Many problems with my a15mk1 any guidance

    First of we made amps ,me and my buddy. my buddys amp sounds great, mine is little fuzzy sounded and the dunamic and strong bottom is just not there, there is "some" base but the sound ain´t just so great.
    i have several times measured and tryed to compare our amps but just don+t seem to find anything wrong. For the knoledge once i had a short on the blue wire running underneath the toneboard. but i got that fixed.

    first the bass:
    The bass on clean channel is on it´s maximum when the know is at 50% turned and turning it eather to 0 or to max courses the bass level to lower...wierd and the pot is what it should be, atleast compared to what says in the potentiometer.

    second: The smooth switch
    the smoothswitch on the center gives little too clear sound and the up and top position give too dark sound. my friends amp smooth switch has like no noticable differences in the 3 positions, but enough to hear there is something changing.

    third:
    the dynamic of the amp suffers. at first stung to the strings i get loud bass but if i continue strumming the dunamic lovers dramaticly like the juice was running out. and the distortion on the dist channel is much better if fire up the amp and start playing, after while it gets kind of muddy.

    Martin Is there any place i can send this amp, i would like to know what the fuck is wrong with it. I measured all components when i made the amp and i think made a deacent job.

    http://img52.imageshack.us/i/img2400j.jpg/

    ps. once i even tryed with my friends tubes and nothing changed.
    and the tubess glow all ok

    Recommendations for fixing your A15Mk1

    Hi masterson,
    first of all welcome to the forum!
    Let's trying to fix your problems one by one, I assume at least the first two should be pretty easy to fix:

    1) Are you sure, your buddy also has built the A15Mk1 or perhaps the A15Mk2? From Mk1 to Mk2 the tone stack has changed, this update would fix your problem with the bass control. You can find the recommended change of the tone stack in my gallery, it's pretty easy to implement:
    http://forum.musikding.de/cpg/thumbnails.php?album=97&page=2

    2) The smooth switch is pretty simple (just one capacitor and two resistors), so if the sound (with the same guitar and same speakers of course!) is that different, the values or the wiring is wrong. If the sound is much "darker" than it should be (treble missing) and the witing is correct either the resistor is too small or the capacitor is too large. Please be aware, that these values have also been changed from Mk1 to Mk2 (10K => 18K and 8K2 to 19K) so if your buddy owns the Mk2 there is an audible difference ;)

    3) let's focus on that later :)

    Regards,
    Martin

    ok maby ill try to change the clean tone stack.

    no we have the same model mk1 but the diffence is that my buddy has the version with the 100 ohm resistor between the earth and starpoint +
    mine has the newer cabinet transformer.

    we tested both amps with my cabinet.
    same guitar same cabinet and so on.
    tested on directly plugging guitar to the amp and running through my
    gsp1101 to amp loop return.

    ill check the parts for the new tone stack and tomorrow ill go and get them maby.

    changhing the tone stack seems simple on the bass potentiometer side but the circuit board seems to be the harder job to do. for example the shielded cable E needs to be moved further and mine is running underneath the circuit board and if i remember correctly it´s quite tight so there is no change of moving it but to replace it with longer one, and it´s not that simple to flip the board up. i need to unsolder lots of things to do so. so im not too happy on doing it . shiiit.

    any chance of looking at it if i send it to you.... ?
    if i send it to you look at it, make estimate of what is wise to do and we deside what will we do.
    it,s about 60-70€ there and back

    Changing the circuit board doesn't change the sound, it just removes crosstalk in channel two (crosstalk is not happening in all builds, but sometimes you hear the guitar even when the volume is turned fully down - this is solved by changing the board). So if you don't have that problem or don't care about it you don't have to change the board. But hanging the two resistors in the smooth circuit and the tine stack wil definitely change the sound so this is worth trying. I'm sorry to say, but I cant do an analysis/repair because I symply don't have time. Where do you live, there might be another usr being able to help you personally?
    Regards,
    Martin

    I live in finland.

    no i don´t have crostalk.
    do you have any idea why the bass potentiometer on the clean channel acts like mine does ? Being maximum at the center and not the right side

    Hey.

    could there be a problem with the fact that my mk1deluxe kit got delivered with the OT ATRA0427 and my friend has the hammond 125E version ?
    my friends amp got lot more boos to the lead gain, it´s much dunamic, lot´s of base i think my amp got very low bass in clean and distro channel + the distortion is quite muddy.

    Im seriously thinking of asking from musikding how much would it cost if i would order all other parts for the a15mk2 version exept the transformers and chasis.

    i believe the mk1 chasis is ok for mk2 version ?

    course im starting to loose my head with this one.

    although maby i first try unsoldering and measuring the bigger capasitors aroung the bluewire under the bigger board course once i got a short there and i got no audio and lots of heat on the resistors in the power board

    The difference between the Mk1 and Mk2 are just the three changes we already talked about (board layout, clean tonestack, smooth circuit) so you don't have to rebiuld from scratch. And no, the sound differences as you decribe them are not depending on the different output transformer. Are you sure, all voltages are appropriate (as showin in the schematic)?
    Regards,
    Martin

    Hi Masterson,
    1) the popping and cracking is OK, when you touch pins with Audio signal at it (grid, plate, sometimes cathode) with your maesuring tips, you will get this noise, nothing to worry about
    2) Voltages at Power Stage and Power Supply
    I don't see weird voltages, all voltages are inside tolerances (given the higher output voltage from the power supply). The voltages at pin 1 / pin 6 of V4 re the wrong way round, perhaps you've interchanged R38/R39? The voltage drop of 7V at R59 shows, that the overall current of the Amp is OK. What about the voltages at pins 3/4/8 of both (!) power tubes?
    3) Voltages at Preamp
    The voltage drops at R10/R29/R36 are within tolerances, so the overall current is OK. All voltages are also within tolerances (given the higher output voltage from the power supply), so I don't see any weird voltages.
    Regards,
    Martin


    i checked the r38/R39. they are correct. in right positions and measured them the 38 is about 82K and the 39 about 100K like they should be but the voltages are the wrong way around like i measured earlier.... i don´t get how they can be....

    power tube voltages V5:
    pin 3 = DC 295 V
    pin 4 = DC 297 V
    pin 5 = DC -18 V
    pin 8 = DC 28 mV

    power tube voltages V6:
    pin 3 = DC 298 V
    pin 4 = DC 304 V
    pin 5 = DC -18 V
    pin 8 = DC 31 mV

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