• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

Bruno Putzeys Balanced Preamp - Group Buy Part 2

Jump to Latest
#223
edd9000 said:
These:
D300-1-0207_zpsnsrztsz8.jpg


Seos-12 horn, 10" mid range, 18" bass. The horn is 105db+ sensitive and I have had issues finding a quiet pre amplifier. I currently don't have them set up so I cant find out if this pre is quiet enough, I suspect it is.
Click to expand...
Your 105dB/W horns need ~10W per channel to reach maximum output of ~110dB @ 2.5m listening distance.
From a 2Vac Source you only need a gain of 4times to 5times.
Any very low gain power amplifier that has an input referenced noise of <20nV/rootHz will be quiet enough.
Output noise of the power amplifier = 20nV * sqrt(26000-2000) * 5times = 0.015mVac
That is ~115dB below maximum output i.e. ~5dB below the threshold of hearing from 2.5m listening distance and ~5dB above the threshold of hearing @ ~300mm listening distance. It will sound silent.
You should find it easy to beat that 20nV/rootHz in most very low gain amplifiers designed to competantly put out only 10W into 8ohms.

If you use a normal 20times to 30times gain power amplifier, it will produce it's own noise AND apply excessive gain to the noise that has been added by any previous stages. The solution is to apply only just enough "system gain" to just reach clipping of the highest audio transient peaks.
There is a Forum Article on "system gain".
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html

An alternative to hunting down a very low gain 10W power amplifier is to use a Power Buffer that has a gain of ~0dB and apply some preamp gain of +12dB to +14dB using something like B.Putzeys balanced vol pot to generate the 8Vac to feed the Buffer.
 
Last edited:
#224
AndrewT said:
Your 105dB/W horns need ~10W per channel to reach maximum output of ~110dB @ 2.5m listening distance.
From a 2Vac Source you only need a gain of 4times to 5times.
Any very low gain power amplifier that has an input referenced noise of <20nV/rootHz will be quiet enough.
Output noise of the power amplifier = 20nV * sqrt(26000-2000) * 5times = 0.015mVac
That is ~115dB below maximum output i.e. ~5dB below the threshold of hearing from 2.5m listening distance and ~5dB above the threshold of hearing @ ~300mm listening distance. It will sound silent.
You should find it easy to beat that 20nV/rootHz in most very low gain amplifiers designed to competantly put out only 10W into 8ohms.

If you use a normal 20times to 30times gain power amplifier, it will produce it's own noise AND apply excessive gain to the noise that has been added by any previous stages. The solution is to apply only just enough "system gain" to just reach clipping of the highest audio transient peaks.
There is a Forum Article on "system gain".
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html

An alternative to hunting down a very low gain 10W power amplifier is to use a Power Buffer that has a gain of ~0dB and apply some preamp gain of +12dB to +14dB using something like B.Putzeys balanced vol pot to generate the 8Vac to feed the Buffer.
Click to expand...

I typically use an Aleph Mini, 10w, 20db gain. But I also like to use a valve amplifier I have, which has around 30db of gain. Both amplifiers are quiet enough on the horn alone, but connected directly to the DAC there is some hiss. Its not audible from where I sit so its not a huge concern, I also have a cheap balanced to unbalanced converter that allows me to reduce the signal into the valve amp to the point were the noise is inaudible.

My speakers are in storage for a while as I need to build a new rack. All I've been able to test the pre amplifier on is my stand in speakers, a pair of Kef 105s, as you can imagine with 84db sensitivity, they are silent.

I didn't think about a power buffer, I will add that to the long list of things to make.
 
#227
tfboy said:
Those values are a little hyped 😛

The old datasheet says for absolute maximum values:
Input voltage: 60V
Output current: 600mA
Power Dissipation: 2W

However, the newer datasheet for the same absolute maximum values states the same values except for Power Dissipation which is now halved to 1W.

There's an additional note which wasn't present in the previous datasheet:
"Please design your application in such a manner that the power dissipation of the HxR will not exceed
the given values. The thermal dissipation can be calculated using the following formula: (Vin – Vout) * Iin"

In addition, there's a Thermal dissipation under general performance data which says typical 0.5W, max 0.75W. This wasn't specified in the earlier datasheet at all.

So the reduced power combined with the new note to really point it out shows that it's easy to go over this limit without asking it to do something unreasonable.

Looking at the LM4562, the input current is pretty constant for a given voltage regardless of load - around just under 10mA with a +/- 12V supply. So that means around 40mA with four ICs. Which would equate to around 0.25W dissipated assuming an 18V supply to the regs, so I guess we're OK...

Do we have a recommended design for the power source?
Click to expand...
I'm seeing 92mA draw on each rail when supplied by my dual voltage lab supply, (it actually reads 0.10A but always overeads slightly).
For a 17Vin at the regulator and 12Vout the dissipation will be {17-12}*0.092 = 460mW
I see the +ve supply rail dropping by 20mA when the two input selector relays are disabled.
A 12-0-12Vac transformer is likely to place a bit more than 17V on the reg input.
These regs run pretty warm.

I have a couple of copper heatsinks that could be glued to the two sot223 devices on the regs.

I'm thinking of trying that to reduce the reg temps.
Or I can cut a couple of 0.5mm copper flags to solder to the sot223 collectors.
 
Last edited:
#232
I use the preamp to drive a pair of Hypex NC400s (then Shahinian Obelisks)

I am very wary of expressing an opinion on how it sounds, but to my 76 year old pair of ears and without a prolonged listen, it has been well worth the wait (Hows that for avoiding the question)

Very, very quiet without input signal, authoritative,full frequency range for my setup.
Better than driving the amps directly from my dac.

Build it, listen to it and make your own mind up but I don't think you will be disappointed.
Thanks Xavier, regards jtr
 
#233
Final reminders sent by PM to those who haven't responded.

From Sunday, as the components are freed up, I'll let those of you on the waiting list know 🙂

For those who have received their orders but haven't emailed me or posted in this thread, please do so. Thanks :cheers:
 
#239
Great, thanks for the updates, guys 🙂 That's 36 orders received, there are another 29 posted which I'm waiting confirmation of delivery.

One or two have responded to my chaser emails saying they're pulling out. I'm still waiting for other replies - they have till Sunday then I'll offer the left overs to those on the waiting list. 🙂
 
You must log in or register to reply here.
Top Bottom