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Zonzi
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Last Activity: 02-04-2024, 02:31 PM
Joined: 01-30-2023
Location: Strasbourg
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts



    I don't know if it's center tapped, but I would assume it is, since it has a GND wire.

    This idea sounds really intriguing, does it only involve rewiring the diodes ? I was assuming that my mixer already had a full wave rectifier, given the four diodes and the two smoothing caps ?

    Edit : by the way, I tested my mains voltage, and I'm at almost spot-on 230V RMS. So at least one thing appears to be normal in my setup ...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Really interesting thanks ! So what you suggest is that maybe the right transformer was used, but at the time maybe the mains voltage was 220 whereas it's now 230-240V, which would in turn increase the secondary voltage.

    I will try to get a reading of my mains voltage in order to have a better idea of what I'm having to live with.

    Now I hope the article doesn't imply you have to build your own bucking transformer, because I don't really have any tools in that regard
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    I see, thanks. Yeah I guess now it would be unoperable with 120V because it gives me a reasonable 15-20V voltage with 220V primary. I could be wrong, but since the power cord was replaced to EU plig, the transformer would have been replaced as well, otherwise it'd all have burnt up isn't it ?

    The voltage delivered by the power stage is indeed very stable (perhaps noisy or ripple-y but I don't have a scope) so I'm still convinced a better-suited transformer would be best.
    That said,...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    I think I see what you mean, that's in cases like when you have a manually switchable button for voltage adaptation, isn't it ? We have an old Akai AP001C at home that has something like this.

    In my case it seems like it's not the same thing, because there's no switch that I can see. My best guess is that the previous owner replaced the power cord and the transformer with the closest he was able to find, which delivers a bit too much. But I might be wrong of course, and I' m inclined to...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    You're right that's indeed a fuse on the right. Does than change anything ? I just realized... I can know the max. current draw just by looking at it. Sorry about this folks lol. It says T50mA 250V so guess it's a 50mA fuse.



    That's good to know. I also noted the fact that the tab is not gnd, thanks.

    What are the caps for in this scenario ? To block DC from one leg to the other ? Or is there some other trick I don't know about ?


    Thanks for...
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    Last edited by Zonzi; 06-05-2023, 02:48 PM.

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  • Zonzi
    replied to Telefunken L70 speakers, one has a nasal sound with less bass
    in Troubleshooting Audio Equipment
    Re: Telefunken L70 speakers, one has a nasal sound with less bass

    If nobody has an idea then perhaps my question is stupid ! As a matter of fact I don't know a ton about this.

    So perhaps another direction will encourage some answers :
    What if I was to replace the woofer with one that has the same Thiele-Small parameters, or close to it ? Then, if my understanding is correct, the acoustics of the enclosure would react in the same way as with the original woofer, right ?
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts



    Oh God I sure hope they're not, there are like 120 of these exact ones on the board lol...


    But anyway thanks everyone for your input, this is all really interesting. I'm leaning towards buying individual regulators with an added heatsink, so that I can just add it to my power board without switching it out. Plus I can get them at my local shop, which is the last one around here.

    Just to be clear, that would go after the main filter caps, one to...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Actually I don't ! I don't have a controllable psu but I can maybe do a current reading in series with one of the caps or something. Problem is I don't really know where would be a sensible place to check, and if I have to be playing music through the unit at the same time ?

    If I were to add regulators, how would that go ? In series with the bridge rectifier ?
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    It's exactly that. No regulator that I can see. The pic is from before I switched the filtering caps that were corroded, but the new ones are basically the same....
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Hi eccerr0r, sorry for the late answer, I moved to another place in the meantime. Would a good solution be finding a more adapted transformer ? Or maybe trying to add a homemade voltage divider to the power rails ? I'm alright with these, it's just that finding just the type of transformer I'm looking for, has proved rather difficult in past times ! If you know foolproof ways to find some, I'm willing to give it another try
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  • Zonzi
    started a topic Telefunken L70 speakers, one has a nasal sound with less bass
    in Troubleshooting Audio Equipment

    Telefunken L70 speakers, one has a nasal sound with less bass

    Hi everyone !


    Once again I have an issue with old stuff I found for cheap, guess I have a taste for these.


    I bought these two Telefunken L70 speakers for 20€ ([url]https://www.radiomuseum.org/r/telefunken_hi_fi_lautsprecher_box_l_2.html[/url]), and they are in a superb state, component-wise. The box is scratched but I couldn't care less, I'm interested by whether it works or not.

    They do work, and have a really nice sound, but one of the two has a problem with its 8" woofer. It's got practically no bass, and the mids are really...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Welp, as a conclusion for now, I've switched all the resistors going to and coming from the 1458 opamp and it now works. Only the first two channels crap out when going past noon, sound disappears, but that'll be a subject for another post. All the others work well, reverb is nice and dark and I like it a lot overall.

    Thank you to those who shared a bit of their knowledge with me ! I'll mark this solved as the primary issue is fixed.

    EDIT :I can't find how to mark as solved...
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    Last edited by Zonzi; 04-18-2023, 02:48 AM.

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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Hi everyone, it's been a while but I've finally taken the time to measure the transformer output.

    So I'm happy to tell you it HAD BEEN switched-out to adapt to european power : when plugged on 240V it reads 20V to ground, 40V positive to negative. It's not ideal since it should have been 15V to ground, or 30V positive to negative, as specified on the opamps, but at least I haven't been running it at twice the recommended voltage. That's good to know.


    The last question...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Sorry for posting several times in a row, but I've found some disturbing stuff on the board, that makes me question if the job was done properly by the previous owner.

    Around the power supply and the first IC (1458) there are resistors that don't match at all the ones marked on the board.


    The power supply is supposed to have two 100Ω resistors, one for each polarity, but the ones in place are 47Ω.

    Around the 1458 chip, ALL resistors have...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Hi everyone, sorry about the delay, I was busy these last few days.

    So, I got under the board and tested the pots in circuit. They read approx. their value, which is indicated to be 125k. They seem to work as intended, no broken track, otherwise they'd read open circuit after a certain point, right ?

    Also I don't seem to be able to find any info on these... They're 125k pots, and that appears to be a non-standard value, given that I can only find some on ebay for like...
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    Last edited by Zonzi; 02-28-2023, 09:26 AM.

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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts



    I did not, after replacing the 1458 I tried the 4136 that's on the output stage, then the ones on the input stage, and the problem kept coming back. Then I also changed the ones on the unused channels and it ran for an hour with no problem, before I shut it off and went to bed. But some of the old opamps read some weird stuff, two of them have non-matching readings across the pins.

    I keep them all in a distinct bag in order to test them when I get an oscilloscope, or...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Alright guys I have some news ! I've dropped in all the replacement op amps after trying them one by one. I'm happy to say the unit now works !

    BUT, because nothing is ever that simple

    First of all, channels 1 and 2 only work for half the course of the level pot, when going above noon they suddenly stop and no audio is to be heard. I wonder if the pots are damaged or if something else is to check ?

    Second, I have tested all the old opamps compared to...
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    These are all good suggestions, thanks for that. I reckon 1MHz is plenty for audio work but we'll see after my next paycheck yeah
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Oh wow thanks that's good to know. I'll look that up !
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  • Zonzi
    replied to Neptune mixer model 611 - Works for a few minutes then fades out and distorts
    in Troubleshooting Audio Equipment
    Re: Neptune mixer model 611 - Works for a few minutes then fades out and distorts

    Alright we're getting somewhere ! I ordered replacements for all op amps as well as the smoothing caps and the wrong value cap. I'll let you know when they're swapped in.

    I know an oscilloscope would be great but that's a bit beyond my financial means for the purpose I have for it. Maybe if I started making money for my audio repairs ! But right now i'd have a hard time justifying the cost.

    In the meantime if you have any other idea feel free to drop it here !
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