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Old 4th June 2002, 04:43 AM   #1
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Question New dual-mono power amp

Hi all,
This is my first message here on DIYAudio altough I've been reading some of your very interesting posts now and then. I am in the process of building my first DIY stuff i.e a big dual-mono power amp. I want it as symetrical and with the least compromises as possible (yep ! like everybody else ;-) ). Budget is 2000 to 3000$. But as I am still unexperienced in the field of DIY; I would need (and greatly appreciate) some help.

I have already bought my transformers wich will be 2 Plitron LONO (low noise) at 1 KVa each. These with their inrush current reduced by 40% (compared with standard transfo)will allow me to bypass any relays 'cause I won't need them. Electrolytic caps will be Mallory CGS series.

Briefly, EACH CHANNEL will probably be built as follow: 1 KVa transfo, 4 Mallory CGS caps for a total of 120 000 uF (2 of 20 000uF and 2 of 40 000uF), 7 6N-twisted-copper-braids (with Teflon insulation) per wire throughout, copper lugs and stainless and/or brass screws throughout and WBT #0730 binding posts. Main boards are made of Teflon with copper traces. Chassis will consist of 5/16" thick anodized aluminium from top to bottom. Each (channel)will also have their own switch and power cord.

OK this is for the stuff I have but before buying or starting to build anything else; I would truly appreciate your tips or comments on the following questions:

- Is there anybody that could comment on the Plitron LONO sound ?
- What are the advantages of bypassing electolytic caps electrically and soundwise ?

-Can I mixed 70V 40000uF and 75V 20 0000uF cans together and if so, what are the effects of the voltage differences in the sound ?
- What would be the differences (soundwise) between 200V, 400V and 800V bridges ? Is a higher voltage better sounding ? And is using two bridges per channel (one for the + and one for the -) worthwile ?

- Finally, is separating the Led from the audio signal (by using a separate transfo)significant in bettering the sound quality ?

I know it's a whole lot of questions for a first post so I apologize to all for this lenghty message but I sincerely consider that a lot of you have great knowledge in DIY stuff and sometimes far better hearing than the vast majority of audio engineers. Therefore, you guies are my first port of call.

Again, any tips would be truly welcomed.

Best regards,

Marc-André Rodrigue

N.B Sorry for the english, I am french speaking ;-)
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Old 4th June 2002, 05:12 AM   #2
tiroth is offline tiroth  United States
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My recommendation, if you have a budget of $2k-3k (I wish I did), is to build a $150 amp, then build your "good" one. Better yet, build two. The money it costs will be more than recouped in terms of the increased build quality and your improved knowledge behind the decisions you will make.

Perhaps you are already sufficiently skilled/well read that this is not good advice though. It just worries me to spend so much and have such high expectations on what will by definition be a learning experience. I've been building (and rebuilding) circuits, audio and otherwise, for quite a few years now, and there has been a definite progression in terms of build quality.
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Old 4th June 2002, 06:41 AM   #3
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Default Dittos, Rush

Good advice, but he did say he was not experienced. I am, and still would not budget that much on amps.

Good parts does not always mean good sound. Just ask Mark Levinson. Good design gives good sound.

Jocko
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Old 4th June 2002, 07:23 AM   #4
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Talking Good design gives good sound.

That and very good parts give even better sound...... Especially donated good parts and good surplus shopping!

H.H.
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Old 4th June 2002, 07:30 AM   #5
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Maybe he was talking Canadian currency where 1$CAD is only 60% of US dollar.
What is the design based on? Any schematic?
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Old 4th June 2002, 07:40 AM   #6
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Marc-Andre,

Assuming 70V filter caps are a safe rating, then the 75V caps are 5V safer. The "extra" 5V will not sound different.

Bypassing a cap is a way to extend (some might say linearize) a capacitor's bandwidth. I have never heard of a bypass hurting, when done properly. (Biggest mistake: long component leads) With a $2K-$3K budget, It would be OK.

The bridge ratings should be all "sound" the same, assuming safe operating areas. Of course a failed/smoking bridge will sound horrible. Make sure you are within a safe operation area.

2 bridges (1 for each polarity) should be fine, with your budget. I am a big believer in "When you listen to electronics, you are listening to the power supply."

I do not see a point in a transformer for what I assume is the "power on" led. LED stands for Light Emitting Diode. The power supply works because of diodes. It is common practice to bias transistors with LEDs. Transistors themselves are made of diodes. Putting one more diode in that sea of diodes shouldn't make any difference. Plus if the LED Xformer fails, you might think your amp is off, when it is on.

The trick is to have a balanced design, spreading your budget out in the most logical way. Example The most expensive binding posts on a poor design will sound worse than a thought out design with Radio Shack spring clips.

If you would like more responses, you should give more details about your amp. Push-Pull, Single ended? Class A, AB? What are the rail voltages? Who's design are you using? Regulated power supply? And so on.

Regards,

Aud_Mot
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Old 4th June 2002, 04:07 PM   #7
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Regarding the LED. I've heard some opinions before, that they might degrade the sound somehow, however never bothered to check it myself. You don't need a separate transformer for it. If your Plitron is not potted you can make couple extra windings on it, just for the LED. I did it before and it works fine.

With your kind of budget I would also recommend High Speed Soft Recovery bridges from IXYS. You can get them from http://www.percyaudio.com/. 68A/600V bridge would cost you $24. I recommend using two per channel.

You didn't mention anything about kind of solder you would use.... Harry likes 4% silver, I'm using Cardas solder.
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Old 4th June 2002, 05:18 PM   #8
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Thumbs up IXYS diodes

Buy the seperate diodes at Digikey save money. They are great!
I built my bridge in the HotRod Aleph 3 with them. They maybe the best power diodes out there and are the best that I have used. 30 to 40 amps are fine with soft start and heat sinks
on diodes.

H.H.
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Old 4th June 2002, 05:22 PM   #9
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I was checking Digi-Key catalog but couldn't find big enough values. Could you provide part number, Harry?
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Old 4th June 2002, 05:58 PM   #10
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Default Snubbed Diodes

Hi Harry,
Quote:
Buy the seperate diodes at Digikey save money. They are great! I built my bridge in the HotRod Aleph 3 with them. They maybe the best power diodes out there and are the best that I have used.
An interesting study on diode snubber networks is in this recent thread, Worthwhile CDP tweak-SNUBBERS on diodes
and here http://131.109.59.51/images/pdf/Calc...m_Snubbers.pdf

Question - What difference/improvement are you getting with the diodes that you recommending here, and have you tried this snubbing technique ?.

BTW - I have tried lifting one end of each of the paralleled diode capacitors in commercial jap domestic amps and noticed an opening and slight cleaning of sound typically, but I have not tried the snubber setup.
I have however fitted snubbers across transformer primaries, secondarys and DC rails, and noticed cleanup/relaxedness/bass foundation in system sound.

Regards, Eric.
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