The 1nf from chassis to Input Ground, or the R/C Filter?
I know in some cases something as simple as a twisted pair with the ground only connected at one end is sufficient, but assumed maybe in this case I would most likely need both ends grounded.
I guess the only way to find out is as you suggest, trial and error, If I put in the provision to mount a cap from chassis, it will be simple to do should any problems arise.
Remember that this is a pre-cellphone design.
A 100pF with very short leads is more suitable for the modern world
A 100pF with very short leads is more suitable for the modern world
reducing the RF attenuation by reducing the capacitor from 1nF to 0.1nF is hardly good advice for our interference ridden environment.
It would be better to retain the 1nF at the amplifier PCB with a series resistance element to maintain a sensible audio passing filter and then augment that with an ultra low inductance capacitor at the input socket. That input socket located filter uses the cable inductance to create a GHz filter BEFORE the interference gets on to the internal cabling.
I am suggesting a 47pF NP0 ceramic 805/603 smd capacitor across the RCA input socket (without any wires - just soldered directly across the gap between the barrel and the hot pin) and a 680r+1nF RC filter at the input terminals of the amplifier PCB.
I took the liberty of updating DiyGazza's schematic so we don't get confused. Note there is a 2.2k/470pF low pass filter on the input.
Sorry if I've made any mistakes...I'll update it if so.
Still pending is the change to the PSU to use two bridge rectifiers.
Sorry if I've made any mistakes...I'll update it if so.
Still pending is the change to the PSU to use two bridge rectifiers.
Attachments
do not take the speaker, rail decoupling and Zobel to the PSU smoothings capacitors.
That would inject smoothing cap charging pulses on to the amplifier's reference voltage.
That would inject smoothing cap charging pulses on to the amplifier's reference voltage.
Well, I don't know what to tell you, before I read these posts this evening, I made the decision to put a 1nf caps from the input grounds to Chassis Ground, that just left me with the 47nf 440v X Class cap across the switched terminals of the mains switch to help prevent switch arcing and nasty cracks and thumps at switch on / off.
Up until today I had only observed the outputs on a scope, so today was the first chance to fit the top and hope for the best.
I connected the speakers, cringed a little and switched on, and ...... Nothing ... I thought there was something wrong, it wasn't until I removed the speaker grille's and got my ear as close as possible to the tweeters I could hear a faint hiss, and as for hum, absolutely silent, I even went as far as putting my mobile phone on the top of the case and rang it, again, No interference through the speakers.
As I am in the throws of building the Rod Elliot pre amp I didn't have a source to try, but then thought about my Sony Walkman MP3 player, so hooked that up, and was really surprised by how good it actually sounded, in fact I ended up spending a couple of hours listening different albums, It was maybe a little harsh on the top end, but given the source that was no surprise, what did surprise me was how much better and clearer it sounded compared to the 20 year old Technics CD Player and Quad II Mono Blocks, The tracks I mentioned in a post way back, have now come back to life, Certain instruments jump out at you, and the man with the maraca's is back in the room 🙂
I take this as a good sign, and look forward to seeing how it sounds with a new CD Player (won't be a Mark Levinson) 😀 But I have been looking at the Teac P-650 with Burr Brown 24 bit DAC, seems to have some good reviews, and cheap !
Up until today I had only observed the outputs on a scope, so today was the first chance to fit the top and hope for the best.
I connected the speakers, cringed a little and switched on, and ...... Nothing ... I thought there was something wrong, it wasn't until I removed the speaker grille's and got my ear as close as possible to the tweeters I could hear a faint hiss, and as for hum, absolutely silent, I even went as far as putting my mobile phone on the top of the case and rang it, again, No interference through the speakers.
As I am in the throws of building the Rod Elliot pre amp I didn't have a source to try, but then thought about my Sony Walkman MP3 player, so hooked that up, and was really surprised by how good it actually sounded, in fact I ended up spending a couple of hours listening different albums, It was maybe a little harsh on the top end, but given the source that was no surprise, what did surprise me was how much better and clearer it sounded compared to the 20 year old Technics CD Player and Quad II Mono Blocks, The tracks I mentioned in a post way back, have now come back to life, Certain instruments jump out at you, and the man with the maraca's is back in the room 🙂
I take this as a good sign, and look forward to seeing how it sounds with a new CD Player (won't be a Mark Levinson) 😀 But I have been looking at the Teac P-650 with Burr Brown 24 bit DAC, seems to have some good reviews, and cheap !
Thank you for your input and detailed explanations, but given todays results I am happy to leave things as they are for the time being, of course this may change so will be a handy point of reference, what you suggest reminds me of my 30+ years in a job where EMC and noise were both Flight and Mission critical, so please don't take that the wrong way, It's a good thing. 🙂
Thanks. I took the original schematic and modified it using Microsoft Paint. Crude but easy.
What's with the Rod Elliot P97?
Do you need tone controls?
If you are running off turntable you'll need RIAA. Running off CD you can get away with a 10k log pot.
Do you need tone controls?
If you are running off turntable you'll need RIAA. Running off CD you can get away with a 10k log pot.
I'm Building the RIAA Pre amp (P06) The Power Supply (P05) and the Pre Amp (P97) I like to have a little control over the sound for those recordings that just need that little extra "something". 🙂
After that it's onto replacing the anti skate adjustment belt on the Rega Planar 3 R200 arm, I have the belt, but have to admit it's a task I'm not looking forward to, although there is a very good walkthrough / How to over on the vinyl engine forum.
Sounds like you have your hands full for a while. I'm looking forward to knowing how your Rega sounds through the upgraded Maplin amp. Probably not as much as you are. 🙂
The Rod Elliot circuits also have room for improvement when/if the time comes.
The Rod Elliot circuits also have room for improvement when/if the time comes.
Sounds like you have your hands full for a while. I'm looking forward to knowing how your Rega sounds through the upgraded Maplin amp. Probably not as much as you are. 🙂
The Rod Elliot circuits also have room for improvement when/if the time comes.
Yes me too, absolutely, I have a brand new NOS Stylus for the Ortofon VMS20E MKII Cartridge that I got from Denmark / Norway for loads of £££'s but hopefully it will out live me 😱
I also hear that Cassette Tapes are making a bit of a comeback, Damm, I wish I had put in a provision for a Rec Out on the pre amp back panel, might not be too late though, I still have my Teac A-150 from 1980 which I completely re-belted a couple of years back, I was amazed at how well the recordings I did on TDK-SA-X Tapes all of those years ago sounded. That could be the project after the Rega, Re-Cap etc ..
Which of the Rod Elliot projects have room for improvement?