BOZ replacement parts

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Elkaid

Elkaid

Member
Joined 2003
Thanks !

Here's how my new BOZ looks like for now. Still waitin' for transformer :(

Now that it's almost finished, do you think it'll get along with my GainClone ?

Regards,
 

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Elkaid

Elkaid

Member
Joined 2003
Thank you !!!

Thank you everyone !

I finally finished my Gainclone and Bride of Zen this weekend !
With your precious help, I've been able to overcome problems such as mysteriously blown parts, secondaries voltage too high etc...
I also had some troubles such as sound being extremely distorted but I discovered that the 3 chassis should not be in contact together... Grounding problem ?
I wish I could make nice enclosures but my blown budget only allowed me to buy some ready-made 1/32" Hammond aluminium case.

Well, here's some pictures. Don't worry, its sounds better than it looks.

(The blue connector (speakon) cable is the cable between the Power Supply and the Gainclone...)

Thanks again everyone !
 

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Elkaid

Elkaid

Member
Joined 2003
Yesterday, I tried to connect a non-grounded source (my cd-player) and I realized that my preamp is playing very distorted music.

When I hook-up the preamp to my PC's sound card, everything is fine. (I presume that the PC's sound card is grounded)

Am I missing something ?
Is the problem is from my CD player (I guess not) or I forgot something when building the preamp. I get similar results when my gainclone enclosure is touching the preamp's.

Any help would be greatly appreciated !!!
Thanks !
 
Elkaid

Elkaid

Member
Joined 2003
Hi !

First of all, thanks for your comments ! I put a lot of efforts in my first audio project that got beyond prototype stage :)

As you may guess, the gainclone is working beautifully... However, I didn't had the chance yet to try high grade components... only off-the-shelves caps & resistors but I don't feel any needs to upgrade. (yet !)

Thanks to Taco, my problem with Bride of Zen preamp has been found ! Except that little detail, everything worked fine on the first attempt and I'm very satisfied of the results.

Using only the GainClone amplifier, I was feeling that the soundstage was a bit too narrow IMO but connecting the BOZ preamplifier provided a feeling of "openness" (does that word exists ? anyway !) In short, the BOZ preamp adds a very nice impression to the music.

Finally, I must admit that I'm very satisfied with my current setup. However, if I get some loose cash someday, maybe I'll try my hand on an Aleph project but for now, I'll put my efforts on a DIY projector :)

If you're interested in this kind of project, I would be glad to help you if I can !

Sincerely,
 
T

Taco

Member
Joined 2002
Hehe

I had the same problem, I searched on the forum and I found out that the circuit clips at 1 - 1.5 Volt. And my DAC has an output of near 2 volt, so I bought a 100k pot and found out that the clipping was gone with an extra 100k resistor and replaced the crappy pot with a MF resistor.

Nelson stated that you can use 2 pots, one at the input en and one out the output of the circuit. But the resistor is fine for me.

Recently I have put MUR860 diodes in the circuit the differences with the in4007 are clearly hearable.

Suc6 with your projector! :nod:

/Taco
 
Elkaid

Elkaid

Member
Joined 2003
Now that you mention it, I'm quite interested to jump on the MUR860 bandwagon... Everyone seems to greatly appreciate them.

If I have some free time anywhere in a near future, I have a several Amp chip that I would try. (LM3886, TDA7293, TDA7294, OPA541, OPA548 and finally OPA549) I made some experiments with TDA7294 and I got very impressed. Next step would be to compare it with my current LM3875 gainclone.

I'll let you know the results of these experiments. By the way, do you know a good source of heatsinks ?

Have a nice day !
 
Elkaid

Elkaid

Member
Joined 2003
Recently, I was reading about BOZ and I found the following :
from http://members.lycos.nl/Aren/id45.htm
According to mr.Pass, the variable resistor P102 has to be adjusted in such a way that the voltage drop over the resistor R108 (in the absence of an input signal) is 4 Volts. However, in my own homebuilt BOZ I found this to be incorrect. The preamp sounded good using a Nakamichi BX-1 cassette deck or a Sony ST-S370 FM tuner as the signal sources. However, with a Marantz CD-80 CD player there was a nasty form of distortion during crescendos.
Since the volume control is after the gain stage, I assumed that the preamp was overloaded. Therefore, I tried to limit the input signal by mounting a 470 k resistor in series with the CD input. A voltage divider is formed by this resistor and R107, resulting in a greater than 5-fold attenuation of the input signal to the BOZ. Later on, I also mounted 220k resistors in series with the auxiliary and tuner inputs. Although the addition of these resistors resulted in sonic improvement, there was a major drawback: the bandwidth of the preamp was severely limited (-3 dB point between 10 and 20 kHz !). This was due to the gate capacitance of the MOSfets, which together with the series resistors formed a lowpass filter.
Help came from an unexpected source. Mr. Colin Rutter, of Spectral Technologies PTY Ltd., Australia, sent me the following e-mail message: "I have to inform you that the bad sound you experienced with the BOZ is due to the input signal being clipped asymmetrically as setting the bias current to 40 mA by measuring the voltage drop across the resistor may in fact not set the zero point correctly. A CRO (cathode ray oscilloscope) solves this problem or a bit of maths. My Bride of Zen has its idle current set at 32 mA for symmetrical clipping".
Click to expand...

I was wondering if adding a potentiometer between the input and the preamp would have the same nasty effects (lowering banwidth) as adding a resistor ? :scratch:

Also, how can I change the bias ? Using P102 & P202 ? How should I measure it ?

Thanks a lot !
 
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