Hello guys!
This is my very first post here on DIYA! I have a Grundig SV-2000 amp from 1982, which I saved from the trash and been using for a couple years now. I simply go from my PC-s output 3.5 jack to either the MONITOR input or the TAPE1 / TAPE2 input. I have two major problems with the amp:
(1) If the signal coming from my PC is not powerful enough (quieter parts in music/volume is not maxed out on my PC), one (or sometimes both) channel(s) start(s) to fade. This means that only the low frequencies are audible, and they are distorted too. If the signal level increases, the fading goes away, and sounds normal again. Also if I unplug and replug the jack (which gives an impact signal to the amp) this phenomenon goes away for a while, but comes back later on random. This is occurring more often lately. Therefore I assume this is because of some kind of aging problem (elect. caps?).
I am just an amateur, but I figure, that the problem is either the preamp section (or on the controls board before volume pot), because if I do the unplug-replug trick with the amp at volume 0, it makes the fading go away the same way.
So my tips: either old elect. caps, or faulty transistors. at the preamp section
(2) Using the amp with headphone, I can hear the 50Hz constantly as a background. Louder music is "OK", but during quiter parts it is audible. Doesn't matter, which input I choose, or what is the volume level. It is more apparent on the right channel. And exactly the wire of the right channel is directed from the output stage to the output board very near to the transformer. There is an other long wire directing left and right from the output board to the headphone jack. Neither of these two cables are shielded.
Am I right, that by shielding these cables the hum would go away?
AND FINALLY the more interesting topic:
I decided to give this little guy a thorough restoration. I would like to do a quality work with decent parts, but I don’t want to go crazy by hunting for “magical parts”. I already disassembled and cleaned the whole stuff.
(1) As far as I know, it is a good idea to replace all old elect. caps. Is there anything I need to pay attention on besides the correct values and polarities? If I stick to certain brands, does that give me any advantage over the parts I could by at a local shop? If yes, which brands/sources/types would be recommended?
(2) I have some filmcaps and ceramic caps on board too. Should I replace any of these? If yes, what brand, type? At the and there are few shots of the parts from the boards.
(3) Should I replace the puffer caps (currently 2x6800uF / output stage) to bigger ones? If yes, what value is recommended? Brand, type?
(4) Should I replace any of the elect. or ceramic caps to film caps? If yes, which ones, to what type and brand?
(5) Should I replace the darlingtons? They are the same type (GP140 & GP145) on both output stages, but one of them is printed Italy on it, the other one is Motorola. They both seem to be factory installed.
(+1) Do you have any advice on further tasks?
I know that my questions are amateur, but I assume professional eyes could promote my project a lot. Here are the schematics. The red comments are the differences I found between the board and the schematics.
Dropbox - Grundig SV-2000 Service Anleitung.pdf
And some photos:
Dropbox - preamp monitor.jpg
Dropbox - preamp general.jpg
Dropbox - output stage.jpg
Dropbox - control board1.jpg
https://www.dropbox.com/s/gag1gglqfz0jrr7/control board2.jpg?dl=0
https://www.dropbox.com/s/qk5fqivppj5p047/linear button.jpg?dl=0
PS: Unfortunately I don’t have any signal generators (besides my PC) or scopes, therefore the stuff I can do is limited.
I appreciate greatly if you would share your opinion! Thank you all!
This is my very first post here on DIYA! I have a Grundig SV-2000 amp from 1982, which I saved from the trash and been using for a couple years now. I simply go from my PC-s output 3.5 jack to either the MONITOR input or the TAPE1 / TAPE2 input. I have two major problems with the amp:
(1) If the signal coming from my PC is not powerful enough (quieter parts in music/volume is not maxed out on my PC), one (or sometimes both) channel(s) start(s) to fade. This means that only the low frequencies are audible, and they are distorted too. If the signal level increases, the fading goes away, and sounds normal again. Also if I unplug and replug the jack (which gives an impact signal to the amp) this phenomenon goes away for a while, but comes back later on random. This is occurring more often lately. Therefore I assume this is because of some kind of aging problem (elect. caps?).
I am just an amateur, but I figure, that the problem is either the preamp section (or on the controls board before volume pot), because if I do the unplug-replug trick with the amp at volume 0, it makes the fading go away the same way.
So my tips: either old elect. caps, or faulty transistors. at the preamp section
(2) Using the amp with headphone, I can hear the 50Hz constantly as a background. Louder music is "OK", but during quiter parts it is audible. Doesn't matter, which input I choose, or what is the volume level. It is more apparent on the right channel. And exactly the wire of the right channel is directed from the output stage to the output board very near to the transformer. There is an other long wire directing left and right from the output board to the headphone jack. Neither of these two cables are shielded.
Am I right, that by shielding these cables the hum would go away?
AND FINALLY the more interesting topic:
I decided to give this little guy a thorough restoration. I would like to do a quality work with decent parts, but I don’t want to go crazy by hunting for “magical parts”. I already disassembled and cleaned the whole stuff.
(1) As far as I know, it is a good idea to replace all old elect. caps. Is there anything I need to pay attention on besides the correct values and polarities? If I stick to certain brands, does that give me any advantage over the parts I could by at a local shop? If yes, which brands/sources/types would be recommended?
(2) I have some filmcaps and ceramic caps on board too. Should I replace any of these? If yes, what brand, type? At the and there are few shots of the parts from the boards.
(3) Should I replace the puffer caps (currently 2x6800uF / output stage) to bigger ones? If yes, what value is recommended? Brand, type?
(4) Should I replace any of the elect. or ceramic caps to film caps? If yes, which ones, to what type and brand?
(5) Should I replace the darlingtons? They are the same type (GP140 & GP145) on both output stages, but one of them is printed Italy on it, the other one is Motorola. They both seem to be factory installed.
(+1) Do you have any advice on further tasks?
I know that my questions are amateur, but I assume professional eyes could promote my project a lot. Here are the schematics. The red comments are the differences I found between the board and the schematics.
Dropbox - Grundig SV-2000 Service Anleitung.pdf
And some photos:
Dropbox - preamp monitor.jpg
Dropbox - preamp general.jpg
Dropbox - output stage.jpg
Dropbox - control board1.jpg
https://www.dropbox.com/s/gag1gglqfz0jrr7/control board2.jpg?dl=0
https://www.dropbox.com/s/qk5fqivppj5p047/linear button.jpg?dl=0
PS: Unfortunately I don’t have any signal generators (besides my PC) or scopes, therefore the stuff I can do is limited.
I appreciate greatly if you would share your opinion! Thank you all!
At that age probably some electrolytics have dried out, i.e. lost capacitance. That is normal. I agree that 50Hz hum cannot originate from weak power supply filter caps - but as the TO is not an expert he might have mistaken 100Hz hum for 50Hz hum. So it would be better to check these caps as well.
concerning the replacement caps: Electrolytics in that era where not stressed by high-frequency ripple. The ones you have to replace were not better than 85C el-cheapos nowadays are. There is no need for boutique parts. Which is a more of a general rule...
concerning the replacement caps: Electrolytics in that era where not stressed by high-frequency ripple. The ones you have to replace were not better than 85C el-cheapos nowadays are. There is no need for boutique parts. Which is a more of a general rule...
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What a nice little amplifier, both by it's look and by it's electrical design! The pros are it's all discrete layout, the active Baxandall EQ and it's ample guts, the only cons are the Darlington power devices, which were state of the art in those days, btw.
With the SM in front of you, check all voltages. There might be some aberration in the PSU circuitry, then replace the related electrolytic(s). This may cure the hum. No need to additionally shield wires. Remember that the unit once has been working faultlessly in it's present state.
There's also no need to replace any semiconductor just by suspicion, unless they are faulty proven by measurements. Remember the ones with »G« at their designation's beginning are proprietarily made for Grundig, but in most instances could be replaced by stock ones (MPS-A05, TIP140, TIP145, e.g.).
Best regards!
With the SM in front of you, check all voltages. There might be some aberration in the PSU circuitry, then replace the related electrolytic(s). This may cure the hum. No need to additionally shield wires. Remember that the unit once has been working faultlessly in it's present state.
There's also no need to replace any semiconductor just by suspicion, unless they are faulty proven by measurements. Remember the ones with »G« at their designation's beginning are proprietarily made for Grundig, but in most instances could be replaced by stock ones (MPS-A05, TIP140, TIP145, e.g.).
Best regards!
Thank you all for helping me out there. I really appreciate your founded opinions. I've just bought all the replacement capacitors. They are from Jamicon. Hopfully they will do a good job. I also bought two 2.2uF WIMA polypropilene caps to try theM out as input caps. Originally they are 2.2uF elkos.
I will report back with the results and experiences.
I will report back with the results and experiences.
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