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Old 8th June 2002, 09:51 PM   #11
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Thanks 900gripen for your input.
I was waiting for somebody else from Oz to speak up...
I agree the Digi is a very flexible circuit. You also hit the nail on the head when you say there are adaptations of it out there using more up to date devices...
I guess you have your suspicions just like I have mine
Like you I found the MJ802/4502 much bettere than the others until I tried the Toshiba 2SC5200/ 2SA1943. This is another step forward similar to the one over the 2n3055/2955 with the MJ802/4502.
You can get these devices from WES Components in Sydney and they aren't very expensive either.
I can wholeheartedly recommend changing to these devices.
I tried a few other mods but they weren't as significant and you have to be carefull what you change as the open nature of the sound disapears, though there are some mandatory mods that don't affect sound quality so much as increase reliabilty.
Upgrade R6 to a 2w as it gets hot and replace Q3 (BC546, which also gets quite hot and can go pop depending on the ps voltage you are using) with either the MJ340, BF469 or 2n3019 that I am currently trying in that spot. These only affect sound quality slightly, a bit like how many shades of grey are there. If you know what I mean. I would recommend heatsinking this device too. There are a couple of other worthwhile mods but that will do for the moment I think. Are you still using the Digi?, or are you into something else? Perhaps we could share experiences... Or start a Digi Forum, possible title: "How to Hot Rod your DIGI in 6 easy steps or less"
Cheers
tomcat
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Old 8th June 2002, 11:20 PM   #12
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Hi tomcat

I've been following your Digi125 thread, and have looked at the kit available from KITS-R-US. They don't go into much detail except its $39. Is this where you bought your's from?

If so, is this for one amp or two? What is the quality of the PCB?

I have downloaded some Digi125 articles from Paul Cambie's site and the circuit is extremely simple. From the original article it uses two diodes to set the bias but I think I can see a led in the middle of the very poor quality picture on the KITS-R-US site. Do you know if the circuit available from the KITS-R-US site has changed from the original articles?

By the sounds of it, you have replaced all the components, at least the transistors many times. Have you thought of putting in sockets?

Greg
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Old 9th June 2002, 10:42 PM   #13
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Greg,

I think the price is for one board only plus parts. This would give you one channel. The boards are quite small, about two thirds of a business card lengthwise and a about a 1/4" narrower which is quite a feat initself, but awkward to work on because of the close proximity of tracks to each other, etc.
A better alternative is to get the larger boards from RCS Radio in Sydney, Ph: 02 9587 3491. email: rcsradio@cia.com.au
They are located at: 651 Forest Rd, Bexley, NSW, 2207. I'm not sure of the price but I think they are around $8 ea. which is reasonable.
RCS Radio have boards for just about every project ever published in Australia by, ETI, AE and Silicon Chip.
The alternative boards they do for the Digi are quite good, much larger and therefore easier to use by an inexperienced constructor than the small ones. I think they are on the Mk6/7 versions of this board now, which should be the one you can use either TO92 (BC546)/TO5 (2N3019) or TO126 (BF469/MJ340) devices in the position of Q3.
On the question of sockets, I'm not sure they are available as these are discrete devices so you have to solder them in individually. I've seen Paul Cambie's site, but never saw the circuit diagram for the Digi there or anywhere else except the one on the earlier Digi-125 thread on this site posted by Palesha. In the original circuit there is no led amongst the diodes although my friend Mark had thought of the idea of installing a certain type of green led but gave up on it when he couldn't get the right ones here in Oz. In stead we settled on an extra diode making it 3. You are quite right, the circuit is very straight forward to build with no setting up for the novice to worry about. If you want a better copy of the circuit let me know and I'll send you a copy of the whole article, inc circuit diag by snail mail as I haven't a scanner.
Cheers,
tomcat
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Old 12th June 2002, 11:45 AM   #14
ppl is offline ppl  United States
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Humm>
My 2c worth. Small signal 2N5086 & it's comp,MPS-8500/8099,MPS-A18-A20, BC-546 and comp. High volt Predrive or secong gain stage TO-126. BF-469 & 470 as a Higher Ft MJE-340. the MJ15032-15033 TO-220 drivers work well in alot of Audio circuits and MJ-15024 &15025 as outputs as well as MJ-1294 &2195.2SC1302 is also great. my faveroite are the sanken RET transistors. as outputs. Fuji used to make some nice ones also
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Old 12th June 2002, 03:23 PM   #15
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Default Re: sound quality of different transistors?

Hi Tomcat,

Quote:
Originally posted by tomcat
Hi all,

I'm curious if anyone has quantified the differences in sound quality between devices, small signal and output? There has been a lot of work done over the years on the differences between tubes; ie 2A3/300B, 12AX7/12AT7, etc, but not much in the solid state field as far as I know and my cursory search of the net has found apart from some obscure mention here and there.

This question crossed my mind after the huge difference I noticed replacing the ouput devices in my Digi-125 amp with the Toshiba 2SC5200/2SA1943 used in the AKSA amp.
At the time I was emboldened by the success of this experiment enough to consider replacing the small signal devices with MJ15030/1531's but in the end I decided on Toshiba's 2SC4793/2SA1832 which were alittle closer in Hfe/fT to the original BC546/556 devices.

After a lot of fiddling around removing/replacing the devices I plugged the amp back in and sat back for a listen. To my utter dismay and disapointment the music now sounded flat and totally uninvolving. Quickly I pulled the amp apart and reinstalled the original small signal devices, took about half hour and bingo the music was back again!

Obviously the small signal devices were responsible for this remarkable and very obvious change for there was nothing subtle about it...

Anyone have similar experiences/comments/opinions they would like to share?
been there, done it ...
Have compared a lot of transistors in all places, for over 10 years now.

Yes, the 2SC5200 from the AKSA is very good. Just a month ago I repaired a Hirage Le Classe A (30w version of the classic 20w) with these, and the owner couldn't tell the difference. BTW, the Hiraga has been built around Toshiba output devices, and although L'Audiohile scratched away the numbers, pouring water on the plastic cases revealed them. I just don't remember where I wrote down these numbers ...

Re the MJ15030: I once tried it just before the output devices, but found it too slow, too. I prefer for many years now the BD139/140 from Philipps, biased at 6 .. 10mAmps.

Generally speaking: big transistors (get the Ic rating) sound powerful, but slow, especially when biased at current very small compared their max current rating.

regards,
Hartmut from Munich
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Old 12th June 2002, 03:31 PM   #16
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Hi Alfsch,

Quote:
Originally posted by alfsch
I tried different transistors on a standard-design power amp:
- input: bip (BC546b),mosfet(BS107),j-fet(BF245b); sound differce was obvious: ref bip, the fet had finer hi-range, but less resolution on low level( less room), the mosfet bad / sharp highs, maybe by their bigger inp capacity;
- output: power bip, mosfet; ref bip, the mosfet had more room and a little finer hi;
since that time i made my power amps with bip input and mosfet output, this was the optimum configuration for me; but dont forget, this is only one part of the amp-sound, the design begins at the power supply and ends at the kind of wires you use, all parts make a change in sound quality...
I did these comparisons, too, but came to different results: in the input, jfets are very good, if good types are used, like 2SK30 or siblings, otherwise bipolars are better. In the output stage, I tried several years to work with Mosfets, until I gave up, they make too much haze and spoil the flow of music, the ryhtm and pace.

There are big differences in sound between different JFETs, the European stuff is nearly unusable for hifi. Even US types are lacking. If you want to see a good sounding amp with Jfets in the input, look at the various Kaneda realizations (the preamp is on the Bonavolta page, don't know where the power amps are on the net).

regards,
Hartmut from Munich
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Old 12th June 2002, 05:26 PM   #17
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Hi Tomcat,

There are, IMHO, several things one should consider.

I too have replaced transistors and have had both sides of the experience. Bad to worse and bad to better. Here are the things to consider:

Hfe. I have found that Hfe plays a big role in the sound quality one gets in both detail and warmth. In small signal applications one should try a higher beta transistor. One will get more detail and warmth owing to the fact that there is less base current and less Early effect (AKA base width modulation) making for a more stable gain stage. I had an amp once that used transistors of middle gain (100-200) and replaced them with high gain ones. The effect was astonishing. Warmer sound quality, a more tolerable high end, and more detail. The output transistors I retained the same values but a different brand. Yup, a different brand made a big difference in the sound quality also. Deeper bass and sweeter sound.

Basically, I went form Motorola to NTE. Another factor in the attempt to improve the sound. Manufacturer. I do not know if Motorola has a newer factory or not now, but refinement of the silicon, whether laser or (whatever the other type of process is used in cutting the pieces), the doping process, etc. and better "clean rooms" make for a better or worse product. NTE electronics started in the early 1980's with new laser equipped factories, and they make a very good product. I do not yet use any other brand.

As far as IC in audio, I have switched from NTE to Analog Devices. They are more costly but worth every penny.

Time. Yes time. Transistors also need a break in period. I purchased a Sony CD player for my car last year and did not like the sound. Sony components (transistors and amps) tend to sound very hard. This one was no exception. Yet after 8 months all of a sudden the darned thing started sounding so alive and warm. Evidently it needed a break in! But 8 months! It amounts to about 240-300 hours. So perhaps you didn't give your new components enough time to break in.


As regards FETs and MOSFETS, they depend, as with any other component, on the circuit they are in. I love the sound of MOSFETS (thee are ways to get arond the input capacitance problems, as with tubes etc). My first introduction to the FET was in a small phono player my father designed and built for me. It has such a kick and great sound quality for only ten watts (the pre was all FET). But at the time I knew very little about electronics and had not played with FETs until about 1982, ten years later.

Now 90% of my solid state designs are FET/Bipolar mix. I always replace any op-amp circuit with BIFET op-amps.

Anyway, that's my 2 cents worth.
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Old 13th June 2002, 04:31 AM   #18
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Tomcat

Thanks for your pointers.

I followed up on RCS Radio @ http://www.cia.com.au/rcsradio/oldtonow.txt and will probably buy a pair of the mk6 PCBs for my next project, and just in case someone else is interested here's the latest prices.

et1430 $ 7.50 2068A digi-amp 25/ 5Owatt - mk1 1989May
et1430 $ 11.00 2068B DIGI-AMP 75/125watt - mk6 1989May

Their new location is 41 Arlewis St Chester Hill.

Paul Cambie's site had a pdf of the original ETI article in a yahoo briefcase.

As far as sockets go, I thought for experimenting you could do something like this:

http://peufeu.free.fr/audio/memory-9-photos.html

Thanks again, Greg
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Old 13th June 2002, 12:03 PM   #19
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Quote:
Originally posted by Gabevee
In small signal applications one should try a higher beta transistor. One will get more detail and warmth owing to the fact that there is less base current and less Early effect (AKA base width modulation) making for a more stable gain stage.

...

Basically, I went form Motorola to NTE.
The early effect is in fact stronger for higher h_FE transistors. In cascode configuration, however, this should not matter. Whether low h_FE is a problem depends mostly on the impedance of the previous stage .

Excuse my ignorance, but who is NTE?

Regards,

Eric
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Old 13th June 2002, 12:28 PM   #20
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Quote:
Originally posted by capslock

Excuse my ignorance, but who is NTE?
www.nteinc.com
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