cheap Lo-Z to Hi-Z i/p transformer? backwards o/p xformr?

RnFR · Post by **RnFR** » 15 Jul 2011, 11:54

name says it all. anyone know of anything for lo to hi Z input for a decent price? I'm having a hard time finding the proper ratio as well. I've seen anywhere from 1:40 to 1:6. I'm designing a lofi vintage vocal effect that will sound like an ancient mic pre on the edge of breakup, so it's got a bit of grit until you holler into it, then it breaks up nice and nasty, but not in a fuzz box kind of way. more like an old mic pre. it's going to have parallel clean output for monitor sends, a line in for guitar(sounds nice as well) a mic in, and as of right now, just a line out. having just the line out will simplify as well as cheapen the bom. most mixers have line in capabilities anyway, or you can just run it into a DI. it doesnt have to be expensive, as frequency limitation is the name of the game here. I'd just like to find one that is just like those used in those adapters, except in a pcb mount format. anyone have any ideas? maybe one of the 42XXXX models?

RnFR · Post by **RnFR** » 15 Jul 2011, 13:56

I'm bumping this, as Ive added more specific info.

phatt · Post by **phatt** » 16 Jul 2011, 08:16

I tend to think it has more to do with those early circuits than any particular magic smoked transformers.
My 2 sense worth.
Phil.

mictester · Post by **mictester** » 16 Jul 2011, 09:25

RnFR wrote:name says it all. anyone know of anything for lo to hi Z input for a decent price? I'm having a hard time finding the proper ratio as well. I've seen anywhere from 1:40 to 1:6. I'm designing a lofi vintage vocal effect that will sound like an ancient mic pre on the edge of breakup, so it's got a bit of grit until you holler into it, then it breaks up nice and nasty, but not in a fuzz box kind of way. more like an old mic pre. it's going to have parallel clean output for monitor sends, a line in for guitar(sounds nice as well) a mic in, and as of right now, just a line out. having just the line out will simplify as well as cheapen the bom. most mixers have line in capabilities anyway, or you can just run it into a DI. it doesnt have to be expensive, as frequency limitation is the name of the game here. I'd just like to find one that is just like those used in those adapters, except in a pcb mount format. anyone have any ideas? maybe one of the 42XXXX models?

The distortion comes from the microphone preamplifier - the transformer didn't actually do anything (the signals were much too small to cause saturation) apart from impedance conversion. The other thing that the transformer did was pick up hum fields - that was one of the reasons that many manufacturers moved to active replacements for the transformers!

For your purposes, I would suggest an active (op-amp based) balanced microphone preamplifier that's completely clean. You can then manipulate the audio at reasonable levels, without introducing noise (unless you want to). I would suggest a Marshall Bluesbreaker clipping-type circuit and a FET-based µ-amp. You will also want some tone shaping, both before and after the introduction of distortion. You could also add a pot to introduce some 50 and 100 Hz hum, and a white noise pot to really emulate those noisy old microphone preamps! The output of your circuit should be at line-level and balanced so that it will feed a desk channel directly.

RnFR · Post by **RnFR** » 26 Jul 2011, 10:36

I need a small transformer similar to those found inside these adapters-

http://www.amazon.com/gp/aw/d/B0002CZYF ... 54-7554505

I'm having a hard time finding the proper impedance ratio- 250:50k. anyone know a decent model? fidelity is not an issue. i have also heard that it is possible to use an output transformer backward, but there are certain downsides, like voltage loss. the whole idea here is lofi, so I'm not going to blow cash on Jensen, lundahl, etc. I'm trying to expand on an idea that I have for a "vintagizer" for vocals that can be run from stage. I could just use the above adapters, but I'd like to get it all self contained, and in order to get the bypass switching done properly, I would definitely need to bring the transformer on board. i will of course share everything once I've got it all finished.

the wizards beard · Post by **the wizards beard** » 26 Jul 2011, 18:05

Why not buy those and take them apart?

RnFR · Post by **RnFR** » 26 Jul 2011, 21:10

because really, there is no more than a $2.00 transformer inside! I have thought about it, but I haven't justified it yet. the next step is to try a little o/p trannie backwards, then we'll see if I get that desperate.

deltafred · Post by **deltafred** » 26 Jul 2011, 22:05

When I built my first bass guitar (I was 16 at the time) I wound my own pickup. It had very few turns on it so the output was really low. I used a small mains transformer to boost the voltage so it was high enough to drive an amp. It worked quite well and sounded a lot better than without it. The ratio was 40:1 (240v to 6v) and it was about 1.25" cubed. I even managed to squeeze it into the control cavity, just.

If you have he space it might be worth cracking open an old wall wart and give it a try.

Mr.Grumpy · Post by **Mr.Grumpy** » 28 Jul 2011, 16:09

Do you live in the states? Radioshack sells a cheap-o audio transformer. Not the ratio you're looking for, though. 1K primary, 8 ohm secondary.

http://www.radioshack.com/product/index ... Id=2103254

PokeyPete · Post by **PokeyPete** » 29 Jul 2011, 18:49

Would either of these work?

http://www.mouser.com/ProductDetail/Xic ... adSPozo%3d

http://www.mouser.com/ProductDetail/Ham ... ZzOg%3d%3d

dai h. · Post by **dai h.** » 29 Jul 2011, 22:31

what is the transformer supposed to do in the circuit (and the "vintageizer" supposed to do to the signal)? (From what little I understand of transformers), they are tricky to use. The driving input impedance, the way the secondary is loaded (or not loaded), the size, signal level, plus whatever else. affects the signal passed (low end extension, high end extension, "ringing", distortion). If the audio quality doesn't need to be that great(or better if it's poor), then the Audio-Technica loZ-hiZ adapter doesn't look very expensive (I'm guessing at that price it's impossible for there to be a quality transformer inside).

RnFR · Post by **RnFR** » 30 Jul 2011, 01:22

PokeyPete wrote:Would either of these work?

http://www.mouser.com/ProductDetail/Xic ... adSPozo%3d

http://www.mouser.com/ProductDetail/Ham ... ZzOg%3d%3d

well, i think the first one is a HF transformer used in radio tuners. not sure how well it would pass audio. the second is a bit more expensive than I'd like to pay for. thanks for the help, though!

dai h. wrote:what is the transformer supposed to do in the circuit (and the "vintageizer" supposed to do to the signal)? (From what little I understand of transformers), they are tricky to use. The driving input impedance, the way the secondary is loaded (or not loaded), the size, signal level, plus whatever else. affects the signal passed (low end extension, high end extension, "ringing", distortion). If the audio quality doesn't need to be that great(or better if it's poor), then the Audio-Technica loZ-hiZ adapter doesn't look very expensive (I'm guessing at that price it's impossible for there to be a quality transformer inside).

yes, I'm not entirely familiar with transformers and audio, but I know that this specific ratio works well, so that is why I am looking for it. the pedal is supposed to go from being similar sounding to an old mic pre/tape distortion sound from old records, to full on vocal distortion. but, I want it to be able to be used as a guitar or keyboard effect as well. it will have a mic input, a mic thru, a line in, and most likely a single line out. I may possibly put in an output transfo as well, but right now, I'm just planning on using a DI. the circuit is one that ive shown on the forum already, but I'll probably tweak it a bit. one day I just tried it with a mic and the adapter, and it worked great! I've had a couple guys bugging me for something like this for a while, and they were very happy with it. if I can find something cheap, I'll be happy. maybe an off brand besides the AT model will be less expensive, and I can pull it out and pot it.

thanks a lot for the help so far, guys!

dai h. · Post by **dai h.** » 30 Jul 2011, 03:23

Would building the preamp to work with the AT adaptor be unacceptable? (Looking over some low cost Sansui/Hashimoto transformers that are avail. here in Japan--these look similar to the cheap kind used for octavia cloning), they don't look particularly less expensive vis-a-vis the AT adaptor. Possibly if you do a bulk purchase or luck out with surplus or something it's possible, but I'm not sure if they can be found that low ($2) new (I could be wrong!). (I vaguely recall there were a line of clones(?) of the Sansui supposedly made of different materials(lams) that were a bit cheaper, so maybe super cheap ones do exist possibly from some Chinese maker?)

p.s. also, was trying to check out what you were building (schematic), but could only find this (other) thread:

viewtopic.php?f=17&t=13700&p=154682#p154682

RnFR · Post by **RnFR** » 30 Jul 2011, 06:08

wow, i totally forgot about that other thread! threads merged.

in response, i'm not looking for any magic mojo or saturation from the transformer. i just know it gets me where i'm trying to go with this thing. the op amp might be a way to go, but the transformer would be simpler. an opamp balanced out would be perfect though. i already have the gain circuit done. it's basically the Assload Booster.-

viewtopic.php?f=13&t=7182&hilit=Assload+Booster

for some reason, the cascode sounds great with a voice. it doesn't sound like a mic through a fuzz pedal. as far as using a bluesbreaker circuit- that is just not going to happen. i can't stand most diode clippers.

i was hoping to find something similar to the octavia transformers. those cost $2.75 at small bear. the ones in the adapters don't even have a frame! i would have to pot them myself. i was planning on using whatever the frequency response limitations were on the thing to my advantage. i've got an off brand adapter in a drawer behind the stage here at work. i'm going to check the brand after the show. hopefully they won't be $12.00.

dai h. · Post by **dai h.** » 31 Jul 2011, 00:29

I vaguely recalled that there was a vendor selling some low cost trafos with impedances not in that line (the same line as the octavia use ones) and I went to look them up (too see if there was something close to what you are looking for) but apparently they are defunct (an "ocean state electronics").

re: the circuit, I had (a not particularly concrete notion) of "low-fi/vintageness" having something to do with the topology (as someone touched on in that other thread), plus (from what I understand) earlier trafos had a narrower range response (10kHz on the top end may have been standard for a time, then over time gradually higher), so (not sure exactly what but) was thinking something along those lines (a topology that produces more distortion w/restricted freq. response). (But since you already seem to be happy with the cascode, then I guess no need to offer my .000000002 cents.

).

RnFR wrote:the ones in the adapters don't even have a frame!

The metal "tube" enclosure probably takes care of the shielding.

RnFR · Post by **RnFR** » 31 Jul 2011, 01:49

well, that's pretty much what that little inductor does. it gives distortion in a limited bandwidth. i'll be adding a different tone control as well- one that rolls off highs and lows at the same time, in order to have a low fi type sound, or full range vocal distortion for my metal buddies. the one i'm using right now, pans between a set of filters like the one in between stages. it works well, but i'm going to expand on it. i'm very happy with how this thing is distorting, if i wasn't i wouldn't even bother going forth with this project right now. that's really the first step as far as I'm concerned.

dai h. · Post by **dai h.** » 31 Jul 2011, 03:24

RnFR wrote:i'll be adding a different tone control as well- one that rolls off highs and lows at the same time

I think the cheap trafo in the adaptor might already be causing a low freq. rolloff (the roll off should be lessened by driving with a low impedance--for example a mic w/70 ohms output impedance would have better low freq. response than one w/600 ohms output Z). As far as the highs, if you load the secondary down more, this should start rolling off more highs (the downside is that you lose signal voltage which is detrimental to the S/N ratio).

If you at this (spec. sheet/catalog for the above mentioned Sansui/Hashimoto trafos--may need to download Japanese font?) :

http://www.hashimoto-trans.co.jp/frame/stcat.pdf

the higher ratio trafos show a rolloff (20k:1k, 100k:1k, ST-11 and 12 respectively). This page:

http://www2.famille.ne.jp/~teddy/pre/pre3e.htm

shows the ST-12 (100k:1k, approx. USD$5.50 ea.) being used backwards to step up signal from a phono cartridge. (From what I gather) according to the page, several key points are 1) lower driving impedance (phono cartridge output is 40 ohms which helps to extend low freq. response towards something extended, flatter), 2) adjusted loading of the secondary (to reduce high freq. ringing and flatten high freq. response)--downside is a bit of signal is lost, 3) signal levels are small helping to avoid distortion from the small cheap transformer, and 4) the core is grounded--copper foil is added as electrostatic shielding. Of course if you're NOT trying to obtain a conventionally "good"(flat) response, I suppose the info could be used backwards(I wonder if does an octavia makes use of ringing?).

RnFR · Post by **RnFR** » 31 Jul 2011, 03:53

that looks like it could definitely be a great option dai. thanks a lot for your help! I'll take a look at the links later when I have some time. $5.50 I can handle. the cheapest one of these adapter transformers I've found so far is $10, and that involves finding a proper shield and potting the thing. it's either this, or going the opamp route, which still may be an option. but, I like the simplicity of the transformer.

dai h. · Post by **dai h.** » 31 Jul 2011, 06:30

yeah sure.

I'm not trying to recommend that one in particular, but I just like how the author explains his "cheap transformer workaround"(versus buying a "proper" pricier trafo) and the hows and whys of how the cheapie was utilized successfully (for example, he remarks (after checking out the poor freq. response in the lows, basically says (something like), "but wait a sec, the transformer will "see" 40 ohms from the cartridge so let's check out how that affects thing, etc. etc."). If you happen to go for something more upmarket, a *possible* option is looking for a used one (which requires a bit of effort to find one and some luck in there being one available to purchase). I actually managed to find one in that range (a "serious-looking" 600 ohms to 50k one with a mu-metal can--may possibly turn out to have poor freq. response) but it seems to be very seldom that they show up used (possibly better odds "casting a wider net" on ebay, etc. though).

jro900 · Post by **jro900** » 14 Mar 2012, 16:39

Couldn't you try making a reamp circuit like jensen suggests http://www.jensentransformers.com/as/as092.pdf but with a cheaper 1:1 transformer at 600/600 ohms and adjust the output impedance that the effect is seeing with with a trim pot/resistor/ or full size pot for on the fly experimentation with input impedance? I've seen really cheap 1:1 transformers for $2-5. But I am not really sure this is going to work. I'm more of a tweaker than a tech and I happened across this thread in my search for a solution to a project in a similar ball park as yours, RnFR. So I thought I would share what I think my attempted solution to this will be.