2. amps-preamps
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Unsure how to set levels to use tubes and power amp together

Hello to all...

I have a question regarding setting the power amp to work with my preamp:

I have a Wolze Line Level Tube Preamp -2-AX7s and 2-EF86 tubes, playing into a Parasound HCA-750a then to a pair of JBL L25 PRIMA speakers...

In a past forum: it was suggested that I could either play my CD unit directly thru the amp, using its volume controls ( it has independent R&L volume controls on the back of the unit) OR add a preamp, use the volume knob on the preamp, and set the volume controls on the back of the amp, according to how loud ( at what o’clock) I wanted to use the preamp volume.

My confusion relates to a minimal understanding that any electronic device ’amplifying’ a signal introduces distortion in the transmission, and therein lyes my confusion. Do I just set the amps volume control 1/2 way on the back (to minimize the distortion from that piece) and use the preamps volume control, OR do I set the amps volume controls full-on, and just use the preamp volume controls as best I can (even if it means minute adjustments never past about 8:30 on the preamp volume control).

So I’m questioning which piece of equipment’s distortion is better to take a advantage of... And what I should do.


insearchofprat
11 responses Add your response
atmasphere's avatar
atmasphere
11,794 posts
 
Volume pot on pre does not have detents (would/could changing the volume pot to one with detents, give better control?)...
No. You have more control when its continuously variable.

I'd back off on the amp volume controls, maybe to 3 o'clock, and see what you think. Listen to how it sounds and also where your master volume control sits.
insearchofprat OP
189 posts
 
Just tried options -
A) Turn to full on on amp: can't get much past 7-7:30 for normal listening, 9:30-10 way too loud; volume knob on pre very sensitive...
Option B) normal listening at about 9 means cutting the amps power back almost half, goes way loud at 11:30-12...
Volume pot on pre does not have detents (would/could changing the volume pot to one with detents, give better control?)...
insearchofprat OP
189 posts
 
Thanks to all who helped me understand the best ways to handle this - with clear and non- judgemental comments...
oldhvymec
5,101 posts
 
By turning the volume to 100% on the Parasound, you are reducing the number of resistors in the path of the signal from the preamp to the amp's input stage.

I wasn't thinking about it, but that is a great point. Less crap the better.

Might be a sonic nugget there, SQ quality wise, with a simple pot bypass.

I've done it a few times with fuse holder replacements. From OK, sound to outstanding sound. Top to bottom improvement, in a fuse holder and fuse replacement.  Amps, and speakers both..

Regards
gs5556
1,234 posts
 
By turning the volume to 100% on the Parasound, you are reducing the number of resistors in the path of the signal from the preamp to the amp's input stage. Resistors are noisy and the fewer the better. So the answer is there is less distortion with the volume full on.
erik_squires
16,056 posts
 
Hi OP,

Yep, turn the knobs all the way up on the amp unless needed for other reasons.

It may help you to understand that the gain of most preamps and amp electronics is fixed.  The volume knobs only change the level of signal before or after the electronics.

For instance, with an amp, the typical gain is 26 dB (20 times the input voltage).  The volume knob controls the V seen at the input of the amp, but the amp will still amplify 26 dB.

Preamps are often the same, with the volume knob coming after the gain stages.

Yes, less gain = less noise, but you aren't actually adjusting the gain in the devices, just the voltage levels coming in and out.

Clearly, the effective gain is changed, I'm only discussing the gain in the noise generating parts, which is the electronics.

Best,

E
oldhvymec
5,101 posts
 
Same here, 100%, I owned an HCA 1000, too. Great amp..
Parasound is good stuff...

Regards
Post removed 
wolf_garcia
6,695 posts
 
I owned a Parasound HCA 1000 for years (a great amp by the way) and found it sounded best  at the 100% level setting, which is what every other "non volume pot" power amp is by design.
twoleftears's avatar
twoleftears
5,318 posts
 
Volume controls on preamps are reputed to have an optimal range of operation, where the pot operates the best.  So if your volume control goes, say, from 8 o'clock to 4 o'clock, the best range would likely be somewhere between 11 (fairly soft) and 1 (fairly loud).  The recommendation was to set the R+L controls to achieve that range on the preamp.
reubent
6,985 posts
 
Google is your friend......

I Googled "Parasound HCA-750a" and found a link to the Parasound page for this discontinued amp. Right there on the page as the following question:

Q - Where should I set the volume controls on the back of my amp?

A - Under normal conditions you should turn them all the way to allow full power output from your amp. However, if you need to match the volume output of one of our stereo amps with another brand (BiAmping) you could adjust them accordingly.

Set the power amp volume knobs to full. If you feel that you do not have enough granularity when setting your system volume using your pre-amp VC, back off the volume control on the amp until you have useful granularity (steps).
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