SX-Amp and NX-Amp

www.hifisonix.com
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Sorry - I just looked at the schema to remind myself that Q9 and Q11 are the level shifter transistors - I mistakenly assumed you were talking about the drivers.

You can do what you propose, but I have to ask why? The PCB is for BC556 types.

The question about 4.7k and 10k: follow the PCB - it is correct.

I will do an update to the article as soon as a few have been built. I want to catch all the issues the builders find.

Looking forward to hearing your thoughts on the sound!
 

fab

Member
Joined 2004
Paid Member
Sorry - I just looked at the schema to remind myself that Q9 and Q11 are the level shifter transistors - I mistakenly assumed you were talking about the drivers.

You can do what you propose, but I have to ask why? The PCB is for BC556 types.

The question about 4.7k and 10k: follow the PCB - it is correct.

I will do an update to the article as soon as a few have been built. I want to catch all the issues the builders find.

Looking forward to hearing your thoughts on the sound!

Hi Bonsaï

Yes I was talking about the drivers but wanted to remind you that your pcb and your bom and your schematics calls for 45v vce max level shifter transistors (bc557/547) and the max power supply should not exceed that voltage. I can not find BC556 anymore...

I understand from your previous post that the drivers will see a voltage excursion of the total power rail but I am not sure to understand why...

For the sound, unfortunately the power BJT I found only arrives on September 6th to complete the build :eek: for space constraints on my heatsink height I want to stick to to3p devices...

What are your thoughts about using a regulated supply for the front end ( grounding, etc..)?

Thanks

Fab
 
Last edited:
www.hifisonix.com
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Fab,

There has been some discussion on this point re Q9 and Q11.

Please use BC546b and BC556B. These are readily available from Mouser and Digikey. Although the gain range is lower than the 'c' types, they will work fine for the nx-Amp. The Vce of these devices is 65V.

For th drivers, consider way happens whether output is sitting at the maximum +ve output voltage. The I've drive will have its emitter at the - supply voltage while its collector is almost at the + supply voltage. So, the drives, like the output and TIS stages see the full - to + supply rail voltage.
 
www.hifisonix.com
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Re regulated supply: the front end is already regulated with the zeners and filtered. This is a simple design that gives good performance and sound very good ( to my ears - I hope you will agree after you have built yours).

I will do an enhanced version of the nx-Amp using AFEC to achieve very high PSRR - no need for regulated supplies in CFA.
 
PCB Status, Update

All board sets that have been paid for have been shipped, and I expect to ship the rest on Tuesday, or whenever payment is received.

The documentation for the nx-Amplifier is available from Bonsai's web site in a PDF document, including BOM and build instructions, here:

The Ovation nx-Amplifier V2.0

A full set of boards as shipped is shown below. Circuit boards are professionally made, double-sided, solder mask and silkscreen top and bottom side, plated through holes. They are made from Gerber plots provided by Bonsai, the OP of this thread.

nx-Amp PCB
$10 each, $20/stereo set. plus shipping and Paypal fee

PMI (2) received
pinnocchio (2) shipped/received
fab (2) shipped/received
ivanlukic (2) shipped/received
evette (4) 4 shipped/2 received
potepuh (2) on vacation
JethroTull (2)
Cambe (2) shipped/received
Junie (2) shipped
Bill_P (2) shipped
mj777 (2)

nx-Amp PSU+Protection PCB
$10/board, added to the above

PMI (1) received
ivanlukic (1) shipped/received
pinnocchio (2) shipped/received
fab (2) shipped/received
evette (2) 2 shipped/1 received
potepuh (1) on vacation
JethroTull (2)
Cambe (2) shipped/received
Junie (1) shipped
Bill_P (1) shipped
mj777 (1)
 

fab

Member
Joined 2004
Paid Member
Re regulated supply: the front end is already regulated with the zeners and filtered. This is a simple design that gives good performance and sound very good ( to my ears - I hope you will agree after you have built yours).

I will do an enhanced version of the nx-Amp using AFEC to achieve very high PSRR - no need for regulated supplies in CFA.

But only the input stage is Zener filtered. I was referring more the VAS stage...

I have confidence that it will sound nice since it seems to be a mix of Hiraga and VSSA...and I like both amps;)

Fab
 
Bonsai,

Now that my boards are in transit (thanks Peter!) I am thinking about parts and what needs to be bought. I do have a stock of various components in the closet and want to use what I have on hand where possible. That raises a few questions about component ratings and what can be substituted.

On the PSU card it appears that C2 and C10 will never see more than 5 volts in the application. Then would a capacitor voltage rating of say 10 volts or more be sufficient?

Also on the PSU card C4 and C5 are series connected 100uF capacitors. I have some non-polar 47uF electrolytics. Would they be a good replacement for the C4 - C5 series pair?

On the amplifier board, D1 and D2 are rated at 1000 volts. Can I use 100 volt diodes there, like 1N4002's?

Looking up parts at Mouser, D1 and D7 (BZX79) on the PSU card are listed as end of life. They are still available and I plan to use them but at some point they will become unobtanium.
 
@ Bill: I hope some consensus will emerge on the parts, I basically just skipped ordering a few, so I have to get back to it to get a full set.

Pinocchio had a source for the BC556 in C grade, but I have not heard from him about that lately. I do not know how closely B grade parts can be matched, have not tried.

Some parts are not easily available everywhere, for example the optocouplers, and those are already a substitute for the part on the BOM.

KSC3503 and KSA1381 in D and E grade that I have from Mouser tested poorly as a pair, I would not consider those grade devices even close to complementary, although I have no idea how much difference it will make here. My thread about that pretty much died an ignoble death, LOL.

In the case of VSSA, which is also current feedback, they result in increased harmonic distortion, but again, I do not know how much, because I have not seen sims with a matched and un-matched pair side-by-side to compare...

This is the gist of what I found when I tested a few pairs:

... The Fairchild KSC3503 and KSA1381 were originally complementary devices. As of the last year, the only parts which are easily obtainable are the KSA1381E and the KSC3503D. These hardly make a complementary pair any more.

I recently tested 5-6 of each, purchased together from Mouser, and the results were as follows:

KSA1381E , hfe: 180-195
KSA3503D , hfe: 70-78

This means that the E version tests at the high end of the range, and the D version, at the low end of its respective hfe range. In theory the ranges overlap, in practice, not so much.

For comparison, I also tested two pair of original Fairchild 1381E/3503E, which tested quite close around hfe~192 and 185, respectively...
 
R24-R27 588-TUW5JR33E should be 588-TWW5JR33E. We want a vertical resistor radial package and the TUW series is axial.

Pete, thanks for the info on the transistors. Sometimes it is possible to get obsolete parts from places like Rochester Electronics. The KSC3503E is listed at harrykrantz.com, an inventory management company that has stock of obsolete parts. We probably would have to get a quote and buy a relatively large quantity so if this can be done at all it would be a group buy.