Lundahl transformer vs electrolytics on preamp input

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Bob's Mods

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I recently added a switch and some electrolytic caps to my home made preamp which was built with a Lundahl transformer on the input as opposed to the usual electrolytic caps that all lower end preamps are built with. I did this as an experiment to hear the difference between the two and I have to admit, the input transformer beats the caps. There is better definition with transformer for sure.
I was unable to detect a color change though. Some have said a transformer adds slight color. I could not detect any in my box.
If your thinking of building your own preamp, an input transformer is worth consideration. These parts don't come cheap at nearly $70 but if you build the whole thing yourself, its still reasonable. I believe some high end recording consoles use transformer inputs although I could not say which ones. Transformer inputs might be the standard on upper tier preamps.

Bob the Mod Guy. :)
 
Can you please tell me how a couple electro's debalance the mic input? Maybe you meant something else?


NWSM

Also the Lundahls are very Hi-Fi for a transformer. If you want color look at UTC, Sowter, Ect.
 
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They have a high D rating. This is a memory effect. Its a well understood problem.
 
nwsoundman said:
Also the Lundahls are very Hi-Fi for a transformer. If you want color look at UTC, Sowter, Ect.
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So the Lundahls are considered colorless? In what way would a Sowter color the sound? Is it a small effect or very noticable?

Bob the Mod Guy
 
OK. I don't have time today for this. Go read up on transformer coupled inputs vs op amp inputs etc. You can't debalance the balanced microphone output with caps. Maybe I still don't know what you are trying to say. I am a EE with over a dozen years experience so feel free to give details and post up a schematic.

I don't mean to call bullshit unless you are indeed full of it. There is a danger passing misinformation regarding mods to equipment. Folks here can mess up there gear trying to do the wrong things they read on the net.
 
I'm using an instrumentation amplifier for the gain stage, not an opamp. Balanced input, single ended output.
 
I am still unclear. I never mentioned op amp gain stages. I am still trying to understand your intentions regarding input only. You amp is not balanced troughout. You need to DEbalance the input. This is done with an input transformer or opamp or a few other ways using discrete components. I am still waiting for you to teach me how a few caps can perform this task alone. Forget everything after the input stage.
 
nwsoundman said:
I am still unclear. I never mentioned op amp gain stages. I am still trying to understand your intentions regarding input only. You amp is not balanced troughout. You need to DEbalance the input. This is done with an input transformer or opamp or a few other ways using discrete components. I am still waiting for you to teach me how a few caps can perform this task alone. Forget everything after the input stage.
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Bob never mentioned balancing, although he did give a cryptic response to your original question. I think he is substituting the tranny for the RFI filtering cap in front of the IC.
 
I was thinking he was talking about the phantom blocking caps. I was just trying to get clarafication. I would still like to see a drawing to fully understand what he did. He mentions adding a switch and caps. Maybe a phantom power switch and a cap for slow ramp?
 
The caps are the 47uF phantom blocking caps. I substitute blocking caps for the transformer with the simple flick of a switch. The jist of what I'm saying is a transformer input is the better option given a choice between electrolytics or a transformer. Thats it in a nutshell. The ears tell the story.
Sorry if I wasn't clear on that point.
 
I see. Cool. For some reason I first thought you meant that a transformer was replacing the caps, in a debalancing role. My mistake.

I love what transformers bring the party. All my homebrew gear is transformer coupled.

Lundahls are pretty clean relative to many other brands. Jensons are in that same catagory to me too. Vintage UTC's, Sowters, and the like tend to have lower bandwidth and more distortion. That distortion is what makes em great in lots of applications.


What instrument amplifier are you using? Why are you leaving the output unbalanced? Just curious.
 
I use the Burr-Brown INA217. As for the unbalanced output, I don't feel there is a compelling need for balanced lines for a compact home studio such as mine.

Thanks for your input on the transformer issue. I posted this because I feel there are many who do not realize there is a benefit to using them. For the home recordist, it appears the only way to obtain them is as a DIY project. They are a tad pricey but not overly so.

Bob the Mod Guy.
 
There are many benefits to using transformers for sure.

I still want folks to know that you can't just drop in a transformer in place of phantom blocking caps. You must still consider impeadance.
 
Bob's Mods said:
I use the Burr-Brown INA217. As for the unbalanced output, I don't feel there is a compelling need for balanced lines for a compact home studio such as mine.

Thanks for your input on the transformer issue. I posted this because I feel there are many who do not realize there is a benefit to using them. For the home recordist, it appears the only way to obtain them is as a DIY project. They are a tad pricey but not overly so.

Bob the Mod Guy.
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Like my favorite preamps, I couldn't imagine playing a guitar amp without iron on both ends. Many of the transformerless designs today, don't do much for me, unless I want a rather transparent and thinner sound.
 
There is better definition with transformer for sure.
I was unable to detect a color change though.
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Tranformers usually change the color a bit more charteuse, as opposed to the more subdued Earth-tones typical of capacitors.
 
how does one gain enough knowledge to feel confident to do DIY preamps? I'd love to learn but I think I'd need some basic EE concepts covered before anything else. Any suggestions? Community College, Books, Web sites?
 
qbert1 said:
how does one gain enough knowledge to feel confident to do DIY preamps? I'd love to learn but I think I'd need some basic EE concepts covered before anything else. Any suggestions? Community College, Books, Web sites?
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Build or design? Building is fairly easy from a kit, a little trickier from a schematic, but there are PCB layouts available for some of the popular DIY pres. Fabrication is the trickiest part for me, so I limit myself to mods.

Try here:

http://www.prodigy-pro.com/forum/viewtopic.php?t=1277

Design, hell I dunno how to do that.
 
mshilarious said:
Build or design?
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Well I guess design, not so much that I want to make the next Neve-ish clone but rather, I'd like to understand how all this works.

Thanks for the link, I'll try to digest all that first.
 
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