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The Rod Elliot Pre Amp First Power Up
The Rod Elliot Pre Amp First Power Up
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Old 26th October 2017, 12:09 AM   #1
DiyGazza is offline DiyGazza  United Kingdom
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Default The Rod Elliot Pre Amp First Power Up

So after a day of wrestling a bunch of screened cable which has a mind and will of it's own, to the selector switch, I finally got to power up the Rod Elliot RIAA Pre amp and the Tone Control amp.

I powered the RIAA board First, No Smoke ..... Always a good sign, and nothing got hot, surprisingly cool in fact.

Next, the Tone control amp, again no smoke and the op amps just run warm which I would expect.

A DVM on the outputs revealed a voltage of 1mv (0.001v) Both AC and DC, so not really sure if that is an accurate measurement, but with the meter set to AC and the volume cranked up, a finger placed on one of the inputs the voltage rose to about 40mv, so I think that gives a pretty good indication that the amp is actually working, I will know more tomorrow when I can get it on the bench with a scope and signal genny.

I tried the same thing with the RIAA Phono Pre amp, but got nothing, which was strange because I was expecting it to go banana's having such a high gain, and the fact that the op amps were stone cold I knew something wasn't right.

A quick measure around soon revealed that pin 8 of both Op Amps had +15v on them, but pin 4 (which should be -15v) had about +13v on them.

A quick trace back from the -ve terminal soon reminded me that a wire link I kept reminding myself to fit for the last few days, I hadn't

Hopefully tomorrow I'll have time to fit the wire link and do some proper checks, before I hook it up to the main amp.
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Old 26th October 2017, 03:06 PM   #2
traderbam is offline traderbam  Europe
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Following on from the Mosfet amp gurus thread...

I've now got a working Rega Planar 3 too. A drop of Superglue on the motor pulley was all it took.
I also did a new layout of my TI phono amp (page 1 here: http://www.ti.com/lit/ds/symlink/lme49720.pdf) to cure some instability (I'll take a look at the RE phono amp layout for you).
My passive RIAA phono amp is on a breadboard and runs off 9V batteries. Polystyrene and polypropylene except for the Nichicon ES 'litics.
Because I am using a moving coil cartridge I changed the TI design to have an input load of 470 ohms in parallel with 300pF. I tried to make an educated guess at these values by researching other MC phono amps. I'm sure it is not optimum. I also increased the first amp's feedback resistor to 10k to boost the gain by a factor of about 3.

Listening impressions:
Audio Technica F5 moving coil cartridge.
Texas Southside & Peter Gabriel So

Very good. Clean sounding. No obvious tonal imbalance. Good dynamics. Crackles!!! I haven't heard crackles in over 20 years. No evidence of LF rumble. I'd call it competent and enjoyable.

Compared to the No 39...
I had better not say!
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Last edited by traderbam; 26th October 2017 at 03:11 PM.
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Old 26th October 2017, 11:25 PM   #3
DiyGazza is offline DiyGazza  United Kingdom
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Quote:
Originally Posted by traderbam View Post
Following on from the Mosfet amp gurus thread...

I've now got a working Rega Planar 3 too. A drop of Superglue on the motor pulley was all it took.
I also did a new layout of my TI phono amp (page 1 here: http://www.ti.com/lit/ds/symlink/lme49720.pdf) to cure some instability (I'll take a look at the RE phono amp layout for you).
My passive RIAA phono amp is on a breadboard and runs off 9V batteries. Polystyrene and polypropylene except for the Nichicon ES 'litics.
Because I am using a moving coil cartridge I changed the TI design to have an input load of 470 ohms in parallel with 300pF. I tried to make an educated guess at these values by researching other MC phono amps. I'm sure it is not optimum. I also increased the first amp's feedback resistor to 10k to boost the gain by a factor of about 3.

Listening impressions:
Audio Technica F5 moving coil cartridge.
Texas Southside & Peter Gabriel So

Very good. Clean sounding. No obvious tonal imbalance. Good dynamics. Crackles!!! I haven't heard crackles in over 20 years. No evidence of LF rumble. I'd call it competent and enjoyable.

Compared to the No 39...
I had better not say!
Glad you got it up and running, you can play all of those old albums you haven't heard for years now, complete with crackles for that added authenticity

I had the RE pre amp and phono amp on the scope today, It's quiet, very quiet in fact, but there are a few little issues I need to try and sort out.

Looking at a 1Khz Square Wave with the tone controls flat, there are quite large spikes at the rising and falling edges of the waveform, and when the volume control is adjusted, whether it's a square wave or sine wave these spikes keep appearing as the pot is turned, at first I thought it might be the pot that needed cleaning, but now I'm not so sure.

With it connected to the main amp, the volume control sounds sort of microphonic, and you can hear almost a mechanical sound though the speakers as the volume control is turned, so I'll assume I have some oscillation problems.

As for sound quality, it's a job to tell at the moment because I've not been able to crank the volume up much more than a clock radio, but that's another story, another week or so and I'll have the house back to myself again, so can make as much noise as I want during the day

One other thing I noticed is that the volume control is very sensitive, something like a 1\16 of a turn and it's already loud, so need to see where I can alter the resistor values to make it a little more user friendly.
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Old 27th October 2017, 12:07 AM   #4
traderbam is offline traderbam  Europe
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I would suspect instability. Are you using Rod Elliots PCBs or are you using your own layouts?
Have you run test signals in to the phono amp separately from the tone control amp to narrow it down?
I couldn't find a PCB layout on Rod's site.
A few photos might help.
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Old 27th October 2017, 12:52 AM   #5
DiyGazza is offline DiyGazza  United Kingdom
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Originally Posted by traderbam View Post
I would suspect instability. Are you using Rod Elliots PCBs or are you using your own layouts?
Have you run test signals in to the phono amp separately from the tone control amp to narrow it down?
I couldn't find a PCB layout on Rod's site.
A few photos might help.
Well I found the answer to the Gain Problem, It's right there on Rods page, Change R113 and R213 from 33k to 15k

The Phono stage is out of the equation at the moment, that is built onto a separate board, so at the moment the problem lies with the tone control pre amp.

I'm using Rod's boards, so all should be good, but I have heard of people having problems with oscillation with certain op amps, while others have used the same op amps with no problems at all, I'm using the Texas Instruments OPA2134PA's.

I don't think there is a Track layout photo as such on Rod's site, but maybe I can copy the images that are there which shows component positions if that's any help?

Edit: Copyright, not sure if I should post any images from Rod's secure site to a public site, Hmmm

Last edited by DiyGazza; 27th October 2017 at 01:06 AM.
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Old 29th October 2017, 09:26 AM   #6
traderbam is offline traderbam  Europe
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Log potentiometers. ALPS for example are good.

Oscillation, continuous or sporadic, can be caused by grounding, inadequate power supply decoupling and RF coupling. These get more problematic the greater the unity gain frequency of the opamps. Of course (please forgive the common sense) you don't need a 10MHz amp to amplify 20kHz signals. What you need is a linear amp. But there is no reason the OPAs can't work well with some circuit changes.
The grounding and RF question requires seeing the copper trace layout and the wiring between pcbs.
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Old 7th November 2017, 11:25 PM   #7
DiyGazza is offline DiyGazza  United Kingdom
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Problem Solved, Moving to New Thread.
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Old 7th November 2017, 11:30 PM   #8
DiyGazza is offline DiyGazza  United Kingdom
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Default Rod Elliott P97 Oscillation Problem Solved.

Have moved this from the "Rod Elliot P97 Pre Amp First Power Up"

So for those that were involved and or have read the above thread, you will know that I was having Stability and Oscillation problems when the volume control was wound up or down, it was as though the control was microphonic and a 1khz Square Wave had Large spikes of oscillation and ringing on the rising and falling edges of the waveform, also the gain of the pre amp was far too sensitive for the maplin Mos Fet Amps, at about 1/16 turn of the volume control the volume was already at or above a comfortable listning level, the fix for this is to change the volume op amp feedback resistors from 33k to 15k which will bring the op amp to unity gain, so Rod Elliot suggests 22k as a good compromise.

That done, a very helpful member on the ESP Forum suggested adding a 22pf capacitor in parallel with the feedback resistors, and that was it, problem solved, I now have a nice clean square wave, and no nasty spikes when the volume control is turned, I even set the scope for a single shot capture just in case I was missing something, but nada...Nothing.

So How does it sound?

Source: Teac P650 CD Player
Rod Elliot Pre / Tone Control Amp
Amplifier: Maplin 100w Mos Fet Amps
Speakers: Bowers and Wilkins DM602 Series II's
Media CD: Kate Bush - The Kick Inside.

I chose the Kate bush CD as I knew from already owning the original LP how good a recording this was in it's time, with plenty of quirky sounds thrown in for good measure, with the tone controls set just a little past mid point I sat back ready to be awe inspired.....

If I'm honest, it didn't really inspire me at all, it sounded thin, the Tight Bass and clarity that I once new so well just didn't seem to be there.

Not to be defeated, I was eager to test the Rod Elliot P06 Phono Pre Amp that I built in with the Tone control Amp, but.... I had to be careful what LP I used due to the Rega anti skate belt snapping in the max position of 3, it should be set at about the same as the tracking weight, in this case 1g with the Ortofon VMS20E MKII Cartridge, and for test purposes I'm using a OEM Thakker Stylus.

So Source, Rega Planar 3, with Ortofon VMS20E MKII cartridge fitted with Thakker D20E Stylus.
Media: Marshall Hain - Free Ride - Vinyl

I left the Tone controls exactly as they were for the CD, Dropped the arm sat back and..... "BAM" ..... Was instantly transported back to that sound I never thought I would hear again, It was like the system was on steroids, Tight Punchy Bass, smooth but crisp and clear treble, a really impressive sound stage, very open, I don't think I've ever heard the B&W Speakers sound so good, given that they only use a 6" Woofer / Mid unit, I have to say I was completely and pleasantly surprised at what I was hearing, Now all I need to do is to get the CD's to sound the same which will probably only require a little tweaking and I'll be one happy Chappie.

Oh, and then there's the matter of replacing the Rega Anti Skate Belt, which I do have to hand already, So LP Group / Thread be ready for a lot of How, what's and why's.
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Old 9th November 2017, 05:02 PM   #9
kevinkr is offline kevinkr  United States
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The Rod Elliot Pre Amp First Power Up
Please don't start multiple threads on the same topic, that's a violation of forum rules, this thread should suffice. (Threads merged)
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Old 9th November 2017, 08:52 PM   #10
DiyGazza is offline DiyGazza  United Kingdom
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Originally Posted by kevinkr View Post
Please don't start multiple threads on the same topic, that's a violation of forum rules, this thread should suffice. (Threads merged)
Ooop's sorry, Changed it as the problem is now solved, so thought the title was a bit misleading.
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