Well, I could not resist building one myself, so here it is. I used Audiosector boards for amp am ps, and built bridged version with 4780. You can see that I took this project seriously, I even have a soft start circut for 2 X 200VA toroids. PS is with 4X 10000uF, MUR860 plus 1000uF Silmic near the circuit.
And ther result? Quite lousy. Compared to my Vincent SV-236 which goes for less than 1000eur, sound of this amp does not even justify the cost of the parts. I would have been (much) better off with second hand Nad 3020 from eBay.
Now, I am quite puzzled with all the good reviews on the net, so I will do some tweaking, adding some preamp and some other stuff. Any suggestions appreciated.
And ther result? Quite lousy. Compared to my Vincent SV-236 which goes for less than 1000eur, sound of this amp does not even justify the cost of the parts. I would have been (much) better off with second hand Nad 3020 from eBay.
Now, I am quite puzzled with all the good reviews on the net, so I will do some tweaking, adding some preamp and some other stuff. Any suggestions appreciated.
For the LM4780, I found a preamp to be a must. You want to try the LM4780 first as described on Peter's site. I ended up with the plain stereo version which is not bridged or run in parallel and it's very sweet.
I do however prefer the LM3875 and that's the only amp I've ever built that gets away without having a pre. All my others, AKSA 55N+, GB150, NX150, P101 etc sound better with an active pre.
I do however prefer the LM3875 and that's the only amp I've ever built that gets away without having a pre. All my others, AKSA 55N+, GB150, NX150, P101 etc sound better with an active pre.
The Vincent SV-236 appears to receive good reviews also it's an hybrid amp with a tube input stage.
http://www.lefflershifi.com/Library/Products/Vincent/SV-236.htm
There will be no doubt it will sound very different to a GC for better or worse, it maybe the GC just can not compete with the current demand of your speakers.
Speaker sensitivity is not the only key to good sound, I use to use GC's on B&W CDM1 NT's, now I have higher sensitivity full range speakers. I'm sorry to say the GC just does not cut the mustard like a 10 watt Class A SS amp or my much low powered tube, yet the B&W GC combo worked a treat.
http://www.lefflershifi.com/Library/Products/Vincent/SV-236.htm
There will be no doubt it will sound very different to a GC for better or worse, it maybe the GC just can not compete with the current demand of your speakers.
Speaker sensitivity is not the only key to good sound, I use to use GC's on B&W CDM1 NT's, now I have higher sensitivity full range speakers. I'm sorry to say the GC just does not cut the mustard like a 10 watt Class A SS amp or my much low powered tube, yet the B&W GC combo worked a treat.
Hi,
an appropriate pre-amp will present a low source resistance to the power amp input.
Without the low Rs, the volume control will become a variable filter when it interacts with the filter components at the power amp input.
Additionally, a variable Rs will affect the output offset, causing variations in the DC fed to the speaker (when the DC blocking cap is omitted from the input).
I am driving ProAclone 2.5, quite non-sensitive speaker. There are no big improvements, no preamp at all. Softstart circuit is on only for few seconds after the startup to prevent fuses to blow in my house due to high current peaks during startup. I ran it in for few days without a break. I yet have to listen more carefully and do A-B comparison, but the sound, even without direct comparison to Vincent, can be described as dull, closed in, with exaggerated boomy, lose mid bass and impotent low end. I am using 10K alps volume pot, with no cap at the input.
If I could attach a photo, you could see that it's a very tidy layout. It worked from the first second, and no funny noises.
If I could attach a photo, you could see that it's a very tidy layout. It worked from the first second, and no funny noises.
zdr said:
First of all, ProAcs are one of few speakers that seem not to work well with GC (based on feedback I get from people using such combinations).
What you describe as "dull, closed in, with exaggerated boomy, lose mid bass and impotent low end" is exactly the effect I was getting with increased filter capacitance. Once again, those amps work best with no more than 2200uF of filtering, but to appreaciated it, you need more friendly speakers. GC is not a universal amp and it requires proper equipment matching/selection.
You mentioned using bridged version. How exactly is it achieved with your source and Alps pot?
analog_sa said:
It's really hard to say. From my experience a parallel version is hardly a solution or an improvement.
In some systems low cap GC can provide exceptional bass. For instance, in a system described here: http://www.6moons.com/audioreviews/westernelectric/300b.html my low-cap monoblocks (small boxes beside equipment stand in a picture) are used to power 30-foot long straight bass horns and from what I heard, darTZeel has been also considered
could it be supply voltage is too high, got some 22 and 15v tranfos. Maybe current is limited because of that.
damping factor then falls below zero.
It's been a long time since I looked worked on it, but working near the 70v limit on a difficult load...
more torque, less horsepower
anyone a winisd file on proac 2.5 load seen by amp?
damping factor then falls below zero.
It's been a long time since I looked worked on it, but working near the 70v limit on a difficult load...
more torque, less horsepower
anyone a winisd file on proac 2.5 load seen by amp?
ZDR- suggested changes
If by reducing the power supply capacitance does not help in changing the sound quality you may like to try this simple change.
I assume your input impedance to your opamp is 22K, and directly couple to your 10K pot. I like you to put a capacitor(polypropylene or foil type), say 1 or 2.2uf for these 2 reasons:
1. reduce the DC interactions between the pot and the input to the opamp hence affecting the input bias current.
2. any DC output from your source may cause damage to your speaker(assume your opamp is direct coupled).
this will improve the sound.
If by reducing the power supply capacitance does not help in changing the sound quality you may like to try this simple change.
I assume your input impedance to your opamp is 22K, and directly couple to your 10K pot. I like you to put a capacitor(polypropylene or foil type), say 1 or 2.2uf for these 2 reasons:
1. reduce the DC interactions between the pot and the input to the opamp hence affecting the input bias current.
2. any DC output from your source may cause damage to your speaker(assume your opamp is direct coupled).
this will improve the sound.
yusuf said:
AndrewT has given an excellent explanation.
An active pre sorts out the impedance matching that goes nuts with passive pre's, acts as a buffer, drives the source cable. As I said, I have only ever heard one amp that did not benefit from the use of an active pre and that one has the pot in with the power amp.
It's funny the different results people get, particularly when they seem to put more money into a GC. I built Nuuk's basic 3875 using surplus parts and am truly amazed at the sound. It's easily the equivalent of a good SS amp. I've only begun to tweak a few bits here and there. I like it as it's the perpetual "work in progress."
For preamps I use a tube linestage I built, an old Luxman preamp, or none at all. Very happy regardless of the setup. My speakers might be helping though as they're homebuilt bookshelfs that I made using Fostex drivers. Great sound for classical music. Listening to a Beethoven concerto as I type this. Just outstanding.
Good luck and I hope you sort out your GC. It should be worth the effort.
For preamps I use a tube linestage I built, an old Luxman preamp, or none at all. Very happy regardless of the setup. My speakers might be helping though as they're homebuilt bookshelfs that I made using Fostex drivers. Great sound for classical music. Listening to a Beethoven concerto as I type this. Just outstanding.
Good luck and I hope you sort out your GC. It should be worth the effort.
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