Phew, what an effort - but worth it! I'm on top of the world at the moment. My first chasis (hell, first metal working project), and first fully working two channel GC is complete!
This one uses Brian's basic PCB with a 300VA toroid (2x 20v) and Sfernice P11 10k linear pot.
After running it for a couple of hours, I took it to a friends this evening and hooked it up to his Martin Logan Ascent's and Shanling CDT-100 to see what it could do. It didn't appear to have any problems driving the Logans at moderate levels. There was clearly more bass, perhaps a touch more clarity noticeable on the highs, and better overall imaging than the Denon AVC-A1SR that we used as reference.
Still many tweaks to go, but so far I'm a very happy bunny. 😀
(Must thank PD et al. in the metal working thread for all the help and advice, and of course Brian.
)
A bit of a David and Goliath thing going on here...
This one uses Brian's basic PCB with a 300VA toroid (2x 20v) and Sfernice P11 10k linear pot.
After running it for a couple of hours, I took it to a friends this evening and hooked it up to his Martin Logan Ascent's and Shanling CDT-100 to see what it could do. It didn't appear to have any problems driving the Logans at moderate levels. There was clearly more bass, perhaps a touch more clarity noticeable on the highs, and better overall imaging than the Denon AVC-A1SR that we used as reference.
Still many tweaks to go, but so far I'm a very happy bunny. 😀
(Must thank PD et al. in the metal working thread for all the help and advice, and of course Brian.
)A bit of a David and Goliath thing going on here...
An externally hosted image should be here but it was not working when we last tested it.
I have to point out that proper placing of the amp (feet, supporting platform, etc.) is quite influencial on the sound. Putting it on top of Denon is not optimal solution, I would think.
I did some further experiments with a chassis, and it seems like tightening the bolt on transformer is important too. I preferred to tight it only slightly, only as much as needed for firm support.
You might also notice that removing top cover from the amp, has more influence than removing plastic jackets from electrolytics. The sound is smoother and seemingly more air can be perceived. I still keep the top on, but don't tight the screws at all.
Nicely done, BTW. I like the centrally positioned knob and warmth of side panels.😉
I did some further experiments with a chassis, and it seems like tightening the bolt on transformer is important too. I preferred to tight it only slightly, only as much as needed for firm support.
You might also notice that removing top cover from the amp, has more influence than removing plastic jackets from electrolytics. The sound is smoother and seemingly more air can be perceived. I still keep the top on, but don't tight the screws at all.
Nicely done, BTW. I like the centrally positioned knob and warmth of side panels.😉
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Joined 2002
The feet are 40mm square blocks of acrylic roughly 15mm thick. I plan to put the LED's inside the feet, I just hope they don't melt. I don't believe my ears will tell me any different if I remove/loosen the cover, adjust the toroid bolt, or remove the cap jackets - but I'll give it a go nonetheless 😉 I'm looking forward to a thorough listening comparissons once the premium kit version has been finished.
A shot of the internals:
A shot of the internals:
An externally hosted image should be here but it was not working when we last tested it.
Very nice chasis.
PD: are those chips so sensitive for microphonics, that feet/ support platform/ transformer mounting has influence on the sound?
PD: are those chips so sensitive for microphonics, that feet/ support platform/ transformer mounting has influence on the sound?
Yes, nice work Vikash. That's a pro job allround! 😉
Just one thought though!
You measured all your resistors to a decimal place to ensure that you balanced the channels and then you used a pot instead of a stepped attenuator! 🙁
😱 
Just one thought though!
You measured all your resistors to a decimal place to ensure that you balanced the channels and then you used a pot instead of a stepped attenuator! 🙁
😱
Very true
but I felt I was taking on enough for a fist amp without adding diy attenuators to the list. I took some quick measurements of the channel difference on the pot and and it was not good, so I will almost certainly need to change this down the line. At least the pot will be easier to change than the resistors though 😉In fact I found an odd quirk whereby you could only hear output in one speaker until you reach a certain volume. This was still at a low volume but I haven't traced the cause yet.
On a last thought, I don't know if there's enough space in the chasis for an attenuator 🙄
Peter Daniel said:
Hmm, if your amp is that sensitive to such details, maybe you should
consider that your amp is slightly oscillating ?
I never experienced these details having impact on the sound with
stable circuits. Only the unstable ones showed such symptoms...
Or you have incredible detailed ears compared to mine ?
Mike
Is that linear pot law-faked, and of so, with what value resistor?
I believe that law-faked pots can be a bit tempermental at the 'ends'. 😉
Vikash said:
My experience from solidstate amps is, that this can be caused by
an incorrect inputfilter. But i am not familiar with the BrianGT...
BTW, very nice chassis ! I hope i get mine nearly that nice...
Mike
Pot is not law faked yet. Could it be that the channel difference is so far out that is causing it I wonder? I only recall hearing this on the Logan's however.
It's on the todo list, but isn't the taper of a volume control just a convenience feature to match human volume matching - i.e. there's no quality to be gained from it right?
The chips are connected to a plate of copper 4mm thick which is inturn connected to the the aluminium base which is again 4mm thick. I have not tested thoroughly yet, but I found that the chips do not get past warm to the touch, and this is therefore adequate, or even superfluous 😉
Vikash said:
Huh?? Seems to me like you have a HUGE amount of room, especially if you shift the amps slightly. Much more space than what I am attempting at the moment - trying to squeeze 2 GC amps with those big Black Gates on perf boards, a buffer valve and attenuator into a 120mm cube (separate psu, though).
Nice tidy job, by the way! 🙂
I agree with Falcott - there should be room for a stepped attenuator in there! 😉
I have just shoe-horned one into one of my 4 inch diameter pods together with a buffer.
I have just shoe-horned one into one of my 4 inch diameter pods together with a buffer.
Regarding the channel balance problem at low volume, the pot is the culprit. I took some more measurements and the channels seem balanced to within 3% except for at very low levels where it is hugely innacurate. Simply a faulty pot, but otherwise 3% is better than I was expecting (it's rated 10%).
Code:
left right diff. %
0.40 0.40 0.00 0.0
94.30 11.40 -82.90 87.9
411.00 328.40 -82.60 20.1
800.50 711.50 -89.00 11.1
2002.00 1946.00 -56.00 2.8
2552.00 2523.00 -29.00 1.1
3066.00 3086.00 20.00 0.6
4543.00 4591.00 48.00 1.0
5510.00 5597.00 87.00 1.6
6137.00 6208.00 71.00 1.1
6980.00 7125.00 145.00 2.0
7846.00 8040.00 194.00 2.4
8940.00 9180.00 240.00 2.6
9380.00 9610.00 230.00 2.4- Status
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