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Started by jcmbro, September 21, 2018, 02:04:44 PM
Quote from: Cpt. FixIt on September 26, 2018, 06:19:08 AMI have built KMG's LND150 JCM800 as well as his E530 and his microamp for a friend. Aquiring the components was easy, except for a few semiconductors that I had to order from Mouser(together with the transformer for the microamp).You will have to make your own design for the HV-supply, if you don't have any experience designing proper layouts for SMPSs I recommend you use the 12VAC-into-backwards-transformer variety. It is a bit bulkier and less efficient, but you only need a few milliamps anyway.Also, you will have to etch and drill the PCBs yourself, which is rather easy with KMGs single-sided designs, but certainly is some effort compared to just sending away gerber files and waiting for the PCB to show up in the mailbox.Soldering SMDs was a real pain until I realised I needed new glasses and a finer tip for my soldering iron. Don't forget that you will have to have the output transformer manufactured (or wind it yourself), it is a good idea to get in contact with the transformer guys before you start! In my experience they are usually very helpful, and having transformers wound to spec is often cheaper than buying off the shelf (...and you won't find anything for your PA there anyway).
Quote from: jcmbro on September 27, 2018, 05:51:20 PMDon't have any experience with SMD soldering but there's a first for everything right?
Quote from: jcmbro on September 27, 2018, 05:51:20 PMWhat did you use for a power supply? I'm having a hard time finding something that can supply +80V,-80V,-12V,+340V on the cheap.
Quote from: jcmbro on September 27, 2018, 05:51:20 PMAlso what are your output transformers specs? I got some trannies from a broken SS poweramp that i'm going to have rewound by a buddy of mine.
Quote from: Cpt. FixIt on September 28, 2018, 06:43:42 AM- Have a transformer custom made- Look for a transformer with 2x~60V sec and get an extra one with 12V sec. Add a third small 230V(2x115V)/9-10V in reverse, secondary connected to 12V. The preamp draws only a few mA, so that would be an acceptable solution.Or use the step-up powersupply Mikhail suggested and adapt it for the higher voltage. But be warned, the devil is in the PCB layout, you may encounter all kinds of noise and oscillation if you have no prior experience with that kind of stuff.
QuoteI only built the MicroPA and used the suggested Xicon trannie, which is available from Mouser, for about 5 bucks IIRC.If you are going to rewind an existing trannie, make sure to get the measurements done to guestimate the core's specs before you take it apart!If you need help with that, KMG made some excellent posts and also has software to make the calculations more convenient on his webpage.
Quote from: Zozobra on September 28, 2018, 06:47:50 AMFor the B+ you can use a ZVS DC boost converter perhaps? They're only a few bucks on ebay. I've built an ecc99 poweramp with one run from a laptop PSU. I also used a similar bucking smps to supply the heaters.https://www.ebay.co.uk/itm/142934951063Coincidentally I've just ordered a bunch of PCBs for this preamp from JLCPCB and this will be my first foray into SMD soldering! If I like how it sounds I may we knock together a design of my own with fewer SMD components and then make the project public on EasyEDA. I'm happy to have collaborators check on the project if I go through with it as I'm a bit of a PCB layout noob
Quote from: jcmbro on October 07, 2018, 05:05:15 PMDoes anyone know why the -12v bias is passed through BC857 transistors at Q1,Q3 and Q5? I'm curious as to why that circuit is necessary,i believe the valve jcm800 doesn't have a bias control circuit?