Bypassing a turntable's built-in preamp - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 27th April 2014, 02:59 PM   #1
diyAudio Member
 
Join Date: Apr 2014
Default Bypassing a turntable's built-in preamp

I suspect the answer to this will be simple. I was able to get a hold of a nice vintage preamp/power amp (Denon PRA-1000/Denon POA-1500), and the brand new turntable I ordered (Pioneer PL-990) has, unfortunately, no switch to bypass the built-in preamp. I suspect I could get much better audio quality by bypassing the TT's preamp and sending that signal to the PRA-1000's phono input. I have an electronics background and I'm reasonably good with a soldering iron.

Since I'm unfamiliar with TT's circuitry, my question is: what would it take to skip the built-in pre-amp? Just connecting the output of the arm to the RCA connectors instead of sending that to the board? Is that only two cables? I haven't opened the TT yet because I'd like to verify how to do this before voiding its warranty. I would really appreciate any input from someone familiar with this procedure. I could consider also installing a switch to flip between phono output and line output, but something as simple as skipping the built-in pre altogether would do.

Also, once I successfully do this, how do I know whether I should use the Phono-MC or Phono-MM input on the pre?

Thanks!
  Reply With Quote
Old 27th April 2014, 11:09 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
The manual that comes with the turntable should state what sort of cartridge is fitted. MC types are generally quite a bit more expensive than MM types so an MM type seems more likely.

There is a theoretical SNR advantage to having the pre-amplifier right there in the turntable. Are you sure that the one fitted to the table is a dog? Most likely if this was a dirt cheap table and the pre-amp design was an afterthought.

If you decide you want to use the pre-amp in the amplifier disconnect the internal pre-amp from both the output jacks and the cable from the tone arm and run the tone arm connections directly to the jacks. Watch out for noise pick up as the signal levels are quite low.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 27th April 2014, 11:14 PM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Based on the price of the table there probably was not a huge amount of spare cash for the phono stage so you probably will be better off bypassing it. Try it first and make sure the table functions properly for a couple of weeks before voiding the warranty.

It definitely uses a moving magnet (mm) cartridge so use your MM inputs. Hopefully the equipped cartridge is a p-mount type so that you can easily upgrade to something a bit better when the stylus wears out. (Edit: Based on reviews apparently not)
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 27th April 2014, 11:55 PM   #4
diyAudio Member
 
Join Date: Apr 2014
Thanks! I really appreciate the feedback.

I saw some mentions on this forum about using special insulated cables for this, to avoid parasite capacities. Is any certain brand/model/type better to connect the tone arm to the output jacks?
  Reply With Quote
Old 28th April 2014, 12:34 AM   #5
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

YMMV but the inbuilt preamp in the Pioneer PL-990 is hardly
a show stopper compared to the fact its a very basic cheap
turntable, and its nowhere near the sort of turntable to go
go with the Denon stuff, by a very long way, IMO.

Used Acoustic Research EB101 (or a variant) used with
the Red Ed elliptical Ed Saunders Red Ed Cartridge
would be my sort of starting point with the Denons,
if you want vinyl to compete in any sense with CD.


rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 28th April 2014 at 12:42 AM.
  Reply With Quote
Old 28th April 2014, 12:41 AM   #6
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Sreten has a good point, however I figured if you were new to vinyl this would be an ok starting point. You have read the reviews I assume and are familiar with its limitations.

Any decent fully shielded interconnect off of eBay should work fine, there are acceptable and quickly available cables from Radio Shack. Avoid the expensive name brand cables at Best Buy and elsewhere. You are mostly paying for the name on the box.

No specific recommendations as I make most of my own cables specific to purpose.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 28th April 2014, 12:54 AM   #7
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

You can modify the turntable, its not complicated, but its
essentially pointless, the inbuilt RIAA is not the problem.

Fundamental sound quality will barely change.

rgds, sreten.

And yes, the current cables fitted may not work
well if you bypass RIAA and go into a RIAA input.

TBH the fact you can't bypass the internal Pioneer
RIAA is a very big clue as to its ambition level.

Just accept it for what it is IMO.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 28th April 2014 at 01:12 AM.
  Reply With Quote
Old 7th May 2014, 05:21 PM   #8
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
Pioneer PL-990 Turntable Manual - Vinyl Engine
it uses a TA7325P opamp. in a 9-pin SIP. It is single supplied by a un-regualted PS
  Reply With Quote
Old 11th May 2014, 05:38 PM   #9
diyAudio Member
 
Join Date: Apr 2014
Many thanks for the insights. I decided not to mess with it, then... when budget allows I'll just upgrade to a better turntable with a more decent cartridge.
  Reply With Quote
Old 8th June 2014, 07:47 AM   #10
diyAudio Member
 
Join Date: Dec 2013
Location: Oklahoma
Well, anything is possible, and "bypassing" the rather low-end preamp is actually very simple, provided you can wield a soldering iron successfully and work with the very delicate tone arm cables. It is largely a matter of disconnecting the wires coming from the tone arm from the printed circuit board sfter establishing, which of the (hopefully screened) wires is the left and which the right one. As you have no longer an anchoring point for those tiny wires, you could fit a suitable connector to the rear of the plinth, where you could solder the wires directly to the pins. Personally I have done this by using a female XLR connector and used it as originally intended - as a turntable audio connector (mainly for broadcasters) ! The name gives this original purpose away: L=left, R=right and X=common (ground). Now you have a connector for an easily detachable cable, which you can experiment with. The built-in preamp you could leave in place but deactivate, if it has its own transformer - just disconnect the cable to the primary winding. The whole exercise will sadly not make your turntable sound a lot better, but you will probably benefit from less noise and a better frequency response due to a more accurate equalization.
A further refinement could be to fit a small dpdt switch to the back of the plinth, and connect the common (usually middle) tags to the preamp input, one side of the switch to the XLR's L and R. pins (pins 2 and 3 respectively) and two 4k7 resistors to the other side of the switch to form a dummy input load, if the cartridge is disconnected from the internal preamp. This prevents increased noise of open inputs, should the preamp be connected to a power amp without being connected to the pickup cartridge. Mark the switch as "Preamp On" and "Preamp Off". Of course, in this case the preamp power must be permanently on. This wat you can compare the performance of the preamps in the turntable and the amplifier.
Hopefully, all this is not too confusing...
  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
Juma's Preamp for F5 -new built- GentryBa Pass Labs 31 2nd February 2013 12:19 PM
i want to built new preamp maxpou Solid State 8 1st January 2008 08:11 AM
bypassing preamp board in integrated amp woodturner-fran Tubes / Valves 1 21st October 2006 11:35 PM
Has anyone built a transformer coupled preamp? KT Tubes / Valves 0 7th October 2004 03:19 PM
Pictures of my almost-built preamp... mhennessy Solid State 20 5th August 2002 11:28 AM


New To Site? Need Help?

All times are GMT. The time now is 06:59 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