DIY Purifi Amp builds

[mocenigo]

True that. But at the same time, I would also think that the average DIYer would be interested in having an amp that doesn't blow the speakers if you breathe heavily on the volume control.

Well, who wants to blow the speakers if you breathe heavily on the volume control?

Why anybody with 95+ dB efficient speakers is using Class D in a residential setting is beyond me. For PA use, yes. But in a living room? That blows my mind (and ears).

TBH I have that sensitivity because in my experience such speakers are more transparent and dynamic even at ludicrously low volume. I am using concentric compression driver for mids and highs into Le'cleach horns, and this level of detail and transparency is not achieved through any other means in my experience, not even AMT tweeters and ribbons. This is further refined into the upper treble by Visaton TL16H aluminium horns (not high end Fostexs, but again I am using them only for >= 10Khz).

The main "problem" is that those drivers and horns have a very high sensitivity. In fact, the tweeter part of my concentric BMS compression driver has a sensitivity of 108Db, so I use an autoformer to reduce the sensitivity by about 12Db. I also have Dayton Audio PA-460-8 woofers, and those for some reason react better when the amplifier has a very high damping factor... they sort of "sense" the potential power of the amp. I do not need all that power that the 1ET400A provide, but the sound is so clean and transparent, with the smoothness usually associated to SET, that I do not care much. I also still use less total power than a, say, 8W SET, because the latter would probably consume 20W (constant, because class A). So I tick the following boxes: [x] I do not need to multi amp (yet) because the amp covers nicely everything and can provide the right behaviour for any segment of the audible spectrum; [x] I have extremely transparent sound; and [x] I use little power.

Maybe one day I will move to a little 2A3 PP Or maybe just single ended.

True, if I dared drive the amps close to clipping only the woofer would survive, and my windows would shatter. I would probably also end up permanently deaf.

 

[JimB]

... The main "problem" is that those drivers and horns have a very high sensitivity. In fact, the tweeter part of my concentric BMS compression driver has a sensitivity of 108Db, so I use an autoformer to reduce the sensitivity by about 12Db. ...

SO. In your case, you really want NO added gain. Just bypass the EVAL1 input gain stage, for best gain matching with lowest noise and no extra cost.

 

[tomchr]

You could use something like my Modulus-86 or Modulus-186 with a ±24 V power supply and have plenty of power available for the horn drivers. Just saying.

I do understand why some want to use efficient drivers. What I do not understand is why some use a 450 W Class D amp with them.

Tom

 

[tmortimer]

My original idea for an adapter board was to provide a breakout board. This would allow you to experiment with different buffers, regulators, whatnot. It would also allow greater flexibility in the placement of the Purifi modules, including the option of building mono amps.

So here's a crazy thought: What if this breakout board also included a bypassable buffer with, say, 7.2 dB gain with an option to increase the gain by adding a resistor? This would allow those who want to play with buffers, regulators, whatnot to do so and those who want a plug-n-play solution to have that. The only drawback is that adding the extra buffer parts probably add ~$20-25 to the price of the board.

I found myself mulling over how one would use a breakout adapter board with my Universal Buffer. I found it silly that those who are building mono blocks should have to buy two stereo buffers and only use one channel of each. I mean... I don't mind selling more Buffers, but it seems a bit wasteful.

Tom

Mark me down for a pair.

 

[HammerSandwich]

My original plan was to give DIYers a modding platform. DIYers like to put their own flair on things. I then though that it would be pretty easy to accommodate the folks who put modules in boxes as well.

This. If you're happy enough without optimizing the last few dB, you'll just buy an assembled amp or Ghent kit. The people who want more customization probably desire extra flexibility for matching their sources & speakers.

 

[hyperknot]

True that. But at the same time, I would also think that the average DIYer would be interested in having an amp that doesn't blow the speakers if you breathe heavily on the volume control.

Actually, this is a very important point for me as well. I would be using a single source only, a USB DAC, and would be skipping the preamp / passive-preamp stage. But my biggest worry is exactly this, blowing out the speaker because for example the OS resets the volume after a system update.

I was considering using a high quality attenuator, but they really don't come cheap, for example a DACT CT2 for balanced stereo goes for 317 EUR, and that's just a single component! It's more expensive than some really good DACs. So I'm instead looking for a DAC which has hardware volume buttons and which hopefully never "forgets" the current setting after a power out, etc.

What would be a proper solution for this problem using the adapter board or the universal buffer? Would it be possible to set a "max level" on a given amp with DACT like quality for reasonable price? How would that work in practive, the user would experiment with cheap pot to find the max level and then buys 2 fixed resistors from some better quality brand and solders them to the board?

 

[vrdelta]

Mark me down for a pair.

Absolutely interested in this as well!

 

[ChrisPa]

My original idea for an adapter board was to provide a breakout board. This would allow you to experiment with different buffers, regulators, whatnot. It would also allow greater flexibility in the placement of the Purifi modules, including the option of building mono amps.

So here's a crazy thought: What if this breakout board also included a bypassable buffer with, say, 7.2 dB gain with an option to increase the gain by adding a resistor? This would allow those who want to play with buffers, regulators, whatnot to do so and those who want a plug-n-play solution to have that. The only drawback is that adding the extra buffer parts probably add ~$20-25 to the price of the board.

I found myself mulling over how one would use a breakout adapter board with my Universal Buffer. I found it silly that those who are building mono blocks should have to buy two stereo buffers and only use one channel of each. I mean... I don't mind selling more Buffers, but it seems a bit wasteful.

Tom

This sounds perfect
- mono
- breakout
- high quality buffer
(- ability to use alternative buffers if that's what someone really wants)
Allows immediate construction/evaluation of a mono amp
Ticks every box for me
Yes please

 

[mocenigo]

You could use something like my Modulus-86 or Modulus-186 with a ±24 V power supply and have plenty of power available for the horn drivers. Just saying.

I do understand why some want to use efficient drivers. What I do not understand is why some use a 450 W Class D amp with them.

Full disclosure: I am using a 54V dual supply, so the 1ET400A tops at 150W over 8 Ohm (and 300 over 4) ;-)

 

[tomchr]

Ah. Or as I would call it, "a safe-n-sane build".

Tom

 

[barrows]

TomC. I would prefer mono boards, complete with on board buffer/gain stage (adjustable gain via a resistor replacement)- bypass able. Definitely prefer a direct plug in to the Purifi modules (no separate breakout) for a shorter signal path and more compact build. Ability for the user to optionally provide their own local regulators on board (footprint for 781x style 3 pin regs would be nice for those who might like to experiment.

 

[mocenigo]

TomC. I would prefer mono boards, complete with on board buffer/gain stage (adjustable gain via a resistor replacement)- bypass able. Definitely prefer a direct plug in to the Purifi modules (no separate breakout) for a shorter signal path and more compact build. Ability for the user to optionally provide their own local regulators on board (footprint for 781x style 3 pin regs would be nice for those who might like to experiment.

have you rewritten your response? Anyway, I prefer the LT3045, it seems to have less noise, but caps at 15V, wrt the 78xx series. Of course there are 78xx replacements which have much lower noise floor. Since I am in Europe I have eyes those from NewClassD: what do you think of them?

 

[tomchr]

I was thinking to provide more flexibility on the regulators by providing the unregulated supply on some terminals and have you provide the regulated voltage on some other terminals. If you decide to forego regulators and just use the regulated voltage provided by the SMPS1200, you just move some jumpers.

This would allow you to use the regulated supply from the SMPS or whatever regulator you choose. I'd rather not paint myself into a corner by supporting only LM7815/LM7915. Some will want LM317/337 or Hypex HxR12. Others Jan Didden's Silent Switcher. Yet others will use a linear supply. The possibilities are endless.

Tom

 

[mocenigo]

I was thinking to provide more flexibility on the regulators by providing the unregulated supply on some terminals and have you provide the regulated voltage on some other terminals. If you decide to forego regulators and just use the regulated voltage provided by the SMPS1200, you just move some jumpers.

This would allow you to use the regulated supply from the SMPS or whatever regulator you choose. I'd rather not paint myself into a corner by supporting only LM7815/LM7915. Some will want LM317/337 or Hypex HxR12. Others Jan Didden's Silent Switcher. Yet others will use a linear supply. The possibilities are endless.

Tom

I second this. The simpler the better, leaving maximum flexibility.

 

[barrows]

I was thinking to provide more flexibility on the regulators by providing the unregulated supply on some terminals and have you provide the regulated voltage on some other terminals. If you decide to forego regulators and just use the regulated voltage provided by the SMPS1200, you just move some jumpers.

This would allow you to use the regulated supply from the SMPS or whatever regulator you choose. I'd rather not paint myself into a corner by supporting only LM7815/LM7915. Some will want LM317/337 or Hypex HxR12. Others Jan Didden's Silent Switcher. Yet others will use a linear supply. The possibilities are endless.

Tom

Sounds good to me and makes sense.

 

[Zoomer]

I have eyes those from NewClassD: what do you think of them?

They came up in another thread, but not much hard info so far.

 

[mocenigo]

They came up in another thread, but not much hard info so far.

I meant the 78xx compatible regulators, not their amplifiers

 

[mocenigo]

Ah. Or as I would call it, "a safe-n-sane build".

Safety depends on my craziness here. It could still deliver a "first scene of Back to the Future" scenario.

 

[mocenigo]

I was considering using a high quality attenuator, but they really don't come cheap, for example a DACT CT2 for balanced stereo goes for 317 EUR, and that's just a single component! It's more expensive than some really good DACs. So I'm instead looking for a DAC which has hardware volume buttons and which hopefully never "forgets" the current setting after a power out, etc.

Why not a relais-and-resistor-network based attenuator?

 

[Zoomer]

I meant ...

Oops.