Great, thanks
Here is a picture of my amp. It's pretty much like Peters, only in an all-metal "enclosure". Only thing on the front is the LED.
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Monblock vs integrated
Hi,
I built two amps based on Audiosector kits; I am not an expert and I would like your opinion on something I cannot explain.
The amps are:
1. two monoblocks with Audiosector premium kit 300Watt 25V PSU.
2. Integrated amp with external PSU (300Watt, 25V), 50K Noble pot, no input selection, classic kit.
The monoblocks are driven by a passive pre with input selection. Volume is controlled by a 23 step ladder attenuator (taken at diyfidelity.au.com).
The wire between pre and amp is rather short, 40cm (slightly more than 1 foot); it is a Van der Hul cable with Cardas RCA connectors.
When I compare the two amp (same speakers, source and cabling) there is a big objective difference:
the integrated amp plays much louder than the monoblocks. I cannot move the knob more than
2 o'clock with the integrated one because it is too loud.
On the contrary I can completely rotate to full scale the attenuator knob: it plays loud, but clearly at a lower level.
Comparing the quality of sound, it is very similar, however I feel more punch"
from the integrated amp, but this is a subjective analysis.
Why the integrated amp plays so much louder than the monoblocks with passive pre?
I can only see two causes:
1- a fault in the attenuator or in my implementation (wiring, grounding, etc.)
2- impedence mismatch between passive-pre and amp.
Nelson Pass in his article on the B1 input buffer writes:
“It sucks the life out of the music, is a commonly heard refrain
(really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."
Your opinions and suggestions are welcome
thank you
Renato
Hi,
I built two amps based on Audiosector kits; I am not an expert and I would like your opinion on something I cannot explain.
The amps are:
1. two monoblocks with Audiosector premium kit 300Watt 25V PSU.
2. Integrated amp with external PSU (300Watt, 25V), 50K Noble pot, no input selection, classic kit.
The monoblocks are driven by a passive pre with input selection. Volume is controlled by a 23 step ladder attenuator (taken at diyfidelity.au.com).
The wire between pre and amp is rather short, 40cm (slightly more than 1 foot); it is a Van der Hul cable with Cardas RCA connectors.
When I compare the two amp (same speakers, source and cabling) there is a big objective difference:
the integrated amp plays much louder than the monoblocks. I cannot move the knob more than
2 o'clock with the integrated one because it is too loud.
On the contrary I can completely rotate to full scale the attenuator knob: it plays loud, but clearly at a lower level.
Comparing the quality of sound, it is very similar, however I feel more punch"
from the integrated amp, but this is a subjective analysis.
Why the integrated amp plays so much louder than the monoblocks with passive pre?
I can only see two causes:
1- a fault in the attenuator or in my implementation (wiring, grounding, etc.)
2- impedence mismatch between passive-pre and amp.
Nelson Pass in his article on the B1 input buffer writes:
“It sucks the life out of the music, is a commonly heard refrain
(really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."
Your opinions and suggestions are welcome
thank you
Renato
If it is DC coupled then that 80mV of offset is typical.
If a source sends a DC offset, the offset sent to the speaker could be much worse.
Therein lies the problem. One must be experienced enough to recognise the dangers of using DC coupled amplifiers and then make informed decisions on risks and preventative measures that can be taken.
DC coupled amplifiers are not for beginners.
If a source sends a DC offset, the offset sent to the speaker could be much worse.
Therein lies the problem. One must be experienced enough to recognise the dangers of using DC coupled amplifiers and then make informed decisions on risks and preventative measures that can be taken.
DC coupled amplifiers are not for beginners.
Thanks. This measurement is done without any input.
In any case, I was thinking of protecting my input with a 4.7uf Electrolytic cap in series with the input. What should the orientation of the polarity of the cap should be?
Cheers.
What Ohmage is the ladder attenuator - you didn't mention that. Attenuators resist - that's what they do. The less the resist, the louder the amp is - it's that simple. Maybe it's bigger attenuator, like 100K or more. That would do it. It's unusual but possible.
For what it's worth, many people including myself prefer the sound of a 20K pot/attenuator when used passively on such an amp.
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As a basic standard for such an application, use a quality polypropylene film cap, with high voltage rating, almost always bi-polar.
There is almost no limit to how much you could spend on caps, as they have such a colouring effect on the sound generally, and so many people become obsessed and search for years for the ideal de-coupling caps, (often in vein), but as a basic starting point for signal bearing caps, metalised polypropylene is a good start. For very cheap caps of this type, I suggest to use a Wima MKP, and if you want to spend a bit more money and hear good improvements, you might consider something like an Auri-cap from USA, available from Parts Connexion (some values at half price!).
I would try quite a small value, like 1uF or similar.
There is almost no limit to how much you could spend on caps, as they have such a colouring effect on the sound generally, and so many people become obsessed and search for years for the ideal de-coupling caps, (often in vein), but as a basic starting point for signal bearing caps, metalised polypropylene is a good start. For very cheap caps of this type, I suggest to use a Wima MKP, and if you want to spend a bit more money and hear good improvements, you might consider something like an Auri-cap from USA, available from Parts Connexion (some values at half price!).
I would try quite a small value, like 1uF or similar.
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a bit offtopic: you will fall out of your shoes if you realize how many electrolytic caps your musical signal has passed through before it got on your CD....
on topic: for the Audio sector amp I have tried many caps - with different results. Besides some very expensive foil caps also Panasonic FC polarized (!) caps came out good - the winner is/was of course Blackgate bipolars. Only using no cap was better...
on topic: for the Audio sector amp I have tried many caps - with different results. Besides some very expensive foil caps also Panasonic FC polarized (!) caps came out good - the winner is/was of course Blackgate bipolars. Only using no cap was better...
but the recording team gave you what they thought was what needed to be sold for your pleasure.
Thank you for your reply. I also use a 20K attenuator.
My problem is not due to the passive pre since I made a test with a PC driving the monoblocks with the pre and bypassing it: same loudness level obtained.
Renato
So, presumably your passive pre is the Pass B1? Unlikely to be an impedance mis-match then, as the buffer, if made properly pretty much precludes this.
There is no explanation other than what you have suggested, ie. faulty wiring - especially the usual GND issues.
FCs worked out good as signal bearing output caps? That is a surprise. Did you try Auri-caps? How did you find Polypropylene film generally?
No cap tends to blow your speakers if you've got a few volts there
I found something interesting. I read somewhere that caps can vibrate to the detrement of the signal. So I put three little dabs of silicon around the base of the caps to the board. /this steadied the caps and acted as a shock absorber.
The results are good. I could not hear any sonic improvement and it is not a/b situation for me. The suprising thing is how much cooler the chips run! I didn't change anything else and there is a substantial difference in temperature. Cool.
The results are good. I could not hear any sonic improvement and it is not a/b situation for me. The suprising thing is how much cooler the chips run! I didn't change anything else and there is a substantial difference in temperature. Cool.