Entries by Pekka Lehtonen

http://www.xs650chopper.com/2011/01/xs650-banshee-charging-system-swap/

http://www.rmstator.com/en/catalog-years/1996/yamaha/yfz350-banshee/stator-200-watt-flywheel-puller-ignition-coil-kit-rm22808-2

Lisäksi DC-mallin tasuri/regu ja pikkuisen DIY-henkeä sytkäboksiin...

Hommasin taanna 1986 vuoden TT350 Yamahan....

6 voltin AC-s�hk�j�rjestelm� vaihdettiin 12 volti DC systeemiksi. K��mit otettiin XT350 mallista. Tasuri/regulaattori on tehty tasasuuntaussillasta isosta darlington transistorista, zener diodista ja konkasta. L�ht�j�nnite noin 16 volttia ja valo palaa miellytt�v�n kirkkaasti. Tarkempaa kytkent�� voivat halukkaat kysell� kommenteissa.





Sittemmin py�r� on myyty...

Slight modifications to my Tonebenderish fuzz. Put a pot in series with input. In minimum all input signal is fed to the first transistor. With high output pickups this can really drive the circuit in to deep saturation with some serious barf. At maximum it limits the current driving the first transistor. This cleans up the sound and gives a less fuzzy sound. Also dialing down the guitar volume a little bit cleans the "barf" nicely.

After extensive Googling/noodling I came up with this:

#!/bin/bash
mencoder -noidx -oac copy -ovc copy -o tmp.avi $1
ffmpeg -i tmp.avi -f avi -vcodec mpeg4 -b 1700000 -g 300 -bf 2 -vtag divx -acodec copy $1_divx.avi
rm tmp.avi

(copy that to a script file on you pc and run: "./yourscript your_video_file.mkv")

ffmepg alone did not work due to some time stamp bug. By first transferring from mkv to avi container with mencoder and then encoding to DivX with ffmpeg I finally got the video to play on my Bravia TV.

ffmpeg can be used alone but then the audio also has to be recoded:

ffmpeg -i your_input_file.mkv -f avi -vcodec mpeg4 -b 1700000 -acodec ac3 -ab 128000 -vtag divx out_divx4.avi

Using mencoder alone should also be possible but for some reason it just did not work. There was a warning about aspect ratio not been set and thus some header was not written. This probably stopped Bravia from playing the file.

If anyone has an idea how to get subtitles from mkv to the avi please let me know.

Nätti kuin sika pienenä.

30 vuotisen taiteilijauran kunniaksi päätin ostaa 30 vuotta vanhan moottoripyörän. Yamaha XS650:n eli tuttavallisemmin Jytä Jammun tahi Jytärin. Kunnostus/rakenteluprojektia pukkaa. Lähtötilanne oli kutakuinkin tämä:



Sittemmin mopo on purettu osiin ja projekti jatkuu kutakuinkin seuraavin vaihein:

Hiekkapuhallus + jauhemaalaus:
- T-palat + tangon pidikkeet yms
- Keulan alaputket
- Vanteet
- Jalkatapit
- Runko
- Takaswingi

Rakentelua (/muutoksia):
- Ketjusuoja
- Akku/sähkökotelo
- Satula
- Takalokari
- Mummorauta
- Jalkatapit
- Lamppu
- Mittarit
- Sähköt
- Keulan lyhennys
- Starttimootorin poisto
- Rungon korjailut ja siistimiset

Muuta:
- Uusi ohjaustanko
- Uudet sähköt
- Uusi tankki
- Jarruremontti

Eiköhän siinä ole talveksi tarpeeksi puuhaa.

This is a simple 2-stage optical vibe-effect for guitar. I've wanted one for quite some time and now I built it. Mellow and subtle. Not "over the top". This "design" is an adaptation of various Internet sources. Hope you find it usefull. I did. Here are schematics and a VERO-board layout (in EAGLE format): optivibe_micro.sch, optivibe_micro.brd

A reflex cab with a pro audio speaker that is said to be close to the legendary Electro Voice speakers. The cab has approx 48litre internal volume. It is made from 15mm pine plywood. Covered with black felt. It is tuned to approx. 70Hz with 100mm diameter 30mm long tube.



The port has changed to bigger and shorter after the pic was taken.

I'm still testing and getting used to the sound but initially it appears very neutral and un-colored with big bottom. Still needs steel corners and grille.

I wanted a "different" tone control for my Low Gain Amp. By combining modified BigMuffPI tone with modified Marshall bass amp MID control I got this:



Sounds nice. Gives bass/treble tilt and variable mid scoop. For nearly flat response (3dB mid scoop at 540Hz) set TONE to 1 o'clock and MID to full value. Change C23 to 2.2n for less than 1dB scoop. If you try this in your amp please let me know how it works for you.

Pekka

I got hold of an old PA/central radio amp few years ago. I wrote something about it to the old KP here. The amp was not working at the time but had some nice parts: Four EL34's, EF86 and ECC83 in preamp and huge transformers. Also a big and "good looking" (but a little bent) chassis.

Apparently the amp was made in Finland in 50's or 60's. Now the amp got a new life as a low gain (bass)guitar amp. It features two EL34 output tubes, 12AX7 DC-coupled PI and 12AX7 Preamp with Tilt. Mid and Volume controls.



Dis-assembly

I traced out the schematic of the amp and decided that I would not use it as it is. I decided to dis-assemble everything. Most electronic parts went to thrash. Old can electrolytic caps and scary looking mains connectors had to go. Actually I only kept the tube sockets and two red lamps on the front panel. After removing all parts I removed most of the old paint from the chassis.



Output transformer

The OT was huge. It had UL-taps in the primary (actually 57% instead of 43%). The output transformer secondary was for 100V line. I disassembled the transformer core and wound 10 turns of wire over the existing windings. Then I fed a 1kHz signal to this 10 turn coil and measured voltages from all coils. I found that primary had approx. 2000 turns of wire. I calculated secondaries so that I got approx. 6kOhms primary impedance. 76turns for the 8ohm output. I was supposed to measure the tranny but did not have the patience for that. I assembled it to the chassis and wired to the circuit.




Chassis

The chassis is a true classic. Huge and ugly. Bent and scratched. Originally the chassis was painted with blue hammer-tone but someone had painted it over with some white paint. Latex or oil based paint used to paint interior walls in houses or something. I wanted to keep something original in the amp so I painted the chassis with something that claimed to be "Black Hammertone" in a spray can. Well, not quite. It is actually gray and does not look like hammertone. You cant win every time... I did not have to drill any new holes except for the new IEC socket.

Schematic





UPDATE 13.6.2010: Schematic rev. 1.5. With new PI, PPIMV and subsonic filter before poweramp.

UPDATE 21.3.2010: New schematic uploaded.

UPDATE 15.3.2010: Now the amp is pentode connected with NFB to PI. Preamp tubes changed to 12ax7 for more gain. Schematic soon. New Mid controll also coming up.

Sound

Big and clean

Old info: The amp has really low gain and huge headroom. I tried to push the input stage to distort with a booster but 10Vpp signal was not enough for that... The tone control works good at least with a guitar. Nice "Tilt" control with some mid scoop adjustment. Tone control is a version of the Big Muff PI tone. It works nice but I would like a better control for the mid frequencies and may change this in the future. Seems to work great with distortion pedals.

Problems

Due to the 57% UL taps I only got approx 20W of clean output. I was hoping to get over 30W clean and near 40W full distortion. This is a setback. Now I need to add second pair of tubes or change to pentode circuit. That sucks because with pentode I have to use feedback and post PI master volume is not optimal with it. UPDATE 13.6.2010: I have now changed the amp to fixed bias with NFB and PPIMV and it seems to work better than expected. About 60W at full clipping. Maybe more. Definitely more if a 4 ohm cab is plugged to the 8 ohm output.


Pekka

Samaan purkkiin aikaisemmin esitellyn Torso Fuzz 2:n kanssa päätyi tämä Tonebender-variantti. Paras pörinä jota olen koskaan kuullut. Tästä ei irtoa "kevytrosoa" edes yrittämällä. Kaulamikki käyttöön ja soittamaan sooloa Wolfmotherin Love Trainiin. Trankkuina samat OC140:t kuin Torsossa. Muutkin sopinevat. Biasointia voi joutua säätämään.




Pekka

Ok. This one in English. I've been building this amp for four years now. Last two years I was just happy actually playing guitar through it but then I decided to change the power tubes. From EL84 to 6V6GTA. Last month or so has gone in rebuilding the amp. I was only supposed to do quick rebuild on the power amp. Eventually I ended rebuilding the entire thing and actually went through several different versions before settling with this one. Also built a new cabinet.

The topology of the amp is quite traditional. 3 gain stages, cathode follower, PI and pentode Push-Pull power amp. Three 12AX7's and two 6V6GTA's (NOS RCA). The amp is now basically AX84 SEL preamp with 20W core power amp. The preamp has been modified to my taste. The power amp and PI was built from components I had available. This is the first time I have implemented Presence control. The schematic shows the current state of the amp.

Features and specs:

• 2 x 12AX7 preamp
  
• 6V6GTA (RCA NOS) PP power amp with 12AX7 PI
  
• 5AR4 rectifier tube
  
• UralTone power transformer
  
• Hammond Mfg 125E output transformer
  
• Approx. 20W output power at full tilt
  
• Gain, Bass, Treble, Middle, Presence and Volume controls
  
• Two switches for fine tuning the bass in the first gain stage
  
• 3 stage preamp with cathode follower
  
• Traditional tonestack
  

I think I'm happy with the amp now. Had a lo of issues in the rebuild. The old preamp just did not work with the first version of the new power amp. The power amp also oscillated at 30kHz is volume was set too high. I got the oscillation under control but the sound still was not right. Then I ripped out the entire old amp and rebuild it. First the PA, then preamp and then PI. Some fine tuning in the preamp and now things seem ok. Enough gain, cleans up ok from guitar volume. Not too bright but also not "muffled". No strange noises, crackles, hisses or buzzes. Not even at full tilt. The only thing that bothers me is that the Presence control is effective only in the last third of the rotation. Maybe I'll look into it some day...

Sound samples may not become available sometime in distant future.

EDIT 6.2.2010 - Added an adjustable feedback. Turned down the NFB and to my great surprise the sound opened up and really started to growl. I guess it is more Marshall now. The presence does not do much without NFB...

EDIT 9.2.2010 - Bias adjustments, 560ohm G" resistor and JCM800 style 2nd stage with switch. 270nF Presence cap.

Pekka

Kirjoitetaanpas tämä nyt heti nettiin niin kukaan amerikkalainen ei ehdi tekemään järjestelmäpatenttia.

Tarvikkeet: 12V Ledinauhaa (tyyliin tämä), ATX-poweri, ATTINY2313 (tai vast.) mikrokontrolleri, RC5-kaukosäädin, muutama mosfet- tai darlington-transistori.

Mikrokontrolleri (mcu) ottaa sähkönsä ATX:n 5V standby jännitteestä ja on siten koko ajan päällä ottamassa vastaan kaukosäätimen komentoja. Mcu ohjaa ATX-powerin "power on" signaalia, jolla 12V jännitteet (ja siten ledinauhat) saa kytkettyä päälle.

Tarvittaessa mcu ohjaa myös 2 tai useampaa kytkintransistoria, joiden perään on kytketty ledinauhat. Näin saadaan useita itsenäisiä valoryhmiä. Tarvittaessa voidaan tehdä himmennys käyttäen mcu:n PWM lähtöjä jokaiselle valoryhmälle erikseen. Jokaisen valoryhmän ohjaus voidaan tehdä kaukosäätimestä. Kaikkien valojen yhtäaikainen sammutus tehdään sammuttamalla ATX-poweri "power on" signaalista. Koska MCU pidetään koko ajan päällä voi järjestelmä "muistaa" viimeksi käytössä olleet valoasetukset sammuttamisen jälkeen. Tarvittaessa tila tallennetaan EEPROM muistille.

ATX-powerin 3V ja 5V lähtöjä voidaan käyttää samaan tapaan ohjaamaan yksittäisiä teholedejä (huom. virranrajoitus ja kynnysjännitteet!).

Sokaisevan itsestäänselvää.

Pekka

Pakkoloma uhkaa loppua kesken ja säätäminen on saatava päätökseen. Kaamea tuunaus ja virittely tuotti oheisen skeman mukaisen lopputuloksen. Aika ratkaiskoot tämän version eliniän.

Etusta säädettiin urakalla edellisestä versiosta. Toinen putki vaihtui 12AU7:n (NOS Mullard). Kahden viimeisen vahvistinasteen välissä on melkoinen hässäkkä. Takaisinkytkennällä ja muilla säädöillä koitetaan matkia päätevahvistinta edes jotenkin. Päätteeseen piti lisätä konkkia kun pirulainen oskilloi 30kilohertsillä kun nupit oli kaakossa.

Huomisissa treeneissä pääsee kunnolla luukuttamaan. Katotaan sitten malttaako lopettaa säädön ja keskittyä olennaiseen. Tuskin...

Pekka