Yes I have the output from the pre split to drive the ACA and a subwoofer.
Not sure where to go from here. If it is heat related I could test by putting a fan on it temporarily to see if that cures it but it sounds doubtful that's the issue.
Could it be something basic I am just not aware of or simple like a bad power supply or volume pot or cable shielding?
Not sure where to go from here. If it is heat related I could test by putting a fan on it temporarily to see if that cures it but it sounds doubtful that's the issue.
Could it be something basic I am just not aware of or simple like a bad power supply or volume pot or cable shielding?
Did you test the preamp before connecting the input selector panel? You may have a cold slider joint somewhere. Re-touch all solder joints from RCA in to RCA out and. All connection points in between.
If the bias current is correct on the amp core and DC setpoints are correct, the preamp should be working well. It is probably a connection or power supply issue. You are certain the bias current doesn’t change when the distortion sets in? It would be helpful if you can record the distortion sound and post it. Play on ACA and speaker and use phone to record video and post on YouTube. That’s the easiest way. Send me a PM for private link to video of you want vs public posting.
Try a different DC-DC step up. Take some closeup photos of your amp main board and duaghter boards from various angles and post. We might be able to see something.
If the bias current is correct on the amp core and DC setpoints are correct, the preamp should be working well. It is probably a connection or power supply issue. You are certain the bias current doesn’t change when the distortion sets in? It would be helpful if you can record the distortion sound and post it. Play on ACA and speaker and use phone to record video and post on YouTube. That’s the easiest way. Send me a PM for private link to video of you want vs public posting.
Try a different DC-DC step up. Take some closeup photos of your amp main board and duaghter boards from various angles and post. We might be able to see something.
Thanks for the guidance. I did not test the preamp before connecting the selector panel. I will try to bypass it and see if it clears up. One thing though is the volume pot does not attenuate the distortion, it remains at a constant volume regardless of how loud or quite the music is.
I will get some pictures and record the distortion and report back. Thanks again for the help.
I will get some pictures and record the distortion and report back. Thanks again for the help.
Think I sorted out the problem and the preamp has been singing beautifully all day. The issue seems to have been a bad solder joint to the primary left channel rca out. What happened is while I was trying to record the distortion the left channel to the main speakers kept cutting out. This was a new twist and eventually I tried connecting both the speakers and the sub to the secondary rca out with a y adapter and all was good. A bit odd because I run connections from the primary rca out to the headphone jack then to the secondary out. This meant the only connection not testing well was the flying lead from the pcb rca out to the left rca jack. Re-soldered these points and no more distortion or lost signal after a solid day of music.
I am not capable of using the flowery audiophile language to describe it but to my ears it sounds very nice and was well worth the effort. The 10db of gain is the right choice for me, volume goes louder than I want and at full volume sounds like it is right at the edge of the systems capabilities. With the headphones plugged in I have usable volume and again it will go much louder than I care to and sounds great. I have never listened to a high end system so I can't compare but this I know. My buddy spent a bunch on a Bose 2 channel with the small speakers and sub, he seems to be very pleased with his setup. My humble rig is light years better to my ears. But more important it makes me happy.
Thank you X for all the help. Sorry for cluttering up the thread with what was a basic problem. I am grateful you walked me through the measurements because it makes me feel my build is correct and I learned from it.
Attached is a pic of the preamp in its new home on top of my ACA.
I am not capable of using the flowery audiophile language to describe it but to my ears it sounds very nice and was well worth the effort. The 10db of gain is the right choice for me, volume goes louder than I want and at full volume sounds like it is right at the edge of the systems capabilities. With the headphones plugged in I have usable volume and again it will go much louder than I care to and sounds great. I have never listened to a high end system so I can't compare but this I know. My buddy spent a bunch on a Bose 2 channel with the small speakers and sub, he seems to be very pleased with his setup. My humble rig is light years better to my ears. But more important it makes me happy.
Thank you X for all the help. Sorry for cluttering up the thread with what was a basic problem. I am grateful you walked me through the measurements because it makes me feel my build is correct and I learned from it.
Attached is a pic of the preamp in its new home on top of my ACA.
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Congrats Spiggs!!! I knew it had to be something like a cold solder joint. 10dB + 15dB from ACA gives 25dB overall gain and that’s a good place to be. How does it sound compared to using the Schiit as preamps to drive the ACA?
What headphones are you using btw?
Your wooden panel faced boxes look great. Very nice and you have something you made yourself and it sounds great. This is the satisfaction one gets that keeps us firmly planted in DIY.
Beautiful work!!
What headphones are you using btw?
Your wooden panel faced boxes look great. Very nice and you have something you made yourself and it sounds great. This is the satisfaction one gets that keeps us firmly planted in DIY.
Beautiful work!!
Thank you for the kind words, I am please with the way it turned out. You are right, the satisfaction that diy brings is a huge draw for me. I can not thank you enough for making something like this attainable by someone such as myself.
My headphones are the Meze 99 Classics. These are the best headphones I have ever owned but that is not saying much since everything else was bargain basement from a chain store. Not knocking them at all, I like them very much just don't have anything to compare them to in the same price range.
As far as comparison to the Schiit Vali 2 I was using as a headphone/preamp before it is a surprising upgrade. I struggle with putting what I hear into words but what struck me is the greater authority of the finer points of music. Not louder or more dominate or harsh, just more there. Something that makes you want to sit and listen for hours on end and re-visit every record in your collection.
My headphones are the Meze 99 Classics. These are the best headphones I have ever owned but that is not saying much since everything else was bargain basement from a chain store. Not knocking them at all, I like them very much just don't have anything to compare them to in the same price range.
As far as comparison to the Schiit Vali 2 I was using as a headphone/preamp before it is a surprising upgrade. I struggle with putting what I hear into words but what struck me is the greater authority of the finer points of music. Not louder or more dominate or harsh, just more there. Something that makes you want to sit and listen for hours on end and re-visit every record in your collection.
It is singing beautifully! Stereo image is very good, you can really pinpoint where voices and instruments are placed. Better than it was to a very noticeable degree. What is interesting is that I spent a lot of time trying different speaker positioning when first setting them up. Before I thought the sound stage was good but it stopped horizontally at the speakers, now with the Aksa Lender preamp it extends beyond and the music just seems to float even more so above and around disconnected from the speakers in the way it should. What is best though is I can just lean back and listen and be lost in the music. As you said above foot tapping along with head swaying and the occasional somewhat embarrassing unintended sing along. Really making my modest speakers sound way better than they have a right to. A real learning experience hearing what difference a preamp can make.
You did not ask about headphones but I would like to add that this really surprised me. The Vali is billed as a headphone amp that could be used as a pre, the Aksa Lender as a pre that could be used as a headphone amp. The Aksa Lender is a leap better as a headphone amp, I did not expect this. I had thought it would be a better pre and hoped for an equal headphone amp. Not so, it is just so clear yet not harsh and with a realism that startles you into thinking that someone is in the room with you.
Overall I am beyond pleased. I do not feel the preamp lacks in any way with my setup. The gain seems just right with my amp and speakers or headphones, sources switch silently, the size fits right, and sound wise it does great with my speakers. Really taking on this project was the right choice.
I tested the new Melbourne/Yarra today as a verification build. Used it as a headphone amp and the sound was amazingly powerful for only 42mA bias current. +/-29v rails though and 15dB gain.
The YARRA Preamplifier/HPA for Melbourne DB Group Buy
The YARRA Preamplifier/HPA for Melbourne DB Group Buy
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I took another careful look at my genuine 2SA1837's - and I have two batches. One Aksa, who said he got them from the Toshiba factory 10 years ago, and one from an order I placed to Mouser 2 years ago. They may actually be laser etched - but finely done and deep. Not lightly done as on some knock offs. There are a few details like bevels on the epoxy and a small copper circle visible at the bottom of the lower two divets on the front tab. The legs are the biggest giveaway though. New knock offs will not be tinned but shiny plated stamped die-cut metal (maybe not even copper). Genuine will be tinned with Pb solder (before the who Pb free era) smoothly done over partially exposed copper legs.
Here are some photos of front and backside:
Looking at your photo your 2SA1837's, I see the copper in the divets, the bevel on the case, and the tinned legs - I believe you have genuines.
Thanks X for the post. I have a local supplier of 2Sa and 2Sc.
Here is what I have.
Looks to be genuine, isnt it? (pic taken with android camera and shared over whatsapp.
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Here’s another option for folks with an Aksa Lender to swap out boards and try sound of a PCA:
AKSA's Lender Preamp with 40Vpp Ouput GB
AKSA's Lender Preamp with 40Vpp Ouput GB
My Lender HPA has some interesting startup behavior I would like to better understand as I have not seen it mentioned in any of the AKSA Lender threads. When I turn it on it is silent for about 5-10 seconds. Then it emits distortion for another 5-10 seconds, then it is silent again. When I had it driving my ACA and would turn on the system I would first hear the ACA startup sound (HMMmmm) then the Lender (SHHhhhhhh) then the system was ready to go. I recently replaced the ACA with a Modulus 86. Now when I startup the system I still get the startup sound from the Lender HPA but I also notice that if I have music streaming during startup the volume will rise to very loud then back down to the volume as set. Is this common behavior for the AKSA Lender?
You might have too large of a value for the bleed off resistor at the output cap. Assuming you have a 220uF output cap, choose an R value of about 1k to give quick bleed off (under 1 Sec) but still have bass extension.
If you have a large value, what you may be getting is the output cap charging up and taking 10 seconds to discharge.
If you have a large value, what you may be getting is the output cap charging up and taking 10 seconds to discharge.
Hi.
Just bought a few of the 2SC4793 and 2SA1837 myself. Not used the supplier before and they were very cheap so nothing ventured...
They measure within the ranges from 130 to 160 HFE for both components. If they are thought genuine I am happy to share the source.
Best to all.
Just bought a few of the 2SC4793 and 2SA1837 myself. Not used the supplier before and they were very cheap so nothing ventured...
They measure within the ranges from 130 to 160 HFE for both components. If they are thought genuine I am happy to share the source.
Best to all.
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Hi Jotom,
Try comparing yours to the key features on my genuines. There is also the angle of the cut on the pins. Genuine is angled and yours are straight perpendicular. The laser etched labels on yours do not look right. They have a clear left right faster pattern and the genuines are more uniform. Look for exposed copper at base of pins. That’s a good one. The fakes are tinned 100% before they were encapsulated with the body.
Try comparing yours to the key features on my genuines. There is also the angle of the cut on the pins. Genuine is angled and yours are straight perpendicular. The laser etched labels on yours do not look right. They have a clear left right faster pattern and the genuines are more uniform. Look for exposed copper at base of pins. That’s a good one. The fakes are tinned 100% before they were encapsulated with the body.
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