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In the Forum: Audio Discussions
In the Thread: Passive transformer based preamp
Post Subject: Re: Further problems with interstage transformers.Posted by Thorsten on: 10/28/2005
Roman,
 Romy the Cat wrote: |
| Nevertheless, if that bass was truncated between the stages then the devastations are way more severe. |
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That may be so, however an LF response of less than -0.1db down @ 10Hz is what is normally called "ruler flat", so no "truncation takes place, plus note the LF rolloff of a correctly applied transformer is first order, caused by the limited primary inductance.
So, your note of "truncating bass between stages is bad" may very well be right, but a competently designed line level transformer does not truncate bass.
| Romy the Cat wrote: |
| Applications: To make a properly sounding and really LF frequency capable interstage transformers it would require making it huge with very large inductance that makes it very susceptive to pick all type of problems in a chasses. |
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Which is why S&B line level transformers (exception, high level 600R 1:1 Output TX410LO) all come in a mu-metal can that has huge levels of rejection of external fields. And yes, the inductances involved are very large, the TX-102MKIII measures around 1,200H primary inductance at 3Hz measurement frequency and around 0.2V level.
| Romy the Cat wrote: |
| Applications: although a transformer independently might measure quite nicely but being placed between the stages it is a perfect second order high pass filter. |
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No, it is not. At low frequencies it is a 1st order highpass, however the tendency of magnetic core material (especially high nickel content permalloy) to show increased induction with reduced frequency limit even this highpass behaviour.
At high frequencies an ideally loaded transformer is 2nd order, however much depends on winding structures. If you make the leakage inductance the dominant mechanism (this works only with a defined resistive load) the HF rolloff will also be 1st order untill load capacitance and transformers parasitic capacitance kick in.
| Romy the Cat wrote: |
| A interstage transformer is a filter; an output transformer is the filter…. How many filters should be connected in series within one single amplifier? |
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That depends, if one filter dominates, because all other firlters have their turnover frequencies several octaves outside the passband of the dominant filter the answer is "it matters FA how many you connect in series".
| Romy the Cat wrote: |
| What happen when the slops of the different filters within an amsp come together and begin roll of with very high order at stop band? |
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That depends entierly where the high order rolloff is situated. If it is several octaves below or above the dominant pole, very little happens.
| Romy the Cat wrote: |
| A capacitor, quite in contrary, is a self-contained encapsulated element, relatively simple with juts two parameters: material of conductor and material of dielectric. |
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That is sadly pure wishful thinking.
| Romy the Cat wrote: |
| My personal experience with transformer coupling was during to my excrements with making “absolutely transparent buffer” when I used Lundahl amorphous transformers. The results that I was getting were constantly less interesting then with best capacitors I had. |
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First, "AM" cores are still usually simple iron. They are basically slightly more ideal generic cores. High Nickel content permalloy or amorphous material is a very different proposition.
Secondly, transformers that have a significant degree of uncompensated DC in the primary can cause sonic probloblems and usually have poor bandwidth. Remove the DC current and use a transformer where it makes sense (that is where step up, step down or galvanic separation is needed and you do not have such issues.
| Romy the Cat wrote: |
| However, what turned me off very aggressively that the worsening that I experienced with transformer was in a very specific direction. |
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You mean what turned you off was the SPECIFIC way things got worse with SPECIFIC transformers in SPECIFIC applications and you projected the SPECIFIC experience onto the generic subject, which is a logical fallacy.
Note, non of my designs feature interstage transformers with DC offset in the primary. There are very good reasons why that is so.
Yet I use a multitap line level transformer as volume control. There are very good reasons why that is so as well..
| Romy the Cat wrote: |
| The epicenter of it was my visit the Japanese Sacuma-san when I was listening of his amplifiers with 342 transformers. |
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Sakuma uses transformers in the exact reverse way I do. Clearly he seeks a very different sound to myself.
| Romy the Cat wrote: |
| I personally think that problems that I experience with transformer are the ultra low frequency related, as the ULF in transformers do not modulate the necessary “modulation” in the rest of Sound. |
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The ability (or not) of a transformer to pass "ULF" is related to the design. To dismiss all transformers, because some do not pass "ULF" is a logical fallacy, just as to condemn transformers for a lack of transparency is wrong if all that was tested was steel cores and iron amorphous cores.
| Romy the Cat wrote: |
| Tell me T, if someone would approach those guys form S&B, agree to pay much more and would demand something very specific and something that is way beyond what S&B put dally to the dealer’s inventory shelves then what S&B would do? |
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Right now, polietly decline. However if you have time, once S&B have managed to get past current large bulk orders you may find that such a project, which is basically classifiable as research, would interrest S&B.
In the meantime, why not try a pair of S&B TX-102 for fun? The current generation is really good.
BTW, did you note the most recent changes to my LCR EQ Phonostage circuit?
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