Building low noise, euphonic, transformer balanced preamps as a beginner?

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GalenH

Well-known member
Joined
Dec 15, 2022
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50
Location
Portland, Oregon
Hi,
I'm wondering what information is available for a preamp design that I would use as all rounders for folk music. Vocals, acoustic instruments.
I really love the sound of the recordings I made with ART MPA II preamps, with the tubes swapped for rca blackplates. I know they are cheap but they are not starved plate which makes a difference, and the recordings sound great with the tubes upgraded.

Ideally I would like to achieve fairly low noise, good matching, stepped gain for stereo use, 65+ db of gain. I would need phantom power, polarity switch.

As I am a beginner, I'm curious if this is even possible, or if there is a recommended kit.
I like the sound of high impedance, 10k+ ohm preamps like the AEA trp on the mics that I have. I think the TRP is a bit too transparent maybe on these transformerless mics?

I have 8 ll1517 output transformers that I could use to make preamps, if those were useful.

Portable is necessary, I like the 500 series format.

I wonder if I could modify a kit with better transformers to sound better, I don't know. Really a beginner here and I suspect I may be biting off more than I can chew.

Maybe I could gut a cheap mixer and replace the guts with good transformers, etc? Really have no idea.
Alternatively, I'm thinking of getting 4 channels of RND 511, or on the soupy total opposite side of the spectrum, go back to mpa iis. I know these are wildly different preamps.
I like the way the MPA II preamps (with tubes upgraded) sounded round on vocals, taking out harshness, and adding a richness that was very musical to me.

I am trying to give you an understanding of the sound character I am looking for

Weighty, round, full, but open, realistic, not muffled or obviously distorted. Many preamps sound on the harsh side to me. RME onboard preamps are a good example of the harshness that I run away from.

I want something to sound real, but friendly. Does this make sense?

Let me know if you have any suggestions.
 
Just a note of caution; output transformers are generally designed for a specific job in a specific circuit. There are two consequences to this. First, circuits not designed to drive a transformer (like the outputs of an existing mixer) often do not do at all well driving a transformer. And secondly, swapping an existing output transformer for a 'better' one will have largely unpredictable results.

If you want low noise, stepped gain and character then you could try one of the Neve 1290 or a classic API based design. Kits for these and a range of others are available from JML audio (I have no association with them).

JLM Audio Shop

There are also designs based on the famous Helios type 69 modules. There is New York Dave's ery popular 1 bottle tube preamp and my EZTubeMixer designs but neither of those will fit into a 500 series module.

UYou biggest problem is likely to be which one to choose.

Cheers

ian
 
Really interesting question, and a difficult one too. A lot of the qualities you're looking for could be subjective - one person's "weighty" could be another person's "boomy". If you're chasing a specific tone, then it's worth trying as many different preamps as you can to see which have the sorts of qualities that you favour.

I fully agree with Ian's point that buying something with the intent to modify by installing transformers would be risky, particularly as you describe yourself as a beginner. If you want to DIY it, then a proven kit would in my view be the easiest way to go about it (projects where you just buy the PCB and then source the parts yourself, or refurbish and rack a classic module, are great fun but more scope for issues).

There are loads of great kits out there for 500-series preamps that might meet some of your requirements - for example CAPI, AML, Sound Skulptor, JLM, DIYRE, Silent:Arts, Hairball, and many others. Some are inspired by or based on classic designs.

As a recording folkie myself, any and all of these designs will work for folk and acoustic music. Getting hands-on experience with them, or with the classics they're based on, would help you narrow down what you're looking for. It sounds like you favour transformer-based designs, so Neve-style (such as AML's ez1073pre or Sound Skulptor's MP573) or API-style (such as CAPI's VP28) might be places to start. Helios is also an excellent suggestion (my personal preference), though there aren't any Helios-style kits that I'm aware of.
 
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On a side-note, I did a comparison a few years ago between all the preamps I had at the time. I tracked a whole song via a mic splitter, splitting the signal between five different preamps - AML ez1073, CAPI VP28, Audient ASP880, Aphex JPre500 and Neumann V472 - so that the same takes were used for each version, and used test tones to make sure all gains were the same. I found it a very instructive exercise!

I've dug out my files for this and uploaded as a (large!) zip file here: The Well - a preamp test - Google Drive

Within, you'll find notes on my methodology, various screenshots of the calibration process, and seven mixes (with identical, minimal processing) at 24/48 - one version for each preamp, and two more where they were summed through an external summing mixer for interest's sake. Please note that this is a demo of a song which may be released commercially in future, so please don't share further.

Hope this helps with your search.

[Caveat: while mostly acoustic, it's not a particularly folky song!]
 
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There are some cool API type clone projects like the ML12. I built a 4 channel example and finished it over the summer. It's not a difficult build, you just need to source all the parts (and know where to get them) and then rack them up yourself.

I have some PCB's kicking around if you're interested.
 

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Just a note of caution; output transformers are generally designed for a specific job in a specific circuit. There are two consequences to this. First, circuits not designed to drive a transformer (like the outputs of an existing mixer) often do not do at all well driving a transformer. And secondly, swapping an existing output transformer for a 'better' one will have largely unpredictable results.

If you want low noise, stepped gain and character then you could try one of the Neve 1290 or a classic API based design. Kits for these and a range of others are available from JML audio (I have no association with them).

JLM Audio Shop

There are also designs based on the famous Helios type 69 modules. There is New York Dave's ery popular 1 bottle tube preamp and my EZTubeMixer designs but neither of those will fit into a 500 series module.

UYou biggest problem is likely to be which one to choose.

Cheers

ian
Thanks for these thoughts, Ian.

I ran across Steve Hampton's diy tube amp article in tape op,

https://tapeop.com/interviews/30/build-tube-mic-pre/
And I got excited thinking about going tube with jensen or lundahl transformers. I love the sound of tube amps.

However, steve hampton seems to have stopped selling the kit, and I think it would be pretty difficult for me to not use a kit as a total beginner.

Thinking of forgoing the portability of a 500 series preamp and just building something tube.
Do you have any specific recommendations for good tube kits?

On the side of Warm but open and neutralish, for folk music.
 
Really interesting question, and a difficult one too. A lot of the qualities you're looking for could be subjective - one person's "weighty" could be another person's "boomy". If you're chasing a specific tone, then it's worth trying as many different preamps as you can to see which have the sorts of qualities that you favour.

I fully agree with Ian's point that buying something with the intent to modify by installing transformers would be risky, particularly as you describe yourself as a beginner. If you want to DIY it, then a proven kit would in my view be the easiest way to go about it (projects where you just buy the PCB and then source the parts yourself, or refurbish and rack a classic module, are great fun but more scope for issues).

There are loads of great kits out there for 500-series preamps that might meet some of your requirements - for example CAPI, AML, Sound Skulptor, JLM, DIYRE, Silent:Arts, Hairball, and many others. Some are inspired by or based on classic designs.

As a recording folkie myself, any and all of these designs will work for folk and acoustic music. Getting hands-on experience with them, or with the classics they're based on, would help you narrow down what you're looking for. It sounds like you favour transformer-based designs, so Neve-style (such as AML's ez1073pre or Sound Skulptor's MP573) or API-style (such as CAPI's VP28) might be places to start. Helios is also an excellent suggestion (my personal preference), though there aren't any Helios-style kits that I'm aware of.
Well, on the favoring of transformer based designs, I would actually love to make something with tubes, as that is the happiest I've ever been with my audio, and generally love the sound of (properly powered) tubes in recordings. It just sounds round and real to me. In my limited experience.

I see there's one tube design in the kits you listed, from sound skulptor, the MP566, and I'm curious about that one.
As I shared with Ian, there's also steve hampton's tape op article about building your own tube preamp but he seems to have stopped selling the kit. Of course Ian suggested New York Dave's one bottle preamp and his own EZtube Mixer. If I could track down kits of either or at least pcbs and easy to find components I think I could consider starting the process.

I am definitely curious about building that one, but doing it without a kit sounds a bit of an intimidating task.

Do you have any ideas of other tube kits that might fit the bill?

And thank you for sharing your preamp comparison, I will take a listen! And heard what you said about keeping it to myself since the song has yet to be released, will do.
 
That said, if it proves too difficult to find a tube preamp build suitable for folk, ie not too distorted but just warm and big, then transformer balanced builds would probably be a lot easier.
 
Thanks for these thoughts, Ian.

I ran across Steve Hampton's diy tube amp article in tape op,

https://tapeop.com/interviews/30/build-tube-mic-pre/
And I got excited thinking about going tube with jensen or lundahl transformers. I love the sound of tube amps.

However, steve hampton seems to have stopped selling the kit, and I think it would be pretty difficult for me to not use a kit as a total beginner.

Thinking of forgoing the portability of a 500 series preamp and just building something tube.
Do you have any specific recommendations for good tube kits?

On the side of Warm but open and neutralish, for folk music.
If you are a complete beginner then you are probably best advised away from tubes until you are more experienced. I am afraid it seems tube kits are few and far between unless you are into power amplifiers.

Cheers

Ian
 
Good advice there. Dangerously high voltages involved in tube projects, even in the Sound Skulptor MP566.

Do you have reference songs for the kind of sound you're looking for? If so, the equipment used might suggest possible avenues of exploration.
 
If you are a complete beginner then you are probably best advised away from tubes until you are more experienced. I am afraid it seems tube kits are few and far between unless you are into power amplifiers.

Cheers

Ian
Thank you for the reasonable advice, I kind of came to the same conclusion last night after doing some more research on tube safety protocols. I love the sound of tube but the higher power needs and space usage is also a consideration for portability.
 
Good advice there. Dangerously high voltages involved in tube projects, even in the Sound Skulptor MP566.

Do you have reference songs for the kind of sound you're looking for? If so, the equipment used might suggest possible avenues of exploration.
Good advice there. Dangerously high voltages involved in tube projects, even in the Sound Skulptor MP566.

Do you have reference songs for the kind of sound you're looking for? If so, the equipment used might suggest possible avenues of exploration.
Kavi Alexander's recording of Vishwa Mohan Bhatt and Ry Cooder, A meeting by the river, comes to mind, considering the mics I am working with.
I know he was working with custom tube mics with milab rectangular diaphragm condensers, into custom tube preamps, onto tape.
I am working with two rectangular diaphragm condensers, but they are transformerless, and I am wondering how close I can get to his natural, but warmed over sound. It is definitely not overly distorted as you can hear. Just a little more natural than a lot of digital recordings I hear.



Otherwise, I am quite happy with some recordings I made with soundelux u195s and some other mics into ART MPA II preamps with rca blackplate tubes

Here is one song. Same ask as you had, as this song is also unreleased. It's not mixed fully, this is a rough mix, but this should give you an idea of what I am going for between these two.

 
On a side-note, I did a comparison a few years ago between all the preamps I had at the time. I tracked a whole song via a mic splitter, splitting the signal between five different preamps - AML ez1073, CAPI VP28, Audient ASP880, Aphex JPre500 and Neumann V472 - so that the same takes were used for each version, and used test tones to make sure all gains were the same. I found it a very instructive exercise!

I've dug out my files for this and uploaded as a (large!) zip file here: The Well - a preamp test - Google Drive

Within, you'll find notes on my methodology, various screenshots of the calibration process, and seven mixes (with identical, minimal processing) at 24/48 - one version for each preamp, and two more where they were summed through an external summing mixer for interest's sake. Please note that this is a demo of a song which may be released commercially in future, so please don't share further.

Hope this helps with your search.

[Caveat: while mostly acoustic, it's not a particularly folky song!]
I listened to this whole thing, and learned a lot! Listened and took notes, in different orders, on macbook speakers, then austrian audio hix55 headphones, then on yamaha hs8 monitors through a metric halo uln 8. I won't reveal anything about the tests, but I will say that I guessed three out of the 5 correctly. The AML, Capi, and Neumann. I like the Neumann and AML for different things. There was one in particular where something went wrong in the high frequency realm, where I absolutely couldn't listen to it, it sounded like a migraine to me.

ALSO: I love this song! I would love to get your album when it's done. I really like your writing. And the themes are relevant feeling.
 
I found a schematic many years ago (designed by Fred Nachbaur) that i would like to try one day. Not sure if this is something for a beginner but it at least no unobtanium audio transformers are required for this amp. Beware that it has phantom power on the input as a "free" bonus...
In case a transformer is wanted it could be added (maybe best at the output in this case).
 

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Fred's balanced amplifier has "power" on the inputs by virtue of having a common mode DC voltage there, but it isn't going to be "phantom power". Any DC load on the inputs will muck with the input stage biasing, and likely the DC balance as well. This amplifier could be driven from a floating coil, either a transformer secondary or a dynamic microphone, but that would significantly reduce the DC balance adjustment range. It really needs input coupling caps.
 
R12 can be changed (adjusted) for your needs (depending on mic). As said i need to try this one myself but i think it can be done.
The bias of the input tubes depend on a current flow (1.2K load it states) as now they have none.
 
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R12 can be changed (adjusted) for your needs (depending on mic). As said i need to try this one myself but i think it can be done.
The bias of the input tubes depend on a current flow (1.2K load it states) as now they have none.
I would posit that the input tubes have an effectively negative grid bias due to the cathode current flowing through R1(R2) and about half of the DC balance control.
 

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