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Which preamp for Amp Camp?
Which preamp for Amp Camp?
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Old 14th July 2017, 11:54 PM   #1
Skylar88 is offline Skylar88  South Africa
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Default Which preamp for Amp Camp?

Hi Guys, newbie here.

Iím in the process of constructing a pair of Amp Camp amps because Iíve been without decent audio equipment for far too long. Cost is a big consideration right now, so Iím ordering and building as my budget allows. Iím currently waiting for custom PCBís that I designed in KiCad and the heatsinks are on their way too. Next will be the actual components and case.

In the meantime Iím considering my options w.r.t. a preamp. So far, Iíve looked at the following:
Objective2 Headphone preamp
Bride of Zen
Doug Self preamp
New PASS preamp
All are relatively complicated (and maybe too expensive) as a first build. Therefore Iím leaning towards a quick and dirty solution for now. Maybe something simple off eBay, like the LME49720+Shield+ALPS Potentiometer stereo preamplifier kit.

Or the DIY X29F Single-ended DC Class A preamplifier kit stereo preamp kit.

What really bothers me is that I donít know what specs to look for in a preamp. I have read that an output of about 3V is required to drive the ACAís to full power, but very few spec sheets give output voltage. Iíve seen the O2, B1 and BOZ being recommended for use with the Amp Camps.

This is really a difficult decision for me. Obviously, I need something that would do the new amps justice, but without breaking the bank or being a major construction project.

Any guidance and/or recommendations will be appreciated.
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Old 15th July 2017, 12:09 AM   #2
planet10 is offline planet10  Canada
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Which preamp for Amp Camp?
I used Gregg-the-Geeks MooseFET with the Amp Camps & i was thrilled with the performance.

http://classicvalve.ca/docs/MooseFET_docs_v1.pdf

dave
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Old 15th July 2017, 01:46 AM   #3
2 picoDumbs is offline 2 picoDumbs  Australia
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If you are using CD player or DAC as source with 2Vrms output then B1r2 is perfect.
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Old 15th July 2017, 03:04 AM   #4
2 picoDumbs is offline 2 picoDumbs  Australia
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Quote:
Originally Posted by Skylar88 View Post
Hi Guys, newbie here.

What really bothers me is that I don’t know what specs to look for in a preamp. I have read that an output of about 3V is required to drive the ACA’s to full power, .

This is not correct.
The ACA has 14dB of gain, 1.7V peak at the input of the ACA will have the amp clipping.
A buffer preamp is the most sensible choice if you are using cd/dac.
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Old 15th July 2017, 09:09 AM   #5
AndrewT is offline AndrewT  Scotland
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Try with just a Buffer instead of a pre-amplifier.

Add the Buffer after the vol pot and then run the buffer output cable to the power amplifiers.

You may find that you get sufficient volume for all except a drunken party night.

Buffers can be ultra cheap (at least at this testing stage) by using a unity gain dual opamp or two PassB1 channels.
Don't add on a case/ enclosure until after you know what you finally need.
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Old 15th July 2017, 10:11 AM   #6
Skylar88 is offline Skylar88  South Africa
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Quote:
Originally Posted by planet10 View Post
I used Gregg-the-Geeks MooseFET with the Amp Camps & i was thrilled with the performance.

http://classicvalve.ca/docs/MooseFET_docs_v1.pdf

Thanks Dave, I'll have a gander. Your website is very interesting, btw. I found the speaker information particularly useful, since I still also have to get those. I'm leaning towards Tang Band 5" full range drivers in TL enclosures - DIY of course.

Christo
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Old 15th July 2017, 10:16 AM   #7
Skylar88 is offline Skylar88  South Africa
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Quote:
Originally Posted by 2 picoDumbs View Post
If you are using CD player or DAC as source with 2Vrms output then B1r2 is perfect.
Thanks 2picoDumbs. All info is greatly appreciated by me. The source will mainly be a dedicated PC playing flac files (for now at least).

Christo
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Old 15th July 2017, 10:28 AM   #8
Skylar88 is offline Skylar88  South Africa
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Quote:
Originally Posted by 2 picoDumbs View Post
This is not correct.
The ACA has 14dB of gain, 1.7V peak at the input of the ACA will have the amp clipping.
A buffer preamp is the most sensible choice if you are using cd/dac.

Ah, ok. I should have mentioned that the mentioned 3V is for both channels. It's just the way my source put it. What you're saying ties up nicely with the 1.5V per channel that I read about.

I still have to make the connection between dB and the input sensitivity of an amp. Electronics, and audio in particular, has not been my field of expertise. But I'm learning fast...

Christo
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Old 15th July 2017, 10:49 AM   #9
AndrewT is offline AndrewT  Scotland
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double power is +3dB
ten times power is +10dB

double voltage is +6dB
double it again for four times voltage is +6dB plus +6dB = +12dB
double it again for eight times = +18dB
ten times voltage is +20dB
one hundred times voltage is +40dB
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Last edited by AndrewT; 15th July 2017 at 10:51 AM.
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Old 15th July 2017, 11:01 AM   #10
koja is offline koja  Canada
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I will be using Juma's bf862-based preamp (channels tested long time ago but still waiting for me to put it all together with a volume attenuator, since I do not need it 90% of the time). the preamp has ~8dB Vgain.
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