them to replace a bad part or relay.  Can I order a couple of replacement switching boards?  Or put in a request to have some extra boards made available the next time you reorder them?  I have been "borrowing" new switching boards from other VFE boards I have ordered, and I want to build those projects but will need switching boards for them.  I know I can use alternate jacks and switching if I need to, particularly for projects that do not use the split rail power, but I would like to keep the VFE pedals matched with the VFE switching boards.
I have started using the alternate in/out jack points of the board to test everything before installing the board-mounted jacks, since that preserves access to the back side of the board to isolate and fix any issues.  I noticed this morning that the labels for the J1/ground holes and the J2/ground holes are inconsistent from the front side of the board to the back side of the board.  I think the ones on the front side are correct, so don't be confused if things look different when you are checking something on the back side of the board.
VFE Projects / switching board question
May 16, 2018, 03:31:08 PM
    A quick question based on just a few minutes troubleshooting the switching board for the Blueprint pedal since I think the relay for the switching board might be defective.  The audio and switching boards are fully assembled and wired together, but have not been installed in the box.  The wiring connections and positive and negative voltages on both boards look OK, including the 5v power going to the pic.  The LED turns off and on when the momentary switch is pressed.  Plugging in a guitar and speaker, the bypassed signal is OK, but the relay does not switch to the in/out connections that go to/from the Blueprint board when the switch is pressed and the LED comes on.  Continuity exists between the in and out jacks even when the LED comes on when the switch is pressed.  When pressing the momentary switch, I can only hear the relay click with every other switch press, while it remains silent on the other (unlike the soft clicks I can hear for each press on other switching boards).     Is there is another plausible thing to check that would have this same symptom before I unsolder the jack and relay to put in a replacement?   
VFE Projects / Mobius Strip
May 04, 2018, 02:26:45 PM
Built the Mobius Strip and had to troubleshoot it for a little while to find and replace the wrong part I had installed into the board.  It is working now, and I like the sound.  Much cleaner than another pedal I built around the PT2399. 

One simple change I made was using a DPDT on-on-on switch instead of just the on-on called for in the BOM.  The recommended DPDT on-on switch swaps the feedback loops between the two delays (accounting for the "Mobius Strip" name for the pedal), while using the middle position of the DPDT on-on-on switch routes both of the feedback loops into one of the delay channels and just leaves the delay with no feedback on the other.  Sort of hard to describe, but it seems different enough from the other two switch positions that I wanted to suggest it in case others want to try it.
VFE Projects / Part substitution for switching board
April 30, 2018, 05:05:45 PM
Has anyone has used a KY5050 voltage regulator as a substitution for the LP2950 voltage regulator on the VFE switching board?  I had ordered some LP2950s from Tayda Electronics and received the KY5050s instead (showing on the invoice as LP2050.  When I look up the data sheet for the KT5050 I see some references to the LP2950, but nothing saying they are direct substitutes. 
VFE Projects / Alpha Dog -- quick PWR question
December 12, 2017, 02:58:54 PM
What are the values for the 2 caps that go in the places marked "PWR" on the Alpha Dog PCB?  0.1u?  At least I gather those spots are for caps based on the picture of the assembled board in the build document.  I have seen other references to 220n perhaps going there, and still other references to PWR for VFE boards that are referring to higher current resistors.