As a newbie you will not see the pm option but if someone pm's you then you will receive it and be able to reply.
That's great news that you are also in the US! I'll send you a private message later today when I am back at my computer.
Hi Alaiowa,
As a newbie you will not see the pm option but if someone pm's you then you will receive it and be able to reply.
I sent a private message yesterday and wanted to be sure you saw it. No rush on responding. Private messages are found in the upper right corner. The icon looks like an envelope.
I checked and indeed the 851 and the 951 seem out of stock until early next year.
You could use BC550 and BC560 (note the pinouts are different to the 851/951) in the interim until you can get hold of the Zetex devices. If you go down this route, the MC noise will be about 10 dB worse - so once the 851/951 devices are available again, you will have to change them out to realise the full performance of the X-Altra MC/MM.
You could use BC550 and BC560 (note the pinouts are different to the 851/951) in the interim until you can get hold of the Zetex devices. If you go down this route, the MC noise will be about 10 dB worse - so once the 851/951 devices are available again, you will have to change them out to realise the full performance of the X-Altra MC/MM.
Would it interfere with the MM if I were to not use the alternatives you suggest and wait until the ZTX are available? Could I operate the preamp for MM only?
The MM amplifier stage operates completely independently of the MC stage. However, you must populate the power supply section of the MC since the MM front end PSU is derived from the MC power supply reference.
Note you cannot operate the MC input without the MM stage!
Good to know. The BC transistors have a sketchy availability. I was able to buy some from AlliedExpress, as recommended by hadihf, and I am crossing fingers for those to be shipped in January. Thank you for your help!
Hi, I had to use BC550/BC560 instead 851/951 until the original transistors are available again. After flashing U28 and U29, I measured completely same collector voltages of Q1-Q4 (+ /- 1.1 V) and all the other voltages mentioned in point 20 of the assembly instructions. What should I check in the auto zero circuit (I guess there is a problem there)? Thanks.
Those collector voltages are good given you are using BC5XX devices. The auto zero removes any DC offset voltage between the input signal hot and input signal ground.
Put your meter on the lowest range (usually 200 mV) and measure the DC voltage across each input right at the MC RCA input receptacle. You should measure 0 mV. If yes, your preamp is good to go.
The reason why I suggest you measure the offset before and after flashing U28 and U29 is that with them unflashed you will probably measure a DC offset of up to +-30 mV. If you then flash them and the offset goes to 0 mV you then know the servo is most likely working ok.
Put your meter on the lowest range (usually 200 mV) and measure the DC voltage across each input right at the MC RCA input receptacle. You should measure 0 mV. If yes, your preamp is good to go.
The reason why I suggest you measure the offset before and after flashing U28 and U29 is that with them unflashed you will probably measure a DC offset of up to +-30 mV. If you then flash them and the offset goes to 0 mV you then know the servo is most likely working ok.
Thanks. I could not get zero voltages at MC inputs but I measured zeroes at emitors of D1 to D4. Then I realized there are unused RFB1 and RFB2 jumpers that must be flashed to connect inputs with transistors. My bad 🫤
X-Altra MC/MM builder Marko from Slovenia has just advised me that he was able to get OPA2188/9 here
https://www.lcsc.com/product-detail/Precision-OpAmps_Texas-Instruments-OPA2188AIDR_C17271.html
https://www.lcsc.com/product-detail/Precision-OpAmps_Texas-Instruments-OPA2189IDR_C881489.html
Thanks Marko!
https://www.lcsc.com/product-detail/Precision-OpAmps_Texas-Instruments-OPA2188AIDR_C17271.html
https://www.lcsc.com/product-detail/Precision-OpAmps_Texas-Instruments-OPA2189IDR_C881489.html
Thanks Marko!
Finished mine today, and I am pretty proud! I had an issue with the left channel not giving any sound, and then retraced the path and reflowed wherever there seemed to be a missing connection. I used pretty rigid and thick wire for the power supply, so some shaping was required. I had some cat5 cable, but also, some hook up wire from a previous project, so I used some connecting headers, sot it remains practical.
It sounds great! Barely any ground hum (pot turned to max!).
Thank you everyone for the pictures, and especially Bonsai for this awesome device: I heard stuff I never did from my previous tube preamp!
All I am missing are the 851 and 951...
It sounds great! Barely any ground hum (pot turned to max!).
Thank you everyone for the pictures, and especially Bonsai for this awesome device: I heard stuff I never did from my previous tube preamp!
All I am missing are the 851 and 951...