Redd 47 Mic Preamp

[JBB]

Still puzzled by the quoted -130dBu EIN figure.

Thank you. Fixed.

 

[MicDaddy]

Cleeeeeeean!!  ;D

 

[audiophreak]

Beautiful Work !!!   

 

[momomo391]

Can you show or explain how the potentiometers and switched hook up to the pcb in the layout?

 

[cvea]

I have some drip pcb boards for sale:

2 Ultra 47 - $200 USD each plus shipping.
1 Opto 6  (fast & slow drip T4B included) $350 USD plus shipping.
1 EQP1A $250 USD plus shipping.


I have to pay school so I will have to leave these projects for later

 

[JBB]

Can you show or explain how the potentiometers and switched hook up to the pcb in the layout?

http://www.electronics-tutorials.ws/attenuators/t-pad-attenuator.html


Buy together the potentiometer with the PCB .
On this PCB there are input and output.
http://www.hairballaudio.com/catalog/parts-store/attenuators/bourns-600-t-pad-attenuator

 

[momomo391]

Is the input and output potentiometers the boost and gain. Where's the gain adjust knob?  And where are the three switches on the schematic? Is the LOW CUT  or the -20db the ground lift switch?

 

[Winetree]

Plus shipping?
Tired of asking.  List your location in your profile

I have some drip pcb boards for sale:

2 Ultra 47 - $200 USD each plus shipping.
1 Opto 6  (fast & slow drip T4B included) $350 USD plus shipping.
1 EQP1A $250 USD plus shipping.


I have to pay school so I will have to leave these projects for later

 

[ding]

Plus shipping?
Tired of asking.  List your location in your profile

I have some drip pcb boards for sale:

2 Ultra 47 - $200 USD each plus shipping.
1 Opto 6  (fast & slow drip T4B included) $350 USD plus shipping.
1 EQP1A $250 USD plus shipping.


I have to pay school so I will have to leave these projects for later

Plus shouldn't the black market be the place for this kind of stuff. http://groupdiy.com/index.php?board=3.0 I feel it just clutters up a thread unless someone specifically asked for it or it's some kind of a feeler post.

 

[JBB]

/// Where's the gain adjust knob?  And where are the three switches on the schematic?

The first graph - with knob and the three switches
The second graph - my version without knob and the three switches
http://groupdiy.com/index.php?topic=53650.msg684696#msg684696
You can take that give, or themselves  modifying the original scheme .

/// Is the input and output potentiometers the boost and gain. Is the LOW CUT  or the -20db the ground lift switch?

 

[cvea]

Sorry guys. I just updated my profile. I am located at Massachusetts so I believe shipping to California is around $15 or so. I have updated the list below too. Sorry for posting this here. It won't happen again.

plus good vibes!


2 Ultra 47 - $200 USD each plus shipping.  - No longer available
1 Opto 6  (fast & slow drip T4B included) $350 USD plus shipping.
1 EQP1A $250 USD plus shipping.

Plus shipping?
Tired of asking.  List your location in your profile

I have some drip pcb boards for sale:

2 Ultra 47 - $200 USD each plus shipping.
1 Opto 6  (fast & slow drip T4B included) $350 USD plus shipping.
1 EQP1A $250 USD plus shipping.


I have to pay school so I will have to leave these projects for later

 

[Bonsaimaster]

Can someone help me with a switchable Low cut switch. Looking for capacitor and resistor values to make switchable low cut at 30,60,90,120.
Thanks
Daniel

 

[momomo391]

Okay so that helps alot with the switches.  Where do you get the 48v from for the phantom power?  is the attenuator the boost knob, and is there a schematic for the gain and gain adjust knobs?

 

[momomo391]

Can you tell me where to get the 48v from for the phantom power, and how to add the boost and gain potentiometers to the layout? Im trying to build this and i cant seem to be able to figure it out. Also the vu meter doesnt seem to be on the layout, is it on the original schematic somewhere?

 

[j.frad]

very nice job!

 

[Phrazemaster]

Sorry guys. I just updated my profile. I am located at Massachusetts so I believe shipping to California is around $15 or so.

$15 to ship a PCB? Isn't that just a flat envelope with a little stuffing? $5 max? 

 

[iprovlek]

Is this still available!!!

 

[My3gger]

Original or Drip's psu could be improved and simplified, while retaining sound of preamp, have less work with it, specifications can be better, etc.
Why not simply use zeners as voltage reference instead of OA2s, this are known to cause problems for many builders, they take a lot of space, availability on the long run is questionable, etc. Real regulators could be used too, although zeners, maybe with cap multiplier make for a good HT psu. Replacing GZ34 or 6X4 for diode bridges doesn't do any harm to the sound. Fast, low drop diodes have some advantages over 1N4007s, although differences are small, i like them because heater LDO regulators need smaller heatsinks.
Ruffrecords posted schematic for simple phantom psu with TL783, 2W resistor takes care of minimum load for regulator to function on its own, so it is easy one.
We see wrong attenuator at the input of it all the time, output doesn't need to be 200 ohms either and trick for making 200 ohms from 600 ohms seems like not the best idea.  How can phantom work properly with T attenuator, it needs to be U, so one side doesn't have extra resistance. Output att. isn't needed with preamps like this because NFB causes sudden distortion which doesn't sound too nice.
I see no reason for the meter either and it needs buffer to function properly.
Tests show that 40 and 46dB positions are good to have, sound changes quite a bit from one to another. 34dB position gets no use here, it doesn't sound as good as the other two
All of this makes for easier, cheaper, more reliable and higher performance preamp of this type, along many others. G9's psu is pretty easy to make too, those back to back transformers can be replaced to single item.

 

[momomo391]

Thanks dude, that really simplifies the layout. Could you explain how I would use a U pad instead of a T pad, and what values to use. Also what attenuator should I use if the 200 ohm is the wrong one.

I dont know what value to use, but could I use this type of attenuator? http://www.ebay.com/itm/2Pole-23-Step-Rotary-Switch-Attenuator-Volume-Control-Pot-Potentiometer-DIY-New-/251286602182?hash=item3a81d941c6:gWUAAOSwagdXSVys 

Original or Drip's psu could be improved and simplified, while retaining sound of preamp, have less work with it, specifications can be better, etc.
Why not simply use zeners as voltage reference instead of OA2s, this are known to cause problems for many builders, they take a lot of space, availability on the long run is questionable, etc. Real regulators could be used too, although zeners, maybe with cap multiplier make for a good HT psu. Replacing GZ34 or 6X4 for diode bridges doesn't do any harm to the sound. Fast, low drop diodes have some advantages over 1N4007s, although differences are small, i like them because heater LDO regulators need smaller heatsinks.
Ruffrecords posted schematic for simple phantom psu with TL783, 2W resistor takes care of minimum load for regulator to function on its own, so it is easy one.
We see wrong attenuator at the input of it all the time, output doesn't need to be 200 ohms either and trick for making 200 ohms from 600 ohms seems like not the best idea.  How can phantom work properly with T attenuator, it needs to be U, so one side doesn't have extra resistance. Output att. isn't needed with preamps like this because NFB causes sudden distortion which doesn't sound too nice.
I see no reason for the meter either and it needs buffer to function properly.
Tests show that 40 and 46dB positions are good to have, sound changes quite a bit from one to another. 34dB position gets no use here, it doesn't sound as good as the other two
All of this makes for easier, cheaper, more reliable and higher performance preamp of this type, along many others. G9's psu is pretty easy to make too, those back to back transformers can be replaced to single item.

 

[My3gger]

There are many, many threads about mic input U attenuator with links to good online reading. Usually, -20dB pad at the input is enough in most cases with this preamp, 600 ohms Bourns T pad can be used at the output and go well with typical 30k:600 transformer. I rarely use it myself because output level can be set with device preamp is plugged into, this is also what many others do without problems.
Bigger challenge will be PSU, i gave some hints about Gyraf's G9. Ian Bell (Ruffrecords) has some excellent reading too, or if you are into making your own layout. For sure a lot of thought will go into grounding which has to be understood and done well.