I was finally able to find enough time to finish assembly on my second ACA monoblock yesterday. Things went fairly well with set up and adjustment.
I mentioned in a previous post that I had decided to move things along by sourcing the 24V SMPS from Mouser that are being offered with the latest kits rather than building a linear supply right away. I was very impressed with how quiet the amps were with the Meanwell supply.
My indulgence with this project was slipping Semisouth R100A into the Q1 positions with some socket harness’ that I built from scratch so that they could be easily removed if desired to use in other circuits or to try comparing IRF240 or similar transistors in the Q1 position.
The boards are the 1b version. R15 is present @2.21K, R12 is set to 39.2K.
Since all I had for adjusting the amps were voltmeters, after about an hour or so and 3 adjustments I left P1 alone when the voltage at the Q1 drain on both amps settled at about 11.7 volts. During cold start up today they were between 12.1-12.3 volts. They appear to be settling in a little lower at 11.6 volts today after warming up for 40 minutes and one LP side.
I am a little concerned about heat build up. The top covers are set in place for now with probes still in place to make adjustments. I’ve been playing music for a little while. It was quite hot yesterday where I live...over 90F. I had to have the AC on and was trying to hold the ambient temperature in the living room to about 70F to be comfortable. It cooled off quite a bit today, so the AC is not needed, but the ambient temperature is the same in the room.
After the amps played for an hour yesterday I tried holding my palm to the heat sinks of the amps, but it was difficult to leave my hand longer than 5 seconds or so.
I set a temperature probe up for my meter and clipped the probe onto the heat sink in between the fins so it made contact roughly in the center of where the transistors were mounted inside of the amps. My readings were between 119-123F yesterday.
I searched the ACA thread a bit and read that this temperature is in line with what some others have experienced in similar builds but it is toward the upper limits of what is acceptable?
I am a little concerned about being without a buffer for heat dissipation if the amps were to run away due to a higher room temp and/or playing at higher level.
Today I took more temperature measurements about 1-2 hours after starting the amps up. I was using my vinyl playback rig through my lightly hot rodded DCB1 at a moderate listening level that I usually use.
At about 30 minutes into listening I started measuring and found the temp on the center of the outside of the heat sinks to be about 123F on both amps.
I took surface temperatures of transistor Q1 which was 127.4F and Q2 134.3F in my right channel amp. Surface temperatures of transistor Q1 was 144F and Q2 140.9F in my left channel amp. I allowed the temperature probe to sit and stabilize for several minutes with each measurement.
I was curious about why Q1 seemed a bit higher in the left channel amp and took a second round of measurements on the right channel to see if the time that elapsed during testing had allowed more heat to build up. Both transistors in the right channel seemed to have leveled off at about 132F.
I’m thinking these fluctuations are simply due to how hard the amps may be working at a particular moment based on the material I was playing, or a difference in ambient temperature...maybe I was inadvertently breathing in the amp. I tried to be consistent and walked away for the same amount of time as I took measurements.
These transistors are not matched and regardless as to fluctuations in dissipation or the difference from one amp or transistor to another my only real concern is knowing that I am not risking damage or severely shortening the life span of the components by running them this hot.
My understanding is that I should be able to dial in the voltage measurements at the drain of Q1 to about half the power supply’s voltage level.
I don’t know what is to be gained by another 4/10ths of a volt and I don’t want to “turn them up” so to speak if it will just create more heat that I don’t know will be beneficial to performance.
As I said, I have no special measurement equipment...beyond a very simple pocket digital oscilloscope that I’ve never used before and haven’t figured out how to use yet.
As far as my listening impression goes, I would have to say that the most obvious impact in my system that the ACA amps have compared to the LM3875 gainclone I had been using for a few years was a large amount of lower frequency response that now appears to come from the horns that they drive.
My system is simple (a.k.a. unfinished) full range front loaded horns with a Jamo subwoofer that was adjusted to supplement the 28 or so watts that my gainclone produced for the horns.
The gainclone, which gave the impression of having a lot of detail, always seemed completely devoid of any ability to produce anything that could be remotely interpreted as upper bass or low mid range even though the horns and drivers were supposed to be capable of a reasonable output down to 200Hz.
My Jamo sub was dialed up to match the output capability of the gainclone and its crossover set as high as possible to try to get it to help the horns that I allowed to just roll off, but there was obviously a big hole left in the frequency response that was easily missed with any material that required some punch.
When I fired the ACA amps up in the system I had to lower the level and crossover point of the sub more than once to get rid of an overwhelming amount of boomy bass response.
The ACAs sound warmer, but not like I’m having butter and syrup poured in my ear. I sensed I was relaxed with the sound they produced. The gainclone was more easily able to put me on edge when it came to sounds like strings being plucked sharply by a pick, a reed or cymbal resonance...vocalists who hit their T’s hard.
I don’t think the ACAs suffer in the area of detail compared to the gainclone. It is possible that their combination with the laid back sound of the Tang Band 1808s in the horns may not be a perfect match...they are definitely very capable of playing loud enough for me. I am curious what trying the more efficient Lowther DX3s with them in the horns will result in.
I mentioned in a previous post that I had decided to move things along by sourcing the 24V SMPS from Mouser that are being offered with the latest kits rather than building a linear supply right away. I was very impressed with how quiet the amps were with the Meanwell supply.
My indulgence with this project was slipping Semisouth R100A into the Q1 positions with some socket harness’ that I built from scratch so that they could be easily removed if desired to use in other circuits or to try comparing IRF240 or similar transistors in the Q1 position.
The boards are the 1b version. R15 is present @2.21K, R12 is set to 39.2K.
Since all I had for adjusting the amps were voltmeters, after about an hour or so and 3 adjustments I left P1 alone when the voltage at the Q1 drain on both amps settled at about 11.7 volts. During cold start up today they were between 12.1-12.3 volts. They appear to be settling in a little lower at 11.6 volts today after warming up for 40 minutes and one LP side.
I am a little concerned about heat build up. The top covers are set in place for now with probes still in place to make adjustments. I’ve been playing music for a little while. It was quite hot yesterday where I live...over 90F. I had to have the AC on and was trying to hold the ambient temperature in the living room to about 70F to be comfortable. It cooled off quite a bit today, so the AC is not needed, but the ambient temperature is the same in the room.
After the amps played for an hour yesterday I tried holding my palm to the heat sinks of the amps, but it was difficult to leave my hand longer than 5 seconds or so.
I set a temperature probe up for my meter and clipped the probe onto the heat sink in between the fins so it made contact roughly in the center of where the transistors were mounted inside of the amps. My readings were between 119-123F yesterday.
I searched the ACA thread a bit and read that this temperature is in line with what some others have experienced in similar builds but it is toward the upper limits of what is acceptable?
I am a little concerned about being without a buffer for heat dissipation if the amps were to run away due to a higher room temp and/or playing at higher level.
Today I took more temperature measurements about 1-2 hours after starting the amps up. I was using my vinyl playback rig through my lightly hot rodded DCB1 at a moderate listening level that I usually use.
At about 30 minutes into listening I started measuring and found the temp on the center of the outside of the heat sinks to be about 123F on both amps.
I took surface temperatures of transistor Q1 which was 127.4F and Q2 134.3F in my right channel amp. Surface temperatures of transistor Q1 was 144F and Q2 140.9F in my left channel amp. I allowed the temperature probe to sit and stabilize for several minutes with each measurement.
I was curious about why Q1 seemed a bit higher in the left channel amp and took a second round of measurements on the right channel to see if the time that elapsed during testing had allowed more heat to build up. Both transistors in the right channel seemed to have leveled off at about 132F.
I’m thinking these fluctuations are simply due to how hard the amps may be working at a particular moment based on the material I was playing, or a difference in ambient temperature...maybe I was inadvertently breathing in the amp. I tried to be consistent and walked away for the same amount of time as I took measurements.
These transistors are not matched and regardless as to fluctuations in dissipation or the difference from one amp or transistor to another my only real concern is knowing that I am not risking damage or severely shortening the life span of the components by running them this hot.
My understanding is that I should be able to dial in the voltage measurements at the drain of Q1 to about half the power supply’s voltage level.
I don’t know what is to be gained by another 4/10ths of a volt and I don’t want to “turn them up” so to speak if it will just create more heat that I don’t know will be beneficial to performance.
As I said, I have no special measurement equipment...beyond a very simple pocket digital oscilloscope that I’ve never used before and haven’t figured out how to use yet.
As far as my listening impression goes, I would have to say that the most obvious impact in my system that the ACA amps have compared to the LM3875 gainclone I had been using for a few years was a large amount of lower frequency response that now appears to come from the horns that they drive.
My system is simple (a.k.a. unfinished) full range front loaded horns with a Jamo subwoofer that was adjusted to supplement the 28 or so watts that my gainclone produced for the horns.
The gainclone, which gave the impression of having a lot of detail, always seemed completely devoid of any ability to produce anything that could be remotely interpreted as upper bass or low mid range even though the horns and drivers were supposed to be capable of a reasonable output down to 200Hz.
My Jamo sub was dialed up to match the output capability of the gainclone and its crossover set as high as possible to try to get it to help the horns that I allowed to just roll off, but there was obviously a big hole left in the frequency response that was easily missed with any material that required some punch.
When I fired the ACA amps up in the system I had to lower the level and crossover point of the sub more than once to get rid of an overwhelming amount of boomy bass response.
The ACAs sound warmer, but not like I’m having butter and syrup poured in my ear. I sensed I was relaxed with the sound they produced. The gainclone was more easily able to put me on edge when it came to sounds like strings being plucked sharply by a pick, a reed or cymbal resonance...vocalists who hit their T’s hard.
I don’t think the ACAs suffer in the area of detail compared to the gainclone. It is possible that their combination with the laid back sound of the Tang Band 1808s in the horns may not be a perfect match...they are definitely very capable of playing loud enough for me. I am curious what trying the more efficient Lowther DX3s with them in the horns will result in.
Attachments
Although the temperatures sound excessive, in reality they are well within safe limits for the semiconductors.
Even at 100C/212F (case temperature) it is rated for 12 amps. So set the amp up at normal operating temperature and then forget about it.
And you just might find the louder you play it, the cooler it runs
so no worries there either.
Even at 100C/212F (case temperature) it is rated for 12 amps. So set the amp up at normal operating temperature and then forget about it.
And you just might find the louder you play it, the cooler it runs
so no worries there either.Attachments
LOL...thanks for the giggle.
I’ve been very grumpy since an attempted listening session this AM when a mysterious scratchy static-like noise started emanating from my speakers in the middle of the first track of Melody Gardot’s My One And Only Thrill.
It appears I have an recurring unpredictable issue with the Boozehound phono amp I assembled a few years back. There were some issues getting it to work properly from the beginning. I had to order some extra JFETs to replace some that came with the kit because they were either defective or I damaged them during asssembly.
I also had issues trying to find a quiet power supply for it. It seemed to work fine at first with an old SONY laptop supply I had that was feeding a miniDSP at the same time. The miniDSP did always added some humming to the system.
Eventually that laptop supply died on me, I stopped using the miniDSP and resorted to a battery supply for the phono amp. I can’t put my finger on when, but I started attributing the noise to the battery voltage dropping too low or the fact that it was overcharging to 25-26 volts and overdriving the circuit.
It’s a very frustrating situation, I tried screwing around with the signal connections and tonearm ground but that didn’t eliminate the problem. I also decided to open up one of the NiCd battery packs and removed two cells to drop the voltage down to 22.5 volts. I still got the noise afterward.
Sorry about the sidetrack...thanks for the feedback on the ACAs. I hope I can sort things with the phono or put together a replacement soon so I can be enjoying them more.
Might wander around on the circuit board in the preamp with a soldering iron and reheat every junction. Cold solder joints (even if the look great on the surface) will cause noise like described. If it is definitely isolated to the preamp OK. If not, you might do the same on your ACA boards.
Those were my thoughts as well.
I isolated the noise to the phono amp. The right channel in particular. Having separate pots in my preamp for each channel helped. There was only very faint noise coming from the left channel that seemed to be a result of whatever chaos was going on in the right. When I disconnected the inputs this became apparent as the noise in the right channel went through the roof.
I pulled the board out of the case. Things started coming back to me as I looked over the solder joints on the board. I had been struggling with old solder that had built up some oxidation when I originally stuffed the board.
I cleaned everything off with a brush and alcohol and then took a close look with a magnifying loop. I could see that things didn’t look that good on the JFET I had replaced previously. I reworked the joints with some fresh flux and solder.
I rigged up a way to power the circuit up and connected a RCA pigtail to the output of the problem channel so I could test it for noise.
Either I fixed the noise or it decided to stop just to screw with me. I left it powered up for a half hour or so and didn’t hear a peep.
I’ll test it again tomorrow. I think I’m going to take this opportunity to integrate the battery supply inside the phono amp case with a voltage meter and a switch system to charge and select either the battery or an external source for power.
I was able to enjoy the ACAs with a different source anyway while tinkering on the phono amp.
Hi SHN,
If you're considering building any of the amps mentioned and machining is not
your forte, consider buying a deluxe chassis from the diyaudio store.
One thing I will add to 6L6's answer is that if you're in Canada, you may
want to budget more to account for shipping and HST. The two most expensive parts
of the amp are the chassis and transformer/power supply and unfortunately
the parts for both are heavy and expensive to ship. Not a deal breaker by any means,
but just something to keep in mind.
And yes, the Aleph J is really nice and can take a balanced input. In fact, I built mine
only with balanced input.
Cheers,
Dennis
Thanks again for being so helpful. I just found out the cost of the chassis so I think I am going to budget CAD1,000. I have had some basic machining/fitting training many years ago but I don't have the tools anyway so I am going to have to bite the bullet and support the diyaudio store a little at the same time.
on Iceland ?
Polar ice caps are melting due to high number of class a amps build and used on Iceland (maybe Greenland too?). That's much more likely than chinese hoax i'd say...
Any icelanders out there?
Yes. It requires 1 resistor and 1 RCA jack. I need only to build it and photograph it, and it will be part of the guide.
If you are interested in Monoblocks but only have RCAs, you'll be fine, go ahead and order 2 ACA kits.
Could You have both bridged options Option 1 and Option 2 in the same Chassis at the same time. It will be cool to be able to use it optionally in bridged and in stereo for unbalanced sources. I have two kits ;-)
I agree. From what I can gather, you can either build:
- An RCA Stereo (by not including the XLR input and the extra wiring)
- An RCA Stereo / Balanced Monoblock
- An RCA Monoblock (non balanced)
I see your motivation of not needing to reassign speaker wires, etc.
I have no idea how an RCA to XLR with shorted signals to both pins would perform or how it would affect sound quality / phase / etc? I am not yet all that familiar with all of this, but that could be route to force an 'RCA Monoblock' using the XLR input (albeit also loosing the balanced wonders )?
- An RCA Stereo (by not including the XLR input and the extra wiring)
- An RCA Stereo / Balanced Monoblock
- An RCA Monoblock (non balanced)
I see your motivation of not needing to reassign speaker wires, etc.
I have no idea how an RCA to XLR with shorted signals to both pins would perform or how it would affect sound quality / phase / etc? I am not yet all that familiar with all of this, but that could be route to force an 'RCA Monoblock' using the XLR input (albeit also loosing the balanced wonders
)?
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