• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

A Heretical Unity Gain Line Stage part III

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#87
dsavitsk you were right, excellent email service. I already got a reply. Indeed the Cinemag transformer is less expensive than the Jensen at only US$45 each, compare to the Jensen at 79$.

The CMLI-15/15Cs in stock at this time. However, the CMLI-15/15B is. At this price, I'll probably order a pair in a few days.

Here is my own version of the Line stage schematic based on what I read and understood. The HV relay timer is just a suggestion. I need to build a prototype and see what kind of timing I can actually get using the suggested parts. I included most of the suggestions and remarks found into the DIY Magazine article in the schematic.

Any comments to improve it are welcome 😉
 

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#91
Thanks SY, but the beautiful work, it is you that did it first 😎
I just put it into a slightly different form. I like to have detailled schematic and parts list before getting into a project.

Your article on the preamp was a pleasure to read. The design discussion was very informative and the desing is well thought and elegant. Thanks for sharing it with us. I may have some PCB design to share within the next 1-2 weeks as well.

And by the way, thanks also for the latest mod. I already included R9-R10 change to led into my schematic.
 
#92
One quick observation- on the parts list, you have the LEDs as "high efficiency." Those will work assuming Vf reasonably close to 1.7V for the red, but plain old surplus cheapies will often be even better. The best I've found so far (thanks, daanv!) is the HLMP-6000.
 
#95
Algar-emi (or anyone else) - by any chance would you be thinking of getting some PCBs made for this? If you are, I would love to be in on it!

I know it can be done P2P, but as broskie says the chances of actually doing it are much higher when a PCB is used compared to P2P.

Fran
 
#96
Algar, I would have done this myself, but I can't edit pdfs. The RC coupling is preferably 0u01/10M, not 0u1/1M. The former has two advantages- first, my totally-unproved-but-I-believe-it preference for using the smallest practical coupling cap; second, 20dB greater rejection of any servo noise or distortion.

I'd go in on a few boards myself.
 
#98
I was not planning to go with commercial PCB, just to make my own set. To do so, I would need at least 30 kits and I don't want to get into an other group buy right away.

I can certainly make some for you SY, to thank you.

For the others guys, well, it will depend. They are made by hand, take time to make, to drill and the bare pre-sensitized boards are expensive.
I let you know the price and you may decide to get a set.

Take note that I'll probably just do just one run of these PCB's. So decide in advance and express your interest.

Thanks SY for the comments, I miss these values. Here the corrected preamp schematic and parts list, version 1.2
 

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#100
Algar-emi - I know diddly squat about making PCBs but I know of a few other fellas who have gone to a company called Olimex in Bulgaria. Results are good and prices reasonable. They allow different boards on one sheet.

olimex

Don't worry about parts etc etc etc. Just teh boards would be enough - everyone can go buy their own parts in mouser or where ever.


I also well understand the amount of work this would be. I don't think it would be unreasonable to think that you should have a few quid left over at the end!

Fran
 
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