Retrobike Forum Index

It is currently Sat Dec 03, 2016 6:33 am

* Login   * Register * Search  * FAQ

Forum rules


**Classified Rules & Guidance - Feedback - Dispute Procedure - Gold Trader Status - All Adverts Need A Price - 5 Adverts Maximum - Leave Prices In Sold Adverts**



Post new topic Reply to topic  [ 1706 posts ]  Go to page Previous  1 ... 92, 93, 94, 95, 96, 97, 98 ... 171  Next
Author Message
 Post subject: So it continues...
PostPosted: Wed Feb 27, 2013 10:38 pm 
Retro Guru
User avatar

Joined: Thu Oct 13, 2011 9:30 am
Posts: 958
Location: Malvern
A brace of good quality OPA134 op-amps to replace the not so hot (though state of the 'fet input' op amp art of the time) TL071s in the pre and power amp - a starter for ten. Also some decent speaker connectors to replace the woeful original spring push ones. A mod also done by Quad to later 405's.

Image

Got the pre-hooked up to my 'phones this eve. Bass is super tuneful, treble nice and sweet and easy - bass definitely easier to follow than the Arcam. Mid... jury out. Slightly 'thick' sounding maybe? Maybe lacking in detail? I know the op-amps will reduce the noise level, but detail? Who knows... one step at a time.

Pleased with the effort that's gone into the power supplies on the pre, will leave that alone aside from faster rectifiers. Still not convinced that I need a buffer on the CD input - may add a 'straight through' switch to the 'Aux' card, with a bit of attenuation - one less active stage must be a good thing. Input switching, uses CMOS 4066's from eons ago, which apparently add 0.01% distortion all by themselves. (I designed a pre back in about '85 and thought about using them, but gut feeling led me to abandon the idea and I used CMOS latches to drive telecoms relays instead) Yes, 0.01% is low, very low, but it can be bettered by later versions of the 4066 so I will probably look there. Torn though as ideally I would fit reed relays rather than relay on CMOS (spit!) to do my switching but I dont want to make it less 'Quad' so I'll try Maxim's versons of the 4066 which have huge bandwidth an should be almost an order of magnitude better THD-wise in a low signal level switching application, which generally means other aspects of performance will be better also.

It's never going to be the most transparent of pre's, but it is a lovely piece of design work. A joy to work on and to use. The power amp however, that has the potential to be truly phenomenal. A very clever design, and something I'm sure will respond to reworking with a few modern ideas and components applied sensitively. Arise FrankenQuad! :twisted:

<edit> listening to some old Rage Against the Machine - bass guitar is about as 'real' as I've heard on anything. Yes, the low end certainly does have some serious dynamics!


Top
 Profile  
 
PostPosted: Wed Feb 27, 2013 11:55 pm 
Retro Guru
User avatar

Joined: Thu Oct 13, 2011 9:30 am
Posts: 958
Location: Malvern
Do people really fall for this sh*t?

http://www.ebay.co.uk/itm/New-FORODEO-C ... 3f224cec28


Top
 Profile  
 
PostPosted: Thu Feb 28, 2013 10:53 am 
King of the Skip Monkeys
King of the Skip Monkeys
User avatar

Joined: Wed Nov 07, 2007 4:34 pm
Posts: 26146
Location: Moomin Valley
apache wrote:
Do people really fall for this sh*t?

http://www.ebay.co.uk/itm/New-FORODEO-C ... 3f224cec28


Yes.

Ask anyone who paid real money for a pair of these:

Image


Top
 Profile  
 
PostPosted: Thu Feb 28, 2013 11:34 am 
Retro Guru
User avatar

Joined: Thu Oct 13, 2011 9:30 am
Posts: 958
Location: Malvern
The premise is bullshit, but at least you get some stuff in the box :wink:

The blurb about those caps is nonsense. If anything, the ones that he dismisses are better (more conductive), if you could imagine that there was a mechanism to cause problems in the first place that is! I just couldn't bring myself to sell stuff like that - wouldn't be able to sleep at night! :lol:


Top
 Profile  
 
PostPosted: Thu Feb 28, 2013 9:36 pm 
retrobike rider / Gold Trader
retrobike rider / Gold Trader
User avatar

Joined: Fri May 08, 2009 10:01 am
Posts: 11207
Location: Stockport, staring at the Peaks
Back with another question :wink:

One of the 'is this any good' variety:
Sherwood RD6103R amp

Likely to be surplus very soon and wondered if it was worth owt or if it was any use to anyone here? Cost me £60, not that that means anything really! :lol:


Top
 Profile  
 
PostPosted: Thu Feb 28, 2013 9:51 pm 
Retro Guru
User avatar

Joined: Thu Oct 13, 2011 9:30 am
Posts: 958
Location: Malvern
Not a lot I'm afraid. Karma it to a mate or something?

http://www.ebay.co.uk/csc/i.html?_from= ... te=1&rt=nc


Top
 Profile  
 
PostPosted: Thu Feb 28, 2013 10:18 pm 
Retro Guru
User avatar

Joined: Thu Oct 13, 2011 9:30 am
Posts: 958
Location: Malvern
For those of you who enjoy this sort of thing, I have been working on the AUX (CD) input card again this evening. I've replaced the TL071 op-amps with the OPA134's, reduced the gain a little more by changing the input voltage divider to approx 10:1 (which is a wee bit low now!).

This the original Quad AUX card

Image

and this is as mine stands now

Image

You can see the op-amp is configured as a unity gain buffer (all of the output returned to the inverting input) which has high input impedance (Z) and low output Z. I think this may impact the cutoff frequency of the output coupling, so the next step may be to remove the input and output coupling caps as there should be no DC at the output of the opamp. However, this begs the question "why bother with the buffer at all?" as my CD player has low output impedance anyway. Therefore I will probably end up with the below!

Image

This is simply a 10:1 attenuator to reduce the level from the CD player to suit the sensitivity of the preamp - though something like 6:1 (change R600/601 to 330k) will probably be more appropriate.

Subjectively, it sounds perhaps a bit 'faster' (which could be a subtle roll off of VLF which removing the coupling caps will reveal) and more forward.


Top
 Profile  
 
PostPosted: Fri Mar 01, 2013 9:15 pm 
Retro Guru
User avatar

Joined: Thu Oct 13, 2011 9:30 am
Posts: 958
Location: Malvern
There it is! :D

Changed the rest of the op-amps on the main board, did some local decoupling of supplies to op-amps, hand matched a load of metal film resistors in the signal path, replaced capacitors in the signal path, and bypassed the caps on the aux card because (as I suspected) there is negligible DC offset.

Image

I knew there was transparency in there waiting to get out. Deep bass restored, speed undiminished. Imaging is becoming three dimensional where it was always wide and defined. Oh yeah! The pre is really starting to rock! Looking forward to getting that power amp to the best it can be, as it already slays the Arcam which sounded restrained in comparison.


Top
 Profile  
 
PostPosted: Sun Mar 03, 2013 7:23 pm 
Old School Grand Master
User avatar

Joined: Sun Jan 06, 2008 2:36 pm
Posts: 4007
Location: uk
2 x AD8610 opamps for sale, taken out of a new headphone amplifier, so used for a few hours only....pics later, soldered in an 8 pin carrier if thats the right word. £10 posted
Image


Last edited by greenstiles on Mon Mar 04, 2013 1:44 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: Sun Mar 03, 2013 9:23 pm 
Old School Grand Master
User avatar

Joined: Sun Jan 06, 2008 2:36 pm
Posts: 4007
Location: uk
Spotted these ESL63's, seems a fair price.....miss mine...
http://www.ebay.co.uk/itm/Quad-ESL-63-M ... 460d422424


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1706 posts ]  Go to page Previous  1 ... 92, 93, 94, 95, 96, 97, 98 ... 171  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: integerspin and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

About Us

Follow Retrobike

Other cool stuff

All content © 2005-2015 Retrobike unless otherwise stated.
Cookies Policy.
bikedeals - the best bike deals in one place
FatCOGS - Fat Chance Owner's Group

Powered by phpBB® Forum Software © phpBB Group