4-channel gain stage with DC-servo for MiniDSP - Page 3 - diyAudio
Go Back   Home > Forums > Commercial Sector > Manufacturers > miniDSP

miniDSP Low cost, modular Digital Signal Processor (DSP) kits for the DIYer from miniDSP.

Reply
 
Thread Tools Search this Thread
Old 12th July 2013, 09:18 PM   #21
DrDyna is offline DrDyna  United States
diyAudio Member
 
DrDyna's Avatar
 
Join Date: May 2007
Blog Entries: 3
Quote:
Originally Posted by CharlieLaub View Post
... it's a mystery why they don't get to it, when many of their customers are begging for it and lack of output voltage is one of the main complaints about their platforms??? It's a big fail on their part IMHO.

-Charlie
They have the MiniAMP, perhaps it could be another similar product, MiniLD or something, offering a jumper selectable gain from 3 or 4 db up to 20 or so, and it could just piggy back onto the MiniDSP.

Hey, there's an idea, create a gain stage that's the same size as the MiniDSP and put one of those long-pin style connectors on the edge of it so it could be piggied onto the MiniDSP!

__________________
"We may have to blast.." -Doc Brown
  Reply With Quote
Old 12th July 2013, 09:26 PM   #22
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
The ADAU1701 operates on a 3.3VDC supply, and I see on the data sheet there's an internal 1.8VDC regulator. That pretty much explains the limited voltage output capability of the on-board analog outputs. The only way to achieve more voltage is to add external circuitry. That would necessarily complicate the design.....which obviously they have in the balanced version.

I don't see why a person would need more than 2VRMS capability. The power amplifiers must have very low voltage gain?

Cheers,

Dave.
  Reply With Quote
Old 12th July 2013, 09:36 PM   #23
DrDyna is offline DrDyna  United States
diyAudio Member
 
DrDyna's Avatar
 
Join Date: May 2007
Blog Entries: 3
It's the same logic that could be applied to saying we don't need a pre amp...because any cd player can output 1vrms..which can drive an amplifier...all you really need is a 100k pot and we should all be good to go!

Realistically, if you want to be able to drive (the majority) of amplifiers to full power, you need a gain stage between the source and the amplifier, especially with record companies like Chesky, that have taken a stance against the "loudness wars" and started producing recordings that are quite low level, comparatively. If one uses a MiniDSP as advertised / pictured, it doesn't offer a single DB of gain...a situation which becomes a problem if you try to drive multichannel receiver inputs as I am, or amplifiers which require decent voltage to reach full output....which quite a few are, considering they're designed under the assumption that 99% of users will have a gain stage between the source and their amplifier.
__________________
"We may have to blast.." -Doc Brown
  Reply With Quote
Old 12th July 2013, 10:21 PM   #24
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
Yeah, I understand, but that's an input signal level issue (primarily) and not an output voltage capability issue of the interim device. Do you see what I mean?

Cheers,

Dave.
  Reply With Quote
Old 12th July 2013, 10:34 PM   #25
DrDyna is offline DrDyna  United States
diyAudio Member
 
DrDyna's Avatar
 
Join Date: May 2007
Blog Entries: 3
Quote:
Originally Posted by Davey View Post
Yeah, I understand, but that's an input signal level issue (primarily) and not an output voltage capability issue of the interim device. Do you see what I mean?

Cheers,

Dave.
I do. I just think that the unit should offer a little gain, as it's intended use is between a source and and amplifier.. they should make it more clear that it's really just a buffer..so if a customer applies a Linkwitz transform, a heavy bass note will clip the unit at even a relatively quiet setting.

Really, the problem is two fold and goes beyond amplifiers that take a bit of juice to get revved up...the problem is also as Charlie said earlier, applying a Linkwitz transform or low shelf...effectively robs you of that amount of gain, so using the unit to EQ an open baffle speaker essentially results in a loss of gain in whatever amount your highest boost is set to. Need 10 db of boost at 20hz? Congrats, you now have a -10db loss-stage.

There are two places in the MiniDSP where you can add 12db of gain to any frequency.. Wouldn't it be magical if the unit had 24 additional db of gain beyond the maximum setting of the overall volume control?

Meh, I dunno. The whole thing stems from them wanting the unit to be able to be ran from USB power...flexible, but inflexible at the same time.
__________________
"We may have to blast.." -Doc Brown
  Reply With Quote
Old 12th July 2013, 11:04 PM   #26
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
Remember, equalization only serves to extend/flatten the response of a driver. If you think about it another way, the amount/type of EQ required is essentially irrelevant to this issue.

Yes, if you applied a Linkwitz Transform with much boost you would be asking the miniDSP to apply a voltage gain above zero db at certain frequencies. However, you would normally be adjusting the gain of that channel lower by an amount approximately equivalent to the gain you applied to achieve the same SPL.

The ultimate limitation still remains regardless of the amount of EQ applied. You have 0.9 volts available to a power amp with X-db gain, to a speaker with X-sensitivity and X-displacement capability.

Regarding programmed gain in the miniDSP......You can certainly program gains greater than 12db.....even more if you want. Thinking of the device as limited to unit-gain is not literally correct.

Cheers,

Dave.
  Reply With Quote
Old 12th July 2013, 11:14 PM   #27
DrDyna is offline DrDyna  United States
diyAudio Member
 
DrDyna's Avatar
 
Join Date: May 2007
Blog Entries: 3
Quote:
Originally Posted by Davey View Post
... However, you would normally be adjusting the gain of that channel lower by an amount approximately equivalent to the gain you applied to achieve the same SPL.
mmm..I'm not sure I follow on this...I was under the impression that the dipole rolloff is a loss @ 6db/oct below the first dipole peak, so equalizing it requires the reciprocal boost. I imagine that you could EQ it inversely, so that it's all done with loss to achieve a flat response, but then, aren't we just losing anyway?

I guess what I'm getting at is..the unit has a set amount of voltage it can supply, which is really the same as the input sensitivity..meaning the unit is incapable of actually applying any gain at all...it would make more sense if the I/O overall volume sliders maximum position was at 0 like it is, but the meters extended a further 24db (as what's graphically indicated by any of the EQ settings) and the unit had enough gain to cover...gain...?

I could be completely wrong in my thinking, it just seems more natural that the unit's butt should be able to cash whatever checks it's EQ curves can write

I love to be wrong, and I learn from being wrong, but I'm having a hard time with this one, lol.
__________________
"We may have to blast.." -Doc Brown
  Reply With Quote
Old 13th July 2013, 12:16 AM   #28
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
The miniDSP IS capable of applying gain. (I'm not sure where the misunderstanding is here.)

Yes, the maximum voltage output is a hard limitation, but if you program the unit for 12db gain it can/will achieve it. BUT, you'll have to reduce your maximum input to approximately 0.22 volts (-12db from 0.9 volts) to avoid possible clipping.

Dipole roll-offs don't necessarily need to be programmed with boost (above unity) settings. With the miniDSP you can usually achieve your goal by selecting the opposite slope shelving filter and applying a negative gain.

Cheers,

Dave.
  Reply With Quote
Old 13th July 2013, 12:37 AM   #29
DrDyna is offline DrDyna  United States
diyAudio Member
 
DrDyna's Avatar
 
Join Date: May 2007
Blog Entries: 3
Quote:
Originally Posted by Davey View Post
BUT, you'll have to reduce your maximum input to approximately 0.22 volts (-12db from 0.9 volts) to avoid possible clipping..
Right, this is exactly my point. I guess its just semantics.

If 0 is the maximum level on the indicators before clipping occurs, you have to think of the filter scale with 0 db at the top, meaning any positive adjustment at any frequency represents a loss of output capability at all other frequencies..we appear to agree perfectly about what it actually means..and what its actual capabilities are...the main difference is I'm of the opinion that it could have been done better..perhaps even so that the scale literally provides what it does visually.
__________________
"We may have to blast.." -Doc Brown
  Reply With Quote
Old 13th July 2013, 01:04 AM   #30
DrDyna is offline DrDyna  United States
diyAudio Member
 
DrDyna's Avatar
 
Join Date: May 2007
Blog Entries: 3
I really just have one idea, after thinking about it, the best way to describe it is....the output voltage capability should be able to exceed the input voltage capability by whatever tomfoolery the unit can be visually programmed for.

It really would be a better unit if that was the case. Just because we can say "well if you think about it like this...."

Input level meters should be in the red at 0...output level meters should be in the red at +24.
__________________
"We may have to blast.." -Doc Brown
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
DC servo and gain stage board with output zobel CharlieLaub Analog Line Level 0 11th February 2011 09:01 PM
Transformer based voltage gain + unity gain stage? soundcheck Solid State 2 10th August 2010 02:44 PM
DC blocking cap in feedback path or DC servo? roender Solid State 27 19th September 2007 09:40 AM
Balanced DC servo for balanced stage ? CheffDeGaar Solid State 8 9th July 2003 02:39 PM


New To Site? Need Help?

All times are GMT. The time now is 02:11 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2