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 ;-)
 
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.
 
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
 
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.
 
Snubbed Diodes

Hi Harry,
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, http://www.diyaudio.com/forums/showthread.php?s=&threadid=3894&highlight=snubber
and here http://131.109.59.51/images/pdf/Calculatin_ Optimum_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.
 
The eye is on the hole and not the doughnut. The design should start with a well designed and executed amplifier circuit and the power supply should be designed to the circuit. However, knowing ahead of time that monster power is desired, it is common to spec out the monster power supply. As a power engineer I would highly discourage the use of IXYS parts due to horribly, disasterous experiences with many of their different components. Has any of the more experienced designers ever thought about switching power in thier amps. It can reduce the size and weight dramatically, and the efficiency is hight increased as well.

BeanZ
 
BeanZ,

Switching power supplies (and their variations) have been tried in commercial power amps for years. Everybody thinks they can do it, then abandon the design. In the consumer market, they tend to blow up, creating a service nightmare.

The closest successful example I can think of is the Carver amps. As I recall they are not a true switching PS, but do aim for efficiency and advantages. For what ever reason, they are not popular among audiophiles (audio purists)

Switching power supplies are cheap to build, but not cheap to repair. Being modular is a case of good and bad. Most computer techs will just buy a new PS, not repair one. This is do-able when there many companies that make PC style power supplies.

In the context of this forum, linear supplies are easier to understand, design, build, test, and repair. They have the reputaion of "sounding" better.

Also this is the forum for sound, not practicality. That explains all the people building high power single ended solid state amps that are 12- 25% efficient.
 
Praudio said:
HPotter,the good sounding solution is 2 bridges;
one for + and one for - , to do that you need 2 secd. winding and
if I well remember the Plitron Lono has 4. I do this way for many
years.

And I always do it as well. However, as I mentioned before I had some bridges failures (when using inrush thermistors) so I wanted make them a bit stronger.;)
 

mlloyd1

Member
Paid Member
2001-02-25 7:10 pm
Northern Iliinois
I think it was Radio Electronics (RIP) some years ago that featured a power MOSFET based amp that used a switching power supply. I know the guy that did the power supply design. The amp designer's name escapes me at the moment, but he sells kits of the projects. Look in the thread on distortion analysis and you'll see his name with pointers to his web site.
OK, OK I just remembered - reinhard metz
mlloyd1
 
Aud_Mot said:
BeanZ,


...In the context of this forum, linear supplies are easier to understand, design, build, test, and repair. They have the reputaion of "sounding" better.
Also this is the forum for sound, not practicality. That explains all the people building high power single ended solid state amps that are 12- 25% efficient.


All of the above points are accurate. In fact, my high power dual mono amplifier uses a huge 1500VA linear unregulated power supply, so I do implement them as well. I am just fishing for people who want to try something new. Good answer Aud_Mot!

BeanZ
 
Scorpion,

Since we are slightly off topic of the thread lets address the original neophyte. It is recommended to choose an amplifier design which you want to implement. There are lots of projects which you can execute yourself and range in all classes of amplification. Not knowing your background a good book to look at is :High Power Audio Amplifier Construction Manual, by Randy Slone and the Audio Power Amplifier Design Handbook, by Douglas Self. These are good references however not absolutely necessary. The next expensive investment after the power supply and the enclosure is going to be the heatsinks. The size of the heatsinks are dependent on the class of amplifier you build. Class-A amplifiers require huge heatsinks, AB require large heatisinks, Class-T requires tiny heatisinks. I assume that quality throughout the entire range is desired so I have eliminated class-D. Class-T is very difficult and quite different to implement. Heatsinks can be found at surplus shops for cheap. Buying them new are extremely expensive. Once class is decided the next investment will be the output transistors. No matter what class you choose or what kind of transistor output )MOSFET or Bipolar, this is the next expensive investment. Complementary pairs are quite often chosen for best quality. Bipolar pairs are MJ15003 /4 pair or the MJE21193/4 pair. Though with most of the available projects online it will tell you the best parts for the application. What are your requirements?

BeanZ
 
Mr Feedback, thanks for that article by Jim Hagerman, very interesting reading indeed. Makes a change from my typical “that looks about right” approach.

Aud_mot, actually Linn use switching supplies on their Klimax amps, regarded as very good amps indeed. Yes switching supplies can be difficult to design and repair, but they have many advantages over a conventional linear supply.

I felt tiroth’s suggestion to build a smaller amp as a first project was a very worthwhile suggestion.

Cheers,

Pete
 
Hi all,

thank to all for you very kind answers. As it is only my second post on this site, I don't know (yet) how to respond personnaly to each and everyone of you therefore my reply will cover many of your comments.



TO TIROTH:

I am not sufficiently skilled or have a great knowledge in DIY stuff. That is why I am on this site to ask pros like you guies.

Money was spent this way: 600$ US (1000$ CAN) for the Plitron LONO transformers (2 at 1KVa ), another 600$ US (1000$ CAN) for the boards, wiring and components and 300$ US for the all-around 5/16 '' thick chassis, machining and anodizing.

I am not looking for exotic stuff but just trying to have tips to maximise my efforts with the components I have. Of course, I will be tweaking and tunning the amp for a year or two (and might change some components along the way). Anyway, it's all about system synergy and more than everything the final product will have to be pleasant to my ears.


TO JOCKO HOMO AND HARRY HALLER:

Of course, good parts does not always mean good sound (altough it might help). To me it's all about synergy. Synergy between the components in the amp and between the amp and the rest of my system and more importantly between the final sound and my level of pleasure !!! :)

I bought lot of stuff from a surplus store. For exemple, Mallory CGS capacitors cost me a total of 70$ CAN (45$ US) for 4 70V 40 000uf and 8 75V 20 000uF !!!

TO HPOTTER AND AUD_MOT:

I was talking canadian dollars, sorry for the mistake !! :) . Here are some important details that all of you should know :

This circuits I will use are built here in Montreal by a friend that has over 30 years of experience in the audio field. He personnaly knows the owners (see inventors) of companies like Sim Audio, Classé, Totem (years ago) and especially Tenor Audio (recently)and has sometimes helped or commented on their project (some of the Tenor Audio stuff are now on the market). This guy has been building amps for more than a decade. I listenned to some of them, they are incredibly musical and...they sound true.

The circuits I will use are his. I don't have a great knowledge of DIY and that's why he'll help/supevised me. Here are some details about the boards:

Bipolar boards with 4 outputs per channel mounted directly on board, working in class AB, running at +- 64V, Teflon OFC 4 onces (like in big Levinson) board with a dielectric of +- 2, trace fully balanced, impedance fully balanced, heatsink and output transistors mounted directly on board so it is fully operationnal even without a chassis, each electrolytic can is bypassed by a prolypolen cap (Solen for now) directly on board. These boards will be my starting point but any comments on how to improve them are truly welcomed. I might try to scan them and provide a picture.

As far as LEDs are concern, I am wondering why companies that build big and expensive amps (like Gryphon, Burmesteer for exemple) seperate the LEDs from the audio path if they're are no differences in the sound or why display can sometimes be turned off. It might just be a marketing strategy. I'm inclined to think that LEDs might make a difference in sound, even slightly but again (as someone once told me) some golden ears can hear flies fart....;-)


TO HPOTTER, HARRY HALLER AND ALL:

It seems like there is no consensus on wether IXYS bridges are the way to go (at least it seems to be the opinion of BeanZ). Comments on the sound of Digikey diodes and/or IXYS bridges would be appreciated.

After reading your posts I have no doubt that 2 bridges per channel are the way to go. That's exactly what I am going to do. I'll just have to select the proper one.

I will use 4.5% silver AND 3% solder (? brand ? it will be provided by my friend). Both are better sounding than anything eslse I have tried this far. Now wich will go where is another story. I'll have to experiment. In my experience Cardas solder gives weight and ambiance but at the detriment of pace and rythm. It muffled a little too much the sound for my taste. The 3% solder I am using has IMHO the qualities of the Cardas but offer a more natural and transparent presentation of the stage . The 4.5% solder (while lacking in body and warmth) is clean, fast, transparent, vivid and has superbe detail retrivals and do the pace and rythm thing extremely well. It sounds better to me than any 4% I've tried.

In my experience putting the solder in that order give the best results: 4.5-3-3-4.5 (in my speaker`s crossover).

Again, thank to all for your kind answers

Best regards to all,

Sincerly,
Marc-André Rodrigue