Musical Fidelity preamp p3a - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th July 2006, 03:41 PM   #11
diyAudio Member
 
Join Date: Apr 2004
Location: ventimiglia
Default op amp replacement

one of the better solution,if your problem is the noise is the Linear op amp such LT1028/1128(single).In europe is hard to find but Distrelec have this one.
This increase dramatically the performance for all the parameter,but in this case you must verify whit a scope the stability margin and oscillation in power stage.
  Reply With Quote
Old 29th July 2006, 04:11 PM   #12
hoshy is offline hoshy  United Kingdom
diyAudio Member
 
Join Date: May 2006
Send a message via ICQ to hoshy Send a message via MSN to hoshy
Thanks but it's not the opamps that are the problem (check my last post)
  Reply With Quote
Old 29th July 2006, 04:19 PM   #13
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the line stages should be almost hiss free. Your hiss could indicate a component/s gone faulty.

Have you tried removing the socketed chips from their sockets and cleaning as best you can?

The designer has gone to a lot of expense to avoid electrolytics in the main board. But a few, very small electros, may usefully be swapped for polyester and better still polypropylene. It does depend on what the electros are doing.

224K is that 220nF+-10%?
105K is that 1uF+-10%?
__________________
regards Andrew T.
  Reply With Quote
Old 29th July 2006, 05:07 PM   #14
hoshy is offline hoshy  United Kingdom
diyAudio Member
 
Join Date: May 2006
Send a message via ICQ to hoshy Send a message via MSN to hoshy
Yes, you're right about the capacitor values and tolerances.

I'll pop out the chips now and clean them up with a delicate wire brush.
  Reply With Quote
Old 29th July 2006, 05:14 PM   #15
hoshy is offline hoshy  United Kingdom
diyAudio Member
 
Join Date: May 2006
Send a message via ICQ to hoshy Send a message via MSN to hoshy
No joy with cleaning the contacts. But still, it makes me feel better
  Reply With Quote
Old 31st July 2006, 06:45 PM   #16
hoshy is offline hoshy  United Kingdom
diyAudio Member
 
Join Date: May 2006
Send a message via ICQ to hoshy Send a message via MSN to hoshy
Hi all,

I'm very keen to try and reduce the hiss on the preamp. Can anybody give me a few pointers?
  Reply With Quote
Old 31st July 2006, 07:17 PM   #17
sreten is online now sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

You say the phono stage is of no interest, fine.

The output noise on the pre-amplifier is related to its gain. Gain
is needed for tape, radio etc but much less is needed for CD.

Tape etc is usually ~ 200mV maximum, whilst CD
is 2V maximum, a difference of x10 or 20dB.

I'm guessing the noise is related to CD use and due
to the topology not being optimised for CD inputs.

Could you sketch out the topology, i.e. the positions of
the gain stages, tape buffer, volume control relative to
the inputs and outputs etc and the R value of the
volume control would be useful.

Maybe all you need is another switch on the front, for CD.

/sreten.
  Reply With Quote
Old 31st July 2006, 07:28 PM   #18
hoshy is offline hoshy  United Kingdom
diyAudio Member
 
Join Date: May 2006
Send a message via ICQ to hoshy Send a message via MSN to hoshy
Thanks very much for your response. It's much appreciated.

The white noise is present regardless of what is connected to the amp.

I could try to sketch out the areas of the amp if you feel it's worth it. It will take me some time as I'm new to this.

edit: I should note that I get the same level of hiss regardless of volume control position.
  Reply With Quote
Old 31st July 2006, 10:19 PM   #19
hoshy is offline hoshy  United Kingdom
diyAudio Member
 
Join Date: May 2006
Send a message via ICQ to hoshy Send a message via MSN to hoshy
Hi,

After some more testing I discovered that the hiss only affects the buffered outputs. The direct ones a dead silent. This is fantastic

The buffer is just two skanky old transistors, one for each channel I presume. Would this be something like an emitter follower? I'm going to have the board out of the chassis to investigate further.

I don't particular need to use the buffered outputs, so far the only difference I can tell is that they sound louder through the power amp. I've yet to test if the really sound different in tonal qualities and dynamics. Sitting hear now it seems they're a bit flatter in sound but that's perhaps my imagination.

Perhaps I could build a new buffer stage with a modern pair of opamps. I have a NE5532 lying around and a pair of LM394 amps. I removed them from the MC circuit as I'll never use it and I thought they may be handy.

Before I think too much about that though I'd like to know more about the buffering of outputs in general, for that matter, there's two sets of inputs on the power amp, one seems direct and the other goes through a set or resistors and caps that (when switched in via the external switch) seem to kill the bass and make the amp sound very thin. I use the direct ones.

Thanks again to everybody.
  Reply With Quote
Old 1st August 2006, 07:20 AM   #20
nonoise is offline nonoise  South Africa
diyAudio Member
 
Join Date: Jun 2006
I still have an earlier model so please confirm if correct
Does the pre amp have two output options (active / passive)
By swapping between the two output type’s one could make a more informed decision as to the main culprit.
The input selector switch tends to be a source of bad and or intermitted connections
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Musical Fidelity A1x or A 120 which one is better ? Bernhard Solid State 4 9th December 2012 10:24 AM
Musical Fidelity A2 preamp AD797 oscillate sviru Solid State 23 5th November 2012 02:05 AM
Musical Fidelity MVT mk3 preamp line-stage rmgvs Solid State 31 1st March 2012 12:45 PM
Musical Fidelity The Preamp mosfet1 Solid State 0 12th December 2006 12:22 PM
Musical Fidelity B1 NamWong Solid State 1 29th April 2004 02:46 PM


New To Site? Need Help?

All times are GMT. The time now is 02:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2