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Croft OTL 3 Amplifier Service / Check Up

Hi David as these things go one of my Quads has developed an issue and needs to go back to Andrew Jones of Aquadthing to be serviced or repaired so will have to wait till that is all completed before I can get down to the issue at hand . I have six NOS Mazda PL509 valves and have been trying to get a further two of the same type so that I can do a full valve change . Not seeming able to find a further two except at very silly prices. Sourced some Brimar NOS and will see if using them with the Mazda will be okay . Once I get the complete sets of valves it will be back to Glenn as they will need biasing and my model does not have the external bias points that appeared on some models which make it easier . At least you are only a short drive from Glenn while not long in miles the last part of the journey after you leave the motorway is a bit of a drag . Lets hope that a complete new set of valves giving out the best it can do will work .

With regard to my set up it is a very strange one for lots of others. I only use a digital signal either from a CD transport (Theta Data Basic ) or a streamer/player (Rpi4 Allo Digione Signature) which feeds a digital output in to my MiniDSP DDRC 22 D which then adds DIRAC Live DSP and feeds the treated digital signal to an Arcam D33 DAC which powers the Croft OTL 3 Direct . All of the volume control is in the DDRC 22D in the digital domain .
 
Apologies for going slightly off topic but I'd be interested to hear about the benefits you have derived from the Minidsp unit with your Quads.
Has it been worthwhile? Did you do some room checks in advance?
I have been tempted to try something similar for my Quads (63s not 57s).
 
@RichardA I first used MiniDSP a DDRC 24HD when I was converting a pair of passive two way speakers (KEF103) to active and using this I had DIRAC Live added and this made the sound and the room integration so much better that I progressed from there to using a DDRC 22 D for DIRAC and an 8 X 10 Digital crossover from MiniDSP to make an active three way with stacked KEF 103 .

The Quads are not an option for being made active or I would have considered this but the only person know to do was Tim P of EAR and I believe he set them on fire. So knowing that DIRAC Live worked well I wanted to find a way to treat the Quads passively . The DDRC 22D worked me for as I only use digital sources . There is a DDRC 22 A with all analogue inputs and outputs and a DDRC 22A/D which has both inputs . Recently DIRAC have greatly improved their software with an upgrade and the new version as well as being easier to use deals with lots of other issues in room like time alignment and reflections . This proved ideal for the Quads and enable me to use them in the very odd way that I do in room and still get an excellent musical response . I have to say that with the supplied UMIK Calibrated mic and just a sensible approach to doing a full DIRAC session you can get superb results . There are two way to use the Mic flat calibration which means you pint the mic head directly at the speakers being measured and then you can add a 90 Deg calibration file . Using this which is intended for setting up AV systems you point the mic head at the ceiling and measure from the various points . This was ideal for the Quad being a dipole and spitting out equal sound at the rear on to a back wall and then getting bounced sound from side walls . The DIRAC reading from 90 deg sorts all of this out and depending on your choice of measuring (tight focus , normal focus , wide focus) you can get the Quads to image over a much wider area without that narrow band which is more comfortable to listen to . With DIRAC the options to adjust are almost limitless so many choose to only deal with the bass but i use a wide range across the full music spectrum and it just works .
 
Many thanks for such a comprehensive reply. Super helpful.

bencat said:
@RichardA I first used MiniDSP a DDRC 24HD when I was converting a pair of passive two way speakers (KEF103) to active and using this I had DIRAC Live added and this made the sound and the room integration so much better that I progressed from there to using a DDRC 22 D for DIRAC and an 8 X 10 Digital crossover from MiniDSP to make an active three way with stacked KEF 103 .

The Quads are not an option for being made active or I would have considered this but the only person know to do was Tim P of EAR and I believe he set them on fire. So knowing that DIRAC Live worked well I wanted to find a way to treat the Quads passively . The DDRC 22D worked me for as I only use digital sources . There is a DDRC 22 A with all analogue inputs and outputs and a DDRC 22A/D which has both inputs . Recently DIRAC have greatly improved their software with an upgrade and the new version as well as being easier to use deals with lots of other issues in room like time alignment and reflections . This proved ideal for the Quads and enable me to use them in the very odd way that I do in room and still get an excellent musical response . I have to say that with the supplied UMIK Calibrated mic and just a sensible approach to doing a full DIRAC session you can get superb results . There are two way to use the Mic flat calibration which means you pint the mic head directly at the speakers being measured and then you can add a 90 Deg calibration file . Using this which is intended for setting up AV systems you point the mic head at the ceiling and measure from the various points . This was ideal for the Quad being a dipole and spitting out equal sound at the rear on to a back wall and then getting bounced sound from side walls . The DIRAC reading from 90 deg sorts all of this out and depending on your choice of measuring (tight focus , normal focus , wide focus) you can get the Quads to image over a much wider area without that narrow band which is more comfortable to listen to . With DIRAC the options to adjust are almost limitless so many choose to only deal with the bass but i use a wide range across the full music spectrum and it just works .
Click to expand...
 
Hi Guys,
I have been trying to reach Glenn via email for several months now but have received no reply. Even tried several time sto call but no answer & voice box full!!
I have had commisioned a pair of special built OTL 3 SAs monobloc & also got of him one of his Charisma development prototype (standard black case) along with a standard Super Micro A since early 90's & as they have been in storage for over 20 years I would like them service checked. At the very least I would like to check the bias on the amps. Both the amps have the external taps & adjustment points. Can somoeone here explain to me in detail how I can use my multimeter to check & if nesessary adjust the bias on them?
 
@Alex Apostolakos I believe that Glenn is not very well and this is the reason that he has not been in contact with anyone for a while . Where in the UK are you based ? I you can let us know then we can advise some one closer to you to who could help . I regret that I have no details at all on the technical details of checking the bias on the OTL 3 because mine had no external taps and were checked and done by Glenn when i owned the amp . I have now sold the Croft so have not had any need to contact Glenn recently .
 
I have a problem with a Croft 25/7 combo. About 3 years ago Glenn fixed a problem on the power amp.... any ideas where to take a Croft amp to now? I've lost a bit of volume on one of the channels (phono side), also there is some distortion. It's not the fuses, going to order valves but I don't think they're likely to be the cause. Slotting in an external phono stage does not chase the problem away.

I am in Hebden Bridge, West Yorkshire, and have contacted my default repairers Wilkinsons (Colne), however they are quoting weeks and weeks and I would have my amps for none of that time, I'd rather avoid that as I don't have a spare to slot in.

Can anyone suggest a trustworthy person who could repair Croft valve amps? I've come up with Audioflair and Deco Audio but they are dan sarf and my preference is somewhere more local so that I can avoid the expense and risk of posting.
 
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