DIY Audio Projects Forum

I can't believe straight after placing this post I lost another 1ohm 1W resistor. Now replaced with a 1ohm 5W wire wound. While I was performing open heart surgery I cleaned up a few connections and am now enjoing the B1-low on volume but clean on delivery.

I have discovered my recently built BoZ is right channel heavy. Well time to scrub-up and go back in. Nurse!

Hey I'm aproaching my 1000th post. Do I win a chicken.

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Projects: Oatley K272C - headphone amp in a tin can | "VoXDeuX" - Inexpensive two-way speaker | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

Hi Mark, if you feed the preamp with a regulated supply you should be able to reduce the capacitor size and resistor rating. What type of wallwart are you using?


Yes, a whole chicken actually! Please let me know where to send it!

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[ DIY Mains AC Power Cable Cord ] - [ K-12 Tube Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

I still have a few posts to go before my 1000th but it is looming up. In Australia we do not have canned chicken but we do have canned Ham etc. I'm not sure a canned chock would really get my gastric juices going. It looks awfull but it may well be very nice.

Back to Bozs and B1s: I have commented a few times on how good the bass is with these preamps. I think it is due to the fact that there are a couple of 10,000uf caps in the PS cct. Of course at switch on they suck many amps as they charge up. Nelson's suggests these should be 15,000uf. I happen to have a bag of 10,000uf so I'm using those. I'm thinking in the next build to use three 10,000uf this will bring the total storage to 30,000uf where Nelson feels it should be. I would seperate each with a 10ohm resistor to add a little more filtering.

The 1ohm 1W resistor pops because it takes the full in-rush. As stated else where I movng to 5W wire wounds. All good.

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Projects: Oatley K272C - headphone amp in a tin can | "VoXDeuX" - Inexpensive two-way speaker | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

You would think after 40+ years of electronics and constructing dozens and dozens of projects you would not miss a thing. Well the latest BoZ had a few construction errors. I thought I would post them here so if others have the same problem they will know where to start looking. Yes learn by my silly mistakes. Problem is I've built a few of these excellent preamps now (still one more to go) so I'm getting a little !@#$%^&!

First there was no left channel -> the left channel input was hard wired direct to ground. Cut away the ground connection.

Preamp sounded distorted with no volume -> The one ohm (1ohm) resistor which feeds the first 10,000uf cap decided to let the smoke out. Therefor no power to the brd. Replaced with 1ohm 5W wire wound.

Sound out of balance, right channel louder than left but only slightly -> no 10ohm source resistor on left channel jFET, the source was connected straight to ground. Added a 10ohm source resistor and removed ground connection. This will also occure if the PS voltage falls low.

So there you have the main problems I experienced with this build. Silly mistakes which sometimes can be hard to track especially on vero-brd. The way I look for some problems is put your meter on resistance with one lead to ground (power off) and check you get the same resistance values at each leg of the FET. This is how I found the 10ohm source resistor was missing. Then put one meter lead to V+ and do the same thing. This will identify missing or wrong value resistors. Easy to do. Check read values against schematic.

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Projects: Oatley K272C - headphone amp in a tin can | "VoXDeuX" - Inexpensive two-way speaker | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

OK guys read and weep. Here it is: Mongrel Dog Audio capless SE Boz. That's right a Secpial Edition!!

My new Oppo BDP-83SE has input caps but my 6AS7 SET has no input caps. So make a preamp with no input caps but good output caps. In this capless SE version of BoZ I have no input caps but retained the 10uf polypropelene caps for the output. Also the output caps have been snubbed by 0.1uf polies.

Nelson suggests a total of 30,000uf for his B1 whose PS I stole a few ideas from. But only having 10,000uf caps I used three to get the filtering/storage up. Also I used a simple RCRCRC filter network. 1ohm/10,000uf/10ohm/10,000uf/1ohm/10,000uf. Each 10,000uf cap is snubbed. Silver plated wire wrap wire is used throughout. Input hookup wires and power wires were threaded through tiny bead chokes. Multiple earths (negative voltage) connections were made. Bitumanised Al foil laid in the top and bottom of the Hammond anodised Al case. Silver solder, Alps pot and 4oz brass added once more to a quality build.

Hard to judge sound quality at this point with only a brief listen. I will follow up. Not sure it can out "B1" the B1 but it does have stacks of gain. Huge sound stage - massive.


http://mongreldogaudio.blogspot.com/201 ... e-boz.html

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Projects: Oatley K272C - headphone amp in a tin can | "VoXDeuX" - Inexpensive two-way speaker | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

very nice work mark. you are an artist

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My DIY Audio Projects:

• Jean Hiraga Le Monstre - DIY 8W Class A Amplifier
• Jean Hiraga's Super Class-A Amplifier

I'll assume that is not a BS artist??!!??. Funny you mention that. I have always had this affinity to build beautiful ccts. I think I'm a bit DDHD (or something).

This maybe the last I build. I'm going to get rid of the B1. For parts only and through in the 19V 3A supply for nix.

BoZ on 19V is the way to go. What are you using for a preamp Dan??

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Projects: Oatley K272C - headphone amp in a tin can | "VoXDeuX" - Inexpensive two-way speaker | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

Awesome Mark. Can you show an underside of the pcb. I see you are liking that SPC wire wrap.

Cheers

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[ DIY Mains AC Power Cable Cord ] - [ K-12 Tube Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

Happy to report the sound is excellent. Good deep bass, best so far, extremely detailed mids and smooth treble. Best BoZ to date. With no input caps the sound is much more focused and sound stage is very wide and deep.

I'm running it on 18V. On 35V it can get a little harsh. It was noted on other forums that lowering the PS voltage improved the sound. I would have to agree.

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Projects: Oatley K272C - headphone amp in a tin can | "VoXDeuX" - Inexpensive two-way speaker | "VoXItBassO" - stereo 12" sub-woofers ]
Website: [ retro-thermionic ]

Very nice case Mark. How does this compare with your Silicon chip preamp ?

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Kind Regards,
Dinesh

Some of my diy audio projects:

• Elliot Sound Products - P3A 100W Amplifier
• TMM 2.5 Way Loudspeaker with Scanspeak 18W8546
• 2-Way MTM Loudspeaker with Scanspeak 21W8554 and D2904-7100