A Tube Mic Pre for a Ribbon Mic

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cpsmusic

Well-known member
Joined
Dec 3, 2013
Messages
292
Location
Melbourne, Australia
Hi Folks,

As I mentioned in another post I'm currently setting up a small home studio for preproduction and songwriting. I'm thinking of getting a Focusrite Scarlett 6i6 to use as my interface.

I'm also looking at getting an RM-5 Ribbon Microphone Kit to use  as my main mic.

Just wondering what an appropriate tube mic pre for a mic like this would be. I'm looking for something that would be at home in a lower-end studio in case I need to drag my gear in there. I have intermediate-level experience with tube gear having built several tube guitar amps.

ATM, I'm thinking of something like an RCA OP-6 or a Tele V76m.

Any suggestions?

Cheers,

Chris

 
I have several ribbons similar to the kit you are looking at, and I really like them with discrete solid state  preamps.
I have Neve, Api, and Jensen 990 preamps and they are all great. I have a RCA BA2 tube pre that is really great but not always better. And with a ribbon I sometimes want more than 40 dB of gain for acoustic instruments.
I'm just about done building a V76 though... and looking forward to trying it out.
Getting the transformers / chokes for tube preamps can be a challenge.
On another note, if I were doing a small home studio, I would at a minimum have a great tube condensor and large diaphragm dynamic, in addition to a great ribbon.
 
Hi Chris,
  You should have a look at Ian's eztube mixer eurocard amp. With a cinemag input and carnhill (or even edcor)output transformer you will get pretty amazing results. I have a cheap mxl ribbon mic and it sounds great trought this preamp.

Regards,

Pierre
 
Ribbons generally need more gain but it depends on what the source spl is.  Many pre's start to get noisy when maxed out so the noise floor is a concern when ribbon mic'ing quiet sources. For voice it should be "fine"... As a room mic on a quiet gtr part it may be "less fine". In front of a medium loud amp it's "no worries".

Most of the ribbons are fig8 pickup pattern too so the sound picked up from the back is also a concern but you can also use the nulls at the sides to reject certain sounds very well.

Cheers!
-jb
 
0dbfs said:
Ribbons generally need more gain but it depends on what the source spl is.  Many pre's start to get noisy when maxed out so the noise floor is a concern when ribbon mic'ing quiet sources. For voice it should be "fine"... As a room mic on a quiet gtr part it may be "less fine". In front of a medium loud amp it's "no worries".

I'm mostly going to be recording relatively quiet acoustic instruments - acoustic guitar, violin, double bass, banjo, harmonica, etc. Building a tube preamp with enough gain but without too much noise is my main concern. The more I trawl the web, the more unsure I get!

If people could only have one tube mic pre for a ribbon mic, what would it be?

Cheers,

Chris
 
cpsmusic said:
If people could only have one tube mic pre for a ribbon mic, what would it be?
One which was quiet with loadsa gain.

You buy this from Ye Olde Unobtainium Shoppe.

What do you hope to get from your tube pre?  It won't be quiet & loadsa gain.
 
ricardo said:
cpsmusic said:
If people could only have one tube mic pre for a ribbon mic, what would it be?
One which was quiet with loadsa gain.

You buy this from Ye Olde Unobtainium Shoppe.

What do you hope to get from your tube pre?  It won't be quiet & loadsa gain.

I want a preamp with some character.

I'm also interested in older technologies and as a guitarist, have a background building tube stuff.

I realise that there's a trade-off between gain and noise and that this is significant in the case of ribbon mics.

That's why I posed the original question.
 
cpsmusic said:
I want a preamp with some character.
For the type of recording you do, you'll certainly get loadsa hissy character.

Maybe use a modern SS preamp and get your tubey sound later in the chain.
 
cpsmusic said:
ricardo said:
Maybe use a modern SS preamp and get your tubey sound later in the chain.
What would you suggest?
Build a dedicated ribbon preamp.

I describe such a beast in my Yahoo MicBuilders directory under ActiveRibbon as RibbonDMP3.doc

You'll have to ask others how to get a tubey character.  My suggestion would be a simple cathode follower but that might be too clean for you.

But you'll find the RibbonDMP3 still useful after you get fed up of 'character'.
 
I think tubes get a generally bad press where noise is concerned. It is true, there are lots of noisy tube designs available but that is not the fault of the tubes.

Most ribbon mics look like a 150 ohm resistor to the mic pre. The inherent noise in this resistance is about -131dBu. If you have a perfect mic pre with 70dB of gain, then the noise of this resistor will be amplified by 70dB and it will be  -61dBu at the output. This is basic physics and there is not getting away from it. Most good semiconductor amplifiers add a couple of dB of noise of there own so you end up with noise around -59dBu. You will find amplifiers that claim to do better than this but that is only by judicious choice of af measuring conductions. and weighting filters.

I recently built the prototype of my 'Classic' tube pre. It has a gain of up to 70dB. Its EIN measures -123dBu at 70dB gain which means the noise at the output is -53dBu, just 6dB worse than a really good SS pre.

Cheers

Ian
 
ruffrecords said:
I think tubes get a generally bad press where noise is concerned. It is true, there are lots of noisy tube designs available but that is not the fault of the tubes.

Most ribbon mics look like a 150 ohm resistor to the mic pre. The inherent noise in this resistance is about -131dBu. If you have a perfect mic pre with 70dB of gain, then the noise of this resistor will be amplified by 70dB and it will be  -61dBu at the output. This is basic physics and there is not getting away from it. Most good semiconductor amplifiers add a couple of dB of noise of there own so you end up with noise around -59dBu. You will find amplifiers that claim to do better than this but that is only by judicious choice of af measuring conductions. and weighting filters.

I recently built the prototype of my 'Classic' tube pre. It has a gain of up to 70dB. Its EIN measures -123dBu at 70dB gain which means the noise at the output is -53dBu, just 6dB worse than a really good SS pre.

Cheers

Ian

Is a schematic of your Classic Tube Pre available?
 
I just completed 4 channels of Ian's Classic pre a few days ago.  Although I haven't had enough time with it to give a full evaluation, I will say it has gain for miles and doesn't strike me as being particulary hissy or noisy.  I've built a pair of his EQs that use a similar (same?) topology for their gain stage and they are very quiet. More importantly, they sound great!

I plan on using the preamps for recording quiet sources (classical guitar, early plucked instruments, small chamber ensembles, etc.) with ribbons, dynamics, and condensers. Judging by the sound that came out of the monitors when I first tested the units, I'll be more than happy with them.

Links to the  schematic , support documents, and related threads  are available via Ian's White Market thread as well as how to purchase PCBs for the project.
 
rmaier said:
I just completed 4 channels of Ian's Classic pre a few days ago.  Although I haven't had enough time with it to give a full evaluation, I will say it has gain for miles and doesn't strike me as being particulary hissy or noisy.  I've built a pair of his EQs that use a similar (same?) topology for their gain stage and they are very quiet. More importantly, they sound great!

I plan on using the preamps for recording quiet sources (classical guitar, early plucked instruments, small chamber ensembles, etc.) with ribbons, dynamics, and condensers. Judging by the sound that came out of the monitors when I first tested the units, I'll be more than happy with them.

Links to the  schematic , support documents, and related threads  are available via Ian's White Market thread as well as how to purchase PCBs for the project.

Thanks!
 
rmaier said:
I just completed 4 channels of Ian's Classic pre a few days ago.  Although I haven't had enough time with it to give a full evaluation, I will say it has gain for miles and doesn't strike me as being particulary hissy or noisy.  I've built a pair of his EQs that use a similar (same?) topology for their gain stage and they are very quiet. More importantly, they sound great!

I plan on using the preamps for recording quiet sources (classical guitar, early plucked instruments, small chamber ensembles, etc.) with ribbons, dynamics, and condensers. Judging by the sound that came out of the monitors when I first tested the units, I'll be more than happy with them.

Links to the  schematic , support documents, and related threads  are available via Ian's White Market thread as well as how to purchase PCBs for the project.

Hi,

I just want to make sure that I'm not confusing things - the preamp PCB is the one listed in the Ruff Records Price List as the Classic Mic Pre V3?

And the HT and Phantom supply boards work with this preamp?

Also, I couldn't find any support documents or threads specifically related to this preamp - where are they?

Cheers,

Chris
 
cpsmusic said:
Hi,

I just want to make sure that I'm not confusing things - the preamp PCB is the one listed in the Ruff Records Price List as the Classic Mic Pre V3?

And the HT and Phantom supply boards work with this preamp?

Also, I couldn't find any support documents or threads specifically related to this preamp - where are they?

Cheers,

Chris

It is a relatively new board (came out February 2015) but there is some documentation for it in this folder:

https://www.dropbox.com/sh/6sugvbi40rhf0zv/AACNwz_B2QjzCwxomQENkxZ-a?dl=0

and in particular you should look at this document:

https://www.dropbox.com/s/mxax09g6aa8tog7/Classic.pdf?dl=0

The HT and phantom boards work fine with this but you will probably find it more cost effective to use the Lunch Box PSU board instead which combines HT, phantom and heater supplies on one PCB for less than the cost of the phantom and HT boards. Details of the lunchbox PSU are here:

https://www.dropbox.com/sh/7ezl5le96x49j3e/AAAKNVCdegZSG-MZGwhX_W6Na?dl=0

Both the Classic pre and the Lunch Box PSU were first discussed in the Lunch Box thread:

http://groupdiy.com/index.php?topic=53765.msg686243#msg686243



Cheers

Ian
 
Look up the schematic of the Gates M5215 (5879-based) or the Gates M5215A (EF86 based) microphone preamplifier used in radio station consoles of the period.  These preamps operate off a regulated DC supply (approximately 310 v at 10 mA per channel) and 6,3 v AC was used on the heaters.  DC heating may buy you a few more dB in noise reduction.  Ribbon mics like the 77DX were used for broadcast purposes for years, so this preamp will work with a ribbon mic.  The gain of the Gates preamps is around 40 dB.  The broadcast consoles used a program amplifier to raise the signal off the passive mix buss to +4 dBm or a suitable reference level to drive audio processing gear and peak limiting before the transmitter input.  Your console or recorder should have sufficient gain (20 dB or so) after the preamp to obtain suitable record level.

There are schematics of the Gates preamp on line.    The original transformers may not be available but suitable substitutes can be found.  The UTC A-10,  A-11,  A12 should work for input,  UTC A24 should work for output.    The original M5215 series preamps were on a printed board. 

Be prepared to select tubes to find quiet ones for the input stage so have a few tubes on hand.  As far as powering the preamps, a 300 volt supply can be built using a 6X4 rectifier, a pair of 0D3 or 0A2 regulator tubes in series for HT regulation, and a bridge rectifier and series pass transistor regulator for DC filament heating.  I like the 6X4 (or 6X5) indirectly heated rectifier for HT since there is no surge voltage associated with other rectifiers.

If you want to experiment with special purpose tubes, the triode connected D3A (7721) makes a good input tube.  The Western Electric 417A (5842) triode is another choice...but special precautions ARE required with these high performance tubes!

The choice of input transformer is important for good shielding and response.  I have good reports about Lundahl and Sowter (UK) transformers.
 
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