Im finally doing surgery on my BOSOZ preamp. I have a BOZ preamp that Ive been using for the last two decades that I totally love. I never had much motivation or time to finish my BOSOZ. For the last 6 months Ive got too much time on my hands
I probably built the BOSOZ in 2005 or so and i had some power supply magic smoke when i attempted to bias the circuit. Did some sketchy things back then with the seperate power supply. I finally fixed the power supply last week, so figured Id starting fixing the preamp section. I have a 4 deck 10k DACT attenuator on the output of the circuit which I dont want to change. My question is on P1 and P2 ....which I blue wired a couple of 10k pots....I want to get rid of them and repace the two with fixed resistors
Would 10kohms be the ideal value or?
Also would it be possible to change the bias pot with a fixed resistor? Without biasing this specific circuit? I was hoping that there may be some known value that would work. I want to get rid of this pot as its almost impossible to tweak easily
Thanks (ignore the white wire as this poor BOSOZ has been a storage bin for far toooo long)
I probably built the BOSOZ in 2005 or so and i had some power supply magic smoke when i attempted to bias the circuit. Did some sketchy things back then with the seperate power supply. I finally fixed the power supply last week, so figured Id starting fixing the preamp section. I have a 4 deck 10k DACT attenuator on the output of the circuit which I dont want to change. My question is on P1 and P2 ....which I blue wired a couple of 10k pots....I want to get rid of them and repace the two with fixed resistors
Would 10kohms be the ideal value or?
Also would it be possible to change the bias pot with a fixed resistor? Without biasing this specific circuit? I was hoping that there may be some known value that would work. I want to get rid of this pot as its almost impossible to tweak easily
Thanks (ignore the white wire as this poor BOSOZ has been a storage bin for far toooo long)
Its been 20 or so years since I looked at what I did, but i followed my BOZ preamp as far as I can tell and I know I dont have line level sources that would overload the circuit and have to be attenuated. I did read your answer about the "instead of P3 and P4 put 5k fixed resistors ...... or leave them out and replace R11 and R12 with 5K" but at this point I really dont want to change it
Thanks
Thanks
I built mine years ago also, love it! I use it with ACA mono blocks. Using the schematic, I built mine with:
- replaced P5 with 430 ohm fixed resistor, which gives 10dB of gain with the lowest distortion and noise levels (this is the value Nelson uses in the article for the graphs)
- I used a four section 5K pot for P3 and P4, I've never had to adjust off of 0 Ohms. If I were to build it again, I would delete P3 & P4 and just use a jumper from R10/R12 to output+ and R9/R11 to output -.
The only change I made to the circuit was replacing P5 with the 430 ohm fixed resistor, every other part is exactly what Nelson recommended. When I adjust P3/P4 towards 5K, the volume is reduced and at 5K it is muted fully. I've used this preamp to drive:
- ACA v1.6 converted to v1.8, balanced and single ended
- M2x (single ended)
- ALEPH J balanced and single ended
- ALEPH J with semisouth output devices, balanced and single ended
- J2 EUVL clone, balanced and single ended
- F6 single ended
- F5t mono blocks, balanced and single ended
- Hafler DH200
- Hafler 9270
All the amps were driven with no issues, this is the preamp I use for testing and breaking in all amps I work on. Same with all the phono preamps I've built and worked on. I love how it will input and/or output either single ended or balanced.
I would definitely move the 10K to the input side of the circuit.
The volume control pots are supposed to be at the output-
https://www.passdiy.com/project/preamplifiers/bride-of-zen
We will place the volume control at the output of the circuit, giving us a higher output impedance than is typical. Depending on the position of the volume control, the output impedance will range from 0 to 1.5 KOhms.
Normally you see the volume control potentiometer at the input to the preamp circuit, and in this way you can insure that the input will not be overloaded. Placing the potentiometer at the output has two advantages, however, the first being that all circuit noise will be attenuated as the volume setting is reduced. Placing the volume control at the output allows the input of the gain stage to look directly at the source. This improves the bandwidth and distortion of the circuit by providing a lower RC figure for the input capacitance of the MOSFET. If you desire to place a potentiometer at the input of the circuit, feel free to do so before the input coupling capacitor in place of R107.
https://www.passdiy.com/project/preamplifiers/bride-of-zen
We will place the volume control at the output of the circuit, giving us a higher output impedance than is typical. Depending on the position of the volume control, the output impedance will range from 0 to 1.5 KOhms.
Normally you see the volume control potentiometer at the input to the preamp circuit, and in this way you can insure that the input will not be overloaded. Placing the potentiometer at the output has two advantages, however, the first being that all circuit noise will be attenuated as the volume setting is reduced. Placing the volume control at the output allows the input of the gain stage to look directly at the source. This improves the bandwidth and distortion of the circuit by providing a lower RC figure for the input capacitance of the MOSFET. If you desire to place a potentiometer at the input of the circuit, feel free to do so before the input coupling capacitor in place of R107.
thank lgreen, this is from the BOZ which is my main preamp and I love it.
My confusion is on the BOSOZ which I built 20 or so years ago but never finished. Im fixing it now and was trying to minimal changes but probably should move the DACT volume pot to th input. I was hoping it wasnt critical as to Nelsons BOSOZ article and the way my current BOZ performs
My confusion is on the BOSOZ which I built 20 or so years ago but never finished. Im fixing it now and was trying to minimal changes but probably should move the DACT volume pot to th input. I was hoping it wasnt critical as to Nelsons BOSOZ article and the way my current BOZ performs
I think that BOSOZ is the same as BOZ don't feel guilty about those volume pots on the output. Here is BOSOZ-
https://www.passdiy.com/pdf/balzenpre.pdf
There are four potentiometers also shown if Figure 3. P1 and P2 can be
used to attenuate the input signal. Because the balanced input
characteristic is perfectly preserved if P1 and P2 are set at the same
value, they perform best as precision ganged controls, but this is not
essential otherwise. P1 and P2 can be used to protect the input from
higher voltage signal sources, or they can be used as volume controls.
P3 and P4 perform attenuation at the output, and can also be used
either as a volume control or simple gain adjustment. P3 and P4
attenuate the output noise of the circuit as well.
Mine has been running since 2002 with some changes along the way x-ccs-bosoz now.
https://www.passdiy.com/pdf/balzenpre.pdf
There are four potentiometers also shown if Figure 3. P1 and P2 can be
used to attenuate the input signal. Because the balanced input
characteristic is perfectly preserved if P1 and P2 are set at the same
value, they perform best as precision ganged controls, but this is not
essential otherwise. P1 and P2 can be used to protect the input from
higher voltage signal sources, or they can be used as volume controls.
P3 and P4 perform attenuation at the output, and can also be used
either as a volume control or simple gain adjustment. P3 and P4
attenuate the output noise of the circuit as well.
Mine has been running since 2002 with some changes along the way x-ccs-bosoz now.
Sooo long ago? Seems like yesterday! In 2017 I even drilled balanced 2.5mm TRRS and unbalanced 3.5mm headphone jacks into my build, volume pots on the output like intended. Drives efficient headphones wonderfully. Though output vol pots for headpohone loads seems extremely risky!
