jsteiger

VP312DI 500/51x 312 Preamp...PROTO PICS ON PAGE 2!!
« on: May 29, 2010, 05:41:02 PM »
Hi guys,

Since I have ordered prototype PCB’s  and finalized the artwork, I figured I would share what I have been working on as of late.

This is the Rev B version of the VP312DI that I started a few months ago. I think I first mentioned it on the HiZ Plug-In thread that [silent:arts] and I have been working on. That thread is here, BTW.

My original Rev A design was HiZ Direct Inject into the input transformer only. I wanted to be definitely different than a 512c or BAE’s version, which are HiZ into the DOA.

My brother Mike happens to be a bass player. Not an average player but a phenomenal player. He is also a tone freak. He has been on the “perfect tone” search for all of our lives. In his distaste for any bass amp he has tried, I told him to pick up a couple hundred watt power amp and take my TAB V71 home for a few days. He was amazed by what a great, pure sound this gave him. I proceeded to whip up a quick Bo Hansen DI, built on one of my old, stripped “build it like a 312” VP25 boards. After using this DI for a few minutes, he said he had no use for the TAB V71 and asked how much I needed for the 312 Frankenstein DI. This was done around the time I received my VP312DI Rev A proto boards.

So, next he took my VP312DI Rev A board home along with a few DOA’s. For HiZ Plug-Ins he had a Jensen passive, Pikatron passive, IC active (OPA2604) and Peter Purpose’ FET version. After a week or so of playing with both preamps and many combo’s of DOA’s and HiZ Plug-In’s…Mike told me that he wanted all the options in one preamp. He thought it would be a total mistake to not have Bo’s circuit as an option. So, the Rev B version was born.

Mike currently has multiple basses and used them all in these tests. His current favorite is a Spector that was originally custom made for Tom Hamilton. He also used his pair of Stambaugh Twins along with about 6 others. Yes, he has a problem.

OK, enough yakking. Here’s the run down.

-Basically, it’s the same mic pre circuit as the VP312. I have added a post DOA Elna coupling cap along with a Wima bypass. This can all be user bypassed with a .1" shunt-jumper on the PCB (for standard 312 circuit). I have found significant DC offset from the DOA depending upon which brand of DOA is being used, especially in Bo Mode. The Mute switch is not very quiet this way and we don't want to harm the 2503. This was very apparent when using as a bass amp front end.

-1/4" HiZ jack is auto-switching with a DPDT relay when a plug is inserted. For this I am using a little vertical relay PCB that can be soldered or with a .1” socket.

-Default DI mode is myself and Volker’s Plug-In HiZ PCB. This signal takes the same path as a microphone, thru the input transformer. This means the normal mic input pad will also be available for use while in HiZ Plug-In mode. It will be -15db on this one in lieu of the standard –20db. Volker and I have decided to not alter any of the HiZ circuits from Dan, Peter, Fabio and so on. Some have more gain than others so the pad may be needed on some occasions. The operating voltage for the HiZ Plug-In is switchable between 16V and 24V. A 51x rack will be required for 24V operation.

-I am using 3 NKK G-Series Ultra Miniature Toggles to not only select Bo Mode but also select a few options that go with Bo Mode. This took me a little time to find the right toggles and engineer all of this to fit/work properly. I was highly inspired by Peter Lazaro’s brilliant use of the mini toggles as he did for his EQN project. So, thanks Peter!

-The top of the 3 ultra mini toggles is "Post 2622". Flipping this switch activates the 2nd plug-in relay. Activating this relay is only possible if a 1/4" plug is inserted. HiZ signal is then routed thru Bo Hansen's popular DI circuit. This is Post 2622 or directly into the DOA. Relay control signal is taken from the DI jacks ring when a 1/4" plug normals the ground signal from sleeve to ring.

-The middle ultra mini is Bo's -10db DI pad that is only active if the top switch is in Post 2622 mode.

-The bottom ultra mini is only active if the above 2 have been switched to the right. It was found by accident like a lot of cool things. It creates a Low Pass Filter that mimics the "perfect Jaco Pastorius tone", according to my brother Mike. He loves it so I figure other bass players will find it useful as well. Plus, it's pretty unique on a pre like this.

Sorry for the long drawn out explanation. I get carried away.

Here are some pics and stuff.

Faceplate artwork pdf


Gerber file screenshot of all 3 boards


Close up of DI board with Bo’s circuit


Mechanical details on how the 3 boards connect pdf


Plug-In Relay PCB front and back


Final (hopefully!) proto boards are due in here June 7th.

Regards, Jeff
« Last Edit: June 21, 2010, 10:50:31 AM by jsteiger »
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zayance

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #1 on: May 29, 2010, 05:50:22 PM »
 8)

[silent:arts]

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #2 on: May 29, 2010, 07:30:53 PM »
this result was beyond my thoughts once we started to chat about DIs :o

Holger


jsteiger

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #4 on: May 29, 2010, 08:03:46 PM »
this result was beyond my thoughts once we started to chat about DIs :o
Yes, mine too Volker. You know what this means right? We have to build the rest of the plug-in circuits and make sure they are good. I still have yet to build the DK FET version or the Jensen FET version. I have built the FB circuit but it is dead. I will have to confer with you to make sure my transistor choices were correct. I have not had the time to trouble shoot it.

FWIW, the Pikatron transformer with an APP2055 is a killer combination. One of the fav's for us.

Cheers, Jeff
Visit the CAPI store at http://www.capi-gear.com

CAPI is not affiliated with, endorsed by, or sponsored by API.

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #5 on: May 29, 2010, 09:17:11 PM »
Liking the sound of this  :)
Could this be built as a stand alone unit Jeff, or do I need to finally bite the bullet and get a lunchbox? Just thinking how useful it would be to have a smallish portable unit.
regards
Chris

[silent:arts]

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #6 on: May 30, 2010, 06:24:02 AM »
have to go to my late-shift at work now  >:(
but will finally order the missing parts tomorrow for final testing :D

Pikatron - they call me every two weeks asking for an order :o ::)

Denyle Guitars

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #7 on: May 30, 2010, 09:26:55 AM »
This looks just about ideal for me. I can't wait to get my hands on some.

okgb

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #8 on: May 30, 2010, 09:29:28 AM »
If one is going to the effort of having an dedicated D.I.
then why not make it flexable if that's all it will do
I'm In !
GKB Audio / Greg Boboski

jsteiger

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #9 on: May 30, 2010, 11:01:28 AM »
Liking the sound of this  :)
Could this be built as a stand alone unit Jeff, or do I need to finally bite the bullet and get a lunchbox? Just thinking how useful it would be to have a smallish portable unit.
regards
Chris
I have not really thought about this one as a standalone unit. I suppose one could build a pair of them in a 1RU enclosure. If the same ultra mini toggles are used, a recessed milling would have to be done on the back of the front panel as they mount .0625" from the front of the faceplate. These could always be done with standard toggles and flying leads. The t-pad is PCB mounted on this one to help keep everything together so it is in a fixed location but could also be wired with flying leads I suppose.

This looks just about ideal for me. I can't wait to get my hands on some.
;D ;)

If one is going to the effort of having an dedicated D.I.
then why not make it flexable if that's all it will do
I'm In !
It is also a full fledged 312 mic pre. The DI circuit is not switched into the circuit until a 1/4" plug is inserted. So, the best of all worlds.  :)

Best, Jeff
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gar381

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #10 on: May 30, 2010, 03:46:08 PM »
Very nice peice of Engineering Jeff !!  :o :) :)

GARY
RETIRED.....  from 51yrs in Show Biz

gar2520, gar1731,garAM10,gar918 DOAs at  http://capi-gear.com/catalog/index.php?cPath=71_72
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dandeurloo

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #11 on: May 31, 2010, 01:00:15 AM »
looks super cool!
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horvitz

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #12 on: June 03, 2010, 03:20:51 PM »
Oh, I'm totally in!  I think that my Stambaugh will love it as well :)

BTW, have you been OK with those NKK switches?  I tried out a couple of their rotary switches on my summing project and they seemed to not break very cleanly.. there was always a pop.  Perhaps the toggles are better.

jsteiger

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #13 on: June 03, 2010, 04:04:38 PM »
Oh, I'm totally in!  I think that my Stambaugh will love it as well :)
Yes, for sure. BTW, my brother picked up a Fodera over this past week end. He has some serious issues. It was a trade for his R bass and some other stuff. I hope this one makes him happy.  :)

Quote
BTW, have you been OK with those NKK switches?  I tried out a couple of their rotary switches on my summing project and they seemed to not break very cleanly.. there was always a pop.  Perhaps the toggles are better.
I will let you know soon. My latest proto boards are coming in tomorrow morning. I have not actually used them in a circuit yet. I think the G series is suppose to be some award winning product. Who knows what that means exactly.

Best, Jeff
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CAPI is not affiliated with, endorsed by, or sponsored by API.

Denyle Guitars

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #14 on: June 03, 2010, 08:11:09 PM »
I picked up a Wal a few weeks ago. Can I be your brother? :D

jsteiger

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #15 on: June 03, 2010, 08:41:14 PM »
I picked up a Wal a few weeks ago. Can I be your brother? :D
Haha!! Well, if you sell it and get a Smith or Watson or something in a few months, you qualify!  :D  He's on the never ending search. He had a great Alembic Exploiter back in the mid '80's that he never should have gotten rid of.  :-\
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Ryake

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #16 on: June 05, 2010, 11:42:39 AM »
I want 2! Looks great Jeff, I too am a bass player searching for the tone holy grail. Currently I go into a Radial JDI then a 512c.

jsteiger

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #17 on: June 06, 2010, 05:47:23 PM »
Hi guys,

The Rev B proto boards came in this past Friday. This is the first chance I've had to really look at them. Now, I just need to get everything built up! Anyone have more hours in the day?

For the meantime, here's some PCB porn  ;D




The vertical plug-in relay boards are in red.

Cheers, Jeff
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CAPI is not affiliated with, endorsed by, or sponsored by API.

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #18 on: June 06, 2010, 07:32:13 PM »
Nice.  You just don't stop . . . do you . .?




Hairball Audio

Re: VP312DI 500/51x 312 Preamp with Super Flexible HiZ DI
« Reply #19 on: June 06, 2010, 10:07:04 PM »
Very very nice  ;D
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