rabstg said:
That is funny.
I originally ordered two 25-0-25 400va transformers. A couple of days later I saw the 28-0-28 and knew it would get me closer to the +/- 39VDC of the original KSA50 so I sent a question through Ebay asking if he would give me a deal on two of those since they only show one in the add. He wrote back and gave me a good price for two so I bought them. Well, when they arrived I discovered they were the same 25-0-25 400va that I already have. I sent him an email and he gave me his phone number to call him. I asked if rather than shipping them back if he would just give me a really good price on them and free shipping an the pair of 28-0-28's, which he did. So now Ihave an extra pair of 25-0-25 400va trannies that will give me a good excuse to build something else.
Anyone interested in talking to John directly, email me and I'll give you his number. I told him I would spead the word around here. You'll get a better deal if you call him.
Actually you hook them in series and use the center two wires for the center tap. The 28-0-28VAC will give you 28*1.414=+/-39,5 rails less rectifier loss. I'm using one per side for the new one and I used only one 30-0-30 500vA for both on the first one. I'm anctious to see how much difference I can hear. If it's enough I may change the first one.
Blessings, Terry
I installed the pair of 500VA, 28-0-28 volt trannnies in place of the 25-0-25 and the results are that at 400ma of bias the rails sit at exactly +/- 40 volts which is exactly where I wanted them to sit. The rails had been at about +/- 36 volts with the 400 VA, 25-0-25 volt trannies. The interesting thing was a jump of 70ma of bias with just a +/- 4 volt increase of the rails!! I hadn't checked it in a couple of months but I doubt that it woulda drifted this far up..... So for those that are wondering the Anatek 500VA 28-0-28 toroids are probably the way to go. They are cheap and alwys available, quality look decent... but there is no ground shield, a small thiing in a low gain device shch as these amps.
Mark
Addendum: I forgot to mention there is a CL-60 current inrush limiter in series with each tranny's primary winding.
Mark
Addendum: I forgot to mention there is a CL-60 current inrush limiter in series with each tranny's primary winding.
Re: Re: Xfmrs
How about Micheal Percy? I understand that he usually gets things shipped fairly quickly. I was thinking about using him myself since I missed the first group buy. But I cant realy start on this for a few months anyway, as I have some other obligations through the end of the year.
On another suject, I was just looking at the schematic for the Classe DR-3 and was reminded that it included an optional phase inverter for bridged operation. Since I have four boards and two chassis, it looks like maybe I have an answer to my earlier question of how to use the stuff I have to best advantage: two stereo amps in two chassis that can each be bridged for mono operation. I am more than a little rusty at analog electronics, so is there any reason that I can't configure my clones for bridged operation that I am missing? Is offset voltage going to be a problem? And what about increased dissipation?
rabstg said:
How about Micheal Percy? I understand that he usually gets things shipped fairly quickly. I was thinking about using him myself since I missed the first group buy. But I cant realy start on this for a few months anyway, as I have some other obligations through the end of the year.
On another suject, I was just looking at the schematic for the Classe DR-3 and was reminded that it included an optional phase inverter for bridged operation. Since I have four boards and two chassis, it looks like maybe I have an answer to my earlier question of how to use the stuff I have to best advantage: two stereo amps in two chassis that can each be bridged for mono operation. I am more than a little rusty at analog electronics, so is there any reason that I can't configure my clones for bridged operation that I am missing? Is offset voltage going to be a problem? And what about increased dissipation?
Mark
Looking at the serial no of 456 I think the KSA100 I have is most likely a version 1.0
I am possibly a bit over- emotional about this amp. I can still remember the day as yesterday when I bought it home and swopped it out with my Quad 405 Mk2. My jaw dropped when the amp started playing. I have never since had the same experience with any other amp. The jump was so big that subsequent amps just sounded incrementally better here and there but nothing to the effect that recreated the same magical experience.
Needless to say - as much as I loved my Quad equipment- it was a speedy divorce afterwards.
Jozua
Looking at the serial no of 456 I think the KSA100 I have is most likely a version 1.0
I am possibly a bit over- emotional about this amp. I can still remember the day as yesterday when I bought it home and swopped it out with my Quad 405 Mk2. My jaw dropped when the amp started playing. I have never since had the same experience with any other amp. The jump was so big that subsequent amps just sounded incrementally better here and there but nothing to the effect that recreated the same magical experience.
Needless to say - as much as I loved my Quad equipment- it was a speedy divorce afterwards.
Jozua
Jacco
20 Years ago Quad was very expensive in South Africa and considered very much high-end. Most of the serious audiophiles replaced the Din plugs with RCA's in order to use "audiophile" cables.
Your comments also shows the difference in what is considered high-end audio in what was then considered as "remote" countries. In a certain sense audiophiles close to the source (living near the manufacturers) do not realise how lucky they are.
I consider that KSA100 Mk.1 as a collectors piece and money well spent.
Jozua
20 Years ago Quad was very expensive in South Africa and considered very much high-end. Most of the serious audiophiles replaced the Din plugs with RCA's in order to use "audiophile" cables.
Your comments also shows the difference in what is considered high-end audio in what was then considered as "remote" countries. In a certain sense audiophiles close to the source (living near the manufacturers) do not realise how lucky they are.
I consider that KSA100 Mk.1 as a collectors piece and money well spent.
Jozua
Re: Re: Re: Xfmrs
Unless you run 4 ohm or less loads bridged, I doubt if dissipation will be an issue. I was thinking the same, except I do not want to insert an opamp or another active stage, I will just run a resistor (same value as the feeback resistor ..12k?) from channel A's output to the feedback input of channel B while shorting out channel B's input. This creates an out of phase differential signal from one channel to the other. In this case only channel A is driven. Channel B input shorted out and driven by the FB loop of channel A. All it takes is a toggle switch and a resistor to bridge 2 channels. This neat little trick is employed in the old Adcom 555's.
niles said:
Unless you run 4 ohm or less loads bridged, I doubt if dissipation will be an issue. I was thinking the same, except I do not want to insert an opamp or another active stage, I will just run a resistor (same value as the feeback resistor ..12k?) from channel A's output to the feedback input of channel B while shorting out channel B's input. This creates an out of phase differential signal from one channel to the other. In this case only channel A is driven. Channel B input shorted out and driven by the FB loop of channel A. All it takes is a toggle switch and a resistor to bridge 2 channels. This neat little trick is employed in the old Adcom 555's.
From: "WLabs" <wlabs@ix.netcom.com>
To: "Troy St.Germain" <stgrab@yahoo.com>
Subject: Re: welbornelabs # 11834
Date: Fri, 21 Oct 2005 09:08:30 -0600
We should be able to ship the balance on Tuesday of next week
Thanks for your patience.
Regards,
Ron Welborne
Welborne Labs
E-Mail:
wlabs@ix.netcom.com
To: "Troy St.Germain" <stgrab@yahoo.com>
Subject: Re: welbornelabs # 11834
Date: Fri, 21 Oct 2005 09:08:30 -0600
We should be able to ship the balance on Tuesday of next week
Thanks for your patience.
Regards,
Ron Welborne
Welborne Labs
E-Mail:
wlabs@ix.netcom.com
Hi,
thinking back to how an inverting opamp works. An opamp set to a gain of times one, the in line input resistor should equal the existing feedback resistor as you said but you also need to disconnect the lower leg resistor that is connected to ground through the DC blocking cap. Using the same opamp analogy you should connect the non inverting input to ground with a resistor equal to the parallel combination connected to the inverting input i.e. 6k0. This is to minimise the output offset from the inverting amp.
thinking back to how an inverting opamp works. An opamp set to a gain of times one, the in line input resistor should equal the existing feedback resistor as you said but you also need to disconnect the lower leg resistor that is connected to ground through the DC blocking cap. Using the same opamp analogy you should connect the non inverting input to ground with a resistor equal to the parallel combination connected to the inverting input i.e. 6k0. This is to minimise the output offset from the inverting amp.
Jozua,
I can well imagine that your jaw did drop. There is a site around about upgrading the Quad 405, it shows the before and the after results and its amazing what can actually be done to one. Overall the original is not a very good amp and the Krell was such an immense jump in quality over the Quad that I completely believe your statement. If yours is a version 1 only Krell could tell you but on Lloyd Mclean's site there are schematics for three of the KSA-100 versions.... plus the KSA-80 and othersHERE
Mark
I can well imagine that your jaw did drop. There is a site around about upgrading the Quad 405, it shows the before and the after results and its amazing what can actually be done to one. Overall the original is not a very good amp and the Krell was such an immense jump in quality over the Quad that I completely believe your statement. If yours is a version 1 only Krell could tell you but on Lloyd Mclean's site there are schematics for three of the KSA-100 versions.... plus the KSA-80 and othersHERE
Mark
This is possibly a stupid question but I'll ask it anyway: I just came across a deal where I could get two 55-0-55 350VA toroids on sale for the same price as one 28-0-28 version. I am not a power supply expert, but I can divide 55 by 2, so I was curious if there is some PSU configuration that would allow me to use the 55-0-55 to generate the VDC needed for the Krell clone and what the downside of doing so would be.
philiprst said:
If the transformer has 120V/240V primaries you could use the 240V tap (in the US). Or take half the secondary windings off, if you can be bothered.
Downside of both of these is that the wire that makes up the secondary will be thinner than that usd on the 28V version, which may or may not be a problem. Isn't 350VA a bit marginal for the Klone anyway?
I have a 1kVA transformer with 70-0-70 secondaries, I'm going to have a go at rewinding it with four 28V secondaries with the fattest wire I can find...any exiting fires, I'll post photos.