Topic: Greetings... my new mic preamp.

[dactylus]

Starting the design of the switchboard. Still need to add the 48V converter schematic on this board.


1st :
2nd: 48V CH1
3rd: Polarity Reverse CH1
4th: Polarity Reverse CH2
5th: 48V CH2
6th: POWER ON

I know you guys didn't ask for the polarity reverse, but I'm trying to see if I can design the switchboard for the homestudio users as well.  Either way, if you *really* don't want it, I can just remove the switch and short the connection inside. 

My *problem* is Switch #1.  What could it be?

I really don't see the need for two switches for 48V, one switch would suffice and be preferable to me.  I think that the vast majority of us here would want a single switch for 48V. 

I also think that the polarity reversal option is not one that would be desired by this group.

I would prefer toggle switches to pushbuttons too.

Thanks for asking for our input!!   

1st : POWER ON
2nd: 48V CH1 & CH2
3rd:  on/off switch for vu meter/lights

[ohr]

My *problem* is Switch #1.  What could it be?

I am probably in the minority around here with this request...but if you have a spare switch, then I'd like to see a "ribbon" switch such as on the Grace m101 which is described at:

http://www.gracedesign.com/products/m101/m101.htm

or for those that would like to be safer in disabling 48v for extended periods of time without the chance of accidentally turning it on in the field...could there be an internal switch or jumper to disable the 48v circuitry?

[PH]

I use ribbons alot too, and that would be really cool but maybe problematic to implement. I think the 48v on/off toggle is essential but I just see the need for one switch to operate both channels. Same with the HF toggle.

I don't ever flip the phase, even in the studio. If I need to do that I'll do it in post.
Truly poor mic technique if you need to flip the phase in the field, and you should retire from taping immediately.

[digifish_music]

Here's a summary of the above suggestions, features I think are important, what switch they go on is unimportant...

Essential -

1. Unit on/off
2. P48V on/off

Suggestions -

3. Metering on/off
4. Metering brighter/dimmer
5. High Pass (~80 Hz knee on/off)
6. Toggle P48V and P6V (for plugin power mics?) ... perhaps a disaster waiting to happen?
7. Stereo-linked limiter toggle on/off
8. Peak hold switch
9. M/S decoder switch
10. Ribbon mic mode (+48V phantom power is locked-out to prevent potential damage to ribbon microphones, the impedance of the mic input is raised from ???k Ohms to 20k Ohms)
11. 10 dB pad.
12. Test tone.

digifish

[F.O.Bean]

Starting the design of the switchboard. Still need to add the 48V converter schematic on this board.


1st :
2nd: 48V CH1
3rd: Polarity Reverse CH1
4th: Polarity Reverse CH2
5th: 48V CH2
6th: POWER ON

I know you guys didn't ask for the polarity reverse, but I'm trying to see if I can design the switchboard for the homestudio users as well.  Either way, if you *really* don't want it, I can just remove the switch and short the connection inside. 

My *problem* is Switch #1.  What could it be?

I really don't see the need for two switches for 48V, one switch would suffice and be preferable to me.  I think that the vast majority of us here would want a single switch for 48V. 

I also think that the polarity reversal option is not one that would be desired by this group.

I would prefer toggle switches to pushbuttons too.

Thanks for asking for our input!!   

1st : POWER ON
2nd: 48V CH1 & CH2
3rd:  on/off switch for vu meter/lights

I like this method as well

But if you do go w/ 6 swicthes/toggles, I suggest the last one be a switch for the vu/metering to turn them on/off as well

I LOVE the look of that box w/ those kickass switches

Does that one have transformers in it I sure hope its at least an option!

[Chilly Brioschi]

Nice choice of omp!

I might just have to get me one; I haven't put a kit together since....    .....  an Eico 730 ?   




Is the portable stereo pre coming out as a kit, or are you assembling them?

[fivefishdiy]

Ok... thanks for the ideas and replies! Good stuff.

Okay, the extra switch will be used for VU Meter ON/OFF function.  This actually makes sense as turning off the VU Meters will give you a bit longer battery life.

Also, all the switches have been replaced from the PushButton type, to the mini-Pushbutton type, to TOGGLE SWITCHES. ... per popular demand.  I'm going to set them back farther also so you just have a small "stick" showing up in the hole. This makes accidentally toggling them a small chance.

ohr

or for those that would like to be safer in disabling 48v for extended periods of time without the chance of accidentally turning it on in the field...could there be an internal switch or jumper to disable the 48v circuitry?

Yes, there is an internal jumper. This should also save a bit of battery life if the 48V converter section is disabled.


Bean

Does that one have transformers in it Huh? I sure hope its at least an option!

Yep. It will be available with or without transformers. See this mockup photo.

The footprint will also allow the use of Cinemag or Jensen transformers. (of course, Jensen trafos will be more expensive)..... and *may* offer Lundahl transformer option too... (have to check if there is enough height and space clearance). The Lundahl option will probably be more expensive than the Jensen as it will involve additional hardware parts.

[boojum]

Nice choice of omp!

I might just have to get me one; I haven't put a kit together since....    .....  an Eico 730 ?   

Man, you must be old.  I put an Eico together, mono, in HS.  And it worked!   

[ero3030]

Ok... thanks for the ideas and replies! Good stuff.

Okay, the extra switch will be used for VU Meter ON/OFF function.  This actually makes sense as turning off the VU Meters will give you a bit longer battery life.

Also, all the switches have been replaced from the PushButton type, to the mini-Pushbutton type, to TOGGLE SWITCHES. ... per popular demand.  I'm going to set them back farther also so you just have a small "stick" showing up in the hole. This makes accidentally toggling them a small chance.

ohr

or for those that would like to be safer in disabling 48v for extended periods of time without the chance of accidentally turning it on in the field...could there be an internal switch or jumper to disable the 48v circuitry?

Yes, there is an internal jumper. This should also save a bit of battery life if the 48V converter section is disabled.


Bean

Does that one have transformers in it Huh? I sure hope its at least an option!

Yep. It will be available with or without transformers. See this mockup photo.

The footprint will also allow the use of Cinemag or Jensen transformers. (of course, Jensen trafos will be more expensive)..... and *may* offer Lundahl transformer option too... (have to check if there is enough height and space clearance). The Lundahl option will probably be more expensive than the Jensen as it will involve additional hardware parts.

Ok... thanks for the ideas and replies! Good stuff.

Okay, the extra switch will be used for VU Meter ON/OFF function.  This actually makes sense as turning off the VU Meters will give you a bit longer battery life.

Also, all the switches have been replaced from the PushButton type, to the mini-Pushbutton type, to TOGGLE SWITCHES. ... per popular demand.  I'm going to set them back farther also so you just have a small "stick" showing up in the hole. This makes accidentally toggling them a small chance.

ohr

or for those that would like to be safer in disabling 48v for extended periods of time without the chance of accidentally turning it on in the field...could there be an internal switch or jumper to disable the 48v circuitry?

Yes, there is an internal jumper. This should also save a bit of battery life if the 48V converter section is disabled.


Bean

Does that one have transformers in it Huh? I sure hope its at least an option!

Yep. It will be available with or without transformers. See this mockup photo.

The footprint will also allow the use of Cinemag or Jensen transformers. (of course, Jensen trafos will be more expensive)..... and *may* offer Lundahl transformer option too... (have to check if there is enough height and space clearance). The Lundahl option will probably be more expensive than the Jensen as it will involve additional hardware parts.

what r u going to do for your 2nd trick!!!   this guy has something goin on!!

[Gutbucket]

Just read through the whole thread and look forward to watching the continuing development.  Looks great.  Fantastic feedback/design process.

I don't have much to add other than the suggestion that if the layout allows, it would be great to have all the connections on one side, which I think would greatly aid in cable routing in the bag. The inclusion of an unbalanced 1/8" stereo output in addition to the XLR's would be both convenient for running into small mini-jack input flash recorders (either as the primary recorder or as a backup) and also allow for easy patching out to others if using the XLR outs.

Thanks for the good work!

[Chilly Brioschi]

PM sent on a stereo pre with Lundahls, kit or assembled...

between the That Op-Amp and the Lundahls, I need to hear this thing, no question



Boojum-

The Eico 730 is an A.M. Modulator, as in A.M. radio broadcast, for, in this case, ancient Ham radios.
It was way before my Hi-Fi listening days.
We did modify the amp for high fidelity instead of high intelligibility. This caused much consternation by other Hams as it was bandwidth intensive in their eyes. This was not completely the case, as A.M., in general is a bandwidth hog, but not nearly as bad as F.M.

But I digress!  I want to hear the Lundahls in a portable Pre!!!

[PH]

I agree with gutbucket here. All connectors on the same side or preferably the back.
I like the stereo-mini output idea. (1/8 plug)

I thought I saw mention of mini-XLR's. I would not go that route unless absolutely critical. I would think that would actually discourage sales and I certainly wouldn't want to have a set of expensive
Right Angle mini XLR's made up. I would actually use another frame if that were the case. I love the blue case, but if you can't make it work easily, don't force it and certainly don't add work to your end by having those difficult to drill holes. There are other cases that might work, or you could make the design and have the case prefabbed like Grace does with his.

I'm loving the design and feedback process. I look forward every day to seeing the next step.
BTW yall, FiveFish has graciously offered to let me try out one of this 4 ch transformerless designs in a few weeks.
I plan on using it for a record I'm starting July 22, so I'll be sure to post some reports and sound clips.

[Gutbucket]

BTW yall, FiveFish has graciously offered to let me try out one of this 4 ch transformerless designs in a few weeks.
I plan on using it for a record I'm starting July 22, so I'll be sure to post some reports and sound clips.

Looking forward to that.  More of what really counts most.. the sound.

[jerryfreak]

wow! just saw this, looks great. I wanted to put in a third vote for all connectors on the back

if power consumption is a big deal, you might want to consider having a 12V phantom circuit via internal jumpers as well. schoeps and i believe several other mics run fine on 12V phantom

[H₂O]

+T This is great watching some one design a pre-amp in almost real time.  Almost like watching American Chopper

Nice design

Comments:
1. I would suggest All connectors on same side preferably back
2. I would make two version one with transformers and one without (or as you have said make input/output transformers an upgrade option with add on board)
3. Unbalanced out would be a nice addition on a gold plated 1/8" jack - lots of people run Edirol R-09's which take unbalanced in's
4. Selling as a kit would be nice as well for those who like tinkering
5. External Power supply - as others have said 9V preferably - 12V is not too bad using Lion batteries but alot more 7.2 - 9V avail these days with DVD players and RC Car popularity
6. Metal poly film Caps as an option instead of electrolytic caps with audio signal circuit


If these have already been discussed, my apologies