1. The input DC blocking capacitor is required to isolate the output offset adjust biasing network from the volume control.
2. Yes, the circuit will drive small speakers. Some kind of thermal protection circuit and short circuit protection on the output is suggested, as well as bigger heatsinks.
3. RJM Audio
2. Yes, the circuit will drive small speakers. Some kind of thermal protection circuit and short circuit protection on the output is suggested, as well as bigger heatsinks.
3. RJM Audio
About to commence build using recently arrived 4.2b boards.
Will be using closed loop configuration and driving AKG K240's (1970's originals @600 ohm)
Any pointers to optimise for these headphones appreciated.
One question....I read of the tight thermal bonding for the transistors Q13/16 and Q15/14...
The bom makes no mention of any isolation pads for these transistors... is that an assumed given or do I just bolt them all together with their heatsinks as one big thermal mass without any isolation??
Will be using closed loop configuration and driving AKG K240's (1970's originals @600 ohm)
Any pointers to optimise for these headphones appreciated.
One question....I read of the tight thermal bonding for the transistors Q13/16 and Q15/14...
The bom makes no mention of any isolation pads for these transistors... is that an assumed given or do I just bolt them all together with their heatsinks as one big thermal mass without any isolation??
Richard, I really like your designs and have spent some time reading about them on your website. Now I have one question regarding the Sapphire: Are any modifications necessary to use it as a line stage amp instead of using it as a headphone amp?
Has anyone used the sapphire together with one of your phono stages to build a preamp including phono stage?
Has anyone used the sapphire together with one of your phono stages to build a preamp including phono stage?
The optional changes are given in the Sapphire BOM file. You can reduce the bias current and change the gain to optimize it as a line stage, but you don't have to do either if you don't want to.
ok, I should have looked at the BOM sooner. I thought it would just be a list of parts but this is more like a design manual. very impressive! thanks!
might sound like a strange question but is the Sapphire equally well suited to be a line stage as well as headphone amp or would it be a better headphone amp than line stage (or the other way round)?
might sound like a strange question but is the Sapphire equally well suited to be a line stage as well as headphone amp or would it be a better headphone amp than line stage (or the other way round)?
Hmm, calling it a "Design Manual" is a nice suggestion, thanks! I'll look into making that change.
I use Sapphire 4 for both my preamp and my headphone amp.
The preamp build is described in a old blog post, here. I've replaced the Sapphire 3 boards shown with the updated rev 4 circuit, but the physical layout is unchanged.
Boards assembled and working... offset set at 5mv but can go lower.
Testing on the bench with a discman and Lightspeed attenuator .
I did use thermal paste because....why not..
I note that the Q14/15 pair runs noticeably warmer than the Q13/16 pair.....just the finger touch test but the same for both boards...
I am about to take them inside to the main system and will raid the medical cabinet for the digital thermometer and recheck..
Otherwise....sounding great and no hiss clicks pops hum sparks or worries of any sort...!!
Having built the Emerald Phono stage and now the Sapphire I have to say that these are the most diy friendly projects I have ever encountered.
The build guides are comprehensive and the "Design Manual" provides great insight and options...and best of all they power up and work first time.
Thank you Richard for sharing and supporting !!
Testing on the bench with a discman and Lightspeed attenuator .
I did use thermal paste because....why not..
I note that the Q14/15 pair runs noticeably warmer than the Q13/16 pair.....just the finger touch test but the same for both boards...
I am about to take them inside to the main system and will raid the medical cabinet for the digital thermometer and recheck..
Otherwise....sounding great and no hiss clicks pops hum sparks or worries of any sort...!!
Having built the Emerald Phono stage and now the Sapphire I have to say that these are the most diy friendly projects I have ever encountered.
The build guides are comprehensive and the "Design Manual" provides great insight and options...and best of all they power up and work first time.
Thank you Richard for sharing and supporting !!
Glad to see that the "Design Manual" idea gets so much traction.
Thanks for the quick reply, Richard! I think this has to be my next DIY project. I'll now try to understand the circuit. I've built a few opamp based designs, no discrete circuitry so far. ....apart from an ACA and B1 I guess but that is super simple.
Thanks for the quick reply, Richard! I think this has to be my next DIY project. I'll now try to understand the circuit. I've built a few opamp based designs, no discrete circuitry so far. ....apart from an ACA and B1 I guess but that is super simple.
That's strange. With 30 mA bias neither pair of transistors, nor the heatsinks, get appreciably warm. The heat dissipation of each pair is less than 1 W total.
Check the voltage drop across R17 and R18. They should be equal and the current, computed as I=V/R, should be the expected value for the bias current setting.
Richard
Fingers are such sensitive things....
I remeasured with the thermometer and Q14/15 pair is only 4 degrees C warmer than Q13/15.
Voltage drop across R17 and R18 measures the same for each.
Bias current measures 39 mA and highest heatsink temp is 42 degrees (20 above ambient) so all appears as expected and normal.
I remeasured with the thermometer and Q14/15 pair is only 4 degrees C warmer than Q13/15.
Voltage drop across R17 and R18 measures the same for each.
Bias current measures 39 mA and highest heatsink temp is 42 degrees (20 above ambient) so all appears as expected and normal.
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Hi guys! I have a few questions about the components of the 42b4 version. I gave a look at the comments here (at least 30 pages ) but I could not find answers.
1) I wanted to know if there is any problem or major difference by replacing the KOA-speer 1/4W with vishay-dale rn55 1/8W and nichicon UKW1E332MHD with panasonic ECA1EHG332.
If you think there are better options, even for other component, just tell me!
2) What is the main difference between using 1 or 2 toroids? Is the isolated one a noticeable improvement?
) but I could not find answers.1) I wanted to know if there is any problem or major difference by replacing the KOA-speer 1/4W with vishay-dale rn55 1/8W and nichicon UKW1E332MHD with panasonic ECA1EHG332.
If you think there are better options, even for other component, just tell me!
2) What is the main difference between using 1 or 2 toroids? Is the isolated one a noticeable improvement?
Talking of through-hole miniaturization, whatever happened to the tiny 1/8W through-hole resistors that were commonplace perhaps 20 years ago? They would be a perfect choice for such a board, few resistors in a preamp need more than 1/8W dissipation after all.
I rarely see boards using them. Before progressing to SMT (mainly 0805) I used them quite a bit to keep PCB area under control.