My latest infatuation - transformers
Posted 25th October 2014 at 08:11 AM by abraxalito
Updated 6th November 2014 at 11:51 PM by abraxalito
Updated 6th November 2014 at 11:51 PM by abraxalito
I've found that some of the el-cheapo trafos (18rmb each) at a shop at the local electronics market are of split bobbin construction. This makes bodging up an audio OPT from two mains trafos a fairly straightforward matter.
I bought some with 9-0-9V and others with 0-12V secondaries. Then I disassembled them (fortunately they're not varnish dipped) and swapped out the 220V primary bobbin for the secondary of the other one. This gives me a trafo with 18V on the primary and 12V on the secondary, a step down of 1.5:1, impedance ratio of 2.25:1. So it makes a 4R drive unit appear as 9ohms to the chipamp.
And when I applied this to the output of the bass/mid of my chipamp (residing in the Phenix active speakers, its a TDA7265), apart from it sounding quieter I suddenly realized how much power supply noise I was still listening to. Incredible
So if you want to know if your chipamp PSU decoupling is really up to snuff, see how much difference a 1.5:1 trafo makes. Subjectively it 'distanced' the sound, Frank's 'disappearing speakers' trick once again
Update - bought some more 15VA trafos, this time with 15V secondaries. After taking them apart, I tore out the primaries (the wire is thin (0.15mm) so unwinding isn't recommended unless you have an hour or more to while away, just cut through the whole caboodle with wire cutters and recycle the wire as copper scrap). In lieu of the 220V primary I wound a 7.5V secondary (0.8mm wire, around 0.3R) making these 2:1 step down. The application is my now long-in-the-tooth D1080 MkIIs where a pair of TDA8947s drive the units. I'd recently discovered there was a substantial mis-match in that the units are 4R and the 8947 is not at all suited to such a low impedance load, given it has a bridged output. A 2:1 ratio trafo transforms these units into 16R, a perfect match. So far I've only done the trafo mod to the bass/mids but the effect is quite repeatable, much improved dynamics and a shifting backwards of the music so that the speakers now seem rather incidental to the goings-on. Don't forget a 3,300 or 4,700uF 'lytic in series with the primary though to prevent trafo saturation with the DC offsets typical from chipamps. The D1080s have undergone such a remarkable transformation that I shall have to buy up a few more pairs now....
Update2 - now have wound and installed the tweeter trafos. These are much easier and quicker to wind as the design equations indicate much fewer turns are required for HF duty. I use ferrite cores, similar to Ferroxcube EQ25 and 40turns for the primary, 20 for secondary. I'll post up a pic of the end result in due course. I've only wound a couple of pairs so far, the wire might benefit from optimizing as I'm concerned about HF losses and with the wire thickness I use (0.6-0.8mm) there may well be considerable proximity effect losses. Listening now and Leonard Cohen's voice has not been more engaging in its emotional impact, addictive stuff The soundstage depth is the best I've ever had from a pair of integrated electronics actives - these speakers have the active XO mods I talked about in an earlier post but still only use TL084s.
Update3 - I've now uploaded a pic of the tweeter trafo. As you can see its dminutive, under 30mm across and about 20mm high.
Update4 - I'm experimenting now with a smaller size of transformer. I found another vendor where their 10VA trafos cost 9rmb - half the price of the 15VA ones. But on disassembling the first one I found that they're not making the best use of the winding window - more copper can be got in These also aren't split bobbin which is an advantage for doing custom windings (rather than re-using ready made ones) because there's no shroud holding the two bobbins together, meaning more space for windings. So it may well be that a 10VA with optimized windings can equal or exceed a 15VA. Stay tuned
Update5 - added a pic of the 'unwrapped' electronics from my 2nd pair of D1080s - I figured I needed the electronics out in the open to better optimize the SQ. Besides that the cabinet was severely constraining how many caps I could tack on to the supply The trafos for bass/mid now are 9rmb 10VA types, wound for 2.5:1 step down. Needless to say the sound is awesome, a major incentive for me to persue higher step down ratios...
I bought some with 9-0-9V and others with 0-12V secondaries. Then I disassembled them (fortunately they're not varnish dipped) and swapped out the 220V primary bobbin for the secondary of the other one. This gives me a trafo with 18V on the primary and 12V on the secondary, a step down of 1.5:1, impedance ratio of 2.25:1. So it makes a 4R drive unit appear as 9ohms to the chipamp.
And when I applied this to the output of the bass/mid of my chipamp (residing in the Phenix active speakers, its a TDA7265), apart from it sounding quieter I suddenly realized how much power supply noise I was still listening to. Incredible
So if you want to know if your chipamp PSU decoupling is really up to snuff, see how much difference a 1.5:1 trafo makes. Subjectively it 'distanced' the sound, Frank's 'disappearing speakers' trick once again
Update - bought some more 15VA trafos, this time with 15V secondaries. After taking them apart, I tore out the primaries (the wire is thin (0.15mm) so unwinding isn't recommended unless you have an hour or more to while away, just cut through the whole caboodle with wire cutters and recycle the wire as copper scrap). In lieu of the 220V primary I wound a 7.5V secondary (0.8mm wire, around 0.3R) making these 2:1 step down. The application is my now long-in-the-tooth D1080 MkIIs where a pair of TDA8947s drive the units. I'd recently discovered there was a substantial mis-match in that the units are 4R and the 8947 is not at all suited to such a low impedance load, given it has a bridged output. A 2:1 ratio trafo transforms these units into 16R, a perfect match. So far I've only done the trafo mod to the bass/mids but the effect is quite repeatable, much improved dynamics and a shifting backwards of the music so that the speakers now seem rather incidental to the goings-on. Don't forget a 3,300 or 4,700uF 'lytic in series with the primary though to prevent trafo saturation with the DC offsets typical from chipamps. The D1080s have undergone such a remarkable transformation that I shall have to buy up a few more pairs now....
Update2 - now have wound and installed the tweeter trafos. These are much easier and quicker to wind as the design equations indicate much fewer turns are required for HF duty. I use ferrite cores, similar to Ferroxcube EQ25 and 40turns for the primary, 20 for secondary. I'll post up a pic of the end result in due course. I've only wound a couple of pairs so far, the wire might benefit from optimizing as I'm concerned about HF losses and with the wire thickness I use (0.6-0.8mm) there may well be considerable proximity effect losses. Listening now and Leonard Cohen's voice has not been more engaging in its emotional impact, addictive stuff
The soundstage depth is the best I've ever had from a pair of integrated electronics actives - these speakers have the active XO mods I talked about in an earlier post but still only use TL084s.Update3 - I've now uploaded a pic of the tweeter trafo. As you can see its dminutive, under 30mm across and about 20mm high.
Update4 - I'm experimenting now with a smaller size of transformer. I found another vendor where their 10VA trafos cost 9rmb - half the price of the 15VA ones. But on disassembling the first one I found that they're not making the best use of the winding window - more copper can be got in
These also aren't split bobbin which is an advantage for doing custom windings (rather than re-using ready made ones) because there's no shroud holding the two bobbins together, meaning more space for windings. So it may well be that a 10VA with optimized windings can equal or exceed a 15VA. Stay tuned Update5 - added a pic of the 'unwrapped' electronics from my 2nd pair of D1080s - I figured I needed the electronics out in the open to better optimize the SQ. Besides that the cabinet was severely constraining how many caps I could tack on to the supply
The trafos for bass/mid now are 9rmb 10VA types, wound for 2.5:1 step down. Needless to say the sound is awesome, a major incentive for me to persue higher step down ratios...Total Comments 101
Comments
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Strange as it may seem, the expression "sacrifice bass slam" sends the message, to me, that there [I]may[/I] be an issue with the higher frequencies - the key, "slam" quality of the sound comes from those higher frequencies being in good shape, IME ...Posted 8th November 2014 at 03:26 AM by fas42
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Ah and to me I have a hunch that the bass slam is the result of subtracting superfluous noise, predominantly in the LF. But its only my conjecture, not my experience. For example in this case the slam gets a bit lost because the transformer's adding some noise (noise modulation) in a similar manner to magnetic tape 'softening'. I don't rule out that HF is being affected though so will check out whether my tweeter trafos are contributing some loss at HF. Subjectively though the HF hasn't been cleaner....Posted 8th November 2014 at 03:47 AM by abraxalito
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Have you made sure that there isn't a chance of the treble transformer cores saturating at high input levels? I would perhaps do experiments with multiple cores in parallel to make sure this wasn't happening ...Posted 8th November 2014 at 05:49 AM by fas42
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I rather think that a saturating trafo would sound pretty grim whereas this is a mild effect. I also added more turns than the equation said simply to make the windings fit into two complete layers. More turns means more margin before saturation. Seems rather unlikely yet its possible I've received sub-standard ferrite cores....Posted 8th November 2014 at 07:07 AM by abraxalito
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I see the PSU lacuna rears its head once again over on Tom's thread (if that's not too mixed a metaphor). Reasonable questions about errors and oversights in Tom's "data driven" postings get the brush off once more Posted 21st December 2014 at 12:52 AM by abraxalito
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:rolleyes:, :) ...Posted 21st December 2014 at 01:56 AM by fas42
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Update on the Mod-86 saga - I have now caught sight of a schematic for it. Regulators for the three opamps are indeed LM317L/337L and there's no passive filtering on their inputs, just the usual 100nF input cap. Hence HF rejection, especially on the -ve rail, is going to be poor. The total current draw on these regs looks to be about 10mA which results in a 20kHz output impedance of the order of 4ohms.
My concerns on the thread were initially about the classAB operation of the THAT1200 - however that is dwarfed by the classAB operation of the LME49710 - it sees a load about 1.3k hence its peak output current is just shy of 10mA. To a first order then the peak excursion on the supply rails could reach 40mV.Posted 28th February 2015 at 02:09 AM by abraxalito
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Resolution of the regulator output impedance issue here - https://www.diyaudio.com/forums/chip-...ml#post4254216
Tom's provided measurements of the rail noise - 4mVRMS on the opamp supply +ve when playing out 20kHz at full power.Posted 12th March 2015 at 07:06 AM by abraxalito
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chipamp output transformers.....
would there be a good possibility of audio betterment adding transformers to output of my battery lm3875?Posted 15th November 2016 at 04:40 PM by nige2000
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Yes I think there would be - primarily in the HF region. The bass of your battery amp was awesome but I noticed the HF was a bit less than clean. But use a toroidal for a full-bandwidth amp. I've discovered since doing this experiment that a normal EI transformer gives a fair amount of HF roll-off (above 1kHz or so) due to its leakage inductance.
The transformer should be a step-down which is going to limit the power output of your amp, but you can go bridged to double the voltage swing then step that down with a 2:1 trafo to get back to the same power output. Bridged makes much better use of the power supply too.Posted 16th November 2016 at 01:05 AM by abraxalito
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thats a super idea but dont really want to go bridged right now as that kinda like starting a new project
would it be worth a shot just with a small step down or even 1:1?
i see toroidy making output transformers for tubes, i could ask if theyd make a pair if i had a spec to aim forPosted 16th November 2016 at 01:51 AM by nige2000
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If you have some voltage headroom then go for 2:1. 1:1 gives isolation but can't see any advantage for the amp in that, unless we suspect the speaker cables are picking up common-mode RF and influencing the amp (certainly a possibility, not one I've explored). But if we want to fix that a CM choke is a better option most likely as it'll have lower parasitic capacitance than a trafo.
I got my recent samples made by asking for a 30V primary and a 9V secondary, got them to make them just the same way they'd do those voltages for a mains trafo. Now I think I want a bit more voltage on the secondary, fortunately with toroids you can add windings yourself which will be what I'll experiment with. A 30VA toroid will be plenty big enough as amps don't give trafos continuous duty.
If you need more details/suggestions on what to order do drop me a message or even open a thread about it on Tir Na.Posted 16th November 2016 at 06:35 AM by abraxalito
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messaged you at tir na
if we think its a runner ill open a thread there tooPosted 16th November 2016 at 11:30 AM by nige2000
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let me know when they arrive, looking forward to hearing about the results....Posted 17th November 2016 at 12:23 AM by abraxalito
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well have to get the quote first, shipping is usually killer
could be more than the traffos
i often wonder what sales is like for such items as
PRODUCTS [The "Naked" Zero Autoformers]Posted 17th November 2016 at 12:57 AM by nige2000
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When I built my 'second generation' power amp I got custom toroids for the mains supply (625VA) and they weren't much more expensive than off-the-shelf toroids. Maybe 30% cost-up, can't remember exactly. The 30VAs I just got made here were staggeringly cheap, including delivery 200rmb for six off. I have this feeling I'm going to be collecting more iron in the next weeks and months, which will be a big pain when I come to move..... They're about half a kilo each I reckon.
On those 'Zero's I can't quite see the justification for the pricing, but I shall have a read of the writing about them.....
I see he gets better bass but attributes that to damping factor - I attribute it to lower noise on the power supply. Most cap-based power supplies have fairly high impedance in the bass, due to being caps. To get say 10mohm impedance at 40Hz takes shed-loads of capacitance (400,000uF) - have you ever seen a poweramp with that much capacitance on the rail? I have, my own chip amps....SavePosted 17th November 2016 at 02:35 AM by abraxalito
Updated 17th November 2016 at 02:46 AM by abraxalito -
off the shelf is much more here from farnell/mouser etc than getting them made direct.... usually.....
especially if your getting a few of em or anything out of the mainstream
how does an opt put lower noise on the amp ps?Posted 17th November 2016 at 04:34 PM by nige2000
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The OPT is transforming the impedance of your speaker, so for example with 2:1 step down, the amp is 'seeing' 32ohm for an 8ohm speaker. This means the current drawn is 4X lower, with lower current drawn from the supply its modulation by the signal is reduced by 4X.
The noise on the supply generated by classAB operation is the primary 'evil' in audio, because its correlated strongly with the music, so it confuses our brain into thinking its part of the music.Posted 18th November 2016 at 01:33 AM by abraxalito
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so 1:1 isnt applicable to lower noise?
just a matter of leverage?
sound of class d vs class ab ?
given both has oceans of capacitance
just ordered 2x15v and a 25v out traffos
enough to get the feel of it i think
usually takes a month to recieve
Impedance Matching TransformersPosted 18th November 2016 at 10:41 AM by nige2000
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1:1 has no benefit when connecting to speakers that I can see as speakers have no need of isolation, being already isolated totally.
Sound of classD vs classAB is a very interesting subject, one I've thought about a fair bit in the past couple of weeks. The reason for my thinking is playing with what's effectively an open-loop classD amplifier - my Popu digital amps - and adding lots of caps to its power supply.
PSRR of amps is a thorny subject because the measurements (if there are any at all) aren't normally done in a real-world scenario so tend to be next to useless. Why I like my Popu amps is they obviously have no PSRR to speak of, being open loop and classD. So they provide a fairly predictable basis for PSRR experiments, unlike other amps where the PSRR is practically unknown. Its a topic for a whole discussion rather than a comment on a blog post. You could open a thread on it but it would likely degenerate into a slanging match between those who listen and those who trust DSs.....Posted 18th November 2016 at 11:09 PM by abraxalito
