My Take on X-BOSOZ

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#1,421
I was never able to get my X-BOSOZ to work properly had no problem with the power supply boards. But never had the gain out of the pre after changing parts over and over I gave up now I use one half of one power supply to power my B1 with out any problems.
 
#1,423
I hate that I didn't finish this. Does the attenuator go between the output of this pre and the input of the amp? The whole reason I went for this pre was because I thought it would be a good match for my Aleph-X. I built the Aleph-X with balanced inputs and wanted to see if using a proper preamp would make it sound as magical as everyone said it would. So far, I am disappointed in it. I have tried it with a Bryston pre and a Sony EP9ES DAC. Both have given me very satisfactory results from the other amps I built. I think the A-X is just a bit shy in the lower frequencies which may be due to my only running 14.75V rails. Anyway, I had hoped that using a balanced pre might make a difference so I bought the kit.

I can finish it pretty easily but will have to buy some more FET's. I seem to have misplaced one of the packs that came with the kit. I only have enough for one board. Twisted Pair matched them so I will have to order a few so I can try and match them as well.

I still have to figure out what to do for an attenuator.

Thanks, Terry
 
#1,424
Hey Terry, Welcome back. I haven't been doing much DIY lately but the answer to your where to put the attenuator is yes. If after the premp it will attenuate the preamp noise as well as the signal, but you need some form of balanced attenuator. If before the preamp you can use any single ended attenuator. Before will work fine if there's not much of a run to your source(s).
 
#1,427
I saw that on your website. This is what comes up.

Kits
Joshua Tree Single-Ended Complete Kit (Controller + Relay Driver Board + Relay Board + Parts) $145.00 USD Out of stock
Joshua Tree Balanced Complete Kit (Controller + Relay Driver Board + 2 Relay Boards + Parts) $205.00 USD Out of stock
Joshua Tree Single Relay Board Kit (1 Relay Board + Parts) $65.00 USD Out of stock
Boards
Joshua Tree Single-Ended PCB Set with Pre-Programmed PIC (Controller + Relay Driver Board + Relay Board) $45.00 USD
Joshua Tree Balanced PCB Set with Pre-Programmed PIC (Controller + Relay Driver Board + 2 Relay Boards) $60.00 USD
Joshua Tree Single Relay PCB (additional) $15.00 USD

So if I go that route, what would I need to order so I would have a balanced stereo preamp?

Thanks, Terry
 
#1,428
Hi Guys,

I'm not sure I will complete the Preamp. I haven't heard too many success stories about it and I don't want to invest that much in an attenuator. Besides, I was building it to drive my aleph-X because it has balanced inputs but I am so dissatisfied with the A-X that it will likely become something else in the near future.

However, I do have the power supply completed and would like to know if it can be used as a PS for a power amp and if so, how much voltage and current I might be able to use it for. Any suggestions would be greatly appreciated.

Blessings, Terry
 
#1,429
Depends on the transformer but likely it will be better used in another preamp project. Voltage too high in proportion to current capability. Maybe a headphone amp.

The best place for the attenuator is after the balanced preamp but you can put it ahead of the preamp. Any decent pot will do.

If you never fed your AX a balanced signal you haven't taken advantage of supersymmetry. You may like it more when properly fed. 😉
 
#1,430
I suppose I should at least finish it to see if it was worth the money I spent. Could you give me examples of decent pots to use for this so at least I can try it? Mouser part numbers would be a big help.

That Aleph-X has been my biggest disappointment in DIY. I wish I could get it right. I do have some decent mixing consoles that are balanced. I suppose I could try one of those to see if it makes a difference.

Thanks, Terry
 
#1,431
OK, I finished mounting everything. I bolted the outputs to heatsinks. I seem to have one side working and one side not. On the working side I am seeing about 90mA between the PS and the +V on the pre. With a 1.4Vac sine wave on the input I am seeing 1.2Vac on the output. The voltages aren't perfect from side to side but maybe close enough. The PS puts out +78.2, -21.7 with no load. Connected to the working board it is drawn down to +71.6, -18.5

The non-working side hardly drops at all. I am supposing something is not turning on but I don't know. I am attaching the voltages on for each board in hopes someone can look them over and give me an idea where to look.

Thanks, Terry
 

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#1,432
On the dead side, QX, the current source bottom center is not turning on.

Are your supplies regulated?

On the working side double check the values of the input and feedback resistors. R14, 15, 18, 19. and the input load resistors, R16 and R17. Are you feeding it a balanced signal or is the unused input grounded?

Slight mismatching of Q4 and Q5 on the good side is causing the drain voltage differential, but it's not a big deal since you are capacatively coupled.
 
#1,433
BobEllis said:
On the dead side, QX, the current source bottom center is not turning on.

Are your supplies regulated?

On the working side double check the values of the input and feedback resistors. R14, 15, 18, 19. and the input load resistors, R16 and R17. Are you feeding it a balanced signal or is the unused input grounded?

Slight mismatching of Q4 and Q5 on the good side is causing the drain voltage differential, but it's not a big deal since you are capacatively coupled.
Click to expand...

Thanks Bob,

What causes QX to turn on? The device seems to measure OK with a ohm meter.
I am using the power supplies that came with the kit.
http://www.diyaudio.com/forums/pass-labs/67448-my-take-x-bosoz-4.html#post765913

I don't think I had both inputs shorted. That may be the reason.

Thanks, Terry
 
#1,435
Hi Bob,

Looks Like D1 is open. I can't get a reading in either direction with my ohm meter. The closest I had was a 9.1V zener so I tried that in there. It does turn QX on but R1,2,6 &7 get really hot. Of course I am all out of 1N5235's so I guess I had better order some.

That brings up another issue. while disconnecting things, I guess there was some juice left in the caps on one of my power supplies and the + lead touched the ground and took out the IRF610, smoked a few 1N4004'S and one of the 33v zeners. I had the IRF610 and plenty 1N4004's but I don't have any 33V zeners. Can I use two 27V and one 12V to replace the two 33V zeners?

Thanks again, Terry
 
#1,436
With a 9.1V zener in there you're running around 189 mA instead of the 75 design point, so no wonder the load resistors got hot! If you change R8 to 68R 1/2W or more you'll be back in the 75 mA ballpark with a 9.1V zener. To give you more parts bin options.

To figure current, assume Vgs is 4V. Since R2 is connected to the Source and the rail you can see that there must be 5.1V across it. Then it's just Ohms law to set or find the current.

You can string together a number of whatever zeners you have handy to reach the correct voltage without worry. You can even string together 7 x 9.1V and get close. The rails would be slightly lower if you do that. The actual rail voltage is not critical.
 
#1,439
This is nuts, I just smoked another part. I'm burning stuff up over ten cent parts. I'm going to set this thing aside and order all new parts for the PSU and that section of the pre boards. I don't want to end up messing up the PCB from changing parts over and over.

Thanks so much for your help Bob. Hopefully the next time you here from me on this subject I will be reporting on how good it sounds.

Now where are those B1 Mesmerize boards I got the other day? 😀
 
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