All I can suggest is using a balanced to SE converter like BTSB. The Aksa Lender was not designed for balanced input. It’s a major change and basically a new design.
Aluminum IMS PCBs (SMT of course) for good heatsinking. These were built by Vunce as the front ends for the SuSyLu 100W Class A amp. Clamping or RTV can be used to provide a lot of heatsinking. This will allow running a high 120mA bias current for driving lower impedance headphones.
I am looking for a preamp. Browsing DIY audio and picking up ideas. I was going to go passive again but realized I want to try something different. The amp I built at the moment had 26 DB gain. Has anyone built Aksa with the lowest 4v option? Genuinely seeking some drive for my Wolverine to listen mainly to jazz. Thanks
Not 4V but I built a 24V version with lower gain that I have been using as a combination pre and headphone amp. Sounds great.
This preamp was designed for 48v supply. A lower voltage would require redesign of the DC setpoints.
I finally got around to taking pictures of my properly-housed AKSA-Lender.
I wanted a minimalist look, so I moved the source selection switch to the back. As of now, it stays on the single source connected to it. To get from the 8-pin connector to the source jacks, I re-used the selector PCB, mounting it to the base and soldered pairs of wires to the RCA connectors.
An acquaintance has an amazing machine shop attached to his garage, and he drilled the holes for the front and back. The volume knob is salvaged from a Carver 900 receiver, as is the extension rod and teflon bearing.
Power comes from a 12V 15 watt adapter, stepped up to ~51v by a regulator (rear left), and thence through the CLC filter (front right).
In the process of installing everything, I took the opportunity to swap the volume potentiometer for an ALPS RK09-L12B.
Thanks again to @AKSA and @xrk971 for making this design a reality.
Kind regards,
Drew
I wanted a minimalist look, so I moved the source selection switch to the back. As of now, it stays on the single source connected to it. To get from the 8-pin connector to the source jacks, I re-used the selector PCB, mounting it to the base and soldered pairs of wires to the RCA connectors.
An acquaintance has an amazing machine shop attached to his garage, and he drilled the holes for the front and back. The volume knob is salvaged from a Carver 900 receiver, as is the extension rod and teflon bearing.
Power comes from a 12V 15 watt adapter, stepped up to ~51v by a regulator (rear left), and thence through the CLC filter (front right).
In the process of installing everything, I took the opportunity to swap the volume potentiometer for an ALPS RK09-L12B.
Thanks again to @AKSA and @xrk971 for making this design a reality.
Kind regards,
Drew
I still have to:
- install feet
- trim the source selector switch spindle
- mount the LEDs properly
But while I am here, I have an issue with the amp that I'd like to address:
I'm using my cell phone as the source, with the earphone jack plugged into the AKSA-Lender via an RCA adaptor cord.
The power amp stage is an original spec MoFo, running on twin 19V power supplies.
Speakers are 8 ohm Dayton Audio PS95-8 "Point Source Series" 3 1/2" drivers.
I have adjusted the AKSA-Lender voltage regulator so that the voltage at the input posts is 48V.
The volume knob turns from 12 o'clock to about 10 o'clock. I can get decent sound up to about 8 o'clock, but any higher and there is a noticeable amount of distortion. While at this high setting (e.g 8-9 o'clock), one or the other channel cuts out, but then returns.
Is this to be expected? Should I expect it to be able to run at full volume?
How can I tell if the problem is the pre-amp or the power amp?
I'd like some clues about what to investigate.
Kind regards,
Drew
I'm using my cell phone as the source, with the earphone jack plugged into the AKSA-Lender via an RCA adaptor cord.
The power amp stage is an original spec MoFo, running on twin 19V power supplies.
Speakers are 8 ohm Dayton Audio PS95-8 "Point Source Series" 3 1/2" drivers.
I have adjusted the AKSA-Lender voltage regulator so that the voltage at the input posts is 48V.
The volume knob turns from 12 o'clock to about 10 o'clock. I can get decent sound up to about 8 o'clock, but any higher and there is a noticeable amount of distortion. While at this high setting (e.g 8-9 o'clock), one or the other channel cuts out, but then returns.
Is this to be expected? Should I expect it to be able to run at full volume?
How can I tell if the problem is the pre-amp or the power amp?
I'd like some clues about what to investigate.
Kind regards,
Drew
Hi Drew,
Very nice build. Superb looking.
The behavior you describe is certainly not correct.
Have you double checked your potentiometer to amp connection and you have the wiring correct? Pot wiper should lead to the input stage.
Can you please measure what the voltage of the output upstream of the blocking cap? Also, how many mA of current is flowing through the pair of input transistors? We need to check if the DC setpoints are direct.
Perhaps @AKSA can chime in with suggestions?
Could this be as simple as the MoFo is out of mojo when the volume pot is almost turned up to maximum?
Amplifiers that don't have any voltage gain themselves like:
MoFo
Firstwatt F4
single-ended-tokin-sit-thf-51s-common-drain-mu-follower-amplifier-45w.371187
total-domination-vfet-tdv-amp-using-2sk2087c.388926
Correction: I am using the ALPS RK27 (Blue) model potentiometer (https://www.parts-express.com/ALPS-RK27-10KA-Audio-Taper-Potentiometer-Solid-Shaft-023-204), NOT the RK09L type.
[ In post #1366, I copied the original model, not the replacement.]
[ In post #1366, I copied the original model, not the replacement.]
1. Potentiometer setup:
As I read the schematic, it shouldn't matter if pins 1 & 3 are swapped.
Nevertheless, this is how it is connected now.
As I read the schematic, it shouldn't matter if pins 1 & 3 are swapped.
Nevertheless, this is how it is connected now.
2. Output stream voltage. this looks to me like the voltage at the 'output' of R10 on one of the daughterboards, or the 'input' of C1027/C127
I read 25.2v and 25.3v.
I read 25.2v and 25.3v.
Those are good voltages about 1/2 between 48v rail and ground so you are not clipping early. It may be that your MoFo itself is clipping? Is it playing loud?
19v supply on MoFo is good for 25vpp max. That’s about 10w into 8ohms before clipping and distortion sets in.
Please measure your output voltage Vrms with a sine wave right before you hear distortion. 8.8Vrms is about where that occurs is my estimate.
19v supply on MoFo is good for 25vpp max. That’s about 10w into 8ohms before clipping and distortion sets in.
Please measure your output voltage Vrms with a sine wave right before you hear distortion. 8.8Vrms is about where that occurs is my estimate.
3. Transistor bias: I think this can be measured by the voltages across R4B (6K8) on the daughterboards.
For this, I read 17.7V, or 2.6mA through R4B on each
[ oof, that was tricky getting those ]
thanks a bunch for taking the time to help! 😍
Kind regards,
Drew
For this, I read 17.7V, or 2.6mA through R4B on each
[ oof, that was tricky getting those ]
thanks a bunch for taking the time to help! 😍
Kind regards,
Drew
That sounds like the right value. I think the long neck pair current is about 2.3mA or thereabouts so you are close. Looks like the preamp is working well. What happens when you connect this to a different amplifier?
The sound at 'breakup' is loud; the QA Tester in me wanted to see What Happens When™ . 🔨
Had I another power amplifier, I would do such a test. But alas, my maker fu is weak, and I have, at present, only my MoFo. The M2X and ACAMini await my attention.
Well, not totally true. I have an old Sansui 5000x and an NAD 7250pe, but I suspect each has voltage gain in their power section already, so I'm not sure that would be a valid test.
Again, I appreciate the time, and even more, the education. At this point, I think we should go with @Vunce 's suggestion that the issue lies with inherent limits of the MoFo, and not with the AKSA-Lender, especially since the bias points look good, and the volume level seems to match what you see in your setup, @xrk971
Kind regards,
Drew
Had I another power amplifier, I would do such a test. But alas, my maker fu is weak, and I have, at present, only my MoFo. The M2X and ACAMini await my attention.
Well, not totally true. I have an old Sansui 5000x and an NAD 7250pe, but I suspect each has voltage gain in their power section already, so I'm not sure that would be a valid test.
Again, I appreciate the time, and even more, the education. At this point, I think we should go with @Vunce 's suggestion that the issue lies with inherent limits of the MoFo, and not with the AKSA-Lender, especially since the bias points look good, and the volume level seems to match what you see in your setup, @xrk971
Kind regards,
Drew
Good morning fellow builders,
I am about to begin my build of this preamp. It will be entirely for preamp use and not HP. In my inventory I have 3 Wima caps, a MKP4 10uF/250V that will fit in the C122 holes, a MKP4 1.0 uF 100V that will fit in the C1023 holes, and a MKS 1.0uF 100V that will fit in the C1022 holes.
Question: Which Wima cap would be best to solder in. I have not decided on the boutique cap route for the input cap as of yet, so would just like to get it built and hear it.
Thanks for the help,
MM
I am about to begin my build of this preamp. It will be entirely for preamp use and not HP. In my inventory I have 3 Wima caps, a MKP4 10uF/250V that will fit in the C122 holes, a MKP4 1.0 uF 100V that will fit in the C1023 holes, and a MKS 1.0uF 100V that will fit in the C1022 holes.
Question: Which Wima cap would be best to solder in. I have not decided on the boutique cap route for the input cap as of yet, so would just like to get it built and hear it.
Thanks for the help,
MM