I own a hartke HA2000 bass guitar amplifier and I'm having some problems with it:
Some months ago the amp started loosing some punch in the bass and treble, the sound is as loud as it used to be but is lacking presence and definition in the low frequencies and clarity in general. The amp is not distorting at all, it still sounds ok but not as good as it used to.
I have some experience fixing amplifiers but I'm having a really hard time to find the problem with this one. Most of the amps I fixed where the usual burnt power transistors, or major failures where the amp will not work at all. I service the equipment for all the bands I play with, I live in southern mexican pacific coast, here there are not good technicians for this kind of work.
How can I troubleshot such a subtle problem in this amp ? I have an osciloscope and function generator, it is allright for most of cases but when I test the amp at diferent frequencies it seems to work allright but it just doesn't sound quite right when I play the bass trough it. I believe is a problem in the preamp, I connected the effect send output to my other bass amp and it didn't sound right either.
Any tips about how to pinpoint the problem with this amp ?
Some months ago the amp started loosing some punch in the bass and treble, the sound is as loud as it used to be but is lacking presence and definition in the low frequencies and clarity in general. The amp is not distorting at all, it still sounds ok but not as good as it used to.
I have some experience fixing amplifiers but I'm having a really hard time to find the problem with this one. Most of the amps I fixed where the usual burnt power transistors, or major failures where the amp will not work at all. I service the equipment for all the bands I play with, I live in southern mexican pacific coast, here there are not good technicians for this kind of work.
How can I troubleshot such a subtle problem in this amp ? I have an osciloscope and function generator, it is allright for most of cases but when I test the amp at diferent frequencies it seems to work allright but it just doesn't sound quite right when I play the bass trough it. I believe is a problem in the preamp, I connected the effect send output to my other bass amp and it didn't sound right either.
Any tips about how to pinpoint the problem with this amp ?
Your on a good start if you ask me... Now that u think its the pramp why not check the speakers too. Once you rule these out then maybe u can look at other things.
I am also thinking cables can have a lot to do with the problem, especially if you are talking about it being another device and not the amp.
I am also thinking cables can have a lot to do with the problem, especially if you are talking about it being another device and not the amp.
These amps have problems with input grounding. Check to make sure the input section has a solid ground. They ground the input stage at the pre-amp. if they ground is weak, the input stage looses its reference and the amp can do all sorts of odd things. there is no direct ground to the output section or power supply from the input. there is a resistor in line to break the ground loop currents.
Also check for broken pots. many can develop hairline cracks that "look" ok but have failed. also check for bad solder connections. these amps have that issue as well.
I have had problems where a component had a broken lead. but the lead was broken where it went through the PCB and from the topside it looked fine. but electrically it wasnt connected to the bottom side.
I have fixed many of these and had all sorts of odd problems with them....
Zc
Also check for broken pots. many can develop hairline cracks that "look" ok but have failed. also check for bad solder connections. these amps have that issue as well.
I have had problems where a component had a broken lead. but the lead was broken where it went through the PCB and from the topside it looked fine. but electrically it wasnt connected to the bottom side.
I have fixed many of these and had all sorts of odd problems with them....
Zc
Still troubleshooting
Of course I checked cables, diferent speaker cabinets, etc. I've playing the bass for about 12 years, I love drumming too and I've been playing drums for 20 years. Hey I'm not that old, I just started early !
Andrew:
I checked the ripple and is allright. I suspected that as the head I'm using now is a old Peavey Mark III from '78 which I rebuilt, the power amp section was completly useless so I built a amplifier board and hooked it up to the Mark III preamp ( I just love this preamp ). It has a very nice punch. That one had exactly the same problem and was a bad filter capacitor in the power supply. It is possible to test properly a 10000 uF capacitor ?
zero Cool:
I checked the ground in the preamp section and found no problems there. I also rechecked the pots, once I was playing in loud rock-ska band and my amp head fell down from the cabinet and I broke a couple of pots and had to change them. I re-checked everything and it seems ok. Beside the amp was sounding fine after I fixed it for about 1 year.
Is true also what you say about broken leads and bad or cold soldering, I thought maybe the problem might be some bad capacitor in the preamp but I don't know how to test them properly. A series resistence meter would help ? Maybe I can get one from ebay if is really worth it.
Of course I checked cables, diferent speaker cabinets, etc. I've playing the bass for about 12 years, I love drumming too and I've been playing drums for 20 years. Hey I'm not that old, I just started early !
Andrew:
I checked the ripple and is allright. I suspected that as the head I'm using now is a old Peavey Mark III from '78 which I rebuilt, the power amp section was completly useless so I built a amplifier board and hooked it up to the Mark III preamp ( I just love this preamp ). It has a very nice punch. That one had exactly the same problem and was a bad filter capacitor in the power supply. It is possible to test properly a 10000 uF capacitor ?
zero Cool:
I checked the ground in the preamp section and found no problems there. I also rechecked the pots, once I was playing in loud rock-ska band and my amp head fell down from the cabinet and I broke a couple of pots and had to change them. I re-checked everything and it seems ok. Beside the amp was sounding fine after I fixed it for about 1 year.
Is true also what you say about broken leads and bad or cold soldering, I thought maybe the problem might be some bad capacitor in the preamp but I don't know how to test them properly. A series resistence meter would help ? Maybe I can get one from ebay if is really worth it.
the only way to properly test the 10,000uf caps is with an impedance bridge, and test the impedance from 20hz to 20khz. if it's a hartke, then i gather there's a preamp tube in there? like a 12ax7? that's a definite possibility for that kind of change in sound in a hartke amp. the same manufacturer makes samson amps, and they are 100% solid state, but the hartke line has at least 1 tube in the preamp.
Still no luck with it. I uploaded the schematics for it in case someone needs them. I was looking for them in the web and couldn't find them so I wrote to Hartke and they kindly sent me the file.
The schematics are here:
http://www.puertobungalows.com/HA_2000.pdf
The schematics are here:
http://www.puertobungalows.com/HA_2000.pdf
ok..... when was the last time you replaced your strings???? do they have any fretmarks in them? if so, they will sound dead.....
i know bass players who replace their strings every time they play a gig because they want their strings to sound good. they don't mind practicing and rehearsing with the same old strings, but when they are on stage, they want new strings.....
i know bass players who replace their strings every time they play a gig because they want their strings to sound good. they don't mind practicing and rehearsing with the same old strings, but when they are on stage, they want new strings.....
New strings every gig ? I wish... I play most of my gigs on the beach so strings here don't last very long. During the high season I play every day for about 5 months with diferent bands and often have to run from one gig to the other, I try to use the strings as long as possible as bass strings are expensive down here.
Anyway I tryied the amp with new strings, and anyway my bass sounds fine with my other amp so thats not the problem for sure. I had to put it back together as my old DIY'd peavey fell down when loading so I used the Hartke tonight and it still sounds muddy.
I thought to rig up a frenquency sweep generator with a 555 as a triangle wave generator and a Cmos voltage to frequency converter. If I input that signal to the amp and set all the equalizations flat, is it possible to check the frequency response of the amp with a scope ?
It is possible to measure the quality of the sound and the linearity of an amp with an osciloscope ?
Anyway I tryied the amp with new strings, and anyway my bass sounds fine with my other amp so thats not the problem for sure. I had to put it back together as my old DIY'd peavey fell down when loading so I used the Hartke tonight and it still sounds muddy.
I thought to rig up a frenquency sweep generator with a 555 as a triangle wave generator and a Cmos voltage to frequency converter. If I input that signal to the amp and set all the equalizations flat, is it possible to check the frequency response of the amp with a scope ?
It is possible to measure the quality of the sound and the linearity of an amp with an osciloscope ?
That's what I first thought as well but didn't dare to bring up and asked for how long he is playing the bass instead. When he answered that he is already playing for 12 years I thought he will know for sure about the wear of strings.
Yes you can do a coarse check of the frequency response of an amp by using a scope and a signal generator - but I would use a sinusoid for that purpose and not a rectangular. I don't know that Harke amp but keep in mind that instrument amplifiers might have non-linear response by design even with tone-controls off/set to neutral. Will have a look at the schematic to check this.
Regards
Charles
Had another look at it.
When the multiband EQ is switched off and the low/high tone control (don't know how it is called on the front-panel but I am talking of VR 104 and VR 105) is set to neutral - then the response should be quite flat. From the huge number of feedback caps used around all the opamps the rolloff at the upper end of the response will be quite steep.
The tube stage is in function all the time. The user can just make a mix to his likening by the use of VR 101 and VR 102. The tube stage doesn't have a neutral FR however (intentionally of course)due to the network after the cathode follower.
Regards
Charles
When the multiband EQ is switched off and the low/high tone control (don't know how it is called on the front-panel but I am talking of VR 104 and VR 105) is set to neutral - then the response should be quite flat. From the huge number of feedback caps used around all the opamps the rolloff at the upper end of the response will be quite steep.
The tube stage is in function all the time. The user can just make a mix to his likening by the use of VR 101 and VR 102. The tube stage doesn't have a neutral FR however (intentionally of course)due to the network after the cathode follower.
Regards
Charles
i'd start by replacing the tube with a brand new one......
yes you can check freq response that way, but sine waves are best for that. feed the sweep control voltage to the horizontal plates of the scope, and rectify the input signal going to the vertical plates, and remember that your o-scope display is linear, not log, so 3db is 1/2, 6db is 1/4, and 10db is 1/10 for signal change ratios. you could build a full wave op amp rectifier and log amp to get a log display on the o-scope, but the linear display method is easier. even easier than rectifying the signal is to set your zero line at the bottom of the screen.
yes you can check freq response that way, but sine waves are best for that. feed the sweep control voltage to the horizontal plates of the scope, and rectify the input signal going to the vertical plates, and remember that your o-scope display is linear, not log, so 3db is 1/2, 6db is 1/4, and 10db is 1/10 for signal change ratios. you could build a full wave op amp rectifier and log amp to get a log display on the o-scope, but the linear display method is easier. even easier than rectifying the signal is to set your zero line at the bottom of the screen.
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