Looking for help. I have built the Elekit Tu-8500 preamp. The phono stage is not functioning. The Vcc and Vee which are supposed to measure +and-12 V are measuring .06 V and -3.6 V. And the phono input is not working, I opened it up twice and fixed solder joints. I’m not sure where to go from here. Any help would be be appreciated.
thanks,
Jeff
thanks,
Jeff
The +/- 12 volt supplies come from regulators IC5 and IC6 respectively. What are the input voltages measured from ground at the regulators (IC5 pin 1 for + and IC6 pin 2 for (-)? The regulator inputs should be around 20Vdc, + for IC5 and - for IC6.
You should have ~14Vac across the two ~ inputs for both diode bridges D1 and D2; what do you measure?
If I were to guess, I'd say a short circuit between IC5 pin 1 and ground (e.g. solder bridge across pins 1 and 2) or pin 3 and ground (e.g. a solder bridge across pins 2 and 3).
You should have ~14Vac across the two ~ inputs for both diode bridges D1 and D2; what do you measure?
If I were to guess, I'd say a short circuit between IC5 pin 1 and ground (e.g. solder bridge across pins 1 and 2) or pin 3 and ground (e.g. a solder bridge across pins 2 and 3).
I’m still getting -3.5 vee to ground and -1 vcc to ground. I checked for solder bridges as above and even tried reflowing any potential suspect solder joints in that section. I’m at a loss as of now. Anymore help would be appreciated. I am fairly new to this, though I have built a half a dozen other projects that worked out fine. Still my trouble shooting skills are still limited. Thanks again
Found my issue. I swapped the two ICs in the phono section. They look and are labeled similar. I got them out and switched them, but I must have damaged one of them. The -12 is reading correct but the +12 is reading -7. I ordered a new part. Hopefully nothing else was damaged as I tried to remove those parts
Oops - easy mistake to make. There's a possibility that's damaged bridge D2. Make sure that C27 and is the correct way around and then with IC5 removed measure the voltage across C27 - you should have ~+20v from the (+) side to ground.
DiyAudio member vkung who sells these can be contacted here.
He will be happy to help and give you replacement parts.
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Forgive my ignorance, but I’m just getting into this trouble shooting. When you say measure the voltage what should my connection to ground be for that measurement. I have a meter, but some of the terminology and methods of measuring are outside my experience so far.
Again, thanks so much for the help John
The ground track is the (-) side of C27. You can also measure across the bridge D2 between the terminals marked (+) and (-) are these are connected to the (+) and (-) of C27 which is across the input to the regulator that was damaged.
Perhaps this should be a new thread - if so, apologies for the confusion. I've completed my 8500, complete with all of Victor's upgrade parts. I'm very satisfied with how things are going so far - but a quick question: I don't have a phono output with which to test the phono inputs. (This is a gift for our son who wants to see how it might do with his turntable.) Is there any reasonably straightforward and safe way to substitute for a phonograph to check the phono input and the switch between MC / MM cartridges?
"Reverse RIAA"
Or: connect preamp out to a CD Input. Turn system Volume down. Connect RCA cords to the preamp input. Put your finger on the RCA tips. Sneak Volume up a teeny bit. If you get a HUGE HUM, then it works. Switch to MC mode. The hum gets huger.
thanks! I don't have a CD input per se - but did get hums from the amp (an 8200) when following these steps. I also need to replace a buggered switch (SW3) in order to get the 3x gain to kick in. Guessing that everything is in order?
Another issue. I've replace the switch (SW3) - but in the process, also had to remove two of the capacitors at C15 and C16: these were the very large Mundorf Supreme Golds that I had ordered as part of an upgrade kit from Victor. After putting them back in, I checked their values - and they are wildly off from the 470mf rating. It's hard to get stable reading at either the soldered points or "topside" from the capacitor leads themselves - but they hover around 41mf and 50mf. (By comparison, the Mundorfs at C11 and C12 register 468 and 469mf at the soldering points, FWIW).So the caps at C15 and C16 seem to be hopelessly buggered.
I have possible replacements - Mundorf MCap Supreme aluminum, which are slightly less expensive than the Mundorf Supreme Gold. If I use these to replace the buggered caps - is it also advisable to remove the other pair of Golds and replace them with the aluminum ones as well? Many thanks in advance for your advice!
I have possible replacements - Mundorf MCap Supreme aluminum, which are slightly less expensive than the Mundorf Supreme Gold. If I use these to replace the buggered caps - is it also advisable to remove the other pair of Golds and replace them with the aluminum ones as well? Many thanks in advance for your advice!
I think you mean 0.47 microfarads, which is the same as 470 nanofarads. You likely won't get an accurate reading of the caps when they are connected to other components. It would be very difficult, if not impossible, to ruin these caps with the voltages in this preamp.
S.
S.
Thanks very much - apologies for the inaccuracy. But I'm wondering if the caps were damaged not by voltage but by the process of desoldering and re-soldering: I would be very surprised - but at the same time, the other caps read what they should read. Unless I get additional advice over the next day or so - I suppose I can just put it back together and see if it works as is. Again, many thanks!
Update. The pre-amp seems to be working properly in every way I can directly test (not the phono input). FWIW: the voltages check out as follows. VCC (+12v): 12.15v. VEC (-12v): -11,87v. (140v): 134v. H- H+ (12v): 12.21. I'm guessing this is within acceptable margins of error? Thanks for all the good suggestions and guidance.
Our son has an Audio-Technica LP120-USB turntable with switchable preamp that then goes via Sonos Connect to an Onkyo TX-8050 receiver/amplifier. We're wondering if using the tu-8500 in place of the preamp installed with the turntable will make any significant difference to the resulting sound - especially since the Onkyo is not a power amplifier as such? The Onkyo has a "Direct mode" and a "Pure mode" that bypasses the tone controls - but this is apparently not the same as having a direct amp input. My primary audio guru here says that it would be like taking water (the signal from the cartridge) into one filter - the TU-8500 - and then passing it into a second filter. There's no guarantee that the resulting "taste" will be any worse/better/neutral than with the current inbuilt switchable preamp. I'm pretty sure he's right - but double-checking with the wisdom of this thread. Thanks in advance -