I'm really frustrated - Need help for tube mic pre in a bad way

[Richie Mann]

I'm so frustrated I want to pull my hair out. I have a small home studio and I have good mic's, a good Focusrite audio interface, good cables. Then there's the $30 Art tube preamp. The preamps on the Focusrite are good, but I really like the sound from a good tube preamp and the Art is just not cutting it. It's OK, but I really want something better, although I don't have the money to buy one outright. I have experience with soldering and electronics, but I've never built anything with tubes before, so I started doing research a few months ago to learn everything I could. All I've wanted to do is find a schematic for a good sounding tube mic preamp that's not ridiculously complicated (the simpler the better, with or without a mixer). The problem I'm having is that there are just too many to choose from! I've found dozens of schematics that seem to fit the bill but I'm just not knowledgeable enough to narrow the list down to one. I'm really hoping someone on this forum will be kind enough to help me out and maybe give me some guidance as to what design is best. Every time I settle on one, a different one starts looking better.
I've managed to wittle my list down to 6:
http://www.gyraf.dk/gy_pd/g9/g9pd.htm Gyratec G9
http://www.gyraf.dk/schematics/tubetech_mp1a.gif Tube-Tech MP1A
http://recordist.com/ampex/schematics/mx35man/mx35.gif Ampex MX-35 (w/ Mixer)
http://www.waltzingbear.com/Schematics/Altec/Altec_428B.htm Aletc 428B
http://www.waltzingbear.com/Schematics/RCA/BA-21A.htm RCA BA-21A
http://twin-x.com/groupdiy/displayimage.php?pid=3027&fullsize=1 Redd.47
I don't expect someone to go through every circuit for me, but I'm sure some of these will stand out, or maybe someone knows of one that's better than these.
Also, I already know that working with high voltages and large amounts of current is dangerous and I'm always very careful.
Thank you in advance!

 

[djn111]

Hi,

Check this thread very easy

http://www.groupdiy.com/index.php?topic=6711.0

DJn

 

[Meathands]

Everything I've read about the REDD 47 makes me really want one. Drip's 47 micro PCB looks quite amazing, too.
http://www.dripelectronics.com/index.php?option=com_content&view=article&id=28&Itemid=54

 

[lassoharp]

Every time I settle on one, a different one starts looking better

I think what you want to do is look at the more practical issues:

1) How much gain do want/need?

2) Do you require a volume control?

The One-Bottle is probably the simplest good tube circuit with volume control - downside is lower gain than what you have with an ART-MP.

The rest of the sound will be determined by the transformers.

 

[gemini86]

to be honest, you're going to end up spending a lot more than you want to if you go with anything but the one-bottle...


The thing is a BEAST... it's simple, and it'll get your feet wet. If the time comes you need something more, then it's easy to add it, since it's so simple.

build a one-bottle, you won't regret it...

 

[CJ]

if you build a chassis with a power supply and some in and out jacks, you  about 75 percent of the way done, thus, you can noodle with the remaining 25 percent all you want, changing circuits til you find the sound you are after.
do you have any tubes laying around? just use what you have if you want to go cheap.
then if you do not like the sound, you keep the same chassis, pwr supply and I/O, so changing the actual amplifier takes about 10 minutes. it might look like a frankenstein chassis after a while, but as long as it sounds good, who cares  nobody should be poking around inside  your projects anyway, 

 

[Richie Mann]

Wow, you guys are great - I didn't think I would get such a fantastic response - I really appreciate the help and suggestions!

And I checked out the one-bottle and I think it's the way to go, plus I love the frankenstein idea CJ 

Thanks for the Drip's 47 micro PCB link meathands, that's something I'll have to look in to

 

[emrr]

The Altec 428B and RCA BA-21A both require specialized output transformers. 

 

[ricardo]

I think you should build the G9.

The main reason, and its an important one, is that you can talk to the designer here.

Many people have built this so most problems are sorted out.

It is a full design with all details worked out including PSU and uses high quality modern parts instead of Unobtainium.

It is the quietest with only the EMI REDD47 challenging it.

 

[Kingston]

It is a full design with all details worked out including PSU and uses high quality modern parts instead of Unobtainium.

It is the quietest with only the EMI REDD47 challenging it.

First of all, G9 is not particularly quiet. It has a problem with PCB design which makes B+ rectifier leak all over audio circuits. Then there's a problem with output transformers mismatched to the output tubes which leads to a high pass filter on all your audio. You can fix these by building an external B+ supply, or changing the output tube (including rewired heaters).

But by that point you might as well make the whole thing point to point.

Secondly, EMI REDD47 is a terrible and heavily outdated fixed gain design. Don't bother building it if you like tube distortion. The feedback network pretty much negates all of that, and when it clips it will just scream with an awful "splash damage" effect. People here like the preamp because it was used by The Beatles, plain and simple. The reputation has nothing to do with the sound, of which is has little. In fact transformers contribute most of it.


What all of this boils down to is that one bottle is a much better beginners tube project. Parts count is very low, everything is easy to obtain and there is no exotic stuff needed, or placebo effects based on history of said design to worry about. or anything serious to fix. There's still a lot of feedback negating much of the nice tube distortion, but at least you can easily rewire it to a non-feedback version.

 

[MatthisD]

Hello Richie, as well as the above mentioned projects it may be worth looking at forum member 'ruffrecords' "poor man's tube gain makeup stage" reasons being; 
It is very affordable hence the name, the PCBs are available per single channel as well as a separate power supply board, if you need more gain than a one-bottle setup you can use two PCBs in series per channel, a very low distorsion preamp but it is limited in terms of the output needs to see a impedance of 10K+ which isn't a problem unless following it with vintage gear with lower impedance inputs (typically 600Ohms), Ian (ruffrecords) is a very helpful person and always has an answer for a question, I haven't heard a G9 or other tube Pre but compared to solidstate preamps I like this alot.
Matt

 

[ricardo]

First of all, G9 is not particularly quiet.

Have you built & tested one of these?  Or the EMI REDD47?

What all of this boils down to is that one bottle is a much better beginners tube project.

Err.rrh.  If you are referring to NewYorkDave's "One-Bottle Preamp" thread, I see 36 pgs with some gold buried in a lot of liquid BS.  There's at least 2 different circuits discussed with a zillion proposals for each component.

I'm sure NYD's original circuit works well but a beginner might appreciate firm advice and maybe (shock! horror!) a PCB and PSU design.  see some of the comments on wiring in the 36 pgs.

Ritchie, Lassoharp's questions are very relevant.  What mikes do you intend to use?  Is it all close up stuff?  For a Coles 4038 ribbon, none of the examples here will be much good.

 

[CJ]

Redd 47 has ef86, which also adds to color,

12ax7 can be grainy, harsh,

12ay7 better

12av7 never tried but heard good things,

6sl7 can be real good

if you use a 9 pin socket, you can interchange tubes very easily except the big octals like 6sl7 and 6sn7,

if you build the power supply and chassis, and I/O, then you can build pultec, la2a, by just changing a few parts,

 

[lassoharp]

Ian (ruffrecords) also has a unique mic pre design that's unlike any of the above mentioned designs.  I'm assuming it's ok to mention this as it was posted in the DIY gallery but you may want to contact him regarding a build.  It looks to have great specs.

 

[gemini86]

It's simply a mu follower using a 6cg7. Add a 1:10 or higher input mic amp and you have around 40dB gain... need more, add another stage for about 60db gain total. But it's going to want to see 10K at whatever you plug it into...

 

[baadc0de]

It is a full design with all details worked out including PSU and uses high quality modern parts instead of Unobtainium.

It is the quietest with only the EMI REDD47 challenging it.

First of all, G9 is not particularly quiet. It has a problem with PCB design which makes B+ rectifier leak all over audio circuits. Then there's a problem with output transformers mismatched to the output tubes which leads to a high pass filter on all your audio. You can fix these by building an external B+ supply, or changing the output tube (including rewired heaters).

But by that point you might as well make the whole thing point to point.

Secondly, EMI REDD47 is a terrible and heavily outdated fixed gain design. Don't bother building it if you like tube distortion. The feedback network pretty much negates all of that, and when it clips it will just scream with an awful "splash damage" effect. People here like the preamp because it was used by The Beatles, plain and simple. The reputation has nothing to do with the sound, of which is has little. In fact transformers contribute most of it.


What all of this boils down to is that one bottle is a much better beginners tube project. Parts count is very low, everything is easy to obtain and there is no exotic stuff needed, or placebo effects based on history of said design to worry about. or anything serious to fix. There's still a lot of feedback negating much of the nice tube distortion, but at least you can easily rewire it to a non-feedback version.

Having built two REDD foursevens, I felt I must chime in. It's just as Kingston described it. The REDDs have the big wow reputation and it is a "big" sound and can be a tad "compressed" in a good way, but when it clips it will tell you that in no uncertain terms. Splash damage actually is a good description for the farty rippy sounds it makes when pushed. Sometimes we like that on DI guitars that are EQ'd to fck and back after the fact. Then again, it's the only tube preamp I have on tap, so we'll see how it fares against G9-51X and V76 when we test 'em out.  But generally, it's loud, brash and forward.

 

[emrr]

Having built two REDD foursevens, I felt I must chime in. It's just as Kingston described it. The REDDs have the big wow reputation and it is a "big" sound and can be a tad "compressed" in a good way, but when it clips it will tell you that in no uncertain terms. Splash damage actually is a good description for the farty rippy sounds it makes when pushed. Sometimes we like that on DI guitars that are EQ'd to fck and back after the fact. Then again, it's the only tube preamp I have on tap, so we'll see how it fares against G9-51X and V76 when we test 'em out.  But generally, it's loud, brash and forward.

I keep saying this, and understand that it's hard for people to get it until they've heard it in use.  The lust is illogical and faddish, at best.  A preamp with significant negative feedback and stiff PSU C is not anything like a guitar amp.  It won't make the distortion you hear in your head. 

 

[ricardo]

baadc0de, thanks for your experience of the REDD47 sound.  That's exactly what I'm after.

Doug, I'm not sure if you are commenting on REDD47 sound or about NFB tube amps with stiff PSU in general.  Is this from experience?  Do you like them?

I'm waiting for comments on G9 sound especially its noise performance.  But from experience please .. rather than " its got PCBs so can't possibly be as good as hand wired P2P by virgins."

What PCBs promise is repeatability.  If you build one from a good circuit and it doesn't hum or oscillate, it's likely others can do likewise and get the same performance  ... especially if all connectors and the transformer are also on board so there is no wiring. Yes I know this is impractical with most tube circuits.

You rarely get this with P2P and I'm surprised there are not more pics of successful P2P layouts on this forum.  If I was building a Mullard 5-20 amp, I'd want to start with the EXACT P2P layout in their book.

 

[lassoharp]

But generally, it's loud, brash and forward.

Ah yes, the seldom heard adjectives for tube amps.  I don't know if I would include brash as a general term but in contrast to the creamy & pleasant sound they can often generate I would have to mention that they can have a very visceral, forward, bold, earthy kind of sound - even call it rambunctious with no NFB to level things out.  None of this is really a bad thing.   

 

[alexc]

rambunctious

That's it! Exactly. 

My 2cents

If I was to do another mic/instrument preamp it would be a straight ahead, 2 stages of simple grounded cathode with a volume pot in between and your choice of output section - srpp or parallel feed or whatever.

Kind of guitar preamp style.

As people have said, negative feedback tube preamps are very clean.

Not really worth all the bother over, say, an API style transistor preamp, which is a lot simpler, cheaper and easy to build.
And they too sound just great.

I've built the G9 (varied it a little so didn't encounter the noise and roll off issues)  and it certainly works as advertised.
It is a high quality preamp and very, very CLEAN.

The Redd47 too, and again, clean.

Work fine, great to have etc. But not all that ''different' in sound, to my ears.

'Guitar amp style' preamp stages with no NFB can be clean to dirty.

They have the 'character' that makes them different from everything else.

Good luck with it!

Oh, and I think PCBs can be just as 'variable' as point-to-point.
It's all a function of care of system construction and choice of components.

Cheers