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Rega Brio (one channel dead)
Rega Brio (one channel dead)
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Old 24th May 2018, 05:00 PM   #51
jaycee is offline jaycee  United Kingdom
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If you have no problem sourcing parts, it might be worth looking at whats available in IPAK/TP/TO-251-3 to replace a TO92L part
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Old 24th May 2018, 09:49 PM   #52
Depaj is offline Depaj  France
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I found some BD139-10 and BD140-10 from on-semi on mouser. the higher hfe version is once again on order (shipping date january 2019, I'll pass). I always power up and do a first test with a dim bulb, I'll scope the output to look for oscillation. Some suggested to change the op amp for a ne5532, but you would stick with the original TL072 ?
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Old 24th May 2018, 09:59 PM   #53
jaycee is offline jaycee  United Kingdom
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TL072 would probably be best for it's lower output offset. TBH this topology of amplifier doesnt lend itself to low distortion, so i wouldnt bother upgrading the opamp...
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Old 25th May 2018, 06:34 AM   #54
Ian Finch is offline Ian Finch  Australia
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I don't think its a good idea to use higher hFE range parts than specified in the Brio. Having watched a couple of boards burn as I was testing them, I can justify stability warnings. I would only use standard or -10 drivers, unless you like the chance of a heat and smoke finale with your music

We should also be careful how we interpret hFE measurements. The cheap Ebay parts testers seldom give results that relate to manufacturer specs, as their test current is about 2mA max. Results can therefore be anywhere, depending on the Hfe V Ic characteristic curve of the transistor. The table shows differences for BD139 at more realistic currents. BD140 is quite similar. As jaycee suggests, anything apart from heat dissipation that applies to BC639/640, will also apply to BD139/140.Philips - datasheet pdf

Hi Depaj, I'm sure you know that you can buy ST Micro BD139/140 products from Element 14, RS components, Profusion, Reichelt and other distributors in Europe. Mouser seem to deal with a lot of suppliers but now they hold very few stock lines of useful through-hole parts. It's annoying and FWIW, they have lost my business.
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Last edited by Ian Finch; 25th May 2018 at 06:36 AM.
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Old 25th May 2018, 07:43 AM   #55
haiqu is offline haiqu  Australia
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Quote:
Originally Posted by Depaj View Post
I found some BD139-10 and BD140-10 from on-semi on mouser. the higher hfe version is once again on order (shipping date january 2019, I'll pass). I always power up and do a first test with a dim bulb, I'll scope the output to look for oscillation. Some suggested to change the op amp for a ne5532, but you would stick with the original TL072 ?
FET op-amps work best in DC feedback circuits. Unless you like having your output slammed against one of the rails, leave it as a TL072.

If you want it tweakable/swappable, separate that function from the input amplifier circuitry.
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Old 25th May 2018, 10:45 AM   #56
nigel pearson is offline nigel pearson  United Kingdom
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The KS parts I listed should work out if the base emmiter direction is factored in. As far as I know centre collector with reversed b,e. Thus they are 180 degrees rotated.

If you note all they were was good versions of the BC639/640 in style.

TL072 seems to work better if used in a power amp. I would sepeculate the JFET input and resistor output current limiting helps. NE5532 might be trouble.

CDIL BC639 Transistor NPN 80V 1A TO92 | Rapid Online
CDIL BC640 TO92 80V PNP Low Frequency Transistor | Rapid Online
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Old 27th May 2018, 01:01 AM   #57
mjona is offline mjona  New Zealand
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Default From a Different Perspective

There is a consistent pattern of burned out resistors in three Brio amplifier cases where the suggested solution is to replace some transistors with parts rated for higher power.

The closed loop gain of the whole is 150k/1k plus one which is the minimum gain of a series feedback system. This is to obviate the need for any line stage.

It has been suggested that the gain of the discrete component stage of 11 times could be reduced.

Unfortunately the gain of a TL072 declines to one at 3MHz so if the entire amplification relies on this, the point at which the gain reduces to one is 3MHz divided by 150 or 20kHz.

A consequence of increasing the closed loop gain (discrete stage included) increasing sensitivity for input sources also heightens that to any disturbance on the feedback line.

Fuses are undesirable in speaker lines and one way to deal with this is to include them in the feedback loop and run a resistor in parallel to maintain dc conditions.

There is a snag in this scheme as the fuse is thus a part of the signal source so if it is caused to blow in some extreme event the effect is going to be magnified 150 times.

Further in this instance there is a 22 p lead compensation capacitor in the feedback line which lowers the impedance path to the feedback terminal at high frequencies.

I attribute the burned out resistors to instability caused by fuses blowing under conditions of drive heavy enough to blow output fuses. Increasing fuse ratings, resistor ratings, or transistor ratings is not the answer to this.

My solution is to place the 22p capacitor and place it between the inverting input of the op.amp and its' output providing a feedback path at high frequencies that will not be directly influenced by such as a blown output fuse.
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Old 27th May 2018, 08:12 AM   #58
Depaj is offline Depaj  France
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A lot has been going on since the last message I saw, I'll have to take some time to go through all of this. I was wondering though, didn't rega come up with a solution for these issues in their newer versions of the Brio or did they just completely modify the whole circuit ?

The TL072 doesn't seem to have taken a hit when the whole thing went up in smoke, I was just curious as to why some suggested the NE5532.

Quote:
Hi Depaj, I'm sure you know that you can buy ST Micro BD139/140 products from Element 14, RS components, Profusion, Reichelt and other distributors in Europe. Mouser seem to deal with a lot of suppliers but now they hold very few stock lines of useful through-hole parts. It's annoying and FWIW, they have lost my business.
I have bought things from the first 2, thing is, as much as possible I try to buy from the same place to reduce shipping and mouser does have a lot of parts that element 14 or rs don't have. Is ST Micro superior in quality than on semi or do you suggest them because the datasheet has more info ?

Quote:
There is a consistent pattern of burned out resistors in three Brio amplifier cases where the suggested solution is to replace some transistors with parts rated for higher power.

The closed loop gain of the whole is 150k/1k plus one which is the minimum gain of a series feedback system. This is to obviate the need for any line stage.

It has been suggested that the gain of the discrete component stage of 11 times could be reduced.

Unfortunately the gain of a TL072 declines to one at 3MHz so if the entire amplification relies on this, the point at which the gain reduces to one is 3MHz divided by 150 or 20kHz.

A consequence of increasing the closed loop gain (discrete stage included) increasing sensitivity for input sources also heightens that to any disturbance on the feedback line.

Fuses are undesirable in speaker lines and one way to deal with this is to include them in the feedback loop and run a resistor in parallel to maintain dc conditions.

There is a snag in this scheme as the fuse is thus a part of the signal source so if it is caused to blow in some extreme event the effect is going to be magnified 150 times.

Further in this instance there is a 22 p lead compensation capacitor in the feedback line which lowers the impedance path to the feedback terminal at high frequencies.

I attribute the burned out resistors to instability caused by fuses blowing under conditions of drive heavy enough to blow output fuses. Increasing fuse ratings, resistor ratings, or transistor ratings is not the answer to this.

My solution is to place the 22p capacitor and place it between the inverting input of the op.amp and its' output providing a feedback path at high frequencies that will not be directly influenced by such as a blown output fuse.
You mean remove the 22pF cap at the end and place it directly on the TL072 ?You seem to have repaired a few so I assume you have tried this, does it affect the sound in any way or is this really just to increase stability ?
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Old 27th May 2018, 08:14 PM   #59
mjona is offline mjona  New Zealand
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Quote:
Originally Posted by Depaj View Post
A lot has been going on since the last message I saw, I'll have to take some time to go through all of this. I was wondering though, didn't rega come up with a solution for these issues in their newer versions of the Brio or did they just completely modify the whole circuit ?

The TL072 doesn't seem to have taken a hit when the whole thing went up in smoke, I was just curious as to why some suggested the NE5532.



I have bought things from the first 2, thing is, as much as possible I try to buy from the same place to reduce shipping and mouser does have a lot of parts that element 14 or rs don't have. Is ST Micro superior in quality than on semi or do you suggest them because the datasheet has more info ?



You mean remove the 22pF cap at the end and place it directly on the TL072 ?You seem to have repaired a few so I assume you have tried this, does it affect the sound in any way or is this really just to increase stability ?
I would not worry over the choice of brands between first rank manufacturers. You should be able to use either and source them from element 14 or RS Components.

In this country there is no charge for freight for RS Component account holders - the downside is much of their range is sold in minimum quantities.

There is a full schematic for the Brio on Hi-Fi Engine in case you are curious about the phono stage.

I had a Brio 3 for a few months but traded it in for a Nait5i so although I have repaired some amplifiers for family and friends this has not included a Brio 3.

The TL072 has not taken a hit since this has inbuilt protection and there is a 100R resistor in series with the output that will lessen the chances of that being triggered.

The NE5532 has a BJT input and there is no blocking input capacitor so the dc output will vary according to the volume control setting - a point possibly overlooked by those who suggested the substitution.

An LF353 is an equivalent to TL072.

To my ears the former has a brighter sound and it might be a better pairing with the changed form of compensation that tends to tone down this characteristic.

To implement the change you could look for some NP0 chip capacitors, and after tinning, solder them between pins 1 and 2 and pins 6 and 7.

The changes before and after would have to be tested by simulations.

There has to be a compromise between THD which is measured on sine waves and transient distortions which might show up as a spike or ripple on square wave signals. To strike a balance a telling measure would be settling time.

My concern is more about mitigating risks of component failure during a malfunction. The closed loop gain of this unit is several times greater than normal and a fuse is part of that circuit.
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Old 28th May 2018, 08:33 AM   #60
Ian Finch is offline Ian Finch  Australia
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Quote:
Originally Posted by Depaj View Post
....I was wondering though, didn't rega come up with a solution for these issues in their newer versions of the Brio or did they just completely modify the whole circuit ?......
As far as I know, only the first (clamshell) Brio uses this particular boosted OP-AMP design. Later models, have been described as tweaked versions but I don't think so. Brio 3 for example, has SAP darlington output transistors and an LTP input stage. The op-amps are only in the preamp, as far as I can see.http://www.audiocostruzioni.com/r_s/...3-12983387.jpg
I haven't yet seen other models like Brio 2000 and brio 2 up close, so I can't really comment further. The current Brio-R model though, has a completely different design again, said to have more in common with Elex/Elicit models.
Quote:
....Is ST Micro superior in quality than on semi or do you suggest them because the datasheet has more info ?.....
Based on your first choice at Mouser, I assumed you had a preference for ST Micro product. I sometimes prefer it because the parameter spread of past supplies has suited some projects and they were cheaper at the time. Still, I don't see any reason to wait a year for parts when you can buy the same product in stock elsewhere.

Most brands seem to be comparable if not the same on Ft, Cob, Ic and Hfe options for audio drivers in low-medium power applications. However, from earlier datasheets I'd describe On-Semi's product prior to the Fairchild takeover, as a slower device. Perhaps it was intended for general purpose rather than audio use. Currently, I believe we are buying ex-Fairchild product from On-Semi and their datasheet has been revised accordingly.
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