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Thread: ROLAND BOLT 30- 60 cycle hum...

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    ROLAND BOLT 30- 60 cycle hum...

    Hi all!
    I have a roland Bolt 30 amp that I just love but it exhibits a pretty loud 60 cycle hum when powered on, with or without a guitar plugged into the input. If I plug into the main in the hum dissapears but I guess thats to be expected.
    This amp uses the pretty rare 7591 power tubes and has the original 1980 RCA tubes in it. So I am awaiting a set of EH tubes to see if thats the problem. Here's what I've done so far to no avail on the hum-
    1] new spague filter caps and electrolytics on the power supply board.
    2] twisted and lifted the heater wires
    3] tried various 12at7 phase inverter tubes. [a 12au7 did noticably quiet the amp, but lowered the volume too much]

    I found this info [scroll down to the Roland bolt 60 info] http://www.geocities.jp/dgb_studio/G_amp_e.htm
    and there's some info and a schematic about adding caps to the power supply to quiet the hum...but I dont really understand schematics enough to go for it. This is my gigging amp and I really need to keep it working! He talks here about adding them to the effects loop wires I think?

    Apparently all the info on mods for the Roland Bolt series amps was at one time available online here- Roland Bolt 60
    but this sight and its forum are defunct and the moderator is MIA :-(

    If any body has this info archived anywhere it would be invaluable to me!! I'd like to install a proper standby switch [the bolt's aren't true standby] and wire in a 3 spring reverb,all of which were at one time available on the Roland Bolt page....but its gone

    Again I'm not really confident with schematics so some hand holding would be needed

    Here's a gut shot of my bolt 30 after the cap job, just cause I like gut shots!



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    Last edited by czech-one-2; 09-13-2014 at 09:56 PM.

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    Don't forget the joker g1's Avatar
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    service notes and schematics available here (click on "documents"): Roland Bolt 60

    The fact that the hum stops when you plug into "main in" means the problem is in the preamp. The power supply and power amp sections are ok and hum free.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Old Timer oc disorder's Avatar
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    If the hum is not coming from the reverb circuit a long shot..(the pot would have to be faulty too)
    check the pre supply it comes from the same winding as the bias for the o/p tubes.
    Should measure 47 volts at B. Couple of filter caps on the pre-board and D9 on the power supply board.
    D9 is a 500mw 47 volt zener.
    Q1 a 2SC1624 may be worth checking too.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Quote Originally Posted by oc disorder View Post
    If the hum is not coming from the reverb circuit a long shot..(the pot would have to be faulty too)
    check the pre supply it comes from the same winding as the bias for the o/p tubes.
    Should measure 47 volts at B. Couple of filter caps on the pre-board and D9 on the power supply board.
    D9 is a 500mw 47 volt zener.
    Q1 a 2SC1624 may be worth checking too.
    Thanks 4 the replies!
    I removed the reverb tank and wires as it sounded really weak anyway [belton brick reverb trumps it big time!]
    So I guess it looks like the preamp board is the source. I may just re-cap all the electrolytics on that long board with low ESR types and see if that helps.

    Just curious [and trying to learn], what made you single out D9, Q1, C21/C29 ?

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    Old Timer oc disorder's Avatar
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    Just curious [and trying to learn], what made you single out D9, Q1, C21/C29 ?
    Simply because that is the source of the pre-amp supply and as g-one suggests the hum must be in the preamp
    as you observed no hum when plugged into only the power amp in.
    At the top right of the schematic it shows B1 47 volts which comes from the B1 (mid lower left) from the power supply.
    That 47volt zener hold the supply at 47volts (sometimes + or - 2 volts).
    The two caps C21/C29 are the final filter caps for smoothing on the pre-amp supply rail.
    The power amp doesn't use this.
    I wouldn't necessarily replace all of those but as you were saying you were not confident with schematics, I was
    drawing your attention to those areas which , where hum is concerned are a good place to start and hopefully
    eliminate from the list. (C5 and C30 might be worth looking at too!)
    Being able to see the hum on an oscilloscope as ripple superimposed on the dc makes it easier to trace in some circumstances.
    Measuring the supply gives a few clues too .
    Sometimes I just "tack" lightly solder a similar known good cap over the supply at various points to see if I can hear a difference.
    Actually it's probably more likely it has a few cracked solder joints particularly an amp of it's age .
    Check around the switch and pots and any large loose objects !!
    Could even have a hairline crack on the pre-amp board or a loose ground somewhere.

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    Last edited by oc disorder; 09-14-2014 at 11:59 AM.

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    Supporting Member Jazz P Bass's Avatar
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    Q1 is the main element of a circuit called a 'Series Pass Regulator'.
    Transistor-Zener Diode Regulator Circuits
    Series Voltage Regulator | Series Pass Regulator | Tutorial

    C21 & C29 capacitors help smooth out any ripple riding on the output voltage.

    Check the dc voltage at TP 15V & TP 7.5V.
    It should be a steady dc reading.
    Then flip your meter to read Volts AC & read the same two points again.
    There should be a very low ac reading (ideally zero).

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    Last edited by Jazz P Bass; 09-14-2014 at 12:30 PM.

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    Quote Originally Posted by Jazz P Bass View Post
    Q1 is the main element of a circuit called a 'Series Pass Regulator'.
    Transistor-Zener Diode Regulator Circuits
    Series Voltage Regulator | Series Pass Regulator | Tutorial

    C21 & C29 capacitors help smooth out any ripple riding on the output voltage.

    Check the dc voltage at TP 15V & TP 7.5V.
    It should be a steady dc reading.
    Then flip your meter to read Volts AC & read the same two points again.
    There should be a very low ac reading (ideally zero).
    Thanks, I'll check TP 15V and TP 7.5v ...if you can tell me which component/location that is.
    I'll read the 'SVR' tutorial today, thanks!
    Also, is there a common sub for the 2sc1624 ? I have some L7812CV voltage regulators here..
    Also, would a 1N5368 zener be suitable for D9? http://www.gme.cz/1n5368b-p222-195

    And one more question, the two blue 16uf filter caps were originally 22uf, but I upped the large single filter cap from 47uf to 80uf. Any problem there?

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    Last edited by czech-one-2; 09-14-2014 at 03:15 PM.

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    Quote Originally Posted by oc disorder View Post
    Actually it's probably more likely it has a few cracked solder joints particularly an amp of it's age .
    Check around the switch and pots and any large loose objects !!
    Could even have a hairline crack on the pre-amp board or a loose ground somewhere.
    Ok, I inspected and re-flowed the pots, all terminals and a few suspicious areas. Still buzzing. The 'main in' is utterly silent from buzz. The buzz has nothing to do with volume/gain/eq tweeks.The buzz is the same with the volume at zero or 10.
    I tried the 'chopstick' method on all the wires to see if any movment changed the buzz, nope...

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    Last edited by czech-one-2; 09-14-2014 at 03:16 PM.

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    Quote Originally Posted by oc disorder View Post
    The two caps C21/C29 are the final filter caps for smoothing on the pre-amp supply rail.
    The power amp doesn't use this.
    I wouldn't necessarily replace all of those but as you were saying you were not confident with schematics, I was
    drawing your attention to those areas which , where hum is concerned are a good place to start and hopefully
    eliminate from the list. (C5 and C30 might be worth looking at too!)
    Would it be wise to up the capacitance of C21 /C29 from 100/220uf to,say, 220/330uf ?

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    Supporting Member Jazz P Bass's Avatar
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    Why?

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    Supporting Member Jazz P Bass's Avatar
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    It may help to try running a cord from the Pre Out jack to the Main In jack.

    There are Normally Closed contacts on the jacks that get crudy.
    The jumper cord will remove those contacts from the equation.

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    Better filtering?

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    no difference

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    Supporting Member Jazz P Bass's Avatar
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    Unless you actually measure the TP for steady Vdc & how much Vac is riding on them, it is rather poinless to consider upping the values, is it not?

    You could simply throw parts at it.
    It may very well fix it.
    But you will not know what the root cause was.

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    Quote Originally Posted by Jazz P Bass View Post
    Unless you actually measure the TP for steady Vdc & how much Vac is riding on them, it is rather poinless to consider upping the values, is it not?

    You could simply throw parts at it.
    It may very well fix it.
    But you will not know what the root cause was.
    Right, now where do I measure the TP? Sorry, but I need some guidance on this

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    Supporting Member Jazz P Bass's Avatar
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    The TP's are at C (7.5Vdc) & D (15Vdc).

    As there is not a board layout available, you will have to find where the points are.

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    Old Timer olddawg's Avatar
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    Use a scope or an AC volt meter to check for ripple on the preamp power supplies.

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    Old Timer oc disorder's Avatar
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    I'll try to answer..
    And one more question, the two blue 16uf filter caps were originally 22uf, but I upped the large single filter cap from 47uf to 80uf. Any problem there?
    Well they are the ht filter caps (high voltage) shouldn't be a problem well they only feed the tube output stage which you say is working fine .. there is normally no reason to change the value but a lot of people do !

    There is a layout diagram in the "Service Notes (with schematics) >Bolt 30/60 (zip file)" in the link G-one provided.

    The components and test points JPBass mentioned are in the middle of the pre-amp board.
    Click image for larger version. 

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    Please tell us what you measure between those and ground.

    You will notice this area also has a series pass regulator but this time on board AP 142 D9 is a 15volt zener.. !!

    Also C26 47uF 25v,C27 100uF 16v, & C28 another 47uF 25v perform the smoothing/filtering function here.

    I presume the switching function works ? as it uses a cmos ic TC 4016 which contains 4 switches .
    If there was ac ripple in the supply to this it would infest most of the preamp.
    One footswitch controls 4 "electronic" switches at various points in the schematic which reconfigures the pre-amp for overdrive!
    Click image for larger version. 

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    Also, is there a common sub for the 2sc1624 ? I have some L7812CV voltage regulators here..
    No... the 2SC1624 is a NPN transistor it might look like a regulator but it's not although it's kinda acting like one !!!

    You haven't told us what you measured ..measure first then replace if you have that 47 volts or near enough (it's not Nasa here)
    there is no need to investigate further.

    Also, would a 1N5368 zener be suitable for D9?
    No! Check the part list it's a RD 47E - from the NEC data sheet it's a 500mw diode. Although the diode you saw is 47 volts it's a 5 watt
    one , the currents here are miniscule .. the 5 watter wouldn't even know there was any current flowing and thus wouldn't work.
    i.e. wouldn't turn on !
    The data sheet is here for interests sake
    RD4.7E datasheet - 500 MW DHD Zener Diode Do-35

    And to satisfy a nagging thought I have could you make up a shorting jack wire the tip to sleeve (ground the tip)
    and insert it in the reverb switch jack. To make absolutely sure the reverb circuit isn't humming !

    Good luck on your mission !!

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    Supporting Member Jazz P Bass's Avatar
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    Thanks OC.
    I missed the board layout.

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    Ok, I went ahead and replaced all the electrolytics in the preamp [among them were C26 47uF 25v,C27 100uF 16v, & C28 47uF 25v] and I thought it was quieter.......until I put it in the cab and sat next to it. Still got that annoying loud buzz that seems to shift audibly between 2 tones at 2 second intervals. The amp has a Celestion century neo in it with 102DB efficiency. But unfortunately this efficiency really aids that hum too.....
    So tomarrow I'll post my readings at 15v / 7.5v

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    Last edited by czech-one-2; 09-15-2014 at 09:14 PM.

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    Thanks OC for taking the time to post the layout with the component circled, thats going to make taking a reading possible for me.

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    Quote Originally Posted by oc disorder View Post
    You haven't told us what you measured ..measure first then replace if you have that 47 volts or near enough (it's not Nasa here)
    there is no need to investigate further.

    Guess I'm a little slow at heeding advice. At least I know its not the electrolytics...

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    Last edited by czech-one-2; 09-16-2014 at 10:34 AM.

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    Please check the 48 volt supply too and let us know . If you can find R 59 on the pre board ..Roland have it connected to terminal 4 which goes back to terminal 15 on the power supply board. The resistor is 120 ohms (Brown Red Brown) and should have 48volts on one end and 45v on the other with your negative meter probe on ground.

    Attaching a picture showing a regulators internals compared with a transistor.
    As I remember regulators in a 3 pin package were not so readily available back then so people rolled their own as their fathers before them etc etc..

    Here's a 1 meg jpg which may be of use particularly if you can read in reverse !

    It may help to print it out so you can jot notes on it. This should help you find the points and figure out where everything is ..
    you could probably take a better shot of the back of your board and print that too although it may take adjustment of contrast etc.
    With unfamiliar amps I find photography helps to find components on densely packed pcbs.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by oc disorder; 09-16-2014 at 01:50 AM.

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    Oc, I should have checked your last post before removing all those nuts again You guys are incredibaly helpfull.

    Ok, here's the reading:
    TP 15V = 13.4v / 29.2v AC
    TP 7.5v = 6.7v / 14.3v AC
    48volt supply/R59 = 47.3V and 44V

    Just want to confirm that this is the correct AC setting on my meter-



    And while I'm trying to learn and have no shame, what does TP stand for?

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    Last edited by czech-one-2; 09-16-2014 at 10:43 AM.

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    Old Timer oc disorder's Avatar
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    Yes thats the right setting for AC - you would probably find it would read the same on the 600 volt setting but maybe without the decimal place.
    Hmm that ac seems very high even though you have replaced all the electrolytics !
    There's a possibility the chassis ground point is a bit far away and giving us oddball readings.
    Could you do it again but this time use a ground point on the pre-amp board.
    Where C30 and C29 negatives go to ground there is a terminal 5 not far from terminal 4.
    Try re-measuring with black (-'ve) probe on terminal 5 while you're there might as well give us the low down
    on terminal 4 ...'sposed to be 47 volts probably be around 45.
    Those DC readings are near enough .. for interests sake with your meter on AC measure the 6.3 volt tapping on your transformer.
    It should read 6.3 volts unless your wall power is lower than 220volts.
    Be careful .. it may be easier to measure on the tube/valve sockets

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    The amp has been warming up for 30 min or so and using ground pad #5 on the preamp board here are my new readings
    R58 44.6 / 40.6 DC , 12.5 / 12.5V ac
    R59 45v /48v DC , 12.5 / 12.5 AC

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    Last edited by czech-one-2; 09-16-2014 at 11:18 AM.

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    OK, little confusing,
    Now I'm Getting
    R58 98v / 89v AC and R59 98v / 105v AC

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    Old Timer oc disorder's Avatar
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    Well its ridiculous... actually I'm curious if the 13 and 6 volt readings were the same measuring this way with terminal 5
    new test.. measure from that ground point with power off to the ground point you used before resistance reading on 200 ohms scale.

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    Old Timer oc disorder's Avatar
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    Actually is there any history ? did it suddenly start humming at a gig or did you turn it on one day and hummmmmmmmmmm ?

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    Quote Originally Posted by czech-one-2 View Post
    OK, little confusing,
    Now I'm Getting
    R58 98v / 89v AC and R59 98v / 105v AC

    ok oc, I just took the reading from the chassis ground point, same results as above

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    Just got the amp a month ago, havn't used it at a gig yet but plan to next month for a fall tour. So when I say its my gigging amp I mean I'm hoping it can replace the JC-120 that I've been lugging everywhere [and save my spine in the process]
    It had hum when I got it, got worse [more noticable] when I put the Century in. I dont mind some hum, but this is real annoying hum.
    The stock speaker was 35w with a tiny magnet and probably 96db sensitivity.The Century is 100w with a 102db rating.
    Are my AC readings even possible?

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    Last edited by czech-one-2; 09-16-2014 at 12:15 PM.

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    Quote Originally Posted by czech-one-2 View Post
    OK, little confusing,
    Now I'm Getting
    R58 98v / 89v AC and R59 98v / 105v AC

    Triple/ quadruple checked. These are the AC readings

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    Quote Originally Posted by oc disorder View Post
    Well its ridiculous... actually I'm curious if the 13 and 6 volt readings were the same measuring this way with terminal 5
    new test.. measure from that ground point with power off to the ground point you used before resistance reading on 200 ohms scale.
    .3 ohms from pad#5 to the chassis ground point, power off

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    Just tried it with a neighbors meter, r58 = 98/89v AC and R59 = 98/105v AC

    Do these AC readings indicate a big problem?

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    Last edited by czech-one-2; 09-16-2014 at 01:00 PM.

  35. #35
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    Quote Originally Posted by oc disorder View Post
    I presume the switching function works ? as it uses a cmos ic TC 4016 which contains 4 switches .
    If there was ac ripple in the supply to this it would infest most of the preamp.
    One footswitch controls 4 "electronic" switches at various points in the schematic which reconfigures the pre-amp for overdrive!
    Yes, the switching jacks work.
    Here's a high contrast board shot:

    Click image for larger version. 

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