Go Back   Home > Forums > Blogs

Old

Taobao shopping for 'digital' amps

Posted 18th September 2016 at 02:45 AM by abraxalito
Updated 30th November 2016 at 02:32 AM by abraxalito

A number of interesting amps have caught my eye on Taobao of late, they (except for the last) are true digital amps in the sense that they're 'power DACs'. The first is using ST's STA333W which is a phenomenally cheap fully-integrated digital amp chip, hence the very low price of this board - https://item.taobao.com/item.htm?spm=a230r.1.14.19.4wjcvg&id=526018865372& ns=1&abbucket=13#detailhttps://item.taobao.com/item.htm?spm=a230r.1.14.19.4wjcvg&id=526018865372& ns=1&abbucket=13#detail USB input, speaker out but needs an external power brick of some sort, up to 20V.

The second one's a boxed product, albeit with an external power supply. Its using Intersil's D2-audio chipset (D2-41051), the first implementation I've noticed on Taobao. It uses discrete MOSFETs in the output stage. The enclosure and controls look to be in the PS Audio territory, a cut above the usual Taobao cheap stuff - https://item.taobao.com/item.htm?spm...cket=13#detail...
abraxalito's Avatar
diyAudio Member
Posted in Power chip amps
Views 1161 Comments 6 abraxalito is offline
Old

Not Another Gosh-darn EL84 Amplifier!

Posted 17th September 2016 at 06:32 PM by ballpencil
Updated 26th March 2017 at 06:01 AM by ballpencil

.. or NAGA84 for short.

That familiar feeling.. All tube enthusiasts will have a hard time resisting the urge to build an EL84/6BQ5 push pull amplifier, at least to hear for themselves what makes this tube so well-known (and overpriced).

Lurkers of the tube section most probably have already seen the Baby Huey wiki and thread. With such unique local feedback scheme, it's unsurprising that it garners some avid follower. As amazing as the feedback scheme may seem, there are few things i prefer to do differently on that amp. The most prominent thing would be NOT to use a triode for the input/driver stage as the rp of a triode will change with the signal swing and cause inconsistent feedback ratio. That, and the fact that it doesn't measure really well under simulation, motivated me to do my own version of the EL84 push pull amp.

To remove the triode from the feedback equation, there are two options i can think of:
1. Use pentodes, obviously....
Attached Thumbnails
Click image for larger version

Name:	naga84.jpg
Views:	991
Size:	168.2 KB
ID:	2069  
Attached Files
File Type: asc EL84 NAGA84.asc (8.0 KB, 159 views)
diyAudio Member
Posted in Uncategorized
Views 632 Comments 0 ballpencil is offline
Old

Chinese class D amp modules.

Posted 25th August 2016 at 10:42 AM by Stage Sound

I have imported several class D modules from China and all but one have had RFI problems and seemed to me to unusable and probably illegal in a production item. Far to much RFI on the output and looking at the on board components they have only a single stage output filter comprising of a square grey ceramic choke and one or two mylar caps. Has anyone else found the same thing and is there a mod that is known to work? The modules are all very well made using good quality components but like behaving like a radio transmitter.
diyAudio Member
Posted in Uncategorized
Views 747 Comments 5 Stage Sound is offline
Old

Cyrus Two Amplifier & Power Supply Upgrade

Posted 15th August 2016 at 03:28 AM by erictoucan

Cyrus Two would be the best selling and successful British Amp ever made. Definitely, it is the most important product to bring the market standing in its history.

After almost 40 years, it is still a very good amp around. Definitely, very good value for its second hand price.

Cyrus two phone section consists of super matched pair LM394 which is still the best matched pair today.

Here welcomes any idea to maintain and upgrade the Cyrus Two and its Power Supply to improve its performance to race with today's best amp.

For instance,

1. Replace the aged E-cap
2. Replace of coupling cap for better performance
3. Replace low value and better feedback resistor
with higher quality resistor.
4. Replace the important resistors in RIAA section
the best quality type
etc.

However, a lot of component and design is still very good like the Holden & Fisher...
diyAudio Member
Posted in Uncategorized
Views 426 Comments 0 erictoucan is offline
Old

RJM Audio discrete op amp (circuit schematic)

Posted 8th August 2016 at 02:06 AM by rjm (RJM Audio Blog)
Updated 22nd November 2016 at 11:29 PM by rjm

This is my first op amp design which doesn't completely suck.

Now, it's a terrible op amp... don't misunderstand... (Nat Semi will not be making me any offers)... but it does perform the job I want it to do reasonably well: remain stable while providing 6-20 dB of line-level voltage amplification with low distortion, decent PSRR, and sufficient bandwidth.

The main limitation is the distortion at high frequencies rises to -70 dB. The circuit needs less open loop distortion, or more open loop gain above 10 kHz, or both.

You will note the circuit has no current sources. This is intentional. I wanted to see how far it was possible to get without them. Obviously headroom takes a big hit, but distortion and PSRR ended up better than I imagined.

This is a simulation. No guarantee it will work, and there are no safeties (current limiters, input voltage clamps, etc) shown.

PS. Frequency response in image is open loop, while...
Attached Thumbnails
Click image for larger version

Name:	RJM op amp.png
Views:	1082
Size:	97.5 KB
ID:	2067  
Attached Files
File Type: asc 3x.asc (5.5 KB, 184 views)
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 785 Comments 2 rjm is offline
Old

Sapphire Line Preamplifier - My Build Notes

Posted 28th July 2016 at 03:15 AM by rjm (RJM Audio Blog)
Updated 4th December 2016 at 11:55 PM by rjm (add measurement data)

Introduction

This is my build log for relatively basic line preamplifier based on rev. 30f boards of the Sapphire3 headphone amplifier. I modified the circuit to run at lower currents (about 10 mA output bias) and adjusted the gain settings to 10/16 dB.

It is built in a Hammond 1550 cast auminum chassis, with an external Plitron 160VA 2x12VAC rectified power supply. The volume control is a 50k Goldpoint V24 stepped attenuator, while the RCA jacks are rhodium plated from Oyaide. The feature set is limited to two switchable line inputs and an output mute.

Chassis Layout Notes

Audio components are conventionally designed as rack-mounted equipment with all controls on the front panel and all connectors on the rear panel. To try and keep internal cabling to a minimum I'm modelling my preamp more like a recording console with both the controls and I/O on the top plate.

Build Notes

All components mounted...
Attached Thumbnails
Click image for larger version

Name:	sapphire pre topcutout.png
Views:	191
Size:	11.2 KB
ID:	2056   Click image for larger version

Name:	IMGP3513s.jpg
Views:	215
Size:	180.9 KB
ID:	2057   Click image for larger version

Name:	IMGP3523s.jpg
Views:	198
Size:	133.4 KB
ID:	2058   Click image for larger version

Name:	IMGP3552s.jpg
Views:	294
Size:	238.6 KB
ID:	2059   Click image for larger version

Name:	IMGP3537s.jpg
Views:	259
Size:	218.4 KB
ID:	2060  

Click image for larger version

Name:	Sapphire Pre 30f mod.png
Views:	400
Size:	20.7 KB
ID:	2061   Click image for larger version

Name:	pcb-sapp-30f3-brd.png
Views:	402
Size:	25.1 KB
ID:	2062   Click image for larger version

Name:	Sapphire LIne noise baseline.png
Views:	144
Size:	33.4 KB
ID:	2065   Click image for larger version

Name:	DSC_5975s.jpg
Views:	53
Size:	226.2 KB
ID:	2098  
Attached Files
File Type: zip Sapphire Line 30f vol -10dB RMAA report.zip (32.3 KB, 93 views)
rjm's Avatar
rjm
diyAudio Member
Views 562 Comments 0 rjm is offline
Old

Just the buffer, ma'am.

Posted 28th July 2016 at 02:05 AM by rjm (RJM Audio Blog)
Updated 8th April 2017 at 05:37 AM by rjm (added BOM)

I've had quite a few requests for the bboard buffer circuit without the built-in regulators, so here is a bboard 2.1 standalone 2-layer board, measuring 5x8 cm. Gerber files attached in zip file.

It is designed for +/-12 V rails, but the circuit will work with anything from +/-5 V to +/-18 V. A regulated power supply is recommended.

This is a line buffer. It intended to drive cables, not headphones.

Available for $15/pair shipped. Several people have asked me about kits. I figured the BOM was so basic it wouldn't be necessary but I can send you the boards with the parts to populate them for $50/shipped. You will still need to provide the power supply.

BOM attached. (updated to 21f4)
Attached Thumbnails
Click image for larger version

Name:	IMGP3561s.jpg
Views:	174
Size:	219.0 KB
ID:	2063   Click image for larger version

Name:	DSC_5538 d600 sm.jpg
Views:	146
Size:	511.1 KB
ID:	2087   Click image for larger version

Name:	pcb-bboard-21f3-brd.png
Views:	46
Size:	10.5 KB
ID:	2189   Click image for larger version

Name:	pcb-bboard-21f3-sch.png
Views:	116
Size:	14.4 KB
ID:	2190  
Attached Files
File Type: asc bboard buffer 21.asc (4.6 KB, 198 views)
File Type: zip buffer-21f (274x).zip (78.5 KB, 83 views)
File Type: zip pcb-bb-21f4-bom.zip (92.5 KB, 6 views)
rjm's Avatar
rjm
diyAudio Member
Views 665 Comments 0 rjm is offline
Old

Sapphire Line Preamplifier

Posted 24th July 2016 at 01:11 AM by rjm (RJM Audio Blog)
Updated 26th July 2016 at 11:45 PM by rjm

Although the original Sapphire headphone amp can be configured as a line stage, or use as-is as a line stage, I've gone ahead and made a new circuit variant with a new set of boards.

The Sapphire Line (in development) combines the shunt-series regulator, bboard 2.0 buffer and an op amp voltage gain stage. Same basic idea as the Sapphire of course, but with a much less beefy output stage so the low noise regulator can be added and everything still fits on the board.

rev 10e - now with support for 2520 op amp modules
Attached Thumbnails
Click image for larger version

Name:	Sapphire LIne 10d LTSpice.png
Views:	535
Size:	107.4 KB
ID:	2029   Click image for larger version

Name:	sapphire line 10e brd.png
Views:	363
Size:	21.9 KB
ID:	2033   Click image for larger version

Name:	sapphire line 10e.png
Views:	532
Size:	17.5 KB
ID:	2034  
Attached Files
File Type: asc Sapphire Line 10d.asc (10.1 KB, 212 views)
rjm's Avatar
rjm
diyAudio Member
Views 638 Comments 0 rjm is offline
Old

Multi-Channel, High Sample Rate PCM

Posted 18th July 2016 at 01:36 PM by Tam Lin

Here is a multichannel implementation that continues the theme of high sample rate PCM with no logic chips in between the oscillator and the DACs. There are two variations: seven and fifteen channels using USB2 bulk mode transfers up to 1.536M samples per second. More channels and higher rates require USB3.

What I find appealing about this design is that it is easily bread boarded. For USB, use a Cypress FX2 evaluation board. It has a built-in quantum FIFO and packet buffering. For the oscillator, use a Si570 evaluation board. With it, you can easily switch between the 7 and 15 channel versions, 44.1K and 48K based sample rates, 16x and 32x oversampling, and 24- and 32-bit sample frames. For the DACs, use Twisted Pear CODs with SCK = BCK and the format switches set for DF bypass.
Attached Thumbnails
Click image for larger version

Name:	mchsr.png
Views:	161
Size:	13.0 KB
ID:	2020  
Attached Files
diyAudio Member
Posted in Uncategorized
Views 359 Comments 0 Tam Lin is offline
Old

Quick note on line level output currents

Posted 18th July 2016 at 03:58 AM by rjm (RJM Audio Blog)
Updated 22nd July 2016 at 10:41 PM by rjm

Consumer audio standard line level output is -10 dB, 0.316 V rms [dB = 20 * log (V/1V)]. Some devices like computer sound cards can boost that at the max volume settings, my Asus Xonar can do 6 dB or 2 V rms. Quite a lot of digital audio produces 2 V rms output, DACs and CD players and not just computer sound cards.

The amount of output current required by the line driver is the signal level divided by the load impedance, so to estimate the worst case scenario we have to consider the smallest practical load and the largest likely signal. The input impedance of consumer audio is typically 10k to 100k. 10k is the lowest design point, but sometimes people do strange things like drive two components at once which halves the value, or headphones, or pro audio gear with 600 ohm inputs.

The long and short of it, though, is that consumer audio inputs are never normally going to draw more than 1 mA. For pro audio the maximum is meanwhile 3 mA. 5 mA bias current through...
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 578 Comments 2 rjm is offline

New To Site? Need Help?
Copyright 1999-2017 diyAudio