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CAL Alpha produces brutal gain

My system is made of Jolida 302  integrated tube amp , Thorens TD160 + Cambridge preamp and a tablet for simple MP3 background music.
About four speaker sets :AR,Vintage Jamo, Tannoy and Joseph audio.
I recently got a nice CAL Delta transport and Alpha tube DAC.
Everything works BUT , the output coming from the CAL DAC is aggressive. Cannot turn the volume knob over 8 o'clock. I am usually at 9-12 with all others.
The sound is compressed.
I have a very warm relaxed 3d listening set . The Alpha tube DAC seemed like a natural partner...

Anyone experienced such a thing ? 
Too much gain? 
Any idea? 
*Replaced the cables (rca and coax)
** Changed the input channels
*** Checked bias
**** What's next?????
Tnx
ehollander
5 responses Add your response
newbee
4,751 posts
 
Check out the tubes in the Alpha. Lots of times these tubes, when changed by prior owners, can have too high a gain, such as EI 12AX7's (no longer in production). I believe it is possible to use a 12AU7 or a 12at7, which have lower gain. I use new production Mullard 12AX7's (or JJ 12AX7's in mine. I preferred the Mullards. 

If you like their tone as is, then you can get an in-line attenuator which will reduce the gain but not change the tone.

Hope that helps a bit.
dekay's avatar
dekay
5,366 posts
 
It's been a long time, but the first version of the Alpha came with a resistor kit (resistors to be added in order to lower the gain if needed).

Tried 2 versions of the Alpha as well as a Delta in old setups and do recall the higher gain of both the Alpha's, though it was not a problem with the amp (Audion Silver Night) which I believe used a passive preamp/volume pot section, or if not very little gain was involved.

Perhaps someone here can chime in on this as to the values and types of resistors spec'd?

Plenty of internal space on the Alpha, so it should be an easy DIY, or tech job.

DeKay


ehollander OP
2 posts
 
Thanks for trying to help . 
I order a set of JJ5751 these have a 30% lower gain + a set of Mullard CV4004/12ax7
Will roll these and see if there is any improvment .
Any infi on the ressitor kit wil be appreciated .

BTW - anyone cad share any insigh on how good would the Alpha do with tiday's streaming ?

TNX 
Eyal 
newbee
4,751 posts
 
FWIW, the 'in line attenuators'  I referred to are in fact resistors encapsulated into a 'plug' which you insert between the RCA cable and RCA output. Not as elegant or,  probably,  precise as  putting resistors into the Alpha, but a lot cheaper and easily reversible.
georgehifi's avatar
georgehifi
10,312 posts
 
ehollander OP
My system is made of Jolida 302 integrated tube amp


This is probably your problem, this amp only needs 500mV (0.5v) in for full 50watt output.

The Jolida 302 is just a poweramp, with a passive volume control on the input, the gain could be lowered by a competent tube tech by changing the feedback resistor R5, but then C2 will have to change also so the filtering is the same. A good tech could do this in an 1hr and parts are a couple of dollars. 
http://www.drtube.com/schematics/jolida/sj-502a.gif


Or you can go the ugly way which can cause impedance matching problems that aren’t dangerous, and get two inline rca to rca attenuator.
http://www.rothwellaudioproducts.co.uk/html/attenuators.html

Cheers George
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