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Old 10th October 2010, 04:09 PM   #31
bprager is offline bprager  United States
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Thanks as always for an informative answer. So many sites list the positive, but not the potential negatives, its nice to get a balanced presentation. At least in my case, I learn a lot more.

Thanks a lot for your thoughts and info on the high end issue. Like you, I yanked the stock 300's very quickly and substituted Princess mesh tubes that I have liked in the past. They significantly helped in all areas.

I also am playing with both the rectifier and driver tubes. Changing to a GZ34 made a surprising change in the sound, cleaner with better mids. It was a large enough change even my wife noticed it immediately and I swapped again just to make sure I really was hearing a real change. So those are staying in, and the last experiments in tubes, are for the 6SL7. A friend is letting me borrow some ECC85 NOS mullards, a set of 5691's and a NOS 6SL7 whose brand escapes me at the moment.
I figure thats enough to see where to go for now, and then the mods should simply help out the amp overall.

I haven't had a chance to try the TJ tubes and if I get the chance will see if anyone I know have a pair. I have heard good things about the brand in general.

Thanks for your help and all the great info. I appreciate the time you've taken to answer all my questions.

Best regards, Bruce Prager
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Old 10th October 2010, 06:08 PM   #32
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by bprager View Post
I also am playing with both the rectifier and driver tubes. Changing to a GZ34 made a surprising change in the sound, cleaner with better mids.
Try some coke bottle, brown base 5R4GY's. I liked them best.

Quote:
Originally Posted by bprager View Post
the last experiments in tubes, are for the 6SL7. A friend is letting me borrow some ECC85 NOS mullards, a set of 5691's and a NOS 6SL7 whose brand escapes me at the moment.
Try finding Ken Rad's (VT-229 is the type designation if I remember correctly). I know they are priced at ridiculous levels, but they live up to the Hype.

Quote:
Originally Posted by bprager View Post
I haven't had a chance to try the TJ tubes
It is my understanding that the Sophia Tubes come from the factory and are made to identical spec's as those sold under the TJ brand. Of course, there may be differences in selection and warranty etc. that make one a better than the other, but if you have one I doubt you need the other.

Ciao T
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Old 10th October 2010, 08:34 PM   #33
bprager is offline bprager  United States
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Thanks, I'll give them a try. Hadn't heard of them. I looked for Ken Rads but so far the only ones I could find cost more than the amp! But I'll keep an eye out.

I didn't know that the Sophias and TJ's were "related", but it makes sense. The sound of the Sophias are just about what people write about with the TJ's.

Thanks!!

Bruce
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Old 17th October 2010, 10:57 AM   #34
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Hi all, especially to Thorsten,

I haven been planning some mod to my old Consonance Reference 5.0 integrated amp which I think is very similar to M500 the main superficial difference would be the driver tubes. On Reference the input is 12at7, and driver is 12Bh7.

Upgrade i have planned for this amp includes:

1) Power Supply: changing two in-series Rubycon 220uf/450v to one Jensen 100uf/550v electrolytes. I wish I could squeeze in the mundorf tubecap (film cap) but they are expensive and size are too big to fit under the chasis. I will bypass both 100uf with a small value film cap of 0.1uf/630v solen.

2) Cathode Bypass Capacitors: I wish I could replace all of them by film caps but again size is a big concern. For input and driver tube, there are 100uf/16v BG PK for each, I plan to change to the red Blackgate NH series. Cathode bypass on the 300b's 1kohm Dale resistor is a rubycon 220uf/250v electrolytes. This is the main area giving me problem and need some advise here:

a) I want to replace it with film caps, but 220uf film are way too big, i cant' find space in the bottom to fit all these in. 2 x 100uf films are even bigger. Can I go down to 100uf (Axon truecap) ? what would I lose?

b) And a bit more extreme, can I do away the bypass cap completely, and reduce the resistor from 1k to 470ohm to bring back the gain lost in going to unbypass cap? Is this mod worth or it has major flaw?

3) original coupling caps from factory are 0.1uf and 0.47uf Mundorf supreme. I have got some russian ksg silver mica of 0.1uf on hand and planning to replace the 0.1uf Mcap by the silver mica 0.1uf and for the 0.47 Mundorf, i just add the 0.1uf silver mica on top. I have some russian teflon ft-3 but can't decide if i should put in teflon or mica for a while, eventually I settle on the silver mica.

4) for the filament heater supply, originally is rubycon 10000uf/16v, I have some Jensen 10,000uf/65v on hand from past projects and plan to swap these in.

Need help here, and thanks in advance

BTW, my speakers are Bastanis Atlas with gemini dipole tweeter and 18" dipole mandala bass bin

I am from Hong Kong

Last edited by welborne; 17th October 2010 at 11:00 AM.
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Old 17th October 2010, 03:19 PM   #35
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by welborne View Post
I haven been planning some mod to my old Consonance Reference 5.0 integrated amp which I think is very similar to M500 the main superficial difference would be the driver tubes.
Sorry, I have no experience with this Amplifier.

Quote:
Originally Posted by welborne View Post
1) Power Supply: changing two in-series Rubycon 220uf/450v to one Jensen 100uf/550v electrolytes.
I would check other options. I am unsure you would realise a major upgrade from this, instead of first taking care of other areas and fundamental design flaws.

Quote:
Originally Posted by welborne View Post
I will bypass both 100uf with a small value film cap of 0.1uf/630v solen.
I'd be really careful on that. Better use a small value resistor between the electrolytics and the bypass cap and increase the bypass cap as much as possible in value.

The ESR of the electrolytics will be in the region of 1 Ohm or less, meaning an 0.1uF capacitor would only be effective above several MHz, where most axial film types are not very efficient, in fact, most likely you will get several tank resonance circuits above a few 100KHz that make a real mess up there, while not really helping anything in the audio range.

If instead you inserted 33Ohm into the PSU Line and connected a 10uF capacitor after this resistor you would have a system that is effective from 500Hz upwards and can effectively reduce high frequency noise from the supply and likely will give a much greater benefit than swapping out the Rubicon's for more of the same with a different label on it and would reliably have non of the issues your bypassing may (will?) create.

Quote:
Originally Posted by welborne View Post
2) Cathode Bypass Capacitors: I wish I could replace all of them by film caps but again size is a big concern. For input and driver tube, there are 100uf/16v BG PK for each, I plan to change to the red Blackgate NH series.
I think (depends on the exact circuit) you can omit one or several of these. The input most likely without second thought, the driver will depend on the exact circuit. If you look at the Ongaku circuit for example, you find only one cathode bypass cap which is in series with an unbypassed 1K resistor, so 33uF good quality film will do nicely there. The alternative would be to drop the DC coupling and use an interstage coupling cap, which would probably a better choice, all considered.

Quote:
Originally Posted by welborne View Post
Cathode bypass on the 300b's 1kohm Dale resistor is a rubycon 220uf/250v electrolytes. This is the main area giving me problem and need some advise here:

a) I want to replace it with film caps, but 220uf film are way too big, i cant' find space in the bottom to fit all these in. 2 x 100uf films are even bigger. Can I go down to 100uf (Axon truecap) ? what would I lose?
As a fundamental thing, in many circuits the Cathode bypass capacitor values are very much oversized. With generic electrolytic cap's this can help.

In one of his WW article's arch-objectivist Douglas Self compared (measurements) "audiophile" capacitors to the same value generic types (Audiophile types in my reading are cap's designed for good audio performance, which is met only by few of those commonly marketed as audiophile). The audiophile cap had much lower distortion. In addition D. Self found that increasing the value of the generic cap reduced distortion to comparable levels.

I find that often 22uF Film Capacitance can replace 220uF of good quality generic electrolytic capacitors as long as this does not cause problems with low frequency response. For a 300B with a 1K cathode resistor I personally find 33uF the lower limit. Any less and you measurably loose ultra low bass (even if not audible with most speakers).

You can instead of the 220uF electrolytic cap use my style of WE connection, with a 12..15uF/630V film capacitor added from the top (+B) of the output transformer to the 300B Cathode and the cathode capacitor changed to 47uF/160V (to keep size small).

Due to the way the WE connection works, even an electrolytic capacitor is acceptable from the cathode to ground, though a film type is still giving a modest improvement over an electrolytic cap there, but nothing like the kick just the WE Cap alone brings.

If you have time, tuning the WE Cap for best power supply rejection can give a much greater benefit than large amounts of money put into expensive PSU Cap's in a conventional circuit. Indeed, I'd go as far as saying that generic PSU Cap's with a well implemented WE connection sounds better than a generic circuit with monster size super premium film cap's replacing the original cap's and the one on the 300B cathode.

Quote:
Originally Posted by welborne View Post
b) And a bit more extreme, can I do away the bypass cap completely, and reduce the resistor from 1k to 470ohm to bring back the gain lost in going to unbypass cap? Is this mod worth or it has major flaw?
Well, first, if you change the 300B cathode resistor value you change the current in the tube, going to 470 Ohm will essentially nearly double the current, which will fry your outputs crispy quite quickly.

Secondly, the bypassing of the output tube cathode resistor makes sure it has a low effective anode impedance. With a sufficient value bypass capacitor you in essence get the tubes anode impedance.

A simple way of guesstimating the effect of unbypassing a cathode resistor with a triode is to take the value of the cathode resistor, multiply it with the gain (Mu) of the tube and add this resistance to the Tubes own anode impedance.

So, a straight 300B will have around 700 Ohm Anode impedance (and a gain of 4), with a cathode bypass capacitor this will be maintained at all frequencies but very low ones. The output transformer is normally 3K primary, so your effective gain from the tube is 3.2. The Transformer will turn the 700 Ohm anode impedance of the 300B to a theoretical 1.8 Ohm, to which we normally need to add some output transformer losses, which gives the commonly found output impedance of 3 Ohm for the 8 Ohm tap of a "common garden" 300B Amplifier.

If we now have a 470 Ohm cathode resistor (and ignore at the moment the smell of frying expensive 300B Tubes) this resistor will appear now as an effective addition of 1.9 KOhm to the Anode Impedance of our 300B. As it is now run well past official limits our anode impedance should be around 450 Ohm (more current = lower impedance), so in total our output imepdance is now around 2.3KOhm. This means our output impedance from the 8 Ohm tap more than doubles and our gain is down to around 2.2.

So, I think you will find that doing what you suggest is likely a very bad idea on several accounts.

You could convert the amp to fixed bias, but then you need to consider the quality of the final power supply capacitor again very seriously and you would have to probably completely redesign the power supply and you may even need a completely different power transformer. Still, could be worth it.

In your case I think WE connecting the output stage will be the easiest, quickest and highest impact mod, next to properly fixing the 300B heater supply. Next to these two the things you have planned will be mere small change in sonic terms (if not in cost).

Quote:
Originally Posted by welborne View Post
3) original coupling caps from factory are 0.1uf and 0.47uf Mundorf supreme. I have got some russian ksg silver mica of 0.1uf on hand and planning to replace the 0.1uf Mcap by the silver mica 0.1uf and for the 0.47 Mundorf, i just add the 0.1uf silver mica on top. I have some russian teflon ft-3 but can't decide if i should put in teflon or mica for a while, eventually I settle on the silver mica.
Try the various capacitors, you may also find that 0.1uF suffice for the coupling to the 300B, depending on the precise design/schematic of the Amp.

Quote:
Originally Posted by welborne View Post
4) for the filament heater supply, originally is rubycon 10000uf/16v, I have some Jensen 10,000uf/65v on hand from past projects and plan to swap these in.
This may bring a minimal improvement at the expense of a huge lump of cap, but fails to address the fundamental problems. Using Schottky rectifiers instead of the original bridge and a pair of 2,200uF caps with a pair of around 0.47 Ohm resistors between them can bring a by far greater improvement across the board and keeping the 10,000uF rubicon as second cap with 2,200uF first cap and schottky rectifiers will produce even greater gains.

Quote:
Originally Posted by welborne View Post
Need help here, and thanks in advance
I suggest you first clear your head of the accumulated audiophile ** (e.g. the concepts that component swapping without addressing fundamental design flaws can magically transform gear, that most high end designers actually know what they do and their circuits are correct and that the values of a given component is optimal the circuit and you must always replace like for like on values and and ratings, even if it means the much large component is stuck somewhere miles from where it belongs and connected with long wires and so on...).

Then get a circuit diagram, a scope and some basic test gear and find the actual problems, having found them, resolve or at least improve them.

This will allow you to indeed "transform" the gear, but not by magic, but by sound engineering (pun intended).

Don't get me wrong, parts quality does matter quite a lot, but a good design sounds very good with generic parts and even better with excellent ones in the right places, a poor design still sounds poor after thousands of dollars worth of magical caps and so on thrown at it.

Ciao T

PS, I am often in HK on business, if you like, we can meet for yum cha and I can explain many of the principles much better with pen and paper than here.
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Old 17th October 2010, 06:16 PM   #36
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Thanks Thorsten for your time. I sent you an email. You answered me quite some time ago on a question about Schulz th315 too

I found an internal pic of my Reference 5.0

Click the image to open in full size.

Click the image to open in full size.
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Old 17th October 2010, 08:56 PM   #37
bprager is offline bprager  United States
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Default Coupling cap changeout

Thorsten, received everything I think I need, and have mapped out the mods, but the changeout of the coupling cap has me a bit confused.

I am planning on two changeouts based on our discussion.
Looking at the schematic for the M500 you posted, the cap labeled C1 100uf is being changed out to 22uf film caps as per our discussion.

The other coupling cap you refer to I assume is C3? which is 150uf on the schematic.
The confusion is that the link I ordered from specified the new cap as a .22uf cap, which I choose as a Audio note copper PIO.
Am I really changing the 150 to a .22, or do I have the wrong cap (and/or ordered the wrong value cap)?

Also, to make sure I'm in sync with the schematic, the grid choke replaces R6 on the schematic?

Everything else makes sense and I have determined the best way to install them, its just the value of the cap that has me thrown a bit.

Thanks for all your help!!

Best, Bruce Prager

Last edited by bprager; 17th October 2010 at 08:58 PM.
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Old 18th October 2010, 03:59 AM   #38
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by bprager View Post
Thorsten, received everything I think I need, and have mapped out the mods, but the changeout of the coupling cap has me a bit confused.
I am attaching a schematic of the M500 with my suggested MINIMUM modifications applied. This does not show the Filament Supply, but a simple CRC filter, for thse who want to keep costs to a minimum.

The coupling capacitor is marked C2 on both Schematics. Value is uncritical, minimum 0.1uF. My mod schematic shows a 0.47uF coupling capacitor. The 4.7uF/4.7K "snubber" across the 0.47uF cap is the fabled DR.P.

In simulations I have found that making the DR.P cap 10 times the value of the coupling cap and making the resistor in KOhm equal to the DR.P cap in uF seems to work best, but I have not done much experimentation. So feel free to try other values etc.

Quote:
Originally Posted by bprager View Post
Also, to make sure I'm in sync with the schematic, the grid choke replaces R6 on the schematic?
No, R4 (the grid leak resistor).

Also, my schematic shows the original power supply, however I would recommend to convert it to the schematic shown in post #2.

Ciao T
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Old 18th October 2010, 04:11 AM   #39
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Folks,

Quote:
Originally Posted by ThorstenL View Post
I am attaching a schematic of the M500 with my suggested MINIMUM modifications applied.
Just noticed, I forgot to change R5, it is shown as 10K but should be reduced to 100...330 Ohm. Carbon Composite (Allen Bradley etc.) preferred.

Ciao T
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Old 18th October 2010, 03:23 PM   #40
bprager is offline bprager  United States
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Thanks Thorsten.
The pwr supply change is the addition of the 10uf cap before the choke and the move of the 220's? I have that mapped and have the 10uf as a gold Obligatto.
Also, I am adding the 47R resistor and the 22uf cap as was circled in green on the first diagram in post #2.
Didn't realize quite how big that 22uf bugger was going to be however extending the case depth is quite easy so I'll stuff it in somewhere. I notice similar ones are used your new amps. Those are really packed, I definitely admire the skill it took to lay out that much componentry and get it all to fit so well.

I originally ordered .22uf coupling caps. Can/should I still use these, or return them and get .47's? I had picked the copper AN PIO's.

The 15uf and snubber components? Do they need very high quality components or are they not as critical? I could go with Hovland or Auricaps if critical, resistors aren't hard to get.

Everything else seems to match my workplan, so I really appreciate you taking the time for the schematic. It helps to have a frame of reference when you are doing things like this. Otherwise its easy to get lost and misunderstand what goes where.
This was a really big help.


Thanks again for your help and support.

Best, Bruce Prager
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