My BoSoZ time for improvement

[lykkedk]

Hi. I have been using my BoSoZ for some year's now, and I think it's time for some improvement's.

If you take a look, at my Web-page CLICK HERE
You will find a schematic, that i used for my BoSoZ.

I use a 10K Ohm Stereo pot for p1/p2, and a 4.7K Ohm Stereo for p3/p4. (p3/p4) used for Volume-control. The quality of these pot's are not very good, so I would like to 'cut-out' the p1/p2 (I never use, allways turned up to max), and buy an expencive eg. alps-blue. You can see a picture of one at my webpage too.

The ALPS-blue is at 10K Ohm where i now use 4.7K Ohm. I am not interested in using the p1/p2 for volume-control, So my quistions is:

1. If I cut out the p1/p2 (10KOhm), I would then have to place some resistor's instead, but i am in doubt excatly where and how big they must be, keeping in mind I would like a lot of gain ?

2. I am interested in getting a lot of gain, so when I replace my 4.7 (p3/p4) with an 10K the output impedance goe's up (look page 4 at passdiy balanced line stage diy PDF manual) This is a good thing i suppose ?

Actually I don't quite understand this.

I hope you bare with me, not quite understanding this impedance thing, and what is has to do, with gain.

[lykkedk]

I attach this image, so that I better can explain what I have in mind.

As you can see, I would like to replace the p1/p2 with resistor's.

Hopefully someone could explain to me, about gain/impedance, and what to consider here, as i am lost.

[lgreen]

Hi, Not sure about P1/P2, why don't you just remove them and measure each leg's value and replace with 2 resistors each of those 2 values? Sounds like one will be a short/jumper.

I am using a 10K alps blue on mine (see link below). Like you I worried about output impedance being different with a larger R, so I reduced the 100K resistors (R11 and R12) to a value which I forget....I think 60K?

I've asked from time to time here whether this is a proper way to do it but no one answers except to say "see the article" which deals with p1/2 and input impedance but not the output pots and output impedance. So I did some math and it looked close enough for me, plus it sounds good.

If you really want an improvement why don't you make yours balanced instead of single ended? You would only need to add a few items.

Of course making it into an X-CCS-bosoz is an option; I ripped mine apart and redid it as you can see, and its a fantastic preamp. Yours looks very nice by the way.

[lykkedk]

Hi again, I have ordred a nice alps 10K Motor-pot (The motorpart, could be fun later on i think).

I have just tried to connect a 1Khz sinwave from a soundcard, into my scope (see this LINK )

The input at scope is set at 0.20mV, and my amplitude gives me 6x0.02 = 0.12 V
If I connect my BoSoZ with volume all up.
LINK Then I get out with input at scope 0.1V 4.5x0.1V = 0.45 V.

If I divide 0.45/0.12 (Out/In) I have 3.75 witch is my gain ???

Is that's correct, what I am doing or am I missing something

[JCM]

1. If I cut out the p1/p2 (10KOhm), I would then have to place some resistor's instead, but i am in doubt excatly where and how big they must be, keeping in mind I would like a lot of gain ?

At the very most, there will be 10 volts pp across that resistor, it is at zero volts dc potential, which means (10V*.3535) / 10K ohm = 350 uA. 350 uA*10V = .0035W rms. A 1/10, 1/8 or 1/4 watt resistor would easily suffice.

2. I am interested in getting a lot of gain, so when I replace my 4.7 (p3/p4) with an 10K the output impedance goe's up (look page 4 at passdiy balanced line stage diy PDF manual) This is a good thing i suppose ?

You will get slightly higher output amplitude, about a 7% increase. The drain resistor is 750 ohms, so the change from 5K to 10K can't affect it much. To increase gain, lower the value of R15.

Higher output impedance is generally not a good thing - an ideal amplifier has zero output impedance and infinite input impedance.
But it works out okay. If the input impedance (Z) to your power amp was really low, it would definitely not be so good.

... this impedance thing, and what is has to do, with gain.

Impedance is ac resistance. The signal sees a 750 ohm resistor in parallel with a 5K or 10K pot in parallel with the input impedance of the power amp it's driving. It also sees the very small capacitances within the mosfet and other components, but they're so small in the output circuit, they can be ignored.

If I divide 0.45/0.12 (Out/In) I have 3.75 witch is my gain ???

Output divided by input is the gain, yes.

The gain can be increased in this circuit by decreasing the value of R15.

Just replace the input pots with 10K 1/4 watt resistors. Do not leave the 10K resistor replacing p2 out of the circuit, don't ground the gate through the 221 ohm resistor. R13 and R14 then become unnecessary and can be eliminated.

Then increase the gain by lowering R15.

[lykkedk]

Hi.

This I tried yesterday.

Seem's to work allright. I have tried with R15 at 430Ohm, and with 124Ohm, only diffrence, is that I recive a lot of nice gain, with R15=124Ohm. I can't hear any sonic difference. I now also replaced my output pot, with an ALPS 10K motorpot. Everything seem's to be fine, no humming or scratching. (My old pot was a very cheap one). Seem's that a good pot, make's a lot of difference in my circuit.

Now I am looking forward, replacing my Vishay (

See Here )
With 'RIFA PHE 426' aka' Steenoe's cap's. 10Uf 250V

I am excitet, to hear if i can hear any sonic difference. I will let you know.

[Buhl]

Hej Jesper
Du skal helt sikkert prøve at "x'e" din BLS - det er to modstande, og det giver en god forbedring i diskanten - den bliver mere "glat" at lytte til. Prøv at søg på X og bosoz...

Mvh.
Hans

[lykkedk]

Hi.

After testing with my new ALPS pot, I decided to make a new PCB, and add the X to my Circuit.

I have reieved this schematics, but can't figure out, where the PSU should be connected Is it between the R116 and the 1000uF cap (+) And between the R117 and the 1000uF cap (-) ???

I make the hole circuit, so that i futureon have the capability to run balanced, but could someone explain, also howto run it unbalanced.

[lykkedk]

I would like to tell, that my PSU deliveres +60Vdc / GND / -60VDC.

I am nearly finish designing my new PCB, making it, so that I could test, both with or without the 'X-mod'.
Actually, I am making the PCB, so that I can use it as BoSoZ or X-BoSoZ.
I just can't figure out, where to plug the PSU (I know it's a dumb quistion)



Doe's 10uF go with it as C101 / C102 ? (I will test anyway).

Soo PLEASE help me

[JDeV]

Originally posted by lykkedk
I would like to tell, that my PSU deliveres +60Vdc / GND / -60VDC.

I am nearly finish designing my new PCB, making it, so that I could test, both with or without the 'X-mod'.
Actually, I am making the PCB, so that I can use it as BoSoZ or X-BoSoZ.
I just can't figure out, where to plug the PSU (I know it's a dumb quistion)



Doe's 10uF go with it as C101 / C102 ? (I will test anyway).

Soo PLEASE help me

The PSU positive connects to the bottom of R116 and the negative to the top of R117 - if you look on the .pdf circuit. That 60 V101 and V102 is actually the power source Henrik used in his similation software and represents the +60V and -60V of your PSU. You can replace C101/C102 with 10uF. Remember it must be non-polarised caps If you change this capacitor value, you also change the output impedance, not too big a problem. When I made my X-Bosoz, I used 47Uf, gived me the best sound in my setup - together with Aleph30.

Hope this helps.