advertisement


New PCB for shoebox size NAC preamp part V

Hi, PD

Yes that’s why I wrote I have a strange problem with my Starfish

Any idea why its cliping and only on the positive peaks?


Pete
 
No, sorry. I expect Jiim will be along in a minute; it isn't my circuit so I don't have much of an intuitive understanding of it.

Is the problem on both channels? If not try measuring DC voltages in the two channels, and compare the good and bad.
 
OK, check power supply rails, and the operating points of the circuits.

Beyond that, you need Jiim or somebody else who understand the details of the Starfish setup.
 
Since the problem is symmetrical in both channels, it sounds to me as if the problem would be in the power supply, I'd be checking the NERT first then work backward from there.
 
If you're on the very latest BOM then there is likely to be a bit of DC gain in the final stages of the Starfish. It is a good idea to measure the DC voltage at the preamp side of the final amp stage, i.e the DC voltage across C117 and C217. If this is an appreciable percentage of the supply voltage then its the likely cause of asymetrical clippling.

One way to cure it would be to re insert the DC blocking cap in this stages feedback path (C114 and C214). That will reduce this stages DC gain to unity.

I'm presuming that you have all the DC blocking caps in place in the Fish?

John
 
Hi,

Its up to the latest BOM.

It only clips on some tracks on the Densen everything else is fine (other CD tuner TV Turntable)

I might plug it into my signal generator and have a play see just how easly it clips.

Pete
 
Pete MB&D said:
Hi, Chaps

Strange problem with my Starfish, my Densen B410 seems to be overloading it and clipping on some tracks, I thought it was a problem with my Hackernaps but after destructivity testing one at the weekend, 70khz at near full power let all the magic smoke out, I rebuilt it with some MJL4281 etc.
I hooked up the scope to the spare output on the Densen and the output from the Starfish and spotted the clipping only on the positive peaks. The Densen has a 7watt class A amp on the outputs. Every thing else it fine, so do I have a Starfish problem or it the output from the Densen to high? I would have thought the overload margin would be good on the Starfish, the Densen has caused no problems on other setups.

Any ideas chaps?

Pete
Click to expand...



Hi Pete,


I'm not sure if you have a problem or not - It rather depends on what you are putting in. The starfish has a reasonable overload margin but it isnt infinite.

Could you measure what is going in? Once we have some voltage readings we can see if there is a problem.
Your mention of a 7W amp feeding into it sounds a little worrying.

You could also measure the rail voltages with respect to signal ground.

Do you have the coupling caps fitted?

Jim.
 
Hi, Jim

I will measure the rail voltages and the output from the Densen and stick a signal generator on just to see what is going on, probbaly at the weekend.

I have coupling caps fitted and the feedback caps linked out, and is set to x6 gain. I guess if the densen is to hot for the Starfish I will have the attenuate the input, but I want to find out if I have a fault (or I just built it wrong)

Any news os the SNERT?


Pete
 
Pete MB&D said:
Hi, Jim

I will measure the rail voltages and the output from the Densen and stick a signal generator on just to see what is going on, probbaly at the weekend.

I have coupling caps fitted and the feedback caps linked out, and is set to x6 gain. I guess if the densen is to hot for the Starfish I will have the attenuate the input, but I want to find out if I have a fault (or I just built it wrong)

Any news os the SNERT?


Pete
Click to expand...

Hi Pete,

It may be that the densen is a bit hot, or maybe something is out of whack on your fish. We shall see.

I have some good ideas for the new snert, some tested some only theoretical at the mo - but as ever life got in the way. I'm now moving house - big demander of time - good news is I get my a dedicated office/workspace in the new place :) Had forgotten how involved buying and selling houses is.

Jim.
 
Your mention of a 7W amp feeding into it sounds a little worrying.
Click to expand...
Jim - don't worry, it's 99% Densen marketing puff. It's only a (normal) line -level signal, but the output drive stage is capable of sourcing >500ma or so. which multiplied by rail voltage gives a purely notional 7w or something....

Short answer: its a normal line-level source.
 
Hi, Chaps


Yes it was the NERT.
I was getting 9 volts one side and 20 the other.
I had built it on a bit of vero board with big heat sinks for the transistors, and I must have knocked one as a couple of tracks under one transistor where cracked, a couple of solder blobs and its working fine.

I must make a proper one, or wait for the SNERT:)

Pete
 
Hi, Jiiim

Yep it took only 10 minutes to sort, shame I had just spent half an hour digging my recording scope out and checking it was working and setting up the signal generator etc.
So I decided to sort out the horizontal position knob that had been broken off (must have been why the chucked it in the skip) that took me about an hour to come up with a way of extending the broken shaft.


Pete
 
Did anything ever come of the SNERT?, its just that my fish has been in use for the past 2 years and I fancy a bodge!!

Tony
 
Bump.

Also a question.
I've removed the input caps but would like to fit polyprop caps on the buffer output to protect the pot wipers from wear.
How much lower than 10uf can I go?

TIA
 
Well after thinking about fitting a couple of superteddyregs for some years I finally did it.
I removed the nert as it wasn't working properly with the str's it wasn't holding the ground equally I was getting a 5V difference.
It has made a big improvement both the bass and treble seen clearer I had to put the lights on during the inky blackness.

Pictures later.

Pete
 
You must log in or register to reply here.


advertisement


Back
Top