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ubza1234 13th October 2013 05:25 AM

MY LATEST CREATION!!!! valve preamp.
this is my latest mod to my current audio setup.

her name is Marty McFly the Daewoo Matiz. As silly as it sounds, i actually chose a lil ol daewoo (other then rising fuel prices) for the challenge of trying to creat something amazing to listen to, but still quite practical. i believe i very much achieved this. The various speakers, amps etc are a hodge podge of various brands from Kasan, to Dali with Good a ol' precision response 5ch amp which is more then adequate. i am running it in a biamp configuration, running the built in active high pass to the dash mount speakers, and passive low pass to my door speakers (because the amp does not have an active low pass) let me run you through what i have:


These are modified kevlar fibre (i have a feeling they are actually a fibreglass composite) precision response 6x9's. not the greatest on the market, but i really have a thing for plain old school looking speakers without silly plastic mouldings on them or logos. being cheap speakers, i didnt mind modding them. i applied a thin layer of resin to the fibres as they apeared to be just bare fibres, and you could see through the weave from tiny gaps between the gaps of the fiber weave. hard to explain. i also removed the tweeter and glued on a paper dust cap in its place. they sound ok, but i think the doors are leaking a little sound energy because you can feel some of the bass being pushed out the gaps like around the lock jigger, the door handle, window slot etc. i feel if i can seal these up some how i may squeeze a little more bass out of this system. this was one of the first things i did to this car. i was very reluctant because i know how much of a pain bogging fibre glass is to get it to a point where it will look great painted, usually i just cover it in carpet or something as many of you will know, wrapping fiberglass will cover most of the blemishes in bogging. in the end i'm reasonably happy with this door, especially as it was my first ever attempt at glassing a door. before that, the only glassing I had done was building little pod speakers that where wrapped. still a little work to be done to these doors, but all in all i'm quite happy.


these are 3 8" Kansun subs. they are one of the most remarkable subs i have ever used, reminding me of some of the more old school speakers that used to be made. as such, they require a large enclosure for what they are (around 60ish liters for the three) but have a fantastic light weight coated paper cone that does an amazing job at dampening, are quite sensitive (90db) and to my ears they simply do not distort at all, even at high volumes untill they bottom out, which takes alot. each sub is capable of 200wrms. huge. they tend to bottom out when you feed them much more then 200wrms, which is fine for me, based on the increadible clarity, sensitivity and balls they have. they are 8ohm, but i have three in parallel so it works out ok. all this for around $30 each. heck ya. i built the fibreglass enclosure myself, and most of it is around 6 layers thick or more. full of fluff. i measured the internal volume using a musuring jug and bean bag beads. i dont suggest this, its REALLY messy lol. the sound is amazing and tight especially after my latest addition that you will see later ;) Because the car is a tiny daewoo matiz, space was obviously a concern. being the picky prick i am, i wanted my speakers, but i still wanted some kind of boot. so i came up with this. a flat sided square wooden box is a really really poor choice if space savings is a priority. with fibreglass, i could actually mould the enclosure to fit the shape of the car perfectly, like a jigsaw. the enlcosure goes right hard against the metal of the walls, down over the wheel arch and even a little into the wheel well, producing a deceptively massive enclosure. it also makes it lock in place, again, like ajigsaw. as i mentioned before, it goes into the wheel well a little, (the wheel well is square in this car, so i had a spot to dip down into because obviously the wheel is round.) the spare wheel actually locks it in place. as you tighten the locking bolt down on the spare, it pushes the enclosure into the wall cavity harder and harder. try as you might, even with no bolts or fasteners, it absolutely will not budge. the wheel must be removed to remove the speaker.


originally i had some fantastic kasan brand coencident style speakers. (similar to coaxial but a little different) they had a composite kevlar/carbon/paper mid cone, and soft silk dome tweeter. they sounded amazing! but not as good as there replacement.
these are a combination of various brands. the 4" mids are kasan. i chose theses because of how impressed i was with the performance of the 8"s i have in the boot. and they did not at all disappoint. paper cone, clean aesthetic design, amazing sound. next are a very very interesting hybrid tweeter. from what i understand they are surplus stock from dali, (the speaker manufacturer) that contain both a soft dome and a ribbon tweeter. the best of both world. the soft dome sounds how you would expect a great quality soft dome to sound, soft, detailed, clear etc the ribbon tweeter also sounds great however, would be useless without the dome tweeter. when i did a quick listen test with it hooked up to my home pa amplifier (not for car) playing my music from my phone with the eq set so that only the treble was playing, i could hear what each speaker is capable of and what it does and doesnt do well. in a nut shell, the dome gave the "meat" of the treble. it was quite sensitive at these high frequencies. however, lacked the additional sparkle that the ribblon had. likewise, the ribbon lacked any of the "meat" of the treble. only that added sparkle that the dome was not able to produce. together, they are absolute magic. i built the crossover custom for it that was configured as such:
LP 12DB 6K for 4" mids
BP 12DB 6K-14K dome
HP 12DB 14K ribbon

i also tried something different by adding a switch to the top (you will see this in later photos) the switch would switch between two different crossovers for the dome tweeter. one is as above. the other was just a HP 12DB 6K. the idea is that both the dome and the ribbon would recieve audio signal at 14K+ and that the impedence would half at this high frequency, adding even more detail and sparkle at this high freqency. it turned out this was highly unneccesary and made it sound far to "loud" and trebley. it sounded much better just to eq the sound before it reaches the speakers. but was a fun experiment that i learnt alot from.
like the subs, i moulded the back of this enclosure to suit the car. it fits nicely onto the dash and is held in with 2 screws each. it doesnt really need them because of how well it fits on there, but it was a just in case measure. i also aimed the drivers all at me, the driver, cause i'm selfish like that.


i noticed that i was getting alot of alternator noise coming through and i didnt like it at all. i tried all sorts of things from ground loop isolators to capacitors but nothing worked. what you are looking at here was my solution. the 2 carpeted half domes with + and - written on them are essentially transformers. (here's where it gets a little complicated.) i started with a doughnut shaped ferite core. i got a heap of 1mm diameter copper wire. i cut 3meter lengths and put them into groups of 6. i then twisted them together with a drill to make it easy to work with. i would grab two of these bundles and mark one of them so i know which bundle is which by spraying one of the bundles with silver spray paint. (cause silver was what i had) i wrapped them as tightly as i could around the ferrite core. i would do this for both ferrite cores untill all the wire was used up. i would then connect all the ends of the painted/marked wires and solder them together and then solder the un painted ends. this was then potted in fiberglass resin.

what i had made was basically a transformer with a 1:1 ratio. i would connect the power to both coils at the same time, in parallel. this would act just like a 6db low pass filter. but there's more to it then just that. i then reverse the polarity of ONE of the coils. just like a transformer, it would try to feed any AC/noise into the other coil, which is doing the same thing, but in the reverse polarity, cancelling out all noise. i do this for both the positive and negative. then, for good measure, i feed it through a super cap and there we have it, clean power. this gets fed to the second battery. the wire from each group of wires was about 12mm accross, which is roughly the same as a 4 gauge wire. i then have two of these in parallel in each transformer coil, so safe to say, i think there is a small enough electrical resistance to not cause any problems for my setup. in the pic, it was not quite finished, but you get the idea.


i realised very early on that the source of most of my noise problems was the cheap *** head unit i had. it is an absolute useless thing, noisy, unclear and generally pooy. i realised i generally only listen to music from my phone, so why not bypass the head unit all together? i plugged my phone directly to the amp and instantly the sound was amazing. but after i tried splitting it up into 4.1ch, i had impedance issues and lost signal, high end etc but the proof was there, all i need is an impedance buffer and after my experience with my new home hifi valve amp, thats when i thought putting a valve preamp in there just makes sense.
for a long time i read about how people have tried putting valves in there car but they always ran into the same problem; vibration. vibration not only caused damage to the valves, but also cause microphonics where the valve itself acts like a microphone, and played the road and engine vibration/noise to the output to the speakers. the usualy solution was to use military spec valves that where designed for abusive environments and Silicon rings. but they would always run into the same problems: vibration and the valves didn't last too long. so i worked hard to solve this problem with a relatively simple solution: a spring loaded suspension system.

the entire board is susspended on 13 springs. they are all soldered onto a solid copper plates. if the springs where pointing straight up, and you where to push down on them, the springs would try to fold down flat as apose to squashing down because it takes less effort to bend a spring then it does to compress a spring. for this reason, all the springs are pulling the board in various directions, particularly those in the corners. if the circuit wanted to bounce side to side instead of up and down, it would require the spring to compress, which takes alot of effort while up and down only requires the spring to bend, which takes alot less effort. see the image, and it may make a little more sense.

thats all well and good for large bumps that could do some real damage to the valves, but what about road noise? do any of you know how an old school reverb spring works? it would have a spring with a diaphram at each end. you talk into one end, the sould would travel down the spring, to the diaphram at the other end, then reflect back down the spring, play at that first diaphram, reflect back etc so the spring was clealy conducting these sounds very well. what do you do? dampen the spring itself. if you where to touch that spring while talking into the diaphram, the sound would travel down the spring to your fingers, and your fingers would absorb all the energy and it would not reach the other diaphram, let alone reflect back. so this is exactly what i did. i installed plain ol' sillicon onto the springs itself to absorb this energy. simple as pie. as one last resort, i also glued the circuit board to the suspended copper board using silicon also. i can go over and bumps in the road and the preamp doesnt miss a beat. it just bounces.

of course, i had to buy a pure sine wave inverter to power it, as it needs a transformer to work. the inverter was easily fitted under the dash. i also found a little spot inside the dash ontop of the air con condensor that the transformer fitted nicely on, right under the amp itself. but what about all those pesky emfs the transformer puts out? wouldnt they interfere with the equipment? yes it would, so i installed the transformer in a steel project box, soldered the transformer to the box. I used heavy gauge shielded speaker cable to carry power from the inverter to the transformer and the shielding was soldered to the box and the other end travels to the chassis of the car where it is dissipated. i found if i disconnect this wire, it gets VERY noisy so obviously it worked well, and doesnt dirty up the power signal due to my noise filtering power system.

ps i kinda like how i have an amp that runs on high voltage; up to 300v ac. if anyone messes with it, they will know about it! lol

to actually use the amp, i have a headphone socket and switch in a compartment under the head unit. the headphone socket goes to the valve preamp. the switch does a number of things. first it switches the source output from the pooy head unit to the valve amp. so i can listen to the radio if i want to. it also powers up the inverter which in turn powers up the valve amp. aditionally, it has a center position, which turns everything off. on the dash i have put a volume control which is just the existing volume pot that was built into the valve preamp board with leads on it.

but who cares about how it works, the important thing is how it sound, ya?

the sound? amazing. words cant describe how much better it sounds, from treble to bass everything is just fantastic. i never understood how muffled the bass sounded through the head unit. a drum kick through the head unit is more like a quick thud, but with the valve amp, its more of a sharp gunshot that hits deep into your chest. different bass notes tend to vibrate different parts of my body instead of just shaking anything and everything. the midrange is clear and detailed. the treble.. oh the treble.. the most delicate sounds are effortlessly played.. cymbals, chimes, whatever just sound so so detailed. something i didnt expect, the actual amp added a third dimension to the sound, making VERY very spacious with sounds feeling as if they are floating around in my car. at distances, up close, several meters to the left, behind me or just beside me. all from just an amp. incredible. oh, and absolutely no microphonics, even from the bass. it's so good, i can feel myself turning into one of those lovely pretentious audio guys as we speak hahaha

for your own reference, this is the amp i bought YJ 6N4 X4 Maratz 7 tube Preamplifier board-in Amplifier from Consumer Electronics on it cost me a measly $75 with shipping, transformer and valves. can you say bargain? when the cheap Chinese valves blow, i may go with some kind of ex-military valves for a bit more ruggedness, but for now, these are fantastic.

this is the whole thing together. i personally find it quite beautiful. at first i didnt like the crossovers on display like that, but am becoming quite fond of them now. it is finally becoming what i have dreamed it to be. the sound is amazing, it looks amazing, and everything i have installed, i have not done because i have blindly followed the advice of others, each individual modification has been done because i have learnt from first hand experience the what and the why things are done that way. why it sounds best to do it this way. what the science and theory behind it is. i understand it, and i can hear it. that makes me both proud and humbled.

cheers guys, i hope you like it!!!!

ps, i am actually a pest controller in australia by trade, i dont suppose anyone has any advice on how to get a career in this sort of field? anything in audio, i only focus on car audio because i listen to music more often in my car then in my home, but the theory is the same.

ubza1234 13th October 2013 07:25 AM

just painted the top of the caps on the valve amp matt black because the shiny aluminium of the caps was reflecting off the windscreen and was very distracting. next step is to put some black heat shrink over the bloody blindingly bright blue power led..

uidb0080 17th October 2013 06:16 AM

What an inspiration
Hello Mr. McFly
this must be the world first modern car tube amp....
What's it sound like? any chance of hearing it?

ubza1234 20th October 2013 05:26 AM

sounds pretty good :)

wesayso 23rd October 2013 09:29 PM

That preamp is a good twist on things. I like it. My car audio hobby made me build new speakers for my home though, so be careful :D.
Do you have DSP power in that HU?

ubza1234 23rd October 2013 09:43 PM

I started with PA/pro audio, then hifi, then realised I listened (in a way I can focus on it and fully appreciate) to music more often in my car then at home, so I got into car audio. :-)

DSP power? I rarely use the head unit. the switch in the dash switch the power amplifier audio source from the HU or the valve preamp, which is plugged into my phone. but what is DSP power?

wesayso 23rd October 2013 09:53 PM

Things like time alignment, eq and active crossovers are considered DSP (digital Sound Processor)...
My current HU has that onboard and it really helps in a car environment.

ubza1234 23rd October 2013 10:05 PM

oh a processor. I have not really heard one in action yet, so I want to hear what the difference is first. my car is tiny, so everything is pretty equal. the dash speakers/tweeters are only roughly 30cm offset more then the other speaker. so time assignment would only make a minimal difference in theory. but who knows till I try it?

wesayso 23rd October 2013 10:27 PM

Due to the small differences in path length you might not miss it ;).
I drive a small car too, I think even smaller than you. Easy way to get bass though! I only run one 8" sub.

ubza1234 23rd October 2013 10:51 PM

I found doing up this tiny car much more challenging and fun to accomplish in a reasonably practical way. for example, I soon km didn't install 3 subs to just have more bass, but rather to hit that bit lower. and it does hit low, just ask Franky ;)

I did the measurements, my car is roughly 1 foot longer then a smart car and 1 foot narrower then one. but then there is no safety in my car; the doors are I'd say 10cm thick (excluding my speakers) and very tightly packed for what it is, but it means for such a tiny car, it is roomy, relatively speaking. what car have you got?

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