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Old 4th November 2004, 09:23 PM   #1
danza is offline danza  United Kingdom
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Default Inca Tech Claymore Vol. Pot.

Hi there

I was wondering whether anybody may be able to help me out?

I have recently purchased an Inca Tech Claymore amp that has a volume potentiometer
fitted that is the incorrect type. I was wondering whether anyone could tell
me the type/rating of pot that's meant to be fitted to this amp?Any info would be very gratefully
received.

Cheers,

Danza
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Old 2nd August 2005, 09:03 AM   #2
etsang3 is offline etsang3  Hong Kong
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Hi Danza,
Few months ago, I have totally modified a CLAYMORE amp. I have traced its whole circuit diagram. The original Volume should be a 10k (Tyep A). Pls see the drawing attached.
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File Type: jpg line_amp+selector.jpg (73.1 KB, 622 views)
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Old 2nd August 2005, 09:24 AM   #3
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That preamp really needs an upgrading, both in the supply and chip types.

Adjustable regulators, like 3x7 types, will improve things a lot.

Modern types, even if dual, will make thing sound a lot better.



Carlos
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Old 18th November 2005, 06:40 AM   #5
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Default what the?

it wont work as depicted in your schematic there can be no level shifting in the first stage as your outputs appear to be taken from the wrong side of the load resistors.
may be a revised schematic is required.
regards gong bloom.
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Old 18th November 2005, 08:46 AM   #6
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Quote:
Originally posted by etsang3
Hi Carlmark, I have made totol modification to Claymore and would like to share my works. Pls check those pcitures. Good Listening.


Excellent job! Congratulations!

Can you tell us a bit of what changes did your perceive in your listening?

IMHO there are further refinements to make.

1) Go for better chips at the lineamp. TLO72s have been surpassed by much modern DIP types that sound better. Put sockets on the pcb and try different types. Start with AD712s, which is a good working horse.

2) Get yourself a better regulated supply. TNT has some articles on power supplies. A good supply is paramaount for quality audio.

Some changes in your power amp were intriguing.

1) Why did you add emitter resistors at the output? One of the good things of MOSFETs at the output is the elimination of those resistors, which are a necessary evil on bipolar outputs.

2) Did you perceive any changes due to the active mirror change in the amp's second stage?

3) Is your present DC output offset stable enough to eliminate the NFB capacitor?

Good work!


Carlos
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Old 18th November 2005, 11:02 AM   #7
etsang3 is offline etsang3  Hong Kong
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Hi Carlos,

The amp is not owned by me so I've just tested a while and returned to my friend. I have actually mod. it to a DC amplifier which the Freq. Resp. can start from 0Hz now. It is amazing that the DC shift is so stable, it may due to I made a lot of thermal coupling to align the temperature of critical components. Also, Since the amp use MOSFET output device with higher input capacitance. I tuned the idle current to ~200mA (!!! only good thermal transfer is made) and the amp is quite warm now.

Compare before it was modified, the character of the amp did not changed. In addition, the bass is much lower and cleaner. I can hear more type of bass after the mod. This is facilitate by those large filter to reserve energy to be use and extend the amp freq. resp. to 0Hz.
Also, the extension of high end freq. (higher idle current) bring a clearer sound stage (air image) of the background. I tested with a Sound Track CD "Brave Heart" and
I felt like sitting at a big cinema.

1) ..
>>My friend mainly listen to CD so I bypass the flat-amp (taken out the op-amp and bypass) to let the CD signal go to Power-amp stage directly. The sound is not distorted at all. He claimed that he can hear some musical instruments more notable.

2) ..
>>Yes. want to add a power supply (LM317HV) only for the voltage amplification stage of the power-amp. It will make the power-amp sound better.

Some changes in your power amp were intriguing.

1) Why did you add emitter resistors at the output? One of the good things of MOSFETs at the output is the elimination of those resistors, which are a necessary evil on bipolar outputs.

>>I will lost a little voltage swing by adding those but I have good return. These resistors provides local feedback to lower down the distortion of the output MOSFET (hence overall distortion). They help to enhance the bias / idle current stability of the P & N MOSFET (even MOSFET claims negative temperature coefficient, no thermal runaway). The last, with those, I can measure and set the idle current of the O/P MOSFET easier. Ha..Ha..

2) Did you perceive any changes due to the active mirror change in the amp's second stage?
>>I did not actually compare the before and after result. I intend to try my best to change it into a mild Class AB (DC) amplifier so I took special care in those area which will affect thremal stability. Using same device together with good thermal coupling can highly prevent DC drifting of a DC amplifier. So I bought more BD140 and add to that point.

3) Is your present DC output offset stable enough to eliminate the NFB capacitor?
YES. All my DIY power-amps are DC amp and this one is one of the most stable that I have measured. The idle current I set was 100-200mA and the amplifier exhibited good thermal stability. With the case opened and I was swinging-blow the PCB with a 1200W hair dryer from 30cm. There was still no DV voltage drift !

Good work!
Thank you!
(BTW, I am working with my friend on Nait-2 modification and may post the details later)
Revised Circuit Drawing :
http://i20.photobucket.com/albums/b2...ification2.jpg
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Old 18th November 2005, 11:21 AM   #8
etsang3 is offline etsang3  Hong Kong
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Hi gongbloom,
I am sorry that I type the wrong value of R17a in all my drawings. It should be R17a=10k. and wrong drawing of Tr1a and Tr2a load resistors. Pls see the revised one. Are those what you mean.
Thank you.

http://i20.photobucket.com/albums/b2...ification2.jpg
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Old 18th November 2005, 11:29 AM   #9
etsang3 is offline etsang3  Hong Kong
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Hi all,

Sorry that the previous link was an old one.
Here you are.

http://i20.photobucket.com/albums/b2...ification3.jpg
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Old 18th November 2005, 12:08 PM   #10
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Quote:
Originally posted by etsang3


It is amazing that the DC shift is so stable, it may due to I made a lot of thermal coupling to align the temperature of critical components. Also, Since the amp use MOSFET output device with higher input capacitance. I tuned the idle current to ~200mA (!!! only good thermal transfer is made) and the amp is quite warm now.

Yes, termal tracking is not necessary with MOSFETs

Quote:


1) ..
>>My friend mainly listen to CD so I bypass the flat-amp (taken out the op-amp and bypass) to let the CD signal go to Power-amp stage directly. The sound is not distorted at all. He claimed that he can hear some musical instruments more notable.

2) ..
>>Yes. want to add a power supply (LM317HV) only for the voltage amplification stage of the power-amp. It will make the power-amp sound better.

Do you know if the bypass still goes through an active stage? If it does you will need to upgrade that chip.

The power supply I meant for the preamp stages, not the power amp.

You don't really need HV types for the low current power amp stages. Use the regular ones 3X7 types, leaving at least 3v from input to output. You will just not be short-circuit proofed, but I don't think that's a serious problem.

Quote:

>>I will lost a little voltage swing by adding those but I have good return. These resistors provides local feedback to lower down the distortion of the output MOSFET (hence overall distortion). They help to enhance the bias / idle current stability of the P & N MOSFET (even MOSFET claims negative temperature coefficient, no thermal runaway). The last, with those, I can measure and set the idle current of the O/P MOSFET easier. Ha..Ha..

That's a local feedback that I think you can do without. Designers like Nelson Pass or Erno Borbely do not use them, and for a good reason. Find a different way to set the bias.



Carlos
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