Aleph J - preamp gain requirements?
I've just finished building an Aleph J, and its burning in now. So far one thing about its performance has me concerned: it appears to require a substantially higher volume level from my preamp to achieve volumes similar to those I'd been getting from ACAs (both singly in stereo mode and as monoblocks using RCA inputs).
The preamp is a Belles XLM, which has a gain of 5dB. Speakers are Klipsch Kg3.2 with 93dB sensitivity, nominally 8ohms.
I've upped the bias to 0.5v, which helped a bit, but not dramatically. The pattern is occurring for both channels.
Is this to be expected, or, are there build errors lurking somewhere? Thanks in advance for any comments or suggestions.
I've just finished building an Aleph J, and its burning in now. So far one thing about its performance has me concerned: it appears to require a substantially higher volume level from my preamp to achieve volumes similar to those I'd been getting from ACAs (both singly in stereo mode and as monoblocks using RCA inputs).
The preamp is a Belles XLM, which has a gain of 5dB. Speakers are Klipsch Kg3.2 with 93dB sensitivity, nominally 8ohms.
I've upped the bias to 0.5v, which helped a bit, but not dramatically. The pattern is occurring for both channels.
Is this to be expected, or, are there build errors lurking somewhere? Thanks in advance for any comments or suggestions.
No XLRs (yet) so just standard SE inputs via RCAs. I did add jumpers on the PCBs from -IN to GND, so perhaps that should address the grounding issue?
The only departure from the build guides I used was inclusion of copper connectors midway on the input wires, to facilitate easier changes in the future. I've been suspecting the quality of those connectors. Would you suggest I remove them and replace with permanent, soldered connections?
Note:
R1 & R3 = 22.1K
R4 = 221K
If you inserted, by mistake, the 22.1K for R4... the gain will be dramatically reduced.... so please check.
While at it, make sure the R1 & R3 are also of the correct value
because these also work at setting the desired gain (and input impedance)
R1 & R3 = 22.1K
R4 = 221K
If you inserted, by mistake, the 22.1K for R4... the gain will be dramatically reduced.... so please check.
While at it, make sure the R1 & R3 are also of the correct value
because these also work at setting the desired gain (and input impedance)
Last edited:
Its alive!
I'm pleased to report that Extreme_Boky's suggestion led to resolution of the gain issue. I had in fact placed the wrong resistors in R1, R3 and R4. I guess I didn't pay sufficient attention to the designations "221K" vs "22K1". In any event, all is sorted now and the Aleph J is performing beautifully.
I'd like to express my gratitude to Extreme_Boky, Dennis Hui and Zen Mod for taking the time to respond to my post, and sharing your understanding of electronics and the Aleph J circuitry. While I'm at it, thanks also to 6L6 and flohmann for the excellent build guides. And of course to Nelson Pass for making these designs available to the DIY community.
I'm pleased to report that Extreme_Boky's suggestion led to resolution of the gain issue. I had in fact placed the wrong resistors in R1, R3 and R4. I guess I didn't pay sufficient attention to the designations "221K" vs "22K1". In any event, all is sorted now and the Aleph J is performing beautifully.
I'd like to express my gratitude to Extreme_Boky, Dennis Hui and Zen Mod for taking the time to respond to my post, and sharing your understanding of electronics and the Aleph J circuitry. While I'm at it, thanks also to 6L6 and flohmann for the excellent build guides. And of course to Nelson Pass for making these designs available to the DIY community.
Revised layout
Putting both the Guardian 86 and the low voltage ac switch pcb on the back panel freed up some space. As you can see, I am trying to keep the pcb’s as far from the input jack as I can. Does this look okay? Would I be better off putting the Guardian pcb (that is the smaller one) between the input jack and the speaker posts?
Any thoughts would be appreciated. I am anxious to order the panels!
Thank you.
The pictures came out a little funny. The IEC jack is on the lower right hand side as seen from the front panel looking towards the back. The speaker posts are towards the bottom, the input jack towards the top.
Putting both the Guardian 86 and the low voltage ac switch pcb on the back panel freed up some space. As you can see, I am trying to keep the pcb’s as far from the input jack as I can. Does this look okay? Would I be better off putting the Guardian pcb (that is the smaller one) between the input jack and the speaker posts?
Any thoughts would be appreciated. I am anxious to order the panels!
Thank you.
The pictures came out a little funny. The IEC jack is on the lower right hand side as seen from the front panel looking towards the back. The speaker posts are towards the bottom, the input jack towards the top.
Attachments
Thank you very much, Eric and Zen Mod! You saved my Aleph!
I changed the thermal pads to aluminum oxide and now, after more than an hour on, all mosfets are ~50C and voltage on R18 is stable at 400mV. All other power resistors voltage drop is also in a range from 385mV to 410mV. Heatsinks at 45C.
Perfect! Thank you!
To all the fearless amplifier builders: never use fat compresive thermal pads... aluminum oxide rulez.
-Alvis
I changed the thermal pads to aluminum oxide and now, after more than an hour on, all mosfets are ~50C and voltage on R18 is stable at 400mV. All other power resistors voltage drop is also in a range from 385mV to 410mV. Heatsinks at 45C.
Perfect! Thank you!
To all the fearless amplifier builders: never use fat compresive thermal pads... aluminum oxide rulez.
-Alvis
Pass DIY Addict
Joined 2000
Paid Member
Pass DIY Addict
Joined 2000
Paid Member
Aleph is for Sissies
And I still need to build the ultimate Sissy amp - the one with SITs
The "problem" causing my delay is that I already have 4 of 5 amps laying around because they no longer fit on my equipment rack. My recently completed 300B monoblock project sure ate up lots of space on the rack. I foresee a summer project that involves built-in shelving in the media room. That, or I may need to see if I can talk my wife into putting an addition onto the house. Plenty of Class A amps should help keep the extra space warm in winter