gainclone dissapointment

[zdr]

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.

[analog_sa]

Ime GCs are extremely sensitive towards the load they drive, much more than the datasheet indicates. Some combinations just don't seem to work. What are your speakers?

[Peter Daniel]

Originally posted by zdr
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,.... plus 1000uF Silmic near the circuit.

.....Any suggestions appreciated.

I would start with removing those additional "improvements" you so eagerly introduced, probably without listening to the amp in a basic version first.

What is your source and preamp? What speakers?

[rabbitz]

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.

[BWRX]

Hi zdr. If you post more details about your setup before shooting it down you'll likely get more constructive replies.

Have your amps had much playing time? What supply voltages are you using?

[yusuf]

Originally posted by rabbitz
For the LM4780, I found a preamp to be a must.

Can you elaborate why preamp is MUST unless input signal is very low?

Thanks
Yusuf

[PeteM]

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/...ent/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.

[AndrewT]

quote:
Originally posted by rabbitz
For the LM4780, I found a preamp to be a must.

quote:
Originally posted by yusuf

Can you elaborate why preamp is MUST unless input signal is very low?

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).

[zdr]

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.

[Peter Daniel]

Originally posted by zdr
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.

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?