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Post by Deleted on Apr 14, 2015 0:11:42 GMT
If anybody has an interest in constructing the Class A HA/preamp, then please wait a little while longer for further news. The special PCBs may once again become available, and the JLH PCBs will be orderable in lots of 10 for members via their designer (Greg Erskine) The improved PSU PCBs may also be orderable in lots of 10 via Greg. They also permit the use of the faster SM diodes in the bridge rectifier area, (ES1A - ES1D) as well as an additional +12V output and a +5V or +3.3V output using 2 additional voltage regulators. At a recent check,Trendsetter Electronics still has available to order, a few of the special dual transistors for the front end. Recently, the Preamp was compared with a AU$50K Gryphon Preamp, and the Gryphon was judged to be slightly better in the upper HF purity area. A recent capacitor replacement (2n2 to 4n7) in the Offset Corrector area, as well as the use of 100uF Panasonic FC capacitors in both the PSU and JLH areas, instead of the original unreliable Suntan electros, has yielded a further worthwhile improvement in both depth of image and the mid range area.
Alex
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jc
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Post by jc on Apr 14, 2015 0:53:57 GMT
Interesting, lots of temptation there.
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Post by videoguy on May 14, 2015 20:48:50 GMT
I have been in contact with the PCB manufacturer who made the original lot of PCB's for the AKHA. We are gearing up to do another run. Anyone interested in boards for the HA-Preamp, please put your name in. A pair of boards should cost approximately $12.00 ea.; a pair would be $24- USD. That does not include shipping from the U.S. to your location. I hope to have the negotiations with the board mfg. completed by Monday.
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Post by PinkFloyd on May 14, 2015 21:12:45 GMT
I have been in contact with the PCB manufacturer who made the original lot of PCB's for the AKHA. We are gearing up to do another run. Anyone interested in boards for the HA-Preamp, please put your name in. A pair of boards should cost approximately $12.00 ea.; a pair would be $24- USD. That does not include shipping from the U.S. to your location. I hope to have the negotiations with the board mfg. completed by Monday. Count me in for a pair..... let's do this thing Bill! I'm way overdue for a new build and feeling fresh and eager to get involved in a new project. All the best, Mike. Let's put this joint on the map again! |
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Post by jc on May 14, 2015 22:25:41 GMT
Awww, go on then, another pair here.
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Post by videoguy on May 15, 2015 17:34:37 GMT
We are off to a great start! I am nearly done with a part list; it uses Mouser Electronics as source as I am in the U.S. Will post it shortly. It uses Xicon metal film 1% resistors.
Sandy K. 1 pair
C.J. 1 pair
Pink Floyd 1 pair
Bill W. 2 pair
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Post by Deleted on May 15, 2015 22:25:31 GMT
We are off to a great start! I am nearly done with a part list; it uses Mouser Electronics as source as I am in the U.S. Will post it shortly. It uses Xicon metal film 1% resistors. Sandy K. 1 pair C.J. 1 pair Pink Floyd 1 pair Bill W. 2 pair Hi Bill Any interested constructors should be aware that this is not an inexpensive project. Other than a suitable case and components for the main PCBs, there are also 2 x 18-0-18 30VA toroidal transformers mounted in a separate case, 2 x PSU boards, and 2 x JLH PCBs Bill will be making available combined PSU plus JLH PCBs, (2 required) , but if the intention is to use a 1U rack case, you will need to use the PSU and JLH PCBs designed by Greg Erskine (or similar). Greg's PCBs will need to be purchased in lots of 10 from him, and they will be sent directly from the PCB manufacturer. Sharing of PCBs is obviously an option here, but the PSU PCBs have possible use in numerous other small projects. The G.E. designed PCBs are likely to cost around $2.50 each plus delivery, in lots of 10. The PSU PCBs can give adjustable + and - regulated outputs of up to .5A non continuous due to heatsink size used , as well as another 2 fixed voltage outputs such as +12V and +5V if required for DACs etc. depending on the chosen voltage regulators. It can use either through hole or surface mount diodes.
This design can be used as either a Headphone Amplifier or a very high quality Preamplifier. It can also be used for both, but the constructor will have to work out how to implement this himself, as the output resistor values are different for headphones and Preamp. For best results, a high quality attenuator should be used for controlling volume.
At a recent listening session, the preamp was compared with an Au.$50K Pandora Gryphon, and the Pandora was judged slightly better. The prone to leakage Jaycar 2,200uF Suntan capacitors have since been replaced with Panasonic FC electros, and the capacitor under the PCB across the 1M resistor in the Offset Corrector section has been increased from 2n2 to 4n7. I believe that it is now likely to equal, or even outperform the Gryphon Preamplifier. Kind Regards Alex
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Post by videoguy on May 16, 2015 4:08:56 GMT
Hi Bill Any interested constructors should be aware that this is not an inexpensive project. Other than a suitable case and components for the main PCBs, there are also 2 x 18-0-18 30VA toroidal transformers mounted in a separate case, 2 x PSU boards, and 2 x JLH PCBs Read more: rockgrotto.proboards.com/thread/3977/ak-classa-ha-preamplifier?page=83#ixzz3aGopnNh8Sandy K. is correct; UPS delivered most of my parts from Mouser tonight. It has all resistors, most capacitors & all transistors, for the HA. It came to $80- including $8- shipping. Also ordered the case from <www.par-metal.com>. I am using their series 20-16123 w natural Alodine anodizing. It measures 12" x 12" x 3" high, cost w shipping $75-. Just an example of what can be done for our North American members. |
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Post by videoguy on May 16, 2015 4:10:41 GMT
Hi Bill "Any interested constructors should be aware that this is not an inexpensive project. Other than a suitable case and components for the main PCBs, there are also 2 x 18-0-18 30VA toroidal transformers mounted in a separate case, 2 x PSU boards, and 2 x JLH PCBs:" Read more: rockgrotto.proboards.com/thread/3977/ak-classa-ha-preamplifier?page=83#ixzz3aGopnNh8Sandy K. is correct; UPS delivered most of my parts from Mouser tonight. It has all resistors, most capacitors & all transistors, for the HA. It came to $80- including $8- shipping. Also ordered the case from <www.par-metal.com>. I am using their series 20-12123 w natural Alodine anodizing & brushed aluminum front panel. It measures 12" x 12" x 3" high, cost w shipping $75-. Just an example of what can be done for our North American members. Only the top portion in quotation marks is a quote. Did not know how to use the quotation function. |
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Post by Deleted on May 16, 2015 4:59:51 GMT
Hi Bill When you only wish to quote only part of the previous reply, highlight that section and "copy" using Right Click menu .(or Cntl +C ) Then select the Quote Symbol which is the 3rd from the right at the top, and then paste using Right Click Menu into "insert quote here" I usually do the reply first, as the "insert quote here" can be a little temperamental at times.
Kind Regards Alex
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Post by jc on May 16, 2015 16:04:00 GMT
Just as a quick reminder of what this is all about here's my AClass pre/ha with its guts hanging out, I was finishing off the power today (underneath the pre) so wanted to link them together. The PSU is out of shot. With reference to Alex's post above for what's needed, I plumbed for the Khozmo 50Hz stepped shunt attenuator, which as a final addition made a very worthwhile improvement proving that even the Valab stepper was strangling the capabilities of the pre-amp.  |
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Post by Deleted on May 16, 2015 22:41:57 GMT
Hi Chris
Were you able to set the front end balance close to 0 mV when warmed up with the cover on ?
Kind Regards
Alex
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Post by jc on May 16, 2015 23:36:23 GMT
Hi Alex,
Not perfect but at 7mv and 9mv I thought it must be good enough.
Cheers,
Chris
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Post by Deleted on May 17, 2015 0:03:13 GMT
Hi Alex, Not perfect but at 7mv and 9mv I thought it must be good enough. Cheers, Chris Hi Chris I wonder why you were unable to go a little past 0mV in the other direction, and then go back again ? Which diodes are you using for the one in series with the trimpot ? Perhaps not all brands are equal in the low forward voltage area?
Kind Regards Alex
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Post by jc on May 17, 2015 10:46:05 GMT
Out of curiosity is there a fixed way round for using the probes between TP1 & 2? I've also brought in the rest of my SF12 supply to if I can find a couple of better performers.
I've also used the single JLHs in the power that you noted in the pre. I'll pop up a photo after I've tinkered with the SF12 and FEB.
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Post by Deleted on May 17, 2015 11:12:42 GMT
Hi Chris It doesn't matter which way around the DMM probes go. When I clicked on your posted photo, I also then saw an earlier photo of your PA before completion. That's how I saw the single JLHs. You may be able to measure the VF of the existing diodes in circuit using your DMM on Diode Test. Even if you do find some SF12s with a lower VF, don't replace the existing unless you are confident that you can do so without damaging the PCBs Kind Regards Alex |
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Post by jc on May 17, 2015 11:21:58 GMT
If I do go down that road I'll use the snip 'n' graft method  |
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Post by videoguy on May 18, 2015 20:58:05 GMT
We are set to go with the PCB manufacturer. I'm thinking of an initial quantity of 16 boards; so far 10ea. have been spoken for.
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Post by videoguy on May 19, 2015 22:55:44 GMT
There has been a previous discussion concerning the volume control used in the AKHA. It was felt that the standard stereo attenuator from Vintage Audio Lab comprises a choke point for the AKHA. The Dact2 & Khozmo attenuators are pricey $175- to $230- plus. Valab has reintroduced the ladder type level control, in both 50k & 100k values; cost $28- plus $5- shipping. The rotary switch used is the same one used in the standard volume control. The action is smooth & positive. The advantage of a ladder type control is that there are only two resistors in the circuit no matter what level is selected. My feeling is that this design may well eliminate the choke point their regular vol. controls pose. Here is the web address: stores.ebay.com/Vintage-Audio-Lab/Audio-Diy-Parts-/_i.html?_fsub=187871519 CORRECTION: In order to see the ladder type attenuator; go to ebay, in the search bar TYPE LADDER ATTENUATOR. It will come up but make sure you are looking at the unit offered by VALAB is the one you select as there are one or two other vendors offering them. If it does the job, the price cannot be beat. Mine is on the way. 5/22 I just looked at the Valab site & could not find the picture of the ladder control, that was there last week. I will send them a message this weekend asking them to resatore the picture of the ladder attenuator. 5/30 My ladder attenuator arrived yesterday. Very sturdy construction & a very positive feel to the switch action. If you are familiar with the standard VALAB switched controls, the feel is a bit soft. This unit is comprised of 7 decks, the middle one is used only as a spacer. This is a very impressive piece for $28- USD. Once the Yuan is allowed to float the price may triple. Can't wait to see how it performs in the AKHA. |
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Post by videoguy on May 19, 2015 23:01:15 GMT
In the same vein as the ladder control, there are the LS352 & LS313 dual matched transistors for the input stage of the amplifier. I have established a relationship with the supplier & can obtain these devices on a group buy basis; for those building the amp.
Let me know what you all think on this.
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Post by Deleted on May 20, 2015 0:28:22 GMT
There has been a previous discussion concerning the volume control used in the AKHA. It was felt that the standard stereo attenuator from Vintage Audio Lab comprises a choke point for the AKHA. The Dact2 & Khozmo attenuators are pricey $175- to $230- plus. Valab has reintroduced the ladder type level control, in both 50k & 100k values; cost $28- plus $5- shipping. The rotary switch used is the same one used in the standard volume control. The action is smooth & positive. The advantage of a ladder type control is that there are only two resistors in the circuit no matter what level is selected. My feeling is that this design may well eliminate the choke point their regular vol. controls pose. Here is the web address: stores.ebay.com/Vintage-Audio-Lab/Audio-Diy-Parts-/_i.html?_fsub=187871519So you can take look at it. If it does the job, the price cannot be beat. Mine is on the way. Hi Bill I have previously used the earlier Valab attenuators, and the 24 position DACT 2 sounded considerably better. The new ladder types may have narrowed the gap considerably though. A major selling point for the DACT 2 and Goldmund types is their smooth action which is more like a potentiometer. The DACT2 is also likely to have much improved HF separation due to it's construction, and has a bandwidth of 50MHZ. "Their series resistor networks consist of 23 non-inductive, low noise, SMD metal film resistors.
The layout of the PC Boards and the choice of SMD resistors have reduced the signal path to a minimum length (typical five times shorter than conventional stepped attenuator designs with leaded resistors). The PCB design combined with the special resistors also account for the very low series inductance and the very low stray capacitance."
Kind Regards Alex
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Post by funkoid on May 22, 2015 0:08:49 GMT
Would you say someone with minimal experience could build one of these kits?
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Post by Deleted on May 22, 2015 0:26:37 GMT
Would you say someone with minimal experience could build one of these kits? funkoid I wouldn't recommend it, as it is a very ambitious project. There is also an external power supply box with 2 18-0-18 30VA transformers inside it, and some knowledge of AC mains wiring is also required. You would also need to source some of the components yourself. Attached is a photo of my own Preamplifier build of this project. The HA version is almost identical.
Kind Regards Alex
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Post by ematech on May 22, 2015 2:01:14 GMT
I have been in contact with the PCB manufacturer who made the original lot of PCB's for the AKHA. We are gearing up to do another run. Anyone interested in boards for the HA-Preamp, please put your name in. A pair of boards should cost approximately $12.00 ea.; a pair would be $24- USD. That does not include shipping from the U.S. to your location. I hope to have the negotiations with the board mfg. completed by Monday. Count me in |
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Post by Deleted on May 22, 2015 2:32:52 GMT
I have been in contact with the PCB manufacturer who made the original lot of PCB's for the AKHA. We are gearing up to do another run. Anyone interested in boards for the HA-Preamp, please put your name in. A pair of boards should cost approximately $12.00 ea.; a pair would be $24- USD. That does not include shipping from the U.S. to your location. I hope to have the negotiations with the board mfg. completed by Monday. Count me in ematech Don't forget that the PSU PCBs (or similar size alternatives) and JLH PCBs as shown in my photo will also be required, or combined PSU and JLH PCBs as designed by Bill. rockgrotto.proboards.com/thread/10309/power-supply-jlh-combination-pcb If you wish to include it all in a 1U rack case you will need to use the separate PCBs as per the photo. Bill will be able to arrange a small group buy of the 2 special metal can dual transistors per PCB. You will need to ensure that all electrolytic capacitors are the correct way around, and all other components used are at their correct locations before soldering them in, as some of the copper lands are quite small, and component replacement MAY cause damage to the PCB tracks. Regards Alex
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