I'm back! People around here still doing DIY or what? I gave it all up about a decade ago having built a room full of DIY amps, preamps and other audio stuff, no more audio and no DIY, sold most of my store-bought equipment (but kept all of my DIY efforts) and moved onward to other things- like attempting to raise tiny kids.
Every once in a while I have my old audio buddies over for some San Diego IPA's, and the other day I actually tried showing them some of my DIY amps (I have them all gathering dust) to awful embarrassment! One amp would not turn on, another only worked on one channel! Had to switch to scotch to de-escalate the situation and reduce the mocking! You people with your impressive builds and neat wiring with clean layouts cannot probably understand what its like for us common folk to keep up! Aghh! Try to imagine a slob like me- you flip the power button of your DIY amp and stand back- only to have it just sit there and do nothing! At least emit some smoke or buzzing or something.
Some of these DIY projects have not been powered up for 10 years. People were questioning whether the caps needed to be reformed. Not like they are from 1960 but what the heck, I decided to go through everything in a week or two and at least power them up and see if they worked. Well it took about 6 months and here is what happened....
I re-impressed my slovenly self as mostly everything still worked with some new fuses and minor adjustments. There were only 2 major problems which I had to seek warranty service on- the BOSOZ preamp and Krell clone. BOSOZ first. Original project is here- Here.
Ahhhh, fond memories of the BOSOZ and Kari's group buy...NOT! Anyway, the BOSOZ has actually been working fine all this time with its fancy gear-driven volume controls, until the crappy potentiometers locked up! Must be too much torque or the angles the shafts went in...or bad quality as upon inspection the ALPS potentiometers are FAKE (I think). Here is one taken apart - note the absence of individual resistors which the internet tells me should be there in the real ones?
The warranty department spung into action- removing the gears, rewiring the insides and somewhat cleaning up the crazy wiring (I said "somewhat!").
Rewiring....New vs. Old....
Gears removed, no more counting clicks.
Out of the garage came a pair of fairly elusive dual 5K audio taper pots called for in the project (bought years ago). From the surplus store came premade headers with wires and pins pre-attached as there is no way a normal person can connect these headers with the standard pins, plastic inserts and normal wire. Having to do a 9 conductor header manually is the worst and most frustrating job in DIY.
The diode bridge PCBs laid out by me 15 years ago to control the latching relays for input switching via momentary pushbuttons were heavily corroded so the warranty department installed a spare (somewhat less corroded one). More impressively, NAIS data sheets were consulted and math was done using the coil resistances from the datasheets to determine the current drawn on each depression of a pusbutton. Turns out that larger 1A diodes were a better fit for surviveability, so in they go. That's right baby! Doing math on my own without AndrewT!
Not to be happy with just a fix- it was realized that the BOSOZ has enough juice to drive certain headphones, and that balanced headphones are more common now than they were in 2003 when this first started. So out came the power drill and in went a 2.5mm balanced headphone jack on the front panel (directly connected to the balanced BOSOZ) as well as a 3.5mm jack connected in parallel to a pair of RCA outputs and a pair of INA134 differential line receivers. The gain is not very high so don't try this with your HD650s but something like a Beyerdynamic DT770 or earbuds work just fine.
Pay no attention to the fact that the headphone output jacks are located under the "Inputs" text on the front panel.
Now the BOSOZ was back in operation, the warranty department looked over the power supply, noting that the bevy of regulators had a couple not up to snuff and that the LR channel PS boards were slightly hacked to account for the use of one CT transformer rather than dual secondary one the boards expected.
After an outflow of money everything was disassembled, new transformers installed and everything **mostly** right sized. This time low noise LT3015 Neg and LT1963A Pos regulators were installed to run the INA devices (converting the balanced signal to SE for 1 set of RCA out and 3.5mm out).
Every once in a while I have my old audio buddies over for some San Diego IPA's, and the other day I actually tried showing them some of my DIY amps (I have them all gathering dust) to awful embarrassment! One amp would not turn on, another only worked on one channel! Had to switch to scotch to de-escalate the situation and reduce the mocking! You people with your impressive builds and neat wiring with clean layouts cannot probably understand what its like for us common folk to keep up! Aghh! Try to imagine a slob like me- you flip the power button of your DIY amp and stand back- only to have it just sit there and do nothing! At least emit some smoke or buzzing or something.
Some of these DIY projects have not been powered up for 10 years. People were questioning whether the caps needed to be reformed. Not like they are from 1960 but what the heck, I decided to go through everything in a week or two and at least power them up and see if they worked. Well it took about 6 months and here is what happened....
I re-impressed my slovenly self as mostly everything still worked with some new fuses and minor adjustments. There were only 2 major problems which I had to seek warranty service on- the BOSOZ preamp and Krell clone. BOSOZ first. Original project is here- Here.
Ahhhh, fond memories of the BOSOZ and Kari's group buy...NOT! Anyway, the BOSOZ has actually been working fine all this time with its fancy gear-driven volume controls, until the crappy potentiometers locked up! Must be too much torque or the angles the shafts went in...or bad quality as upon inspection the ALPS potentiometers are FAKE (I think). Here is one taken apart - note the absence of individual resistors which the internet tells me should be there in the real ones?
An externally hosted image should be here but it was not working when we last tested it.
The warranty department spung into action- removing the gears, rewiring the insides and somewhat cleaning up the crazy wiring (I said "somewhat!").
Rewiring....New vs. Old....
An externally hosted image should be here but it was not working when we last tested it.
Gears removed, no more counting clicks.
An externally hosted image should be here but it was not working when we last tested it.
Out of the garage came a pair of fairly elusive dual 5K audio taper pots called for in the project (bought years ago). From the surplus store came premade headers with wires and pins pre-attached as there is no way a normal person can connect these headers with the standard pins, plastic inserts and normal wire. Having to do a 9 conductor header manually is the worst and most frustrating job in DIY.
An externally hosted image should be here but it was not working when we last tested it.
The diode bridge PCBs laid out by me 15 years ago to control the latching relays for input switching via momentary pushbuttons were heavily corroded so the warranty department installed a spare (somewhat less corroded one). More impressively, NAIS data sheets were consulted and math was done using the coil resistances from the datasheets to determine the current drawn on each depression of a pusbutton. Turns out that larger 1A diodes were a better fit for surviveability, so in they go. That's right baby! Doing math on my own without AndrewT!
An externally hosted image should be here but it was not working when we last tested it.
Not to be happy with just a fix- it was realized that the BOSOZ has enough juice to drive certain headphones, and that balanced headphones are more common now than they were in 2003 when this first started. So out came the power drill and in went a 2.5mm balanced headphone jack on the front panel (directly connected to the balanced BOSOZ) as well as a 3.5mm jack connected in parallel to a pair of RCA outputs and a pair of INA134 differential line receivers. The gain is not very high so don't try this with your HD650s but something like a Beyerdynamic DT770 or earbuds work just fine.
Pay no attention to the fact that the headphone output jacks are located under the "Inputs" text on the front panel.
An externally hosted image should be here but it was not working when we last tested it.
Now the BOSOZ was back in operation, the warranty department looked over the power supply, noting that the bevy of regulators had a couple not up to snuff and that the LR channel PS boards were slightly hacked to account for the use of one CT transformer rather than dual secondary one the boards expected.
After an outflow of money everything was disassembled, new transformers installed and everything **mostly** right sized. This time low noise LT3015 Neg and LT1963A Pos regulators were installed to run the INA devices (converting the balanced signal to SE for 1 set of RCA out and 3.5mm out).
An externally hosted image should be here but it was not working when we last tested it.
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The Power Supply?
Just when everything was looking good the idiots in the warranty department shorted out (or they exploded on their own) one string of Zeners!
Now that is impressive! Not only did the traces burn up but there is pile of melted goop on there!
Back to Kari's schematic-- but wait there was never a schematic! Yeah I know, I was crying about this before but no one cared. Anyway, the intrepid service department went back and reverse engineered the Kari power supply from the boards- and yes Kari did use the Pass power supply for the + rail but with one discrepency. The Pass original PS drops 80V unregulated across a 4.5k resistor R101 to a reference voltage of about 64 volts wheras Kari uses a 1/4W 1.5K resistor at this location labeled R3. Why?? Beats me.
Kari's board thus places about 16V across a 1.5k resistor, dissipating .17 Watts in a .25 watt resistor. Now given that most people use over specced transformers, your unregulated 80V is most likely higher- my unregulated voltage was more like 91 volts and the voltage reference was 63 volts, putting 28 volts across the 1.5k resistor, causing it to dissipate .52 watts in a .25 watt device-- it is a wonder it lasted this long, but the resistor did not explode so go figure....
The burned board was cleaned (slightly) and in went a 3 watt 4.5K resistor instead of 1.5K, and also a 3 watt 215 ohm resistor (instead of 1/4W 221 ohms) along with 1 Watt freestanding zeners and a new IRF610. The other channel was changed to use 3 watt resistors as well.
Kari's PS board has a CRC filter in the first stage, so turning to the root of the problem our service technician (me) changed the CRC resistor from 50 ohms (3 watts) to 150 ohms (5 watts). Fully loaded the PS board prior to the CRC gets +97 VDC, the CRC outputs 83 VDC unregulated (having dropped 14V into the 5W/150 ohm resistor) and the PS at the end outputs +58.2 volts. The positive heat sink temperature for the output IRF610 has dropped from 123F/54C to 108F/42C (room was pretty cold at 61F/16C).
Everything appears set for another decade on the shelf in the DIY showroom.
Just when everything was looking good the idiots in the warranty department shorted out (or they exploded on their own) one string of Zeners!
An externally hosted image should be here but it was not working when we last tested it.
Now that is impressive! Not only did the traces burn up but there is pile of melted goop on there!
Back to Kari's schematic-- but wait there was never a schematic! Yeah I know, I was crying about this before but no one cared. Anyway, the intrepid service department went back and reverse engineered the Kari power supply from the boards- and yes Kari did use the Pass power supply for the + rail but with one discrepency. The Pass original PS drops 80V unregulated across a 4.5k resistor R101 to a reference voltage of about 64 volts wheras Kari uses a 1/4W 1.5K resistor at this location labeled R3. Why?? Beats me.
An externally hosted image should be here but it was not working when we last tested it.
Kari's board thus places about 16V across a 1.5k resistor, dissipating .17 Watts in a .25 watt resistor. Now given that most people use over specced transformers, your unregulated 80V is most likely higher- my unregulated voltage was more like 91 volts and the voltage reference was 63 volts, putting 28 volts across the 1.5k resistor, causing it to dissipate .52 watts in a .25 watt device-- it is a wonder it lasted this long, but the resistor did not explode so go figure....
The burned board was cleaned (slightly) and in went a 3 watt 4.5K resistor instead of 1.5K, and also a 3 watt 215 ohm resistor (instead of 1/4W 221 ohms) along with 1 Watt freestanding zeners and a new IRF610. The other channel was changed to use 3 watt resistors as well.
Kari's PS board has a CRC filter in the first stage, so turning to the root of the problem our service technician (me) changed the CRC resistor from 50 ohms (3 watts) to 150 ohms (5 watts). Fully loaded the PS board prior to the CRC gets +97 VDC, the CRC outputs 83 VDC unregulated (having dropped 14V into the 5W/150 ohm resistor) and the PS at the end outputs +58.2 volts. The positive heat sink temperature for the output IRF610 has dropped from 123F/54C to 108F/42C (room was pretty cold at 61F/16C).
An externally hosted image should be here but it was not working when we last tested it.
Everything appears set for another decade on the shelf in the DIY showroom.
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Video
Since it is now 2018, I did a short video planning on doing a voice over to describe what was being shown but never got a chance to add audio. So here is the not yet completed video (silent just like in the old days....follow the screwdriver!).
BOSOZ video of Preamp and PS
Since it is now 2018, I did a short video planning on doing a voice over to describe what was being shown but never got a chance to add audio. So here is the not yet completed video (silent just like in the old days....follow the screwdriver!).
BOSOZ video of Preamp and PS
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