I have a diode meter on my test meter , do I have to remove the diode to test it?
Film caps to replace 2.2 uF electrolytics
Bending the leads would be ok.
WIMA MKS2 & EVOX RIFA MMK5 metallized polyester caps are available with 5mm lead spacing so they would probably fit in most spots in the amp.
The main question I guess is it worth replacing the electrolytics with these types of caps? Would it improve the sound? Most of the 2.2uF caps appear to be in the signal path!
Bending the leads would be ok.
WIMA MKS2 & EVOX RIFA MMK5 metallized polyester caps are available with 5mm lead spacing so they would probably fit in most spots in the amp.
The main question I guess is it worth replacing the electrolytics with these types of caps? Would it improve the sound? Most of the 2.2uF caps appear to be in the signal path!
Set it after a half hour of playing music. It will drift a little and seems to be fine with the range of offset your getting and that you can set it to almost zero and it slowly drifts - unless you have a DC servo in the design ( you don't) it will be have as you are measuring now and is fine.
If replacing a cap in the signal path, you want POLY-PRO, not POLYESTER.
Checking diodes: If you half to ask if the amp needs to be switched off, please put the cover back on it. Go find someone local who can introduce you to basic electronics including the kind of safety procedures so you don't kill yourself. A couple of local trade school classes is about all one needs to get going. Serious, what looks like a fun hobby really is, but not so fun when you get fried, fry your test equipment, fry your amp... I am not being condescending , please. It can be serious. These things may sound simple, and for some of us they are. But my father taught me the basics when I was a kid. Years in the AV club, a degree in electronics, 15 years in a lab and a hobby for 40 years. I am by no means an expert; just reasonably skilled enough to blame myself when I screw up.
Checking diodes: If you half to ask if the amp needs to be switched off, please put the cover back on it. Go find someone local who can introduce you to basic electronics including the kind of safety procedures so you don't kill yourself. A couple of local trade school classes is about all one needs to get going. Serious, what looks like a fun hobby really is, but not so fun when you get fried, fry your test equipment, fry your amp... I am not being condescending , please. It can be serious. These things may sound simple, and for some of us they are. But my father taught me the basics when I was a kid. Years in the AV club, a degree in electronics, 15 years in a lab and a hobby for 40 years. I am by no means an expert; just reasonably skilled enough to blame myself when I screw up.
I wish I had time for it all TVR but ive got way too much on my plate at the moment, all my time (and money) is being taken up by a cottage restoration.
All I wanted to do was to breath new life into an old amp as buying a new one is the same cost as half a window, some of a limecrete floor, 300 pamments etc so I figured a few afternoons working on the amp would save some cash.
I totally understand the safety aspect of this which is why I am not jumping into it without first doing my homework.
I think paying someone to do this work would cost more than a new amp, TenAudio quoted 250 quid to do the work.
All I wanted to do was to breath new life into an old amp as buying a new one is the same cost as half a window, some of a limecrete floor, 300 pamments etc so I figured a few afternoons working on the amp would save some cash.
I totally understand the safety aspect of this which is why I am not jumping into it without first doing my homework.
I think paying someone to do this work would cost more than a new amp, TenAudio quoted 250 quid to do the work.
OK, basics 101.
You never even open one without it being unpluged.
A diode is like a one way switch, so long as you "push hard enough". In other words, the diode range has enough "push" which translated to above .7 volts, to conduct one way and not the other. So, on the diode range probe across the diode one way, than the other. You will find it beeps one way and not the other. If you have a bad diode, it will not beep. Now, the circuit can play games with you. With out a schematic, you don't know. Usually the bridge does not have this problem so it is easy to test. In the picture, I thought I saw 4000 series diodes. They are only one amp, so I would be surprised if they were the bridge for the power amp section.
Another test you can do, but this time with the amp powered up. Check the amount of AC voltage on each rail to ground. They should be the same. Check the DC reading. Again, they should be very close.
Provided that checks out, change the main filter caps. The big ones.
You do not need to change anything that is not an electrolytic. Film, ceramic, or mica do not dry out from age. Elna seems to be the preferred brand these days. I have used a lot of Panasonic. I really doubt there is a audible difference in a consumer power amp. Head amp, or ultra high end where everything else is 10 times as perfect, yea, they do make a difference.
Repair, refresh or mod ( changing a cap technology is a mod) without a schematic is for the very experienced. Start slow and don't get carried away or you will have to save up for that last window. That reminds me, I never did the last one on my house.
Still a bit fuzzy here , what does a DC bus look like? The only thing I can think of is a busbar in a consumer unit but there is nothing like that in my amp.
Yes, the main positive and negative DC power supplies points. Not having a schematic, it is hard to point where to measure. I don't know if your fuses are before or after the main caps. Can you get to the bottom of the circuit board where the caps are soldered in? One side of each cap is ground, the other is power.
A power supply rail or voltage rail refers to a single voltage provided by a power supply unit (PSU).Term is generally used in electronic engineering.
Robgilmo: DIYAudio members are usually very helpful and eager to teach. BUT: You have stated that you're trying to save money, and don't have the time to learn even the basics of basics here (never mind SAFETY).
PLEASE purchase a schematic for this amp, and post it here so at least these guys can TRY to save your life -- and perhaps teach you something in the process!
Thanks guys , it's making sense now. I would have to strip the amp down to get under the board.
I shall change the caps first before jumping in any deeper, this stuff is way above my capabilities. Changing the caps and other components I can do quite easily but testing components will require a lot more homework.
Where can I buy a schematic for this amp? There is very little about it on the net. I have found out that it was designed 'in house' by Wharfedale so I guess that the best place to start is with Wharfedale them selves.
I did have one of these amps many years ago with a blown power amp and I can remember trying to get the schematic before with no joy. I managed to get the thing going again by finding a suitable replacement (one of the four 'transistors?' bolted to the big heat sink) so I didnt delve in too deeply, that amp worked fine for a few years before I sold it and bought a marantz.
I shall change the caps first before jumping in any deeper, this stuff is way above my capabilities. Changing the caps and other components I can do quite easily but testing components will require a lot more homework.
Where can I buy a schematic for this amp? There is very little about it on the net. I have found out that it was designed 'in house' by Wharfedale so I guess that the best place to start is with Wharfedale them selves.
I did have one of these amps many years ago with a blown power amp and I can remember trying to get the schematic before with no joy. I managed to get the thing going again by finding a suitable replacement (one of the four 'transistors?' bolted to the big heat sink) so I didnt delve in too deeply, that amp worked fine for a few years before I sold it and bought a marantz.
I askeds Tenaudio for some more detailed info and got this back.
Any thoughts? I know they have done a few of these amps in the past.
I shall be ordering the bits before the week end so would like to get it all nailed down first.
I know this guys DAC's are very popular, what do you guys think? Most of the above to me is above my head apart from the power supply compensation caps although I dont know if changing the value is a good idea and the two brown caps , again upping the uF from 100 to 1000.bias can be set in this amp on 10mV without any problem, this gives warmer sounding at low volumes
brown caps - replacing with Elna Cerafine 220uF/6.3-10V is a v.good solution - you have to measure on existing ones to get the polarity - caps voltage rating is not an issue there - just above 2V if I remember
you can also replace it with a good bipolar electrolytic and add a MKP bypass of 220nf
CRC power supply sounds fine - values 10000uF+0.22R(5-10W)+10000uF - also you may want to bypass the bulk caps with PIO 1uF/160V - and to change bridge rectifier for 10A/1000V
Good thing is to replace a local power supply compensation caps (the 100uf/63V or 220uF/63 - don`t remember)with 1000uF/63V (low ESR would be nice)- better , drier deeper bass
Replacing differential input stage with a valve one is doing miracles to this amp
No schematic (never was published, amp circuit was designed at Quad Acoustics), but it is a very simple design
Any thoughts? I know they have done a few of these amps in the past.
I shall be ordering the bits before the week end so would like to get it all nailed down first.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.