Pre 34 Phono MM transistors

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22-Feb-2018 08:24 PM

Ton

Ton

Posts: 30

I understand why to replacing capacitors and ic's should be done and why replacing resistors most of the time is of no use.

But 34 year old transistors on the MM phone module of a 34, does that makes sense ?

Especially regarding low noise, is it beneficial to replace T1b and T3b (BC214C) or T2b and T4b (BC413) bytypes adviced by DADA ?

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22-Feb-2018 10:04 PM

FBatista

FBatista

Posts: 118

Hi,

Regarding resistors what would you do if a resistor falls out of its value in tolerance? What about very old resistors susceptible to changing value due to heat? Would you leave them in use?

I see a different perspective. 1% metal resistors are so cheap, why not to change?

Check for instance the Dada board for the 405. Most if not all of the resistors are 1% tolerance.

There is the noise issue in resistors too, if I'm not mistaken.

Regarding the 34mm board transistors, I'd change them too, though I have that preamp and phono board in original condition.


Best,

Francisco


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23-Feb-2018 01:30 AM

EJP

EJP

Posts: 1511

There are no 'types recommended by Dada' for the Quad 34, and no need to replace them unless they are noisy or faulty.

Having said that, see Keith Snook's Quad 34 phono upgrade page if you're interested.
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23-Feb-2018 10:09 AM

Ton

Ton

Posts: 30

Hi Fbatista and EJP, thank you both for your replies.

Agree and aware that out of spec resistors (heat) are the exception.

Looked up Keith Snook’s page and he modded the MC phone module.

Found this post (should have started my search with that) on the Dada forum with the same question.

As Joost already indicated, not sure if this mod works for the MM module.

The poster mentioned he would try the mod on his MM module. No follow up unfortunately.

Does any-one knows if and how I could contact (email) the poster of a post ? Is that option available on this forum ?

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23-Feb-2018 12:08 PM

FBatista

FBatista

Posts: 118

Hi Ton,

I totally agree with Stefaan and quote : 

"I guess reducing the noise-level with the MC module is more important than with the MD module as the signal-to-noise level is already a lot better in the MD module..."

Regarding your particular issue, I'd say you're at least an electronics enthusiast, so try and change T2b and T4b and experience any improvement yourself.

I would also say don't neglect the most important part of the circuit, that is, upstream the RCA jacks : so phono cable, tonearm cable quality and connections, headshell and turntable grounding, cartridge condition and adjustments.

I remember the only thing I did to my 34 phono preamp board was changing C1b and C2b from the original 220pF value to 47pF silvered mica (from Dada's webshop btw), but this was a very particular option, to my ear wishes, regardless of cartridge manufacturer requirements.

As to the 34 phono circuit altogether, I really liked the improvement using the LME49710HA, type in IC7 and IC8 sockets.

Best,

Francisco

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05-Mar-2018 05:58 PM

Ton

Ton

Posts: 30

Hi Fbatista,
 
everything "upstream" is ok, up to the cartridge adaptation of C1b C2b.
 
I have been thinking about the LME49710HA as replacement for IC7 and IC8 and have been following the forum discussions on that IC. 
 
What me holds back are the remarks I read in the posts, about the current it draws on a 34, that there seems to be an oscillation/buzz issue on the 34 that needs decoupling caps to cure, and the sound seems to be less warm (quad sound ?)

 
The latter is for me the most important reason not to try the tin hat because I dont want to change the characteristic of a 34 too much. 

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05-Mar-2018 07:22 PM

FBatista

FBatista

Posts: 118

Hi ton,

My 34 is populated with the tin can version of the LME49710 and LME4972, and added the small 5mm 0,1uF poly caps, between (+) and ground, and (-) and ground of each IC.

But I remember I started this mod the way you are about to, by changing IC7 and IC8, probably due to the same reason as you.

There's a certain sound signature regarding the LME49710, quite close to the OP134. But I don't recall it being the dominant "sound statement" of the 34 after all this mods. In my experience the 34 preserves all it's glory after being revised this way.

I remember when I bought it used in original condition, the sound of the TL071P, made in Portugal, where I'm from :) was not pleasing at all. At that time I already had a great standard due to the revised 33 preamp. So I was expecting alot more from the 34 and didn't miss a bit of it's original sound : the curtain thing, polishing notes at the expense of the enriching detail in music.

The hum issue was in my unit due to a ground loop in the power and signal cords. Nowadays I use it with my Serial #4454 QUAD 405, with a single ground connection from the wall socket to the 34 and no ground to ICE ground pin of the 405 or (FM4 by the way). In this system, ground distribution is done by the shield side of the signal cables only.

But regarding any stress (ripple ? Err...) to the power supply of the 34, which is regulated as you know, I can check it again in my scope and post results here.

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06-Mar-2018 12:03 AM

EJP

EJP

Posts: 1511

I've been fitting LME49710s and LM4972 to 34s for years. The sound is not affected adversely. The only decoupling necessary is around IC9/10 as described in the Dada 34 Service Instructions in the Downloads section.
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06-Mar-2018 09:41 PM

Ton

Ton

Posts: 30

Thanx for all the advice. 

I will certainly put the LME49710HA for the IC7 and IC8 on my shortlist. According to the data sheet the round tin hat matches the pin order of the dil OPA replacements of the TL071's and will (hopefully) fit easily into a dip socket. Don't want to solder it directly on the pcb.

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07-Mar-2018 01:01 AM

EJP

EJP

Posts: 1511

Why use the can version? Use the 8-pin DIP version. That's what it's for.
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07-Mar-2018 03:22 PM

Ton

Ton

Posts: 30

To be honest, not sure. 

Everyone was talking about the LME49710HA aka tin hat, I even saw this photo from this post about the LMA
with two  LME49710HA's on  it. 

So I assumed (why making it yourself difficult if there is an easy fit) the HA (the metal can version) was something special compared to the DIP version.



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08-Mar-2018 10:16 AM

FBatista

FBatista

Posts: 118

Well, why not use the metal can version?

According to the webshop, Dada's 405 V3 boards makes use of them.



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08-Mar-2018 11:24 AM

EJP

EJP

Posts: 1511

There is nothing special about the same IC in a different package.

You should use the packaging appropriate to what you have, and what you have is a DIP-8 inline socket or PCB hole-set.
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