I have just finished the amp using the Edcor transformers. Just as I expected, excellent sound, plenty of bass, transparent highs. Inaudible hum on my 98dB speakers. When measuring across the speaker terminals with my Fluke 85 I get 1.4mV of AC noise. I will be taking more accurate measurements when I put the scope on it in the next couple of days. I will now be able to complete the first edition of the manual. For those of you looking to provide your own transformers, I'm very pleased with the GXSE15-6-5K even with the 40-18KHz response. For a $37.01 output transformer, these are hard to beat if you're on a budget. As soon as the custom transformers arrive I will be swapping out the Edcor units.
Attachments
The rear Edcor on the right is the power transformer, the front right Edcor is the first power supply filter choke. There are two additional filter chokes, one per channel, for the driver tube located internally. I will check the 3dB response although my speakers have an F3 of 46Hz. The custom transformers I will be offering with the kit will be flat response from 20-20KHz. I have been wanting to try the GXSE Edcors, and while they don't disappoint for the cost, the xfmrs I am using on my previous build do seem to have a bit more "sparkle" on the high end. I expect the custom OTs that I am having manufactured to be very good on both the low and high end. When I receive them, I will be swapping out the Edcors.
No feedback on this amp. I tried feedback on my previous build and I feel that it took away from the dynamics of the sound.
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When connecting the line-out of a PC or laptop (especially laptop) computer sound card to a tube amplifier that has the signal-ground star-ground point connected directly to the chassis, there is a chance of high-frequency switching power supply noise being induced to the signal path of the tube amp via the ground prong on the computer power cord. (wow, that was one long run-on sentence, forgive me)
This noise can be eliminated by using a "cheater plug" that isolates the PC power supply ground prong. I have experienced this first hand as I am sure some of you have also.
In this amplifier I have included an RC network that connects between the signal-ground star-ground point and the chassis. Of course the ground of the AC input module is still bonded directly to the chassis for safety ground.
I can verify that this method does indeed eliminate any interference that may be induced from the PC switching power supply, without using the "cheater plug".
Just an FYI in case someone was interested.
This noise can be eliminated by using a "cheater plug" that isolates the PC power supply ground prong. I have experienced this first hand as I am sure some of you have also.
In this amplifier I have included an RC network that connects between the signal-ground star-ground point and the chassis. Of course the ground of the AC input module is still bonded directly to the chassis for safety ground.
I can verify that this method does indeed eliminate any interference that may be induced from the PC switching power supply, without using the "cheater plug".
Just an FYI in case someone was interested.
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Getting closer folks. Still waiting on the filter chokes for the driver to be delivered.
If any of you all are in the vicinity, or will be, of JFK airport, that is where my shop is. Anyone is welcome to drop by for a demonstration of the amp and speakers. Just send a PM and let me know.
Scott
If any of you all are in the vicinity, or will be, of JFK airport, that is where my shop is. Anyone is welcome to drop by for a demonstration of the amp and speakers. Just send a PM and let me know.
Scott
A second source input is possible, but typically a stand-alone amplifier, like this one, will only have one input. Multiple source inputs are usually handled by a preamp or passive selector unit. There is room to accommodate a second input by adding a source selector, but this would have to be a modification performed by the end-user.
I am currently working on a multiple-input, all-tube preamp design that will offer a MM phono stage as an option, but I have quite a bit of work to do to complete the design.
I realize that this current SET kit project seems a little bogged down, but let me reassure you, the assembly manual will be complete within a couple of weeks. I have received all the parts for this, minus the custom transformers, and I'm working on putting the kits together. I will be receiving the first set of custom transformers from the manufacturer this week for my approval. If all goes well, as I believe that it will, we're almost there.
Thanks for staying with me on this.
Best regards,
Scott
Except for some obvious things (like the tubes not included), how does it compare to this price wise? : EL34 KT88 SE Single-end Tube Amplifier 10W Kit No Tube - eBay (item 370455174446 end time Jan-09-11 06:40:56 PST)
Post #62 shows the parts that will be included in the basic parts kit. When it is for sale it will be $299.00 + shipping.
The Analog Metric design that you refer to uses a lowish voltage for a KT88.
The ebay offering is for a partial, "Made In China", PCB. There is no valid comparison with the comprehensive kit Scott is offering, price or otherwise.
Custom Transformers
I received the first set of transformers for approval and I am working to install them replacing the Edcor units. The attached photo shows one of the output transformers on the left and the power choke on the right. For reference, the OT measures 4.5" X 3.75" X 2.75" high to the top of the endbell, and weighs in at 7.75 lbs. The power transformer is the same width and depth as the OT but is 3.0" tall, same color endbell.
Scott
I received the first set of transformers for approval and I am working to install them replacing the Edcor units. The attached photo shows one of the output transformers on the left and the power choke on the right. For reference, the OT measures 4.5" X 3.75" X 2.75" high to the top of the endbell, and weighs in at 7.75 lbs. The power transformer is the same width and depth as the OT but is 3.0" tall, same color endbell.
Scott
Attachments
OoooKkkk...... Well looking "nice" so far. Would possibly be interested in a complete kit, including wooden or better chassis. Like most replyers here, am great at soldering and assembly, but do not want the hassle of trying to locate, match, and outsource common parts. Also, really interested in what you come up for a all inclusive pre-amp with multiple inputs, as I like most others would be using the amp and pre-amp for MM phono, CD, DVD, and cassette. (Wish I had the ability and set-up like Will Vincent via Audiogon uses to powder coat his transformer, chassis, etc on his Dynaco rebuilds). Also, PCB or not, the Chinese invasion kits via Ebay are great deals for the money, and can be easily had as all-inclusive kits also.
Also, dont know what your sourcing is for a majority of your parts and the chassis, but have you communicated with this guy?: http://www.diyaudio.com/forums/tubes-valves/179216-cnc-aluminium-chassis-tube-amps.html Some of his CNC work would look and be great if it was powder coated! And he is as enthusiastic as this thread is also to "mass produce". Now if I could just find a decent woodworker for the other portions of the chassis...
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