Gainclone building thread based on BrianGT's boards

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HRmm questions

Hello, I was just now finally putting the boards together (rev 2) and decided to make sure I have the values right for R1 and R2.... R1 = 220ohm

R2 = 22kohm -- was just making sure since I was looking at the pictures in the walkthrough and realized those locations were inverted with Rev 2 of the boards -- and was just wanting to make sure I got this right that the 220 ohm should be next to R3 680 ohms.

Another thing I was wondering about was if it was better to use a nice polypro film cap 200v for the 4.7uf cap (I have a bunch laying around) than the little Panasonics included with the basic kits. For kicks I had measured the Panasonics and came out with a capacitance value of 4.229uF and an ESR of 2.8ohms
the BG premium kit cap measured up to 4.12uF 2.215ohms ESR. Some speaker caps I have laying around: A dayton Nonpolar electrolytic measured up 3.886uF 0.422 ohms ESR (claimed 4uF 10% tolerance), a mylar 4.661uF .009ohm ESR (4.75uF claimed, no tolerance given), and a 4uF dayton polypro that measured 3.962uF .0025ohm ESR.

A few questions for anyone who wants to answer:
Would it be safe to put one of these higher grade caps in place of the panasonic?
Would it sound better? -- Well I'll do the blind testing so long as its safe :)
What exactly does this value control in the operation of the amp, and why is the blackgate so far off from Mfr. spec? They were within about 1% of each other in value by the way and they were ever so slightly polar. The high ESR led to a phase shift with increasing frequency as well.

One more thing... Is it safe to hook a soundcard directly to the inputs of the GC and using the computer as volume control? Thanks in advance
Dylan

Tried to email Brian but I just assume he was busy or away for awhile so I'm posting here :)

Ill surely have some more questions later...
 
brian or peter. when i finshed building one of the gainclones.
i found you had to turn the volume way up on the preamp just to get a good level of sound out of it. now thats it burning in its getting louder and i dont need to turn it up so much.

what i was wondering it this normal burn in?

not complaining it sounds great;)


thanks.........
 
Karma,

I never observed such behaviour, but it may be system (or listener) dependant ;) Good thing it gets louder though.


AAXenoStrange said:

Would it be safe to put one of these higher grade caps in place of the panasonic?
Would it sound better? -- Well I'll do the blind testing so long as its safe :)
What exactly does this value control in the operation of the amp, and why is the blackgate so far off from Mfr. spec? They were within about 1% of each other in value by the way and they were ever so slightly polar. The high ESR led to a phase shift with increasing frequency as well.

One more thing... Is it safe to hook a soundcard directly to the inputs of the GC and using the computer as volume control?

No problem with placing other caps in place of Panasonics, just make sure the rating is 50V or more.

I noticed that placing smaller caps there improves the sound of the bigger ones (especially when using small BG with 1500u Panasonics in Premium kit). The absolut value of those caps is not important and you can use anything in 2-20uF range. It's just that 4.7u BG N is reasonably priced, can also be used for coupling and it comes in 50V rating.

You can connect soundcard, but make sure it doesn't produce DC offset, as the amp is directly coupled. In case the soundcard generates DC offset, a coupling cap should be used.
 
i found out what it was. heatsink was to small and it was overheating if thats normal. i put a bigger one on and now its just
loud.

when the chip overheats does it step down?

still playing with it. so the heatsink used is a factor hmm live and learn:D

thanks peter..
 
Thanks Peter :)

I was beginning to wonder if anyone would ever answer any of my questions :) --

I somehow managed to miss this: http://www.diyaudio.com/forums/attachment.php?s=&postid=331888
At the beginning of the group by thread which made me more comfortable that my guesses about the values of R1/R2 were right.

As for decoupleing caps -- Let me make sure I know what that is... Effectively acts as a lowpass on the input -- higher value the lower the frequency the cutoff is --
Whats a good value?

Thanks a bunch helpin out :)
 
Well, here it is sans chassis. Wired it up and had it playing with my portable CD player and spare speakers. Guess I have to get moving on that chassis.
 

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The sound definitely require some break-in. Initially the sound was very muddy, with the midrange smeared and poorly defined. After a couple of hours of playing, the tonal balance started to improve and the imaging started to sharpen considerably. The higher frequencies in particular became more defined and much, much more dynamic. Interestingly, the DC offset at the outputs started out at 0.126 and 0.780V for the right and left channels, but after playing for awhile they are smaller at 0.045 and 0.022V respectively.

I will be testing a Supersymmetric variation a la Nelson Pass which I hope to complete assembling tomorrow, and will post some comparisons as to the differences.

Cheers,
 

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