Hi Bonsai. I tried the auto zero and both channels work ok. Both channels measured across phono skt read -0.1mv Cross checked with second DVM got same measurement. Checked the servo output and yes the left channel reads higher at 282mv Right 32mv. So lots of headroom left on the LC servo I guess... Is the offset on the phono skts about what you would expect?
This build looks interesting. Thanks for the hard work!
I just ordered the PCB, chassis and most parts. I did see a discrepancy in parts and BOM, shown in red squares below. When R40 et al were changed to 2.2K, the quantity was not increased to 6 pieces. Also, as previously commented in thread, the OPA2189 (which is out of stock) is being specified in the Mouser numbers instead of the OPA2188.
I couldn't locate the transformer (out of stock), but there are presently 7 pieces left at Digikey of this transformer that should fit your PCB. It is 15VAC rated at 3.2VA. The 3.2VA Amgis transformers seem to have the same dimensions as the 3.2VA Talema transformers.
I could not locate the 12-pin DIP switch. However, this one might fit (not certain since I couldn't locate the spec'd part).
Finally, are there dimensions for the rear panel (HxWxD) along with hole locations? I'd like to get one machined from FrontPanelExpress. I'd be happy to upload the file once I have the hold spacings correct. It would include the labelling you show in the article.
And speaking of labels, it isn't entirely clear the effect of each DIP switch (Av values/impedance/etc). Once I understand it, I'll probably forget it after a few weeks, so I'd like to somehow label the rear panel.
I just ordered the PCB, chassis and most parts. I did see a discrepancy in parts and BOM, shown in red squares below. When R40 et al were changed to 2.2K, the quantity was not increased to 6 pieces. Also, as previously commented in thread, the OPA2189 (which is out of stock) is being specified in the Mouser numbers instead of the OPA2188.
I couldn't locate the transformer (out of stock), but there are presently 7 pieces left at Digikey of this transformer that should fit your PCB. It is 15VAC rated at 3.2VA. The 3.2VA Amgis transformers seem to have the same dimensions as the 3.2VA Talema transformers.
I could not locate the 12-pin DIP switch. However, this one might fit (not certain since I couldn't locate the spec'd part).
Finally, are there dimensions for the rear panel (HxWxD) along with hole locations? I'd like to get one machined from FrontPanelExpress. I'd be happy to upload the file once I have the hold spacings correct. It would include the labelling you show in the article.
And speaking of labels, it isn't entirely clear the effect of each DIP switch (Av values/impedance/etc). Once I understand it, I'll probably forget it after a few weeks, so I'd like to somehow label the rear panel.
Attachments
Robert,
1. the BOM was updated after the version you have posted above. Here is the link to the page
audioXpress Supplementary Material | audioXpress
2. That transformer looks equivalent so you should be good to go
3. The 12-way DIP switch you are proposing will work. (For builders sourcing the RS part, it looks like they have linked to the wrong data sheet on their website. The part number however is correct because that's what I bought for my builds)
4. Rear Panel - the PCB set (2 boards) comes with the rear panel pre-drilled, with cut outs and silk screened - you have to throw away the rear panel of the Galaxy housing and use the PCB. If you want to machine a rear panel, let me know and I will dimension up the PCB and send it to you separately. The supplied rear panel is DSTHP and gold flashed.
5. Labels. In the download pack I linked to earlier there is a user manual that details the switch settings. Since the rear panel is quite crowded, I decided just to number the switches and then refer to that in the user manual.
Here is a picture of the rear panel
1. the BOM was updated after the version you have posted above. Here is the link to the page
audioXpress Supplementary Material | audioXpress
2. That transformer looks equivalent so you should be good to go
3. The 12-way DIP switch you are proposing will work. (For builders sourcing the RS part, it looks like they have linked to the wrong data sheet on their website. The part number however is correct because that's what I bought for my builds)
4. Rear Panel - the PCB set (2 boards) comes with the rear panel pre-drilled, with cut outs and silk screened - you have to throw away the rear panel of the Galaxy housing and use the PCB. If you want to machine a rear panel, let me know and I will dimension up the PCB and send it to you separately. The supplied rear panel is DSTHP and gold flashed.
5. Labels. In the download pack I linked to earlier there is a user manual that details the switch settings. Since the rear panel is quite crowded, I decided just to number the switches and then refer to that in the user manual.
Here is a picture of the rear panel
Attachments
Last edited:
Thanks for the reply.
I hadn't realized that the rear panel was part of the PCB. (In re-reading some of the docs, I can now see this; sorry about missing it.) Very clever: I've not seen such use of a PCB. This then means I've no need to spend more money on machining another panel, thanks again!
Yesterday, when I finally went to purchase the cart containing most of the parts from Mouser, I missed getting the last of the 4-pole switches (612-PBH4UEENA). They won't have any until late August, but Digikey has plenty of these switches.
I hadn't realized that the rear panel was part of the PCB. (In re-reading some of the docs, I can now see this; sorry about missing it.) Very clever: I've not seen such use of a PCB. This then means I've no need to spend more money on machining another panel, thanks again!
Yesterday, when I finally went to purchase the cart containing most of the parts from Mouser, I missed getting the last of the 4-pole switches (612-PBH4UEENA). They won't have any until late August, but Digikey has plenty of these switches.
All, I finished my build a couple of weeks back. I found the build itself straight forward. But then I'm experienced with SMT. The BOM issues were a tad confusing. But hey there's no doubt Bonsai is a busy chap, so follow the last BOM and you will not go far wrong. So is it any good? Well the answer is very. I hear a well 'balanced' sound to my ears no sign of harshness, tight controlled bass, oodles of detail and not surprisingly very low noise. Crank the volume up and hardly a peep. My system comprises..
Ortofon Quintet Black S Moving coil PU
Michell Gyro with NCPSU with Michell MK1 Techno Arm
Audiolab 8000Q Pre
Mono blocked SuperSym Amps. (I also recommend).
Tannoy Revolution XT6F Loudspeakers.
Mainly silver interconnects throughout.
I have been using A Trichord Dino Phono Stage with NCPSU, which admittedly is very good. I'm afraid your design Bonsai sounds more musical, dynamic and easier to listen to as well!
I Highly recommend this design to anybody looking to build a phono pre. Its well worth the effort, you will not be disappointed. Bonsai you get 10 out of 10.. Thanks for all your kind help
.
Ortofon Quintet Black S Moving coil PU
Michell Gyro with NCPSU with Michell MK1 Techno Arm
Audiolab 8000Q Pre
Mono blocked SuperSym Amps. (I also recommend).
Tannoy Revolution XT6F Loudspeakers.
Mainly silver interconnects throughout.
I have been using A Trichord Dino Phono Stage with NCPSU, which admittedly is very good. I'm afraid your design Bonsai sounds more musical, dynamic and easier to listen to as well!
I Highly recommend this design to anybody looking to build a phono pre. Its well worth the effort, you will not be disappointed. Bonsai you get 10 out of 10.. Thanks for all your kind help
.
Some advice when placing the resistors and capacitors..
I place all of a particular value on a dissipative box which has a slight lip on its edge. Helps stop the pesky things pinging off to far when you pick them off. I pick one component from that set (say one 10k resistor from 9) and physically measure the value before placing them. Certainly DO this with capacitors as they are generally not marked. Its been known for suppliers to mix these up before now! I recommend ticking off each value from the bill after placing. I did screw up and misplaced a resistor. No problem if you have a tweezer soldering iron. I bought one years ago and I never used it until now. Makes easy work of removing SMT resistors and I guess capacitors. To remove flux I use IPA, Q tips and I find a microfibre cloth can soak up the residue nicely over larger areas (I earth the board when I do this).
I place all of a particular value on a dissipative box which has a slight lip on its edge. Helps stop the pesky things pinging off to far when you pick them off. I pick one component from that set (say one 10k resistor from 9) and physically measure the value before placing them. Certainly DO this with capacitors as they are generally not marked. Its been known for suppliers to mix these up before now! I recommend ticking off each value from the bill after placing. I did screw up and misplaced a resistor. No problem if you have a tweezer soldering iron. I bought one years ago and I never used it until now. Makes easy work of removing SMT resistors and I guess capacitors. To remove flux I use IPA, Q tips and I find a microfibre cloth can soak up the residue nicely over larger areas (I earth the board when I do this).
In my case it was particularly resistors and capacitors. Not hard to find suitable replacements but time consuming. Again, if anyone wants my BOM PM me and I am happy to share it.
Spent the afternoon using my 66 year old eyes and reflexes to mount the caps and resistors. Went pretty well considering I haven't done SMD for 20+ years. Only lost one cap to the dustballs on the floor, and found one resistor value I forgot to order. I think I have a SMD parts kit somewhere, but it may take weeks to find it so I will order more parts.....