Jwjarch,
Nice progress and looking good!
You’ve got a brand new sweet preamp and soon an ALPHA20
First Sound!
I managed to get one channel up and running today. Sounds great so far although I still need to get the 2nd channel working and fully integrate it into my minidsp setup. When I powered everything up the DC spiked at first (I'm guessing this DC is what causes the speaker cone to move?) then settled down to 1mV as it should. After that it was on to the speaker test. I definitely get the cone movement at switch on and no pops or thumps. I'm using the 1000uF at C103. I'm also working on a circuit for the fans using an LM7812 and a couple caps. The idea is the fan will pull air through the first heat sink and push it through the next. I'll monitor temps once I get both channels working. Exciting stuff!
I managed to get one channel up and running today. Sounds great so far although I still need to get the 2nd channel working and fully integrate it into my minidsp setup. When I powered everything up the DC spiked at first (I'm guessing this DC is what causes the speaker cone to move?) then settled down to 1mV as it should. After that it was on to the speaker test. I definitely get the cone movement at switch on and no pops or thumps. I'm using the 1000uF at C103. I'm also working on a circuit for the fans using an LM7812 and a couple caps. The idea is the fan will pull air through the first heat sink and push it through the next. I'll monitor temps once I get both channels working. Exciting stuff!
jwjarch,
Good to see another alpha 20 up and running.
I am a little uncomfortable with the cone movement at startup but have been assured by Hugh and X that it won't do any harm.
Just a thought could a simple toggle switch in line on the positive speaker output solve the issue instead of using relays.
Yes you would need to wait 5 or 10 seconds then flip the switch again I'm not sure if this will work Just asking the Question.
Steve.
Good to see another alpha 20 up and running.
I am a little uncomfortable with the cone movement at startup but have been assured by Hugh and X that it won't do any harm.
Just a thought could a simple toggle switch in line on the positive speaker output solve the issue instead of using relays.
Yes you would need to wait 5 or 10 seconds then flip the switch again I'm not sure if this will work Just asking the Question.
Steve.
JW, Steve,
It is high, I had not realised it was 12.5V.
This all happens because the LTP is slow to arc up at switch on. During the first couple of positive volts on the two emitters, the LTP is not actually working, and the offset at the asymmetric output stage is not controlled.
You can reduce it by simply putting in a 100uF rather than a 1000uF. However, there will be a sound, higher than the present infrasonic pulse which takes around three seconds. If you are happy with a short bump, audible through the speaker cone, this excursion will be reduced to a couple of volts which will never take the voice coil to full extension.
The best option would be to add a three delay speaker connection - I like a mosfet, SS relay - and this is used in most expensive commercial amps. But the complexity mitigates the low cost and simplicity of the ALPHA as it stands. I think I'd go for a 100uF and be done with it!
Cheers,
HD
It is high, I had not realised it was 12.5V.
This all happens because the LTP is slow to arc up at switch on. During the first couple of positive volts on the two emitters, the LTP is not actually working, and the offset at the asymmetric output stage is not controlled.
You can reduce it by simply putting in a 100uF rather than a 1000uF. However, there will be a sound, higher than the present infrasonic pulse which takes around three seconds. If you are happy with a short bump, audible through the speaker cone, this excursion will be reduced to a couple of volts which will never take the voice coil to full extension.
The best option would be to add a three delay speaker connection - I like a mosfet, SS relay - and this is used in most expensive commercial amps. But the complexity mitigates the low cost and simplicity of the ALPHA as it stands. I think I'd go for a 100uF and be done with it!
Cheers,
HD
Very nice work Jwarch! Those are big CPU coolers! Big enough for B.B. even.
I like how big the copper pads are on those. Which part number are those from the HP salavage yard?
That 12.5v movement is a lot. Not everyone’s speakers can handle a 12v slap. Vunce tried a smaller 220uF and said that the pop sound was louder but I wonder if the voltage was smaller.
Could perhaps a longer time constant be applied somewhere on the Aleph circuit that allows the DC bias to rise up to speed slowly. I have seen this done on the bias circuit of the M2 (takes 45sec) but has no dynamic CCS feature like the Aleph does.
For dc protection and turn-on delay I use two independent parallel relays circuits(upc1237) for each channel.
I use different relays or capacitor size in the relay PS so they switch at different timings, this way there's always the same relay that takes the arc.
During the turn-on delay there's also a 20w 8ohm resistor for load instead of the speakers, this 8ohm resistor reduces the arc.
Regards,
Danny
I use different relays or capacitor size in the relay PS so they switch at different timings, this way there's always the same relay that takes the arc.
During the turn-on delay there's also a 20w 8ohm resistor for load instead of the speakers, this 8ohm resistor reduces the arc.
Regards,
Danny
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I think better to have a separate high-quality toggle switch for the speakers.
Keep the speakers wiring away from the power switch. I believe if we can find a good toggle switch it would be better than relays.
12.5V a lot - my Visaton got 40V when my amp had a thermal runaway. Still works fine but I would not do that again.
Everything over 5V can be devastating to some speakers.
Keep the speakers wiring away from the power switch. I believe if we can find a good toggle switch it would be better than relays.
12.5V a lot - my Visaton got 40V when my amp had a thermal runaway. Still works fine but I would not do that again.
Everything over 5V can be devastating to some speakers.
Very nice work Jwarch! Those are big CPU coolers! Big enough for B.B. even.
I like how big the copper pads are on those. Which part number are those from the HP salavage yard?
That 12.5v movement is a lot. Not everyone’s speakers can handle a 12v slap. Vunce tried a smaller 220uF and said that the pop sound was louder but I wonder if the voltage was smaller.
Could perhaps a longer time constant be applied somewhere on the Aleph circuit that allows the DC bias to rise up to speed slowly. I have seen this done on the bias circuit of the M2 (takes 45sec) but has no dynamic CCS feature like the Aleph does.
Thanks for the compliments everyone! This has been a fun project so far. I've done a lot of scavenging around the garage to see how I could make the heatsinks work. I tried it with only 2 but the layout was actually simpler to get it to work with 4. They're HP Dl580 G7 CPU Heat Sink p/n 570259-001. They came up on eBay. 4 for $20 so I couldn't pass them up. They're built for Xeon servers so they can supposedly handle up to 130 watts a piece. If and when I build a BB I'll swap the ALPHA 20 into a Dissapante case and reuse the heatsinks.
Regarding the turn on DC. I definitely don't want to subject my speakers to that every time I switch on the amp. I'll probably mess around with a few different solutions. I have some delay/protect boards laying around that I might give a try. I am worried though that they will steal all the magic out of the signal going to the speakers. What about a DPDT toggle switch with an 8ohm dummy load on the other side? Might be worth a try and potentially inaudible in terms of affecting the signal.
The CapMX might be a good solution also. I have a couple Juma Prasi boards. My only apprehension there is the additional heat that needs to be dissipated just from the CapMX.
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Nice job JW!
Great to see another Alpha born
Also, savvy score on the cpu coolers.
The Juma/Prasi CapMx didn’t workout well for me with the ALPHA20.
Aatto's new 10F/SB23NRXS45 FAST speakers are actively powered by an Alpha 20 on top and an FH9 on the bottom. Nice work!
http://www.diyaudio.com/forums/full...rs225-8-fast-ref-monitor-110.html#post5451669
http://www.diyaudio.com/forums/full...rs225-8-fast-ref-monitor-110.html#post5451669
Nice job JW!
Great to see another Alpha born
Also, savvy score on the cpu coolers.
The Juma/Prasi CapMx didn’t workout well for me with the ALPHA20.
Thank you Vunce. I remember you and X tried out the Juma/Prasi CapMX. Do you think it's possible to use beefier mosfets to get a better result or does that just convert more voltage into heat for no reason?