Preamp Project - variable impedance, etc.
- Thread starter unheardof
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mattmoogus
Well-known member
No you need the 5k in series with the pot (its a variable resistor in this case) so that the transformer is always loaded by at least 5k. I know our 1:4 can handle that low load on its secondary but cant go much lower as its nominally 10k. 5K + the 100k pot lets you sweep the load from 5k to 105k. Loaded with 100k its still quite flat out past 50k(?).
Hmmm I must try this...
M@
Hmmm I must try this...
M@
mattmoogus
Well-known member
The resistor Im talking about is across the secondary of the transformer. Whatever load you put on the seconary is reflected, more or less, to the primary at the same ratio the transformer is. So with our 1:4, which is nominally 600:10k, if you load the seconary with 10k the primary will be 600ohms. If you change that load resistor to say, 20k, the primary will become 1.2k.
The limitation with this is when the transformer changes its freq response too much as you increase the load resistor. Some are much better than others in this regard.
M
The limitation with this is when the transformer changes its freq response too much as you increase the load resistor. Some are much better than others in this regard.
M
unheardof
Active member
[quote author="mattmoogus"]...like I said, is that you must you a transformer that stays pretty flat as you change the load on it.[/quote]
Wow, thanks Matt. Excellent tips!
So would the JLM14 qualify in the "stays pretty flat as you change the load" category? I think we'll go with that and the 99v if budget allows.
I agree that the best way is probably to build it per plans first and then work on mods. Thanks again!
Wow, thanks Matt. Excellent tips!
So would the JLM14 qualify in the "stays pretty flat as you change the load" category? I think we'll go with that and the 99v if budget allows.
I agree that the best way is probably to build it per plans first and then work on mods. Thanks again!
rattleyour
Well-known member
[quote author="unheardof"][quote author="soundguy"]...but there isnt an EQ out there that I have used that is going to mimick what happens when you have a proper load. To my ears its a question of size and efficiency in the circuit much more than a tonal thing like an eq would be. Theres a ddefinite difference between letting the bass into the circuit as opposed to adding bass eq to a circuit.[/quote]
I totally agree, and this is what I'm hoping for with a variable impedance.
[/quote]
Do you guys mean specifically for low impedance mics? [Edited for clarity]
I definitely defer to Soundguy...
I was just saying correct impedance combined with EQ might be a simpler solution than adding extra features on your first DIY build, especially if all your mics are the same.
I totally agree, and this is what I'm hoping for with a variable impedance.
[/quote]
Do you guys mean specifically for low impedance mics? [Edited for clarity]
I definitely defer to Soundguy...
I was just saying correct impedance combined with EQ might be a simpler solution than adding extra features on your first DIY build, especially if all your mics are the same.
mattmoogus
Well-known member
[quote author="unheardof"][quote author="mattmoogus"]...like I said, is that you must you a transformer that stays pretty flat as you change the load on it.[/quote]
Wow, thanks Matt. Excellent tips!
So would the JLM14 qualify in the "stays pretty flat as you change the load" category? I think we'll go with that and the 99v if budget allows.
I agree that the best way is probably to build it per plans first and then work on mods. Thanks again![/quote]
Yep it does. Thats the one weve done the most experimenting with so we know how it behaves. So it should work with the values I described. I know the Lundahl 1538 and 1578 can handle not being loaded but we havnt tried as many combinations as we have with the JLM1:4. Youd have to try it yourself and see what it could take. Ours has less headroom than the Lundahls but this just means a different sound and different applications. And of course once you put the pad in, it can handle line level.
M@
Wow, thanks Matt. Excellent tips!
So would the JLM14 qualify in the "stays pretty flat as you change the load" category? I think we'll go with that and the 99v if budget allows.
I agree that the best way is probably to build it per plans first and then work on mods. Thanks again![/quote]
Yep it does. Thats the one weve done the most experimenting with so we know how it behaves. So it should work with the values I described. I know the Lundahl 1538 and 1578 can handle not being loaded but we havnt tried as many combinations as we have with the JLM1:4. Youd have to try it yourself and see what it could take. Ours has less headroom than the Lundahls but this just means a different sound and different applications. And of course once you put the pad in, it can handle line level.
M@
pstamler
Well-known member
First question: what kind of microphones are you planning on using? The answer will determine how you want to mess with impedance.
If you're using condensers, most of them will be happy with anything 1000 ohms or greater, which means most transformer-input designs. Jensens, for example, typically spec out at 1500 ohms input impedance with the recommended loading, which is 10x the secondary impedance.
Ribbons, on the other hand (well, old-type ribbons like RCAs) like to see a high impedance; they were designed to work into a transformer whose secondary was loaded by nothing but a tube's grid. For that to work optimally, though, you need a transformer that's designed for the job, like the old ones used in 1940s-1950s vintage preamps and consoles. Many modern trannies will have a big resonant peak in the high audible frequencies operating essentially unloaded like this. Of course, you could see if that peak offsets the rolloff of old-style ribbon mics.
Finally, dynamics. Most modern dynamic mics were designed to work into the same sorts of loads as condensers (1k and up), but some older designs, like the SM57, turn out to work best when loaded by lower impedances like 500-600 ohms, which was typical for Shure mixers back when they were designed. I found, in some research my classes at the university did, that the SM57 is a much better behaved microphone with that lower-impedance load, and that you can do the loading either via a multi-tapped primary or by hanging resistors in parallel with the primary, leaving the secondary load resistor alone. (See Recording, this month.)
So...figure out what microphones you'll be using, and plan your project accordingly. If you're like most of us, you have an assortment of condenser and dynamic mics, so you'll probably want something with a 1000-1500 ohm impedance, with loading resistors, but if you have ribbons, it's another story.
Peace,
Paul
If you're using condensers, most of them will be happy with anything 1000 ohms or greater, which means most transformer-input designs. Jensens, for example, typically spec out at 1500 ohms input impedance with the recommended loading, which is 10x the secondary impedance.
Ribbons, on the other hand (well, old-type ribbons like RCAs) like to see a high impedance; they were designed to work into a transformer whose secondary was loaded by nothing but a tube's grid. For that to work optimally, though, you need a transformer that's designed for the job, like the old ones used in 1940s-1950s vintage preamps and consoles. Many modern trannies will have a big resonant peak in the high audible frequencies operating essentially unloaded like this. Of course, you could see if that peak offsets the rolloff of old-style ribbon mics.
Finally, dynamics. Most modern dynamic mics were designed to work into the same sorts of loads as condensers (1k and up), but some older designs, like the SM57, turn out to work best when loaded by lower impedances like 500-600 ohms, which was typical for Shure mixers back when they were designed. I found, in some research my classes at the university did, that the SM57 is a much better behaved microphone with that lower-impedance load, and that you can do the loading either via a multi-tapped primary or by hanging resistors in parallel with the primary, leaving the secondary load resistor alone. (See Recording, this month.)
So...figure out what microphones you'll be using, and plan your project accordingly. If you're like most of us, you have an assortment of condenser and dynamic mics, so you'll probably want something with a 1000-1500 ohm impedance, with loading resistors, but if you have ribbons, it's another story.
Peace,
Paul
unheardof
Active member
I think I may have misread Soundguy slightly, but what I was agreeing with is that different mics are going to behave better and be more efficient at different impedances, so it makes sense to give yourself the option to try to match it up.
I do use mainly consensers, some old, some new. Never really looked at what kind of impedance they want. I also use several different dynamics and even some odd stuff like an old crystal mic that goes with a 3M tube 1/4" recorder. May get into building mics someday (beyond those little Panasonic electrets, been there, done that :grin
.
My point is it might make a difference on some mics, might make no diff on others. But if all it involves is swapping out a 10k with a 5k+100k pot, the question becomes not "WHY" but "WHY NOT".
Having said that, I'm still building the Baby Animal as-is, but once it's rocking, be assured that I'm going to start playing around with it. (After all, aren't we all in this to learn?? :roll: )
And we figured out prices on parts and everything. Looks like we might be able to do a single channel Baby Animal JLM14/99v with DI for under $200, plus shipping. That's figuring in a PSU, a cheap metal case and the connectors, etc. If it goes a little over it's not the end of the world. If the sound quality is even approaching a Neve, Hardy, API, etc, as some have said, then it still sounds like a heck of a deal.
I'm going to move my Baby Animal talk over to one of those threads.
I do use mainly consensers, some old, some new. Never really looked at what kind of impedance they want. I also use several different dynamics and even some odd stuff like an old crystal mic that goes with a 3M tube 1/4" recorder. May get into building mics someday (beyond those little Panasonic electrets, been there, done that :grin
.My point is it might make a difference on some mics, might make no diff on others. But if all it involves is swapping out a 10k with a 5k+100k pot, the question becomes not "WHY" but "WHY NOT".
Having said that, I'm still building the Baby Animal as-is, but once it's rocking, be assured that I'm going to start playing around with it. (After all, aren't we all in this to learn?? :roll: )
And we figured out prices on parts and everything. Looks like we might be able to do a single channel Baby Animal JLM14/99v with DI for under $200, plus shipping. That's figuring in a PSU, a cheap metal case and the connectors, etc. If it goes a little over it's not the end of the world. If the sound quality is even approaching a Neve, Hardy, API, etc, as some have said, then it still sounds like a heck of a deal.
I'm going to move my Baby Animal talk over to one of those threads.
You guys say DIY won't save you money... you don't feel like you are getting a better preamp then you would buy in a store with most of these projects? Aside from some of the "Vintage" gear that cost more than new... but comparing the stuff you can build vs meek for something "cheap" or @valon for an example of good quality but expensive. I know it's a cleaner package and you can claim you have X gear in your studio on paper but for shear performance vs dollar do you guys still think it's more expesive?
Maybe I'm not seeing the big picture as I'm a new guy here... I'm just assuming a green or baby animal is going to be a better pre than my little meek vc3 I picked up from the pawn shop for $130 bucks.
Maybe I'm not seeing the big picture as I'm a new guy here... I'm just assuming a green or baby animal is going to be a better pre than my little meek vc3 I picked up from the pawn shop for $130 bucks.
we've talked about this quite a bit if you search. Everyone has their own opinion about it, but for me the whole point of building myself is so I can have something that is way better than anything I can buy. When you buy commercial gear, component selection is influenced by a companies accounting department as much as it is by a designers ears often. Building yourself you absolutely can take the same circuit and make it sound better, so you are absolutely correct with what you are saying. The flip side is there are a lot of new guys out there that are attracted to DIY thinking they'll save money and if your time is worth anything per hour, you arent going to save a dime. Also, many manufacturers purchase in bulk so if you take your average run of the mill prosumer circuit and bought it, by the time you build it, build a supply, put it in a case, etc, your build might be more expensive, so the budget side of thing is typically a shock for some folks.
dave
dave
Gilligan8
With DIY you might pay less for parts or you might not.
To some of us hours counts when you have lots of things you need to do in your life. I think sometimes people overlook time with DIY
But if you add all the time you spent building it the cost goes up.
If your time is not worth anything to you, maybe you save money.
Write down the time spent on the web looking up and ording parts or in catalogs then the time building, you might be better off with a part time job using the hours spent and buying something more expensive but that might not be as much fun
IMO DIY works when you are building something you can not buy because it is not made or If you do it to learn and have fun. Education alway seems to have a cost.
Things like the case and switches and transformers can add up fast.
One good thing about DIY is if you build a bunch of stuff and/or try different parts you can sometimes make better part and circuit choices for the "sound" or lack of "sound" and the unit is more of what you want. This is a good thing
With DIY you might pay less for parts or you might not.
To some of us hours counts when you have lots of things you need to do in your life. I think sometimes people overlook time with DIY
But if you add all the time you spent building it the cost goes up.
If your time is not worth anything to you, maybe you save money.
Write down the time spent on the web looking up and ording parts or in catalogs then the time building, you might be better off with a part time job using the hours spent and buying something more expensive but that might not be as much fun
IMO DIY works when you are building something you can not buy because it is not made or If you do it to learn and have fun. Education alway seems to have a cost.
Things like the case and switches and transformers can add up fast.
One good thing about DIY is if you build a bunch of stuff and/or try different parts you can sometimes make better part and circuit choices for the "sound" or lack of "sound" and the unit is more of what you want. This is a good thing
Yeah, I definitely wasn't counting time... but I find researching this stuff to be fun... I would be reading this even if I never intended on doing it... I love knowledge so for me it's not an issue. Yes my time IS worth money but I enjoy tinkering with these things and problem solving and accomplishing things.... hell the reason we are making these half the time is just to feed that money pit we call "our music" think about how much money is spent on learning and playing music and for the majority of us it's never going to repay itself... it's just something you must do because you enjoy it
On the flip side I refuse to cut my grass because my time is definitely worth more to me than whatever time it takes to mow the grass! I hate cutting grass
On the flip side I refuse to cut my grass because my time is definitely worth more to me than whatever time it takes to mow the grass! I hate cutting grass
