diyAudio - Blog Entries
Go Back   Home > Forums > Blogs

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Old

Refining the Open Loop Diamond Buffer Headphone Driver (RJM Audio Sapphire 3.0)

Posted 31st January 2015 at 12:28 PM by rjm
Updated 18th March 2015 at 01:52 AM by rjm (add photo of finished amp)

A couple of years ago I built a standard op amp + diamond buffer headphone amplifier, called the Sapphire.

My original circuit (Sapphire 1.x) was the simple four transistor four resistor diamond buffer of the LH0002. Later small resistors (Sapphire 2.0) were added to the emitters of the driver transistors to boost the output bias current.

In this next go-round (Sapphire 3.0), I've replaced the emitter resistors with current sources. This provides a significant improvement in PSRR, over 20 dB in simulation. The output pair has been reinforced in a Sziklai configuration for lower distortion, and the primary output transistors five-way paralleled for improved thermal stability. The output impedance is 1~2 ohms, limited primarily by the output resistor.

It simulates to <-100 dB harmonics for 0 dB (1 V rms) output into 60 ohms. The total circuit standing current is less than 50 mA per channel.

LTSpice files below. R5,R6 on LTSpice...
Attached Thumbnails
Click image for larger version

Name:	Sapphire3 buffer.png
Views:	114
Size:	93.7 KB
ID:	1589   Click image for larger version

Name:	DSC_5407.jpg
Views:	29
Size:	714.8 KB
ID:	1597   Click image for larger version

Name:	Sapphire 3.0f2 sch.png
Views:	37
Size:	23.6 KB
ID:	1599  
Attached Files
File Type: asc Sapphire3 buffer.asc (8.7 KB, 38 views)
rjm's Avatar
rjm
diyAudio Member
Views 463 Comments 0 rjm is offline
Old

Richard Allan Three Way - Rebuild

Posted 27th January 2015 at 02:07 AM by googlyone
Updated 26th January 2015 at 08:02 AM by googlyone

I recently picked up a pair of, I guess, 1970's Richard Allan three way speakers. The line-up are RA drivers with which I am not familiar. Bass, LP10B, midrange LP5B and tweeters - long dead and replaced with mismatched dome tweeters.

Richard Allan was reasonably popular in Australia in the 70's and 80's, and did some pretty good gear. I was interested to see how these went, but did need to do something about the tweeters.

On pulling the drivers out, I noted a few things:
- The LP10B is a 10 inch bextrene cone woofer, using a 1.5" voicecoil rather than the HP10B's 2" coil. It is also very much an "acoustic suspension" driver - read on.

- The LP5B is very much like a 5" version of the KEF B110 - as used in the LS3A. I read somewhere that Richard Allan made a version of the LS3A under license, but that might be an "internet fact".

- The crossover was made by KRIX, a local speaker manufacturer...
Attached Thumbnails
Click image for larger version

Name:	IMG_2241.jpg
Views:	44
Size:	401.5 KB
ID:	1525   Click image for larger version

Name:	Philips_AD0160-T8_Impedance.jpg
Views:	37
Size:	58.5 KB
ID:	1529   Click image for larger version

Name:	Richard_Allan_LP5B_Impedance.jpg
Views:	24
Size:	49.0 KB
ID:	1530   Click image for larger version

Name:	LP5B_Farfield.jpg
Views:	36
Size:	366.4 KB
ID:	1532   Click image for larger version

Name:	LP10B_Smoothed.jpg
Views:	23
Size:	340.1 KB
ID:	1533  

Click image for larger version

Name:	AD0160_Farfield_Raw.jpg
Views:	33
Size:	377.0 KB
ID:	1534   Click image for larger version

Name:	LP10B_Sealed_Impedance.jpg
Views:	32
Size:	340.8 KB
ID:	1535   Click image for larger version

Name:	Richard_Allan_New_Crossover.jpg
Views:	58
Size:	461.3 KB
ID:	1537   Click image for larger version

Name:	System_Final_Response.jpg
Views:	28
Size:	375.9 KB
ID:	1538   Click image for larger version

Name:	System_Both boxes and dev_Response.jpg
Views:	36
Size:	398.2 KB
ID:	1539  

Attached Files
diyAudio Member
Posted in Uncategorized
Views 299 Comments 0 googlyone is offline
Old

Richard Allan 3 Way Rebuild - So What Do They Look Like?

Posted 26th January 2015 at 08:39 AM by googlyone

The Engineer in me led to plots and graphs, but no pics of the speakers!!!

Click image for larger version

Name:	IMG_2237.JPG
Views:	73
Size:	965.7 KB
ID:	1540

With a neat old badge...

Click image for larger version

Name:	Richard_Allan_Badge.jpg
Views:	26
Size:	250.0 KB
ID:	1545

The bass driver is a classic Richard Allan unit, you can tell them a mile away by the red (sometimes blue and black) felt:

Click image for larger version

Name:	IMG_2232.jpg
Views:	57
Size:	489.2 KB
ID:	1541

The midrange has a fair bit of the B110 about it's looks, though it is smaller and behaves quite differently. This thing is very much a product of it's era (1970's):

Click image for larger version

Name:	IMG_2230.jpg
Views:	41
Size:	580.2 KB
ID:	1542

The surround on the midrange is stated as PVC in some literature I found. I kind of believe this, though it has been coated with something sticky. It is not sticky on the back.

The cabinets were in moderately good condition. There were some coffee stains on the top of one, and water stains on the side of the other. In the end I sanded and revarnished them.

The timber...
Attached Thumbnails
Click image for larger version

Name:	IMG_2225.jpg
Views:	25
Size:	532.2 KB
ID:	1543   Click image for larger version

Name:	IMG_2227.jpg
Views:	27
Size:	401.2 KB
ID:	1544  
Attached Files
diyAudio Member
Posted in Uncategorized
Views 261 Comments 2 googlyone is offline
Old

New 12" wide heatsink now available

Posted 19th January 2015 at 03:59 PM by barrredboss

Hello diy'ers! Just wanted to let you know that we now have a 12" wide heatsink available for purchase at our website. Extruded Aluminum Heatsinks from HeatSinkUSA
barrredboss's Avatar
diyAudio Member
Posted in Uncategorized
Views 203 Comments 0 barrredboss is offline
Old

TDA1387 octal DAC looks like a good modding base

Posted 15th January 2015 at 11:55 PM by abraxalito
Updated 13th February 2015 at 03:23 AM by abraxalito

Thanks to Matthieu (Malefoda) for the heads up on this. It looks distinctly like a DAC inspired by the DAC-AH - note not only the 8 DAC chips but also the PCB layout closely follows that design's. The price on Taobao is about half the AH (368rmb) so I shall be ordering up one or more to have a play. Matthieu found it on another website with prices in USD, here - http://www.cart100.com/Product/42124644877/.
Note there are two options here (blue, black) - the cheaper one is a kit of parts I believe, the more expensive ($84) the finished unit. Going on the translation of the Taobao page, the kit does not include the transformers, mains switch or the case.

Update : here's the summary of the mods so far, for details go to Malefoda's thread linked in the comments.

1) Re-route the output ground so the opamp filtering caps aren't subject to injected CM noise from the destination component (amp or pre).

2) Reduce the supply voltage to the output opamps...
Attached Thumbnails
Click image for larger version

Name:	TDA1387taobao.jpg
Views:	222
Size:	67.2 KB
ID:	1522   Click image for larger version

Name:	LeeNOSfilter.jpg
Views:	54
Size:	17.5 KB
ID:	1566   Click image for larger version

Name:	P1010145.JPG
Views:	84
Size:	681.4 KB
ID:	1567  
Attached Files
abraxalito's Avatar
diyAudio Member
Views 628 Comments 10 abraxalito is offline
Old

MUSES premium audio semiconductors from NJR

Posted 14th January 2015 at 11:29 AM by rjm

Have I just been living under a rock or why the hell haven't I heard about this before now!?

http://www.njr.com/MUSES/index.html
rjm's Avatar
rjm
diyAudio Member
Views 244 Comments 2 rjm is offline
Old

Portable headphone amplifiers

Posted 14th January 2015 at 06:07 AM by rjm
Updated 13th February 2015 at 04:11 AM by rjm

The shift of the center of gravity of the high end from component, rack systems to portable continues. Exhibit A

I've also noticed that over the last couple of years the basic blueprint for a portable headphone amplifier as defined by the Sony PHA-1 has now been taken up by all of the major Japanese audio companies.

Sony PHA-1, PHA-2, PHA-3
Denon DA-10
Onkyo DAC-HA200 and TEAC HA-P50 (variants of the same basic unit)
JVC SU-AX7 (report) (seems to be mostly Kenwood DNA)
Audio Technica AT-PHA100
and Fostex hp-p1

For all the above you are looking at a battery powered, slim-cased DAC + headphone amp typically with some sort of guard around the controls. They all feature a good variety of analog and digital inputs, offer switchable gains, and are priced over a range from $200 to nearly $1000.

You are looking at the convenience of having the DAC built in, the small size, and the rechargeable lithium...
rjm's Avatar
rjm
diyAudio Member
Views 325 Comments 9 rjm is offline
Old

Revisiting mods to the Lite DAC-AH

Posted 12th January 2015 at 01:57 AM by abraxalito
Updated 12th January 2015 at 02:07 AM by abraxalito

Last night the battery of my I2S source ran out so while it was on charge, I unboxed my last remaining Lite DAC-AH to have a listen to that, fed from my (mains powered) QA550 wav player. I'd bought 3 DAC-AHs a few years back when I was playing with them.

The differences between the stock DAC-AH and the Ozone Pagoda were apparent in the areas of soundstage depth, dynamics (especially at LF) and coarseness at higher levels. So this got me wondering what would be the lowest hanging fruit in terms of mods to it. My procedure before had been to implement everything I could think of before having a listen - this way its not possible to know which mods are the most effective ones and which can be omitted.

This time I'm going to be a bit more disciplined for the purposes of discovering which mods deliver the best bang for the buck. The first one I'm going to try is a passive LC filter between the DACs and the AD847s. Here's the schematic for it - its using the cheap and...
Attached Thumbnails
Click image for larger version

Name:	DAC-AH-filter.jpg
Views:	112
Size:	37.2 KB
ID:	1521  
Attached Files
abraxalito's Avatar
diyAudio Member
Views 422 Comments 8 abraxalito is offline
Old

DIY ES9018 DAC + LM4780 AMP

Posted 6th January 2015 at 11:30 AM by Maciej Czerwinski

Finished, front:
Click image for larger version

Name:	caly_przod_obud.jpg
Views:	71
Size:	22.0 KB
ID:	1468
back:
Click image for larger version

Name:	caly_tyl_obud.jpg
Views:	59
Size:	23.2 KB
ID:	1469
what's inside:
Click image for larger version

Name:	CALY_OPIS.jpg
Views:	208
Size:	87.9 KB
ID:	1470
This device is built around DIYINHK ES9018 DAC board, with USB to I2C CM6631 converter, also from DIYINHK. USB is the only signal input. Power amplifier uses two LM4780 chips, one per channel in mono-parallel configuration. Power supply for the amplifier is made out of two HP printer power supplies. DAC power supply is more complex, but also uses three, a little bit modified, 12V supplies, wall plug in type, general use ones. Volume regulation (attenuation to be exact) is entirely digital, provided by ES9018 dac chip. It is controlled by PIC16F84 microcontroller via I2C. There is also 3-digit attenuation level display and rotary encoder is used for setting the attenuation level. Details are described in next posts.
diyAudio Member
Posted in Uncategorized
Views 211 Comments 0 Maciej Czerwinski is offline
Old

DIY ES9018 DAC + LM4780 AMP Details part 1

Posted 6th January 2015 at 11:30 AM by Maciej Czerwinski

DAC:
On the DIYINHK DAC board we can find ES9018 chip and ADP151 1.2V linear regulator (VDD) factory soldered. You have to populate the rest of the board yourself. I have soldered:
- ceramic and electrolytic noise filtering bypass capacitors,
- various resistors, mostly in the I/V stage,
- I/V stage op-amps (4xAD797)
- output signal low-pass filter capacitors.
The board is designed for 6 op-amps with SE output. I wanted differential output, so I have done some modifications, following the ES9018 demo board datasheet.

The I/V stage and power amp schematics (one channel):
Click image for larger version

Name:	av_amp_sch.jpg
Views:	254
Size:	67.6 KB
ID:	1478
When the main power is switched off, the relay shorts the power amp inputs in order to avoid oscillations, generated by I/V stage during discharge of its power supply bypass capacitors, to pass to the power amp.

A/V stage section of the DAC board one channel, ES9018 chip side (top side in my case)....
Attached Thumbnails
Click image for larger version

Name:	dac_zbliz_pwzm.jpg
Views:	124
Size:	113.2 KB
ID:	1479   Click image for larger version

Name:	dac_zbliz_pwzm_spod.jpg
Views:	105
Size:	63.0 KB
ID:	1480  
Attached Files
diyAudio Member
Posted in Uncategorized
Views 303 Comments 0 Maciej Czerwinski is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 08:31 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2