I have been using an Ebtech hum eliminator to break a ground loop in the headphone send system at the studio. I would like to build a DIY version of the Ebtech box and wondered if anyone had any recommendations for a decent 1:1 audio transformer.
Roger
They're expensive. A good, wide range transformer for use in a purely passive circuit is $50 and up, and will have loading issues running directly from a guitar.
The active/transformer isolator circuit in the geofex hum-free isolator is about the biggest bang for the buck I've found, if I do say so myself. The transformer is under $3.00, always in stock at Mouser, and the rest of the circuit only costs a buck or two for parts.
Mouser has recently started carrying some Triad audio transformers for about $4-$5 that look to have better specs than the Xicons, and will drop right into the Geo circuit.
I've read that Edcor traffos give pretty good bang for buck... http://www.edcorusa.com
~ Charlie
Hey, Moos! Thanks for mentioning that.
I gave the Edcor site a look, and they do have some pretty good values. Like the PCB industry, the transformer industry is getting more in tune with small quantities and agile distribution. I hadn't looked at their stuff in quite a while. What's new to me is that the transformers cost about half what I remember from the last time I looked, and they sell them with no minimums on line. Neat stuff!
For an isolator, I'd probably go with the PC10K/10K, which claims 20-20kHz with less than 1db variation. That's strong stuff. A guitar would still need a buffer to drive it to be absolutely sure it didn't lose treble, but this transformer doesn't need the low end boost. It's 1.3" by 1.64" (that's 33.8x41.6 mm to the sane world), so it's a little bigger footprint, but the specs look great and it sells for $6.37.
In fact, if it pans out to nearly the specs it claims, it should be a dandy replacement for all guitar isolators.
I was so intrigued that I decided to buy a couple of the PC10k/10ks, but it was two minutes after they closed ... :icon_neutral:
I'll order a couple of them tomorrow for a trial.
Thanks so much for the tips!
Does it matter that I am trying to isolate a line level signal, not a guitar level?
Roger
Only a little. The Edcor stuff is intended for line level, and if you are driving it with something that can drive a 10K load by itself, you could probably use just the isolator transformer. I'm pretty amazed at the specs. They have 600:600 transformers as well if you're running low impedance lines.
You won't believe this, but I whipped up a quickie test with a pair of the cheapo tiny Radio Shack audio isolation transformers and it worked. Not only that but the tone was not anywhere near as bad as I expected with their stated 300hz low frequency cutoff. There was plenty of bottom end.
I don't see these on their web site currently, so maybe they don't sell them anymore.
Roger
Spoke too soon: here they are for $3.99:
(http://rsk.imageg.net/graphics/product_images/pRS1C-2266725w345.jpg)
http://www.radioshack.com/product/index.jsp?productId=2103994 (http://www.radioshack.com/product/index.jsp?productId=2103994)
I ordered a couple of Edcor's PC10K/10K. They specify them at 20Hz-20kHz +/- 1db, which is amazing if true. $6.36 each, and they happily sell direct and sell in one at a time. They also use the USPS fixed rate priority boxes, so the shipping costs are low on numbers under about 25 to 50 of each.
Good to know the RS transformers work for you. I finally wrote Radio Shack off entirely. I consider them to have nothing I want, so it's good if they can surprise use now and again.
Quote from: R.G. on March 04, 2010, 06:43:09 PM
I ordered a couple of Edcor's PC10K/10K. They specify them at 20Hz-20kHz +/- 1db, which is amazing if true. $6.36 each, and they happily sell direct and sell in one at a time. They also use the USPS fixed rate priority boxes, so the shipping costs are low on numbers under about 25 to 50 of each.
Good to know the RS transformers work for you. I finally wrote Radio Shack off entirely. I consider them to have nothing I want, so it's good if they can surprise use now and again.
Those are pretty good specs. Jensen makes some that have similar specs, but they want like $100 for just one. $6.36 is way cheaper!
I wrote off RadioShack about 3-4 years ago now. They have hardly anything in their stores anymore and what they do have is way overpriced. They are a handy source for little 12V transformers and small DC fans, though.
Have you had a chance to test those Edcore's yet R.G.?
Could you use a transformer like that to make a balanced output from a passive guitar?
And if so, would a higher turns ratio be better? Something like 15K/600 maybe?
THX
Quote from: head_spaz on March 13, 2010, 02:39:03 PM
Have you had a chance to test those Edcore's yet R.G.?
They shipped them USPS and they're not here yet. :icon_sad:
QuoteCould you use a transformer like that to make a balanced output from a passive guitar?
And if so, would a higher turns ratio be better? Something like 15K/600 maybe?
That's a problem. A guitar pickup has an internal impedance that runs up to about, very roughly, 100K at the top end because of the inductive nature of the pickups. Loading that down with a 100K load will lose half your treble in the 6kHz to 7KHz region. Lower impedances are worse, and this is the origin of "tone sucking". It is quite difficult to get both low frequency response and high impedance in a transformer. A passive transformer on a pickup will nearly always be a compromise. But you might find one that you like well enough. This line of reasoning is one of the reasons I like to buffer a pickup before transformer matching.
Well... you've just confirmed my reservations.
Buffer it is then.
What about the impedence ratio when using a buffer?
I've been pondering using a FET input stage -> NE5532 -> transformer.
Or... perhaps an OPA2132/4 -> transformer.
Or... how about an OPA2132 -> DRV134 and skip the transformer?
WWTD? (What Would Tesla Do?")
Thanks R.G. ... for all that you do.
sure I miss something...
but if the transformer is driven by a buffer, why couldn't it be a "line" transformer? (with 600 ohm input impedance)?
Quote from: intripped on February 09, 2011, 09:58:35 PM
but if the transformer is driven by a buffer, why couldn't it be a "line" transformer? (with 600 ohm input impedance)?
Maybe it could, if everything else was right. A lot depends on the hidden details.
Transformers are specified in terms of their target impedances, such as 600 to 600 ohms. They also have some other specifications on resistance of the windings, insertion loss, and so on, but the biggest one is probably the frequency response.
600 ohm line transfomers are often designed to a 300Hz to 3kHz frequency bandwidth. What that really means is that when loaded by 600 ohms resistive, they present approximately a 600 ohm load to whatever is driving their primary, and are reasonably flat in frequency response from at least 300Hz to 3kHz. The manufacturer usually says and guaratees nothing about what it does outside the specified frequency range.
But we can calculate what would happen if the transformer was **exactly** as good as the frequency range and other specifications say it is. Generally, the cheaper, smaller transformers are much better on the top end than they have to be. However, the low end is determined by the amount of iron used for the magnetic core, and the amount of copper and care in winding it that was used on the primary. The iron and copper are the primary cost materials for the transformer, so the manufacturer will not give you a whole lot more than the low frequency specification says he has to.
The thing that affects the low frequency response most is the primary inductance. The primary inductance has an impedance that decreases as frequency goes down. The transformer action makes the transformed secondary load appear across the primary, but the primary inductance is always there in parallel with the transformed secondary load. When the impedance of the primary inductance drops to equal the transformed secondary load, it is then "eating" as much signal current as is going across to the secondary load. If the transformer is being driven by the specified primary source impedance, then at this frequency, it is losing half its drive power to the primary inductance, and so this is the "half power" point which is normally taken as the low frequency cutoff. For a reasonably matched source driving the primary, at this frequency the secondary power response is half of what it is at the middle of the frequency band.
If you have a buffer available, you can keep the secondary output voltage from dropping off so quickly by driving the primary harder. If the buffer can deliver ten times as much current to the primary as a matched driver would, then it can keep the secondary voltage up to "flat" by just accepting that 9/10 of the primary current will be lost, but the remaining 10% of the primary current will drive the secondary OK.
And that's why a 600 ohm line transformer might not work. It starts with a small primary inductance. We're using a buffer to make up for the decreasing impedance of the primary inductance. It's easy to get into situations where you don't have a big enough buffer to make a 600 ohm transformer work. It can be done, perhaps by using a power amp chip, but you're well into diminishing returns. And heating both the transformer and buffer to try to make things come out right. So - maybe it would work; it depends on the transformer, the buffer, and how hot things get. It's just easier to use a different transformer, given that many 600-600 ohm transformers are intended for modem duty and not all that good for normal audio to start with.
It's quite different if what you use is a wide bandwidth pro-audio specified 600:600 line transformer. That would be much easier, as it already has a wide bandwidth. The trick is to make cheap semiconductors make up for a cheaper transformer. Good pro audio line transformers are both big and expensive. It's all in the details.
So what is the verdict on the edcor RG?
thanks R.G. for your answer!!!
Now it's clear that the core target is having a wide frequency bandwidth.
Looking at edcor products I find the PC series transformers: 20 to 20kHz freq. response, 1:1 ratio, 1/4W power, and different input & output impedances.
I see everyone is going for the 10k-10k impedance, but what if I choose the 600-600? isn't it the same, or better?
Quote from: trixdropd on February 10, 2011, 02:08:31 AM
So what is the verdict on the edcor RG?
They're in a box on the shelf in my workshop, waiting for me to get back to them. The delay in getting them here was long enough that I had to move on to other issues. :icon_cry:
I'll try to get back to them.
Quote from: intripped on February 10, 2011, 10:16:18 AM
Now it's clear that the core target is having a wide frequency bandwidth.
Dead-on accurate.
QuoteLooking at edcor products I find the PC series transformers: 20 to 20kHz freq. response, 1:1 ratio, 1/4W power, and different input & output impedances. I see everyone is going for the 10k-10k impedance, but what if I choose the 600-600? isn't it the same, or better?
It then becomes a matter of power available to drive them and loading, and a number of other issues arise.
First, you have to consider what is driving the transformer and what the transformer in turn drives. For pedal/isolation use, the input which the transformer drives is usually another pedal or a guitar input with an input resistance of 100K or more, and often these days 1M or more. If the isolator is driving a true 600 ohm microphone input, that's another set of issues. The buffer output impedance will be quite low in all cases, usually much lower than even 600 ohms, so it can drive either a reflected 600 ohm load or anything larger - to *some* voltage level. :icon_eek:
In practice the buffer is usually an opamp, and the commonest opamps can only drive 600 ohm loads with small voltages, perhaps a volt or so. They don't have the internal power/current ability to drive a 600 ohm load to their full power specification. They **might** be able to do it with only a 9V battery as a power source, but it's a maybe. Some opamps like the NE5532 or LM833 do have the ability to drive 600 ohm loads well, so it gets into choices of opamps for buffers.
Because the buffer is driving the transformer, cable, connectors, etc. with a low impedance drive, it has the ability to drive even a 10K:10K transformer well enough to keep cable capacitance issues at bay. So the higher impedance transformers are good enough for the usual issues of driving normal pedal/guitar cable and amps, and may run into problem if the owner thinks "Hey, this is a 600 ohm output, I'm going to use it to drive a 600 ohm input."
So at a first order, 600:600 is OK-ish, and will work in some, perhaps many instances. It is getting into territory where it can be hard to drive and cause oddities with the buffer. My choice as a designer is to sidestep not only the obvious but also the secondary issues, so I like the higher impedance transformers better.
In my opinion, the 10k-10k is better for most pedal use because of the secondary issues. With a wide bandwidth 600-600, you could get good results depending on several issues. "Better" means you have to define what you're measuring.
thanks a lot R.G., I know something about audio transformers, finally!! :icon_surprised:
I keep meaning to order the same transformers you did. I'm not un-happy with the triad transformers in my hum free, but I'm don't really think of them as great either so I was gonna try these. Plus I wanted to order some transformers to make a couple of DI boxes and I was thinking about a couple of those stereo to mono summing transformers to make a passive analog summing box for recording.
> why couldn't it be a "line" transformer? (with 600 ohm input impedance)?
For the same core (same size/cost), a 10K will accept 4 times higher signal voltage than a 600, for same bass distortion.
Unless you must drive 600 ohms or long lines, the 10K is your better buy.
Yes, if you are flooded with good 600:600 iron, use them.
> the cheapo tiny Radio Shack audio isolation transformers
The naked modem transformers. The freq response is much better than you read: a modem tranny must have TIGHTLY controlled ratio and loss 300-3K, tighter than we demand in general audio. Response is useful at least another couple octaves either way.
However the one RS stocks is the smallest size made. I had trouble with bass overload, far less than 1V at 50Hz came out rotten. That's why there's bigger ones, which cost more, the RS buyer didn't know why, so we get the least which is legal on a phone line, and not ameniable to general audio.
OTOH: over in the Car Sound rack there is a lump with RCA plugs. Pull this open, it has two very good 2K:2K transformers inside a shield, and this will take over a volt at thumper frequencies. Cost is $18 or so, but worthwhile.
> I don't really think of them as great either
The little iron sold by Mouser _IS_ good stuff, for its size. The silly-low price is NOT related to "greatness": the price is low because millions of these parts have been made for 50 years, by competing factories. The specs are not hard to exceed: 1K-10K windings are not prone to the troubles of high impedance windings, these parts are small, treble will come out far better than specs.
> stereo to mono summing transformers
Transformers is parallel do not "sum", they "short". Mix with resistors. (Yes, there are ways to sum with transformers, but this opens new problems.)
Quote> stereo to mono summing transformers
Transformers is parallel do not "sum", they "short". Mix with resistors. (Yes, there are ways to sum with transformers, but this opens new problems.)
Sure looks to me like it's a left and right signal inducing a mono signal. I've worked on a few hammonds in my day, it was pretty common to mix with transformers. I know it opens new problems, I'm hoping to exploit these problems for unique sonic characteristics. If I wanted clean summing then I'd just stay inside the computer and would certainly stay away from transformers, but as it is my computer will send out a ping to adjust for latency, I can send out a few tracks to be summed (I'm welcoming crosstalk at this point) and use a matched set of Neumann v476b's and then mix it back in as parallel processing.
The Xicon transformers from Mouser perform extremely well... a bit of peaking at 20-25kHz but the 3db range is down to about 20Hz.
As to driving the transformers passively, I got a clue from the disclaimer from Radial for the all passive Bigshot ABY:
"Keep in mind that the trade off here is tone. When you engage the transformer, even though you are still passive, you are no longer technically 'true bypass'. This means that the tone going through the transformer will be affected unless you place a buffer in front of it. Many pedals incorporate buffers into the signal path. This can be good or bad, depending on the quality of the buffer."
i.e. Save yo money and get, or build, something that works!
I used the Triad trannies to build a Hum Free, they are spec'd at 200 Hz instead of 300, I liked them a bit better than the Xicon's, not a huge difference. I got a lot of bass out of them at a slow roll off, but I also play Bass VI so they just aren't cutting it the way I would like when I switch from guitar to bass. There can be a nice fattening sound from transformer core saturation, this is why I'm thinking of using the Edcors in the same circuit because it looks like they are made with better materials and with a little more care without going expensive. That said, there is something very pleasing about pushing a nice transformer hard, I've got gear with Haufe, Cinemag, Jensen and a few other nice things and they are definitely very musical though not pristine, but musical is what I'm going for. I don't always need the output to be identical to the input as long as it sounds good.
> it looks like they are made with better materials
Both use standard power transformer iron, which is actually very good stuff. And enameled wire, which is usually blameless. Edcor does use nicer-looking bobbin shapes.
> a little more care
There's not a lot of "care" involved. These are simple machine windings.
> nice fattening sound from transformer core saturation
If you are pushing big bass, and it gets mushy, your option is SIZE. Buy bigger. (Yes, Edcor goes as big as you want.)
If size is limited by case or by stray capacitance, there are magic alloys, but saturation can be abrupt, and cost is very much higher. As a part-way compromise, Edcor does offer several "Nickel core" line-match transformers.
Note that small power transformers work at audio. You want both windings in one limp. There is a style with primaries on one leg and secondaries on the other leg, these have a strong ~~1KHz high-cut. However for med-Z to med-Z, a dual-winding 120V+120V primary may be used like a 2K:2K transformer, a good fit between an opamp and a medium-long (<100') line.
Good find on those transformers! I've been mulling over the Xformer coupled ABY for low B (31Hz), looks like this is a real contender.
Hope you get around to testing them RG - this should be really interesting!
Quote from: Mike Burgundy on February 12, 2011, 08:02:06 AM
Good find on those transformers! I've been mulling over the Xformer coupled ABY for low B (31Hz), looks like this is a real contender.
Hope you get around to testing them RG - this should be really interesting!
I will get to them. I re-found them just a few days ago, so I at least know where they are in the shop - not an insignificant advantage! :icon_lol:
I got my edcor 15k/10k transformers is, I got those because I actually wanted them to pad the volume just a little bit. I quickly wired a couple up passive just to check them out and running them after my Boomerang+ it actually sounds really good, there is a little high frequency loss but it only caused me to turn my treble knob from 4 to 5, so not a big deal. It doesn't like being run after my GGG phase 45 and loose all low end when it's on. So this week I'll build them in to a hum free. But all and all, has more low end than the actively driven triad transformers.
Quote from: PRR on February 11, 2011, 10:32:59 PM
> a little more care
There's not a lot of "care" involved. These are simple machine windings.
"EDCOR uses the finest M6 line grain oriented steel cores. Each unit is hand stacked to assure at least 92% stack."
Sounds like a little more care than a wage slave factory in china to me, I know the chinese ones are hand stacked too, but are they paying attention to grain orientation? It may not make much difference, but the extra attention most likely means that the lamination of these cores is better, I've seen a few poorly laminated trannies in my day.
Quote from: wavley on March 14, 2011, 10:18:44 AM
"EDCOR uses the finest M6 line grain oriented steel cores. Each unit is hand stacked to assure at least 92% stack."
Sounds like a little more care than a wage slave factory in china to me,
It's supposed to. However, it's written in Advertising Language, which is an artificial language invented jointly by an adversarial cooperation between advertisers and the courts. It's confusing because they use the same words you do - English in this case - but certain words don't mean what you think they do.
"Finest" for instance, indicates that the thing being described is a member of a "parity class", a group of things which are all very much the same, so they're *all* the finest. M6 grain oriented steel cores are all made the same way, and have to be to call it M6 grain oriented laminations.
Hand-
anything is supposed to sound carefully crafted, the idea being that it's done by a senior technical staff member with a graying beard and a love for getting laminations ....just... right. However, I can assure you that stacking laminations is done by the lowest cost worker they can hire (USA, Japan, China, wherever). It's tiring, mind-deadening work. Any worker that can contrive to do something else will do so.
I recommend the book "Doublespeak", which was enlightening for me. It's quite old now, but you may be able to find a used copy.
Oddly enough, the term "wage slave" was invented in the USA, and applied to the US factory worker, who was bored, tired, and didn't give a hoot about whether what they did on the factory line ever made anyone happy or not. In the 70s and 80s, the oddity that Japanese goods were valued because they worked and American made junk didn't was a massive shock, especially to the rulers of the US industrial world, like GM, Ford, and General Electric. And today, the Chinese are busy offshoring the low-tech labor to cheaper places like Vietnam and starting in Africa themselves.
"Chinese-made junk" is becoming a self-denying phrase like "Japanese-made junk" became a few decades ago. The Chinese sell the world cheap stuff because the foreign (to them) businessmen demand the cheapest possible junk.
And I can promise you that you can get more attention to detail in China than you'll get in the USA, even if you pay a lot less. Stacking laminations is a lot more mind deadening than burger flipping, and you know how much burger flipping jobs are valued here.
And for paying attention to grain orientation, last time I looked, the grain orientation in E-I laminations is along the length of the tongues, so it's impossible to not stack them with the grains oriented the same way. They're punched from the rolled strip in that orientation.
I don't mean to be argumentative; it's just that certain things get repeated over and over and taken for the truth when it's just convenient to say them.
Just out of curiosity, could you measure the low end response on the two setups, the passive Edcors and the actively driven Triads, and post the low frequency -6db points?
QuoteJust out of curiosity, could you measure the low end response on the two setups, the passive Edcors and the actively driven Triads, and post the low frequency -6db points?
I guess I should have chosen my words a little more carefully, I felt a little attacked by PBR for not knowing what I was talking about, when I've been doing this for a number of years and know full well what I'm getting into with these things. By no means am I a "chinese junk" person, I am quite fond of a lot of the audio products coming out of china right now and find it to be well made when you buy the right things. I do think there is a bit of a difference in care taken between transformers made when ordered (it took almost three weeks to ship mine, of course they may just be overwhelmed with work) and hundreds or thousands a day like the triads or xicons. I think it was more of a point of mass produced vs. made to order. But you're right, I've never been in a transformer factory, but I have been a wage slave electronics assembler ;) I paid attention to detail, but I can't say that for everybody there, and for that reason I would never trust the instruments in a Cessna, personally I made ultrasound radiometers, so I had nothing to do with the other stuff. Guess I'm a little spoiled by my NSF job, where just about everybody cares about what they do an quality is the only priority (not that we get paid well, but I do have time to check this page while conductive epoxy cures)
I pirated parts off my old hum free, so I didn't AB them, but there was a noticeable (not huge, but enough) bass roll off when using my bass vi that wasn't there with the edcors.
Luckily, I'm going to leave one wired up passively, for now, and I'm going to build a hum free with one triad and one edcor because one of the amps I'm splitting to is just a little Kalamazoo that I modded and it doesn't have a lot of low end anyway, I was going to socket the coupling cap for that anyway so I could play with it. Of course I'm in the middle of some house repairs, I'm planning on getting to it this week, but I may not.
Quick and dirty measurement shows the triad flat down to about 63Hz, then rolling off. Edcor pretty flat.
Sound wise this shouldn't make much of a difference, but it's just more stuffy on the low end, not as thumpy and clear.
> I felt a little attacked by PBR for not knowing what I was talking about
That was not my intent. I am sorry I gave that impression.
> I'm in the middle of some house repairs
Must be the season. Tearing out two walls, putting in two walls, new tub, vanity, old toilet, and today's chore was converting the WHOLE (94%) water system from haywire cobbled corrupt cracked copper to new tubing and manifolds.
> grain orientation in E-I laminations is along the length of the tongues, so it's impossible to not stack them with the grains oriented
Been messing with a LOT of wood lately. It's the same way. There's a grain, lengthways and cross-way. Wood is several times stronger one way than the other. Joist or shelf really wants the grain running from support to support.
Older transformer iron had about the same property any direction. But they found a way of heating and rolling that slightly reduces cross-grain but improves with-grain property. Like 500 cross and 1000 in direction of grain.
But is that useful? If you build a box, you can't have the grain run all 4 ways, unless you have 4 joints, and joints (butt, dovetail, or lapped) are always weakspots. Transformers are stamped E-I with lap-joint, but you still have some flux going in the un-preferred direction. E-I proportion can minimize but not eliminate cross-grain flux.
Grain-oriented has just enough advantage in larger power transformers that oriented is "the" standard iron for anything bigger than a thumbnail, and not over-priced. (Plenty of exotic cores in the overpriced audiophile world.)
I realized that I measured the xicon tranny the other night, the triad went flat down to 40Hz, they both still sound stuffy on the low end. The edcor sounds a lot better on the low end, but the trade off is that it's twice the size.
Quote from: PRR on March 16, 2011, 01:28:26 AM
> I felt a little attacked by PBR for not knowing what I was talking about
That was not my intent. I am sorry I gave that impression.
It's cool, that's the problem with the written word, sometimes if we're in a bad mood, we think everybody is in a bad mood.
> I'm in the middle of some house repairs
Must be the season. Tearing out two walls, putting in two walls, new tub, vanity, old toilet, and today's chore was converting the WHOLE (94%) water system from haywire cobbled corrupt cracked copper to new tubing and manifolds.
Ha, well at least I'm not alone, tearing down walls, jacking the basement, tearing out the floor upstairs to sister joists, new water heater, putting in a new kitchen...
> grain orientation in E-I laminations is along the length of the tongues, so it's impossible to not stack them with the grains oriented
Been messing with a LOT of wood lately. It's the same way. There's a grain, lengthways and cross-way. Wood is several times stronger one way than the other. Joist or shelf really wants the grain running from support to support.
Older transformer iron had about the same property any direction. But they found a way of heating and rolling that slightly reduces cross-grain but improves with-grain property. Like 500 cross and 1000 in direction of grain.
But is that useful? If you build a box, you can't have the grain run all 4 ways, unless you have 4 joints, and joints (butt, dovetail, or lapped) are always weakspots. Transformers are stamped E-I with lap-joint, but you still have some flux going in the un-preferred direction. E-I proportion can minimize but not eliminate cross-grain flux.
Grain-oriented has just enough advantage in larger power transformers that oriented is "the" standard iron for anything bigger than a thumbnail, and not over-priced. (Plenty of exotic cores in the overpriced audiophile world.)
You know, I have a lot of nice equipment with nice transformers, guess I never bothered to look into the actual manufacturing details, just the junk they taught me in school and my ears.
> the triad went flat down to 40Hz
I'm assuming the Edcor is larger (more iron and copper) than the Triad and Xicon.
Try higher level, 1V 3V or 10V, and 'scope the output. At 10V it would be ample to just listen to the output. Even the larger iron may be in distress at 10V 400Hz, but the little iron may not handle 10V below 1KHz-2KHz.
I gather you know the general tradeoffs, but for others:
The bass/amplitude tradeoff is essentially linear. So for the made-up numbers above, the larger can do 1V at 40Hz, the smaller may not manage 1V at 100Hz without gross mangle.
Taking 0.5V at 82Hz as guitar cord envelope, the larger core is at a quarter of its mangle limit, the smaller core is very near its mangle point.
> more stuffy on the low end, not as thumpy and clear
Below gross overload, iron THD goes down, but never goes away. The less-stressed transformer will have lower THD, which in your test seems to mean "more stuffy on the low end, not as thumpy and clear". (Talking about sound = dancing about architecture.)
Some interesting tests here:
http://www.cliftonlaboratories.com/non-linear_transformer_behavior.htm
Lot to read, and some of it inconsistent.
Apology. I missed this bit of marketing-speak:
"Each unit is hand stacked to assure at least 92% stack."
This is "not the user's problem", or shouldn't be. We might like the winding 100% full of iron, but shellac, burrs, and tolerances mean that won't happen. Larger iron is often assumed 94%-95%, I guess in smaller parts you can't do that good. The reference to "hand stacked" seems odd. Perhaps MASS-produced parts are machine stacked and set well shy of the worst-case interference to reduce jam-up. Obviously a machine can be made smarter. I suspect Edcor is a low-tech place, and at least their low-volume parts they may find it cheaper to hire local housewives (the traditional stackers) than to invest in fancy machinery.
If the electrical response is met by re-designing core to the actual production stacking factor, a 92% stacking factor leads to about 109% more copper resistance and height than an ideal 100%-stacked core. Taking 95% assumption, 3% worse if actually produced at 92%. This is mostly insignificant.
Yes, I have seen some no-name cheap iron which seemed to be stacked 75%. Maybe very-variable lams and over-concerned for production jams? Maybe they stacked to 90+%, but iron improved, or customer complained about price, so they left some iron out to just-hit spec on bass or price?
It's a mature boring product, they have to boast about any little thing they can.
QuoteBelow gross overload, iron THD goes down, but never goes away. The less-stressed transformer will have lower THD, which in your test seems to mean "more stuffy on the low end, not as thumpy and clear". (Talking about sound = dancing about architecture.)
I'm not sure this is an apt analogy, these are pretty common descriptive terms, not to mention all the threads we've had clarifying these terms, like the "Glassy Highs" thread ;) quick measurements showed me frequency response, my ears told me what sounds good. I think further measurements are kind of pointless, we can tell that the edcor is at least twice the size of the triad so it's a given that it will have better low frequency response, so we're just proving what we already know. I do after all like to play my guitar every now and then :D and this thing is only to solve a problem, it's not even fun or makes a cool noise, hopefully I'll box everything up, plug things into it, and never think about it again!