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Old 24th June 2010, 06:20 PM   #1
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Default 1st Gainclone

On the 19th June last year I said I was going to have a go at building a Gainclone.
Well, a year later and I have bought the boards from the far east and bought my own bits and loaded it all up.
It works well, is quiet and was a bit of a pleasant surprise in all sound departments.

I want to remove two components which don't appear on the attached gainclone schematic I found recently.

Can I remove R1 and C5 and replace them with a wire link ?
Will it still be stable and safe plus is there any sound quality to be gained by doing so ?

Many thanks for all the help last year and sorry for the delay

Andrew.
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File Type: jpg GC Schema.JPG (21.6 KB, 250 views)
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Old 25th June 2010, 11:06 AM   #2
AndrewT is offline AndrewT  Scotland
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I can't find R1.
The datasheet details the purpose of C5. (no it's Cs I see), where is C5?
I do not see any of the National "optional" components. Tread carefully, this chipamp may blow itself up and/or take out your speakers, if even mildly abused.

The PCB has C5 and R1.
place them on the schematic.
What is that high power resistor standing upright?

I get the impression that your kit supplier has included the "optional" components. If so then keep all of them and add the few more that are still missing.
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Last edited by AndrewT; 25th June 2010 at 11:11 AM. Reason: misread small print
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Old 25th June 2010, 11:43 AM   #3
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my guess is that R1 (as i see it on the pcb photo) is on the output. I can not be 100% sure.

if you are NOT putting these amplifiers in parallel then you should be able to take out R1 and bridge it. But you need to be 100% sure.

I cannot comment on C5 without seeing the schematic.
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Old 25th June 2010, 06:57 PM   #4
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Default 1st Gainclone

Thanks for the replies.

Andrew T : The confusion is created by me - apologies.
The schema is not the one relating to the photo of my baords.
I recently found this drawing and noticed that the large resistor R1 ( 1R 5 watt ) on the output is not in the drawing and the capacitor C5 ( 1 uf 100 v )
is also missing compared to the drawing I received with the boards.
So, I have assumed ( perhaps wrongly ) that maybe I can get away with removing them.
The whole thing works so well that I'm now thinking I should just enjoy it
and stop tinkering.

Tangmonster : Your guess is correct.
I don't fully understand the term parallel yet in relation to my kit.
I guess if I upgrade to two traffo's + 2 sets of rectifiers and caps in the future then this may be the parallel that you refer ?

There currently is 1 power supply board ( 4 large caps and bridge rectifier ) 300 va traffo @ +25 0 -25 and the two amplfier boards.
You'll have seen the kits on E Bay - not the best but they work.

In your opinion will this simple configuration be safe for the removal of the
1R 5 W resistors at the output or do I just leave it alone ?

Really appreciate the assistance

Andrew
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Old 25th June 2010, 08:04 PM   #5
Dr_EM is offline Dr_EM  United Kingdom
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Sounds like R1 and C5 on the PCB form a Zobel network. This helps ensure stability. You might get away without it, but it depends on your speakers. In fact, it might not be too good having a wirewound (inductive) resistor for R1.

Definately do NOT replace them with a wire link if this is correct, that'll short the output! I'd leave it in, mabye replace R1 for a metal oxide component.
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Old 25th June 2010, 09:12 PM   #6
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Default 1st Gainclone

Dr.EM

Thanks for the advice - noted.
What's wrong with the wire wound resistor ?
Isn't is safe.... or is it poor sounding ?

I hope it's the latter of course as I've already bought some metal
oxide replacements and will fit them as soon as they arrive.

I also wish to fit bypass caps to my power supply caps.
I'm thinking of 20 uf @ a few hundred volt rating but most of these
values seem to be for crossovers, like Mundorf's for example.
Can I still use these caps providing the voltage rating is large enough ?

Many thanks for your help.

Andrew
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Old 25th June 2010, 09:42 PM   #7
AndrewT is offline AndrewT  Scotland
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assemble the Cs caps as National tell you.
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Old 25th June 2010, 10:21 PM   #8
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Andrew T

The schema I posted WAS the NS circuit and.... does not have the two components I questioned.
This is the reason I asked if it was safe to remove them from my version.

The schema I received with my el cheapo boards had a 1 uf cap before the first resistor (1 k ) at input and the 1R resistor just before the output terminal.

If NS circuit works then surely mine will too without these two components.

Am I way off here ?

Thanks

Andrew
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Old 25th June 2010, 10:39 PM   #9
gootee is offline gootee  United States
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Quote:
Can I remove R1 and C5 and replace them with a wire link ?
If you remove a capacitor, you don't usually want to replace it with a wire link!

If the R and C you are talking about happen to be an output zobel network, then replacing them both with wire links would short your output directly to ground!

I think that you really must post an accurate schematic, if you are asking people about making such changes.

Last edited by gootee; 25th June 2010 at 10:42 PM.
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Old 25th June 2010, 10:50 PM   #10
gootee is offline gootee  United States
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Quote:
Originally Posted by AndrewGM View Post
Andrew T

The schema I posted WAS the NS circuit and.... does not have the two components I questioned.
This is the reason I asked if it was safe to remove them from my version.

The schema I received with my el cheapo boards had a 1 uf cap before the first resistor (1 k ) at input and the 1R resistor just before the output terminal.

If NS circuit works then surely mine will too without these two components.

Am I way off here ?

Thanks

Andrew
The input capacitor stops DC from getting in, which could destroy or damage (or merely degrade the performance of) your speakers, under certain conditions. It's up to you to take the risk, if you want to try removing it. You could also consider replacing it, with a larger or better cap, which might extend the low-frequency response of the amplifier, which might or might not be audible.

Is the feedback pickoff point before or after the 1R?

Last edited by gootee; 25th June 2010 at 10:52 PM.
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