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ACA Amp Questions
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Old 19th July 2013, 03:28 PM   #1
mstomaso is offline mstomaso  United States
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Default ACA Amp Questions

I am a self-proclaimed tube head. I am currently running a KT-88 SET amp that sounds pretty good to me (of course) into a pair of Martin-Logan Motion 12s (92 db, 4 ohms).

It took me ten years to get to this point, which is some indication of how excessive-compulsive I am. The amp is a 6SN7-6SN7-KT-88 triode mode with regulated DC heaters and 350 VDC regulated HV supply. I settled on this after running the gamut of 2A3, 300B, CCS loading, shunt fed regs, parafeed, AC heaters, etc etc; you know the drill.

I include this info so you can understand my level of depravity. (I hung around on AA until I could not stand it anymore. :-) )

I am looking for new worlds to "conquer", and I came across the ACA amp, which is exactly what I was looking for in terms of dipping my feet into the world of SE sand amps.

I'm not sure it will drive my speakers in stock form. (If it will, great.)

If not, can I parallel two output transistors if I change the resistor values to get 2 amps from the CCS, and then build an appropriate power supply, use enough heat sink, etc.?

Aternatively, can I double the supply voltage to permit wider swings?

I'm not sure about the impact on the feedback loop. It appears like 20 db to me, but I am not a feedback guy so I'm not sure about that aspect.

Thanks in advance.

Mike
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Old 19th July 2013, 05:02 PM   #2
Nelson Pass is offline Nelson Pass  United States
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ACA Amp Questions
You can start scaling and playing with the ACA, but then you will have another
amplifier, at which point you might look around at other contenders.

Not very likely that the stock ACA will satisfy you into the ML's.

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Old 19th July 2013, 09:28 PM   #3
Loudthud is offline Loudthud  United States
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You should consider the PLH link: https://www.passdiy.com/project

The PLH has plenty of single ended sweetness, and you can experiment with the amount of distortion. I assume you built the KT88 amp, does it use feedback?
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Old 19th July 2013, 10:16 PM   #4
mstomaso is offline mstomaso  United States
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Thanks for the suggestions.

I'm also interested in the Aleph J, and I'm having a hard time finding schematics, BOMs, etc. I'm new to this forum, so if anyone can point me in the right direction I'd appreciate it.

Regarding the KT88 amp, no feedback. I have the KT88s triode strapped and it's just a straight three stage SE amp.
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Old 19th July 2013, 10:51 PM   #5
Loudthud is offline Loudthud  United States
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You will have trouble finding genuine IRF244s for the PLH, you can use IRFP240s. You will have to do your own layout and power supply. I don't know of any PCBs available and you will need very large heatsink(s). So it's not such an easy project. You should be able to find more support for an Aleph J.
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Old 19th July 2013, 10:52 PM   #6
overtheairbroadcast is offline overtheairbroadcast  Canada
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I am also a tube head of sorts (KT88, EL84, EL34 all in SE) but I am also a builder/maker and I also like sand.

Never tried making a transistor based amp, but after reading Make Magazine's website (I also get their paper mag) and reading the threads here, I have purchased the ACA and it is waiting for a chassis and the school year to start (I have kids, so spare me-time is thin in the summer).

As soon as the ACA is done, I am going to tackle the Mini-A or maybe skip directly to the most popular amp if you count thread replies, distinct individual thread topics, and the kudos I read... I am talking about the Pass diy F5.

That will in most likelihood drove your Martin Logans. If not, there is always the F5 Turbo.

Both board sets (F5 and F5 Turbo) are available from the diyaudio.com store.

How ready and set am I? I have all the chips and most of the parts for the F5, but not yet the boards. Mini-A maybe first...
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Old 19th July 2013, 11:07 PM   #7
12B4A is offline 12B4A  United States
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Quote:
Originally Posted by mstomaso View Post
Thanks for the suggestions.

I'm also interested in the Aleph J, and I'm having a hard time finding schematics, BOMs, etc. I'm new to this forum, so if anyone can point me in the right direction I'd appreciate it.
The latest BOM I was directed to was here. You might also want to comb through that thread for general info. The Aleph J boards that are available now in the diyAudio store are intended for this version of the Aleph J (I think) and 6L6 is writing a build guide. One other place I found is the old Aleph 30 wiki that gives some pretty good info on a preceding Aleph design.
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Old 19th July 2013, 11:13 PM   #8
Bones13 is offline Bones13  United States
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ACA Amp Questions
I just looked at the DIYAudio store, and the Aleph J boards seem to already be sold out. I also am trying the ACA amp kit, and have a couple of DIY tube amp kits completed.

My speakers are Zu Audio Essence speakers, that are more of a full range speaker with good efficiency. I am building the ACA first, to test the waters with SS SE. I will consider the Aleph J as the next step, I will stick with my EL34 PP amp rather than build an F5. I need to jump on the Aleph boards next time they run a batch.
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Old 20th July 2013, 12:01 AM   #9
mstomaso is offline mstomaso  United States
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Just an FYI, even though my speakers are MLs, they are conventional cone speakers, not electrostatics.
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Old 21st July 2013, 02:50 AM   #10
george_ct is offline george_ct  Romania
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Quote:
Originally Posted by Loudthud View Post
I don't know of any PCBs available
Yes, it is. Follow these links:
Plh
Plh
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