GoodSoundClub - Romy the Cat's Audio Site

06-05-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	21
Post ID:	21694
Reply to:	21693

Do not worry....

anthony wrote:
Do you still use the fuse shown in the MF channel schematic linked above (not the 6 Channel schematic)?

This find that this fast blow 100mA in B+ supply of output channel is a good idea regardless. In a minor way I will protect your output tube if case your driver go down, which is very unlikely to happen. In a larger picture: in case you are a skilled builder and confident about your skills then you might drop that fuse and juts to experiment with cheap tube initially. In case you are not so experienced builder (like it was in my case) or in case you have 6Ch huge amp with million wire and great opportunity for confusion and accidents (like it was in my case) the present of that fuse would protect you from pricey mistakes and burning the costly DHT. You might have the fuse during the building and then to short it as the amp will be done and the experiments with output tube are over.

anthony wrote:
Well I would have missed that one...so thanks for that. These will be my first amplifier builds so I will probably miss those kinds of things. Can you think of any others that I will probably miss?

Use a light bold as a fuse during the assembly – will save you a LOT worries.

anthony wrote:
Thanks Romy, but I don't know what you mean by AV in the text above. Do you mean dB?

I mean any AV meter you have, would it be DB, VA/AV, volts or whatever you want. I personally use Dorrough, which are very high resolution led loudness/ modulation monitors. They kind of crazy expensive, completely unreasonable, but from time to time you can pick them up at eBay for sub $20. There are many alternative, analog or digital, when you have 14 channels you would like do not run with your Fluke but to have a nice visual representation of your channel does.

anthony wrote:
One more question. The filament supply of the MF Channel has the hum management circuitry on the 4v secondary...do you also use an artificial center tap on the 2.5v secondary? I just thought that it might be one of those "hygiene" things that you left off the schematic. Likewise for the filament supplies of the other channels.

Nope, that is exactly how it is depicted. I have a dedicated transformer from 120V with two full-fill secondaries, one for 4V and one for 2.5V. The switch of tube always would lead for minor adjusting of the 100R resistor. You would not need to do it always as in most cases you will hear the sound of the tube even with some very minor noise. When you find the tube that you would like to spend time then you would balance the 100R resistor to 0mV at the speaker. In some case you will be able to do it but I might not stay there and will run up and down to +-2-3mV: completely not auditable until you stick you head into the horn, turn off your home appliances and stop traffic in 5 miles radius… :-)

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-11-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	23
Post ID:	21698
Reply to:	21697

The starting sequence.

anthony wrote:
Can you remember what caps you used in the HF filter? They are certainly not standard values and I do have a memory of you trialling air caps.

I presume you ask about the F amplifier channel. I use air caps 530pF and 1591pF. If you do decide to use air caps then be advised that they need to be double shielded in steel and aluminum and they are large and will be located in the location where there is a LOT of noise. I do think that that air caps is an icing over the cake and I am not sure that it is necessary. The caps do not recharge (it is where the air caps shine) in this application and they always operate in one polarity and voltage biased. So, I think a good mica or vintage tantalum or whatever you like caps might be working in this application very well.

anthony wrote:
I spent too much time today trying to figure out if I wanted a power switch for these amps and just how I wanted to switch the unit on and off. In the end I have gone for a regular Schurter IEC inlet with a fuse drawer and switch.

This is not so simple. As you turn the amp you kick on the starting sequence. So, naturally you would need a latching switch, which power your filaments and kicks of the high voltage sequence. In my case I always wanted to have the amp to be able to state and stop by pedal in order do not bend by fat body, So I needed an immediate switching latching switch, it means a short pulse (temp contact, or any other immediate event) turn the sings on and off. You can assemble a little schematic that might do it. I went an alternative way and employed a very good powerful 12A relay that did the job for me. I used Magnecraft 711XBXCL-12D, they are expensive (around $25) but they are very good. I am sure there are alternatives….

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-12-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	25
Post ID:	21702
Reply to:	21700

The remote start option.

Hm, I am not sure that pedal is what I would do juts for a full range Milq. The 6-ch Milq is architectural monster and to use a pedal for it is sensible as the PS is separate and in inconvenient to reach location. In a full range everything is “right there” and it is easy to reach. The best that I would do would be the implement a remote starter, or some kind of 12V jack, sorting of which would kick in the initialization sequence for the power amp. This way you could bring both of those feed to the preamp and will be able to stat them. This option does not exclude a pedal if you wish to use it.

The Magnecraft relay that I mention above is obsolete I think (you still can buy it) but there are plenty alternative, including from Magnecraft. The selection of 12V or 120V, DC or AC is completely on you. If you go not for 120VAC then you would need another transformer. I took 12V 2A wall adopter (that has a transformer and rectification bridge), took the plastic cover off and just mounted and in the amps’ PS. So, my 6-ch Melquiades is powered by a telephone wall adopter.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-14-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	26
Post ID:	21703
Reply to:	21702

It will be a sheep in wolfs clothing...

The fullrange Milq will be built in an oversized chassis with the intention of adding maybe two or more channels down the track and perhaps some line level crossovers. So I will up spec. the mains transformers so they can handle a larger draw and will leave room for more power supplies and more amplification stages. Plus it will be tucked out of the way when it is in the room and a little difficult to get to, so the foot pedal will be much appreciated.

Haha about the wall-wart. You would not be the only one to do that. I have boards for a nice dual rail regulated linear supply that will suit things nicely. It is overkill in that is has infinitesimal noise and is really meant for powering parts of a dac but between the two rails I can get 2A which will be enough for the foot pedal and lights and fans et cetera. Plus I will not have a SMPS putting crap back into the power for other components to pick-up...I would like to remove all SMPS on my audio circuit...next will be the PC.

06-15-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	27
Post ID:	21705
Reply to:	21703

The coupling capacitors

Romy, I understand that at some stage you trialled a number of different capacitors and settled upon Electrocube 950B/D not necessarily for the Melquiades but perhaps for some other project. I was wondering if you ever experimented with different coupling caps in Melquiades? Oil caps in particular.

As I mentioned earlier in this thread, these are my first valve amplifier builds so I have not messed around with different coupling caps before but I have heard how caps in speaker crossovers can make quite a noticeable difference, so I am interested in your input here.

Regards,

Anthony

06-15-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	28
Post ID:	21706
Reply to:	21705

To a great degree it depends where the Cap is used.

anthony wrote:
Romy, I understand that at some stage you trialled a number of different capacitors and settled upon Electrocube 950B/D not necessarily for the Melquiades but perhaps for some other project. I was wondering if you ever experimented with different coupling caps in Melquiades? Oil caps in particular.

As I mentioned earlier in this thread, these are my first valve amplifier builds so I have not messed around with different coupling caps before but I have heard how caps in speaker crossovers can make quite a noticeable difference, so I am interested in your input here.

As much as caps in speaker crossovers makes deference, so do they make in coupling applications. In Milq the cap is light duty as the amp never goes A2 and the cap is not change the polarity, still the coupling caps do mater a lot. I did experimented a lot with the coupling caps and I like the Electrocube 950B and MultiCaps, the last unfortunately available only by small values. I did not experimented with new German Teflon caps. I do not like oil caps, at least those that I tried. I feel that oil caps are more suitable for high current applications. Also, do not forget that in context of DSET the coupling cap behavior is kind of defend. If you need large coupling cap for LF amp that you do not care how “dry” it sounds at HF. I find that for MF and HF it is better do not have cap at all, that why in my DH channel I use DB coupling, something that I would not do for ULF….

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-18-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	29
Post ID:	21717
Reply to:	21706

Cap rolling...

Romy the Cat wrote:

As much as caps in speaker crossovers makes deference, so do they make in coupling applications. In Milq the cap is light duty as the amp never goes A2 and the cap is not change the polarity, still the coupling caps do mater a lot. I did experimented a lot with the coupling caps and I like the Electrocube 950B and MultiCaps, the last unfortunately available only by small values. I did not experimented with new German Teflon caps. I do not like oil caps, at least those that I tried. I feel that oil caps are more suitable for high current applications. Also, do not forget that in context of DSET the coupling cap behavior is kind of defend. If you need large coupling cap for LF amp that you do not care how “dry” it sounds at HF. I find that for MF and HF it is better do not have cap at all, that why in my DH channel I use DB coupling, something that I would not do for ULF….

Thanks for your insight Romy. I can see your point about not needing to worry too much in the DSET about coupling cap performance at higher frequencies but I would imagine that the crossover filter caps are quite import at those regions though. Have you experimented with something other than the Electrocubes there?

I ask this because the Electrocubes are not easy to get hold of and end up reasonably expensive by the time I purchase them in a quantity that they are willing to manufacture so I have looked around a little for alternatives. Where you use film in the power supplies I am considering the Mundorf MCap Supreme film caps...they seem affordable and reasonably well regarded when used in power supplies. Likewise I think that I will try them for the larger coupling caps.

Regarding the DSET crossover filter caps, I am thinking of using either Jupiter Copper Foil or V-Cap CuTF...they are both reasonably affordable in the small values, particularly the Jupiters. DSET coupling caps I will probably try the Mundorf MCap Supreme film caps for a start and maybe even a small value Jupiter Copper Foil or V-Cap for the UpperBass coupling cap, just to see if there is any difference.

I will be building the fullrange first, so I might try a few different coupling caps in it if I get enough time with it. I have a pair of Duelund Cast 630VDC 2.2uf sitting around here somewhere that I can try as the coupling cap plus I will be able to try the much less expensive Mundorf MCap Supreme mentioned above and maybe a Jupiter Copper Foil as well. It will be interesting to see if any of those caps seem to work well in the fullrange Milq.

Regards,

Anthony

06-18-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	30
Post ID:	21718
Reply to:	21717

Caps, caps, caps....

anthony wrote:
Thanks for your insight Romy. I can see your point about not needing to worry too much in the DSET about coupling cap performance at higher frequencies but I would imagine that the crossover filter caps are quite import at those regions though. Have you experimented with something other than the Electrocubes there?

In my view the Electrocubes do well across the board. When you are taking about “caps at higher frequencies”, then what do you mean? The line level, the speaker level, the line level between? Do not forget that a RL filter is always preferable over C filter.

anthony wrote:
I ask this because the Electrocubes are not easy to get hold of and end up reasonably expensive by the time I purchase them in a quantity that they are willing to manufacture so I have looked around a little for alternatives. Where you use film in the power supplies I am considering the Mundorf MCap Supreme film caps...they seem affordable and reasonably well regarded when used in power supplies. Likewise I think that I will try them for the larger coupling caps.

I had a few Mundorf MCap but I can’t say anything concussive about them. The Electrocubes are not as expensive as you think. If you look their inventory then you can get them for a few bucks each. Alternativly you can look at eBay and you will always find someone has leftover and sell them very cheap, for $1 per 2uF/450V cap/ I have bought quite a lot of this way.

anthony wrote:
Regarding the DSET crossover filter caps, I am thinking of using either Jupiter Copper Foil or V-Cap CuTF...they are both reasonably affordable in the small values, particularly the Jupiters. DSET coupling caps I will probably try the Mundorf MCap Supreme film caps for a start and maybe even a small value Jupiter Copper Foil or V-Cap for the UpperBass coupling cap, just to see if there is any difference.

I will be building the fullrange first, so I might try a few different coupling caps in it if I get enough time with it. I have a pair of Duelund Cast 630VDC 2.2uf sitting around here somewhere that I can try as the coupling cap plus I will be able to try the much less expensive Mundorf MCap Supreme mentioned above and maybe a Jupiter Copper Foil as well. It will be interesting to see if any of those caps seem to work well in the fullrange Milq.

I do not know anything about them. Feel free to experiment. If you want, after you finish the amp, let me know your address and I send you a pair of Electrocubes 2uF/450V just for reference. Anyhow, there are tone of the caps out there you might find something good. Do not discard the vintage caps, some of them are very good. Also, be advised that most topologies of caps do need to be burn in in order to yield the best sound.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-18-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	31
Post ID:	21720
Reply to:	21718

Caps at high frequencies...

Romy the Cat wrote:

When you are taking about “caps at higher frequencies”, then what do you mean? The line level, the speaker level, the line level between? Do not forget that a RL filter is always preferable over C filter.

It was reference to the range of frequencies that the lower frequency DSET channels with coupling caps are required to pass. Like a typical audio moron I have read a few things online recently about different people using different caps for various tasks in various systems with various listening preferences with various...well you get the idea...but the main talking points seem to be midrange or top-end with not a great deal of talk about differences at bass frequencies, which is where the coupling caps are used in the DSET Milq. I am left with the impression that the DSET will be less influenced by the choice of coupling caps than a fullrange Milq, and that I will probably get good results with a solid performer but not necessarily over-the-top cap in those positions.

However, the caps in the line level filters may be a different matter because they are working with the entire frequency range, so perhaps the best quality caps should be used there. As an aside I think that I may have just found a good source for these filter caps in Electrocube 950B's and am waiting for a quote (someone actually has stock of the smaller values - but not of the larger 2uF caps). If it pans out I will sort out the filters with Electrocubes and then when everything is settled try some other brands to see if there can be any improvement.

Romy the Cat wrote:
The Electrocubes are not as expensive as you think. If you look their inventory then you can get them for a few bucks each. Alternativly you can look at eBay and you will always find someone has leftover and sell them very cheap, for $1 per 2uF/450V cap/ I have bought quite a lot of this way.

I have had an eBay alert set for 6 months now and it has not alerted me of any 2uF caps. I don't live in the US so maybe I only get alerted about the ones that ship worldwide.

On the other hand these people that I found with some Electrocube stock do have 1.5uF and 3uF sizes (apparently), so perhaps those values are ok to use instead of 2uF and 1uF in your schematic.

06-19-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	32
Post ID:	21721
Reply to:	21720

Do not worry about it for now.

Anthony, I think you take the right this in a wrong way. Sure the quality of the coupling caps is important but you truly shall not be worry about it. Make the amp, get comfortable with it and then change the damn cap. It is very simple to do and I am sure you will find zillion caps to experiment with. Do not worry about it for now. For a full range amp 2uP will be enough. The cap and plate impedance will create low pass filter. You want this filter to be a couple octave under the lower cut off of your transformer. If you get at full power -3dB at let say 18Hz then to cut off for the filter at 7-8 Hz would be sufficient. With 2uF you will be somewhere there… Do not forget that you can always parallel the caps, to bypass the caps… there is a lot that might be done.. but later….

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-22-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	33
Post ID:	21729
Reply to:	21721

Second Stage Half-6C33C impedance

Romy the Cat wrote:
Anthony, I think you take the right this in a wrong way. Sure the quality of the coupling caps is important but you truly shall not be worry about it. Make the amp, get comfortable with it and then change the damn cap. It is very simple to do and I am sure you will find zillion caps to experiment with. Do not worry about it for now. For a full range amp 2uP will be enough. The cap and plate impedance will create low pass filter. You want this filter to be a couple octave under the lower cut off of your transformer. If you get at full power -3dB at let say 18Hz then to cut off for the filter at 7-8 Hz would be sufficient. With 2uF you will be somewhere there… Do not forget that you can always parallel the caps, to bypass the caps… there is a lot that might be done.. but later….

I will do it own the track. Going round in circles I was.

Romy, I am checking crossover filter calculations against your DSET schematic and am having a little trouble determining the high pass filter component of the Upperbass Channel. The 0.022uF coupling capacitor is supposed to roll off the high pass at about 60Hz according to the schematic but without knowing the input impedance to use for the half 6C33C I cannot actually check this and look at what effect different sized caps in there will have on the -3dB point. Using 60Hz as the -3dB point and 0.022uF as the capacitor I end up with an input impedance of about 120kOhm for the half-6C33C as you run it in your DSET Milq. Does this sound about right?

Regards,

Anthony

06-22-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	34
Post ID:	21734
Reply to:	21729

I think it is about right.

I think it is about right. The 6C33C for upper base has 100K biasing resistor and 20K to ground in Lpad. That would make ~60Hz. This high pass that unload the LF from the horns that it can’t handle is very important as you do not want driver to pressurize the horn by sound that could not be passed by horn. You need to go with high resolution RTA and plot a low knee of the horn decay, full range. Then you need to get the filter and run it just to be barely visible at the plot. Then drop a half of the octave and it would be your crossover point.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-23-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	35
Post ID:	21743
Reply to:	21734

More Lpads...

Romy the Cat wrote:
I think it is about right. The 6C33C for upper base has 100K biasing resistor and 20K to ground in Lpad. That would make ~60Hz. This high pass that unload the LF from the horns that it can’t handle is very important as you do not want driver to pressurize the horn by sound that could not be passed by horn. You need to go with high resolution RTA and plot a low knee of the horn decay, full range. Then you need to get the filter and run it just to be barely visible at the plot. Then drop a half of the octave and it would be your crossover point.

I have to admit that I have studied the DSET schematic and I just plain missed the Lpads for the 6C33C bias. Kind of obvious really that they should be there considering the variable resistor in that place on the fullrange Milq schematic, but for some reason I missed it.

Romy, do you use an Elma rotary switch with RN60 resistors for these 6C33C bias LPads (Bass, Upperbass and Injection)? What sort of attenuation step should I be looking for here?

Regards,

Anthony

06-24-2015

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Romy the Cat

Boston, MA
Posts 10,184
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Post #:	36
Post ID:	21744
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They are not LPads but they are bitch.

Well, they technically not Lpads but juts regular attenuators even though they connected in “protective mode”. You can go with stabilized impedance to maintain the high pass filter over the coupling capacitor to work properly but I do not feel it is necessary. When you make the real amps you will have the attenuator ruining let say between 35K and 36K to set the real tube bias properly. You will not slide the attenuator from 0 to 50K. The range will be buffered by two resistors up and down and in context of 100K biasing resistor the impedance shift that your coupling cap will see will be near negligible and might manifest a 2-3Hz difference in the slop. Above I told you that I tested the slope with analyzer and I did not detect any meaningful crossover shift while I changed bias.

Now, the type of the resistor is the real bitch question. You do not want rotary switch with great resistors but you rather want a 10-20 turns attenuator. However this is bias and everything you do with bias matters sonically. So, find the best you can get 20 turns attenuators. At the time I did it I had 3 or 4 different types and all of them were as good as fixed resistor. I chose the one that I liked best at that time, I do not remember what it was, I think it was some kind of large 20 turns Vishay for $12. It was however over 12 years back and today you might find better parts. Be advised that quality of soldering and wires and even the layout of the bias wiring in the amp’s chasses is very auditable for whatever reason. I actually was very surprised how sensitive and demanding my 6C33C where for biasing line. I was able to hear the sound change when I loved the proximity of bias wired to mass ground. I am not kidding.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

06-25-2015

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anthony
Posts 338
Joined on 08-18-2014

Post #:	37
Post ID:	21747
Reply to:	21744

Bleeders at shut-down...

Romy the Cat wrote:
Well, they technically not Lpads but juts regular attenuators even though they connected in “protective mode”. You can go with stabilized impedance to maintain the high pass filter over the coupling capacitor to work properly but I do not feel it is necessary. When you make the real amps you will have the attenuator ruining let say between 35K and 36K to set the real tube bias properly. You will not slide the attenuator from 0 to 50K. The range will be buffered by two resistors up and down and in context of 100K biasing resistor the impedance shift that your coupling cap will see will be near negligible and might manifest a 2-3Hz difference in the slop. Above I told you that I tested the slope with analyzer and I did not detect any meaningful crossover shift while I changed bias.

Now, the type of the resistor is the real bitch question. You do not want rotary switch with great resistors but you rather want a 10-20 turns attenuator. However this is bias and everything you do with bias matters sonically. So, find the best you can get 20 turns attenuators. At the time I did it I had 3 or 4 different types and all of them were as good as fixed resistor. I chose the one that I liked best at that time, I do not remember what it was, I think it was some kind of large 20 turns Vishay for $12. It was however over 12 years back and today you might find better parts.

Thanks Romy. I should be able to track something down. At this stage I am thinking of Bourns 3590 series pots.

Romy the Cat wrote:
Be advised that quality of soldering and wires and even the layout of the bias wiring in the amp’s chasses is very auditable for whatever reason. I actually was very surprised how sensitive and demanding my 6C33C where for biasing line. I was able to hear the sound change when I loved the proximity of bias wired to mass ground. I am not kidding.

I don't doubt this statement at all. There are a few ideas for wiring and component layout kicking round in my brain but I think they are for a later stage.

In the 6 Channel Version of Super Melquiades thread at post #89 you mention trouble you were having with some NC relays that you were using to disconnect some power supply bleeder resistors when the amp was turned on. When the amp is turned off these relays make contact again and they conduct power to drain the power supplies backwards into high wattage 50R resistors. I can see that this would be a good idea from both safety and cap lifespan perspectives. Could you please share a little more info about this setup? Does it still function?

You mention 50R resistors and bridging two 6A relay contacts for each power supply. What wattage do you use for the resistors?

Regards,

Anthony

06-25-2015

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	38
Post ID:	21748
Reply to:	21747

A word of warning

anthony wrote:
In the 6 Channel Version of Super Melquiades thread at post #89 you mention trouble you were having with some NC relays that you were using to disconnect some power supply bleeder resistors when the amp was turned on. When the amp is turned off these relays make contact again and they conduct power to drain the power supplies backwards into high wattage 50R resistors. I can see that this would be a good idea from both safety and cap lifespan perspectives. Could you please share a little more info about this setup? Does it still function? You mention 50R resistors and bridging two 6A relay contacts for each power supply. What wattage do you use for the resistors?

I do not remember the specifics with relay. The driver and bias PS are bled the 6C33C’s PS are not. You might do it if you want. You can do it while the PS is running, that would require some current from transformer to be wasted and I do not know if you have a spare current in there. Also, the elevated current would drive the minimum inductance down and would make your choke to be smaller. You can do alternative and on back side of relay to connect a high power resistor, let say 50W. This all does not matter, you can do whatever you want. Just a word of warning if you use the full-range Milq as reference. In the PS of the driver stage it shown L1 20H. For the 100mA the 20H is barley hit the critical inductance. When I measured the critical inductance it did worked fine but to be at the save side I would go ether with let say 30H choke or to drive over the choke 30-50mA more (can be easily set by dropping the volume of R23 resistor). It is not a big deal but it will be more of save side if you do.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

07-02-2015

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anthony
Posts 338
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Post #:	39
Post ID:	21751
Reply to:	21748

They will light up like a Christmas tree

Romy, thanks for the info on the chokes in the fullrange Milq.

Today I have ordered more Milq parts this time for the power sequencing and bleed down. I decided to go for the relay sequenced bleeders for all four power supplies and figured I would be happy with a bleed down time to 50V of about 20-30 seconds. For the four power supplies this is what I calculated:

40,000uF 200V supply = 500R resistor with initial power dissipation of 80W (purchased 500R 100W)
3,000uF 200V supply = 5K resistor with initial power dissipation of 8W (purchased 5K 10W)
9,000uF 400V supply = 2K resistor with initial power dissipation of 20W (purchased 2K 25W)
8,000uF 400V supply = 1.5K resistor with initial power dissipation of 106W (purchased 1.5K 100W)

I decided to go for large ceramic caps with good power ratings so I could avoid heatsinking and also to not rely on the short term power rating of the resistors to get through the initial high power dissipation period of the discharge. In the end the resistors I purchased are big and over-rated for the task but I am happy that I will not be pushing them anywhere near their limits so they should work well for quite some time. Looking at the calculated initial current draws I have similarly purchased relays with over-specified contact current ratings...I certainly don't want them to weld.

Downstream of each bleeder resistor will be a LED to show that charge is draining, or not. So there will be one LED to tell that AC power is available and the standby DC power supply is running, three more LED's for the power-on sequencing relays and then four LED's that will light up when the bleeder circuits are activated on power-down. That is 8 LED's on each amplifier, which is ridiculous and could make the whole thing look a little like a Christmas tree if I am not careful, but I have chosen low intensity red lights so hopefully they will ruin neither my night vision nor my impatience for bright LED's on audio gear.

Regards,

Anthony

07-03-2015

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anthony
Posts 338
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Post #:	40
Post ID:	21752
Reply to:	21683

More on the "inductive" LPad

Romy the Cat wrote:
anthony wrote:
Sorry Romy, I was not clear enough, but the resistor that I am questioning is in the Fundamentals Channel (not the MF Channel as I believe you referred to in your previous post) between the OPT and the S2.

Ah, the Fundamentals Channel, that is totally different story. I have a regular highly inductive 16R L-pad in there, just at the speaker level. The upper knee of the Fundamentals Channel is second order 1000Hz at line-level and you do want to drive as much as possible HF out of this channel. The additional inductive roll off at top only helps to this Channel, even I do not think that it is truly auditable.

Romy, are you able to give me an example of a regular "inductive" LPad? I am struggling. Those that I can find don't state whether they are inductive or not. I have ordered a cheapy from Parts-Express but I have no idea if it is inductive or not...probably not.