Pre amps

Okay, Ive got a problem with my set-up, Im bored. The valve amp is basically a power amp with a pot, its uses El34's with two 6u8a's handling the input. I did love it but now its sounding too laid back, great with acoustic but anything else isnt great.

Its got to the point were Ive packed it off to my mates conservatory whilst I redecorate the lounge, usually I would work round stuff like that.

So what next? My first thought turns to a valve pre but funds are abit tight, I could DIY something if anyone has any ideas???

 

second hand audio research pre. ls2 can be had for 500/600 is hybrid and sounds fine

 

I'd try borrowing a valve pre... putting the volume up full on the pot on your power amp, and using the volume control on the active pre.

If that doesnt work, then perhaps to look at different amps?

 

I'd change the EL34s for KT88s and stick a panasonic pot in, perhaps shunted with some vishays. If you do a pre later you can pull the panasonic and vishays out and stick them straight into the pre.

 

I was actually going to change the pot. It came with a simple 20K pot as standard, I changed this for a 50k blue alps and I swear its lost some sparkle.

 

Try a stepped attenuator.

 

Put the other one back in and see (hear)

 

I will be trying the old one again when I get the amp back.

I have been looking at these:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=50598&item=5783788377&rd=1&ssPageName=WDVW

Ive also found a few sites with plenty of detainls of how to construct one plus Excel spreadsheets for working the resistor values.

 

I would go for a shunted design. Although the quality of a pot is still important, it's not as determining.

Or make one yourself using a nice valve like an 6SN7 http://www.diyparadiso.com/6sn71.htm

or a more common 12AZ7 (ecc83) http://www.joeltunnah.com/buffer.html

 

Croft Vitale pre amp

The Croft Vitale pre amp is also very simple, only one valve (ECC81 on the right) for amplification. The previous owner replaced the ECC81 with a ECC82, probably to lower the gain. There are very few passive components soldered to the ECC81. The other two valves ECC83 on the left are for RIAA equilisation.

There is plenty of space inside the Vitale for modification. Adding a EZ81 rectifier valve and a choke should be pretty straight forward.

The single gang potentiometers are not the best quality ones and the other components are not expensive, but the Vitale sounds good. The more expensive and newer Croft amps tend to have a beefier toroidal transformer and a valve rectifier rather than solid state diodes.

Hon

 

welcome to upgrade-itis

T-bone, I ahve a musical fidelity x-pre for sale.

This is a 2 valve 4 input preamp with 2 x6922s in the signal path, no transistors, I am not sure its widely known that its just valve!!

No hums buzzes, ex cond., original box, any use? £160 inc post, got to be the biggest unknown bargain in hifi, a valve pre!!! for that cheap.

 

Hmmm tempted, I'll PM you. By the way you wouldnt have tried this with the dynavox by any chance?

 

not yet, been playing with other things, tried with a 300b, pretty good.

 

thats a good price for the xpre

 

transcendant sound grounded grid pre amp - rawks.

 

Yes I'd second that

 

I can only find this on GG so far:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=59170&perpage=10&pagenumber=2

 

Try a BP

You could try adding a Border Patrol power supply (£500-600). It worked a treat on my valve integrated, made it sound a lot stronger and clearer. Contact Definitive Audio for details: Tel: +44 (0)115 97 33 222.

I think they used to do a money-back guarantee - if you don't like the mod, they'd undo it and give you a refund. Not sure if this still applies.

 

THe Ground grid is seriosuly good unit for the cash, and can well improved upon.
We used the Border Patrol Pre and Bp 20's in last years Heathrow show, The pre was good, but I perferred the GG Wm

 

Accuphase.