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Old 27th May 2011, 04:46 PM   #1081
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Hi Salas,

I am getting 21v AC from my 18-0-18v R transformer, so I may have to use the spare 15v one I have. There is no heat generated from the IRFP140 and IRFP9140s, the 10R resistors get slightly warm as do the MUR diodes. I measured 1.3v drop across the 10R resistors, so I have 130ma in each half of the PS = 260ma total - slightly hot-rodded?

The regulated DC is 10.2 and 9.5v - need to verify this as I only checked briefly - will this need attention?

The power supply I have knocked together to feed 8 v into the switched volume controller board, which has its own 5v regulator, is generating more heat than the "slightly hot-rodded" DCB1. tapped into the unregulated DC, I have 2 parallel 10w 47ohm resistors feeding a 7812 reg and then a 22ohm resistor in series. Is there a better way of doing this? If I am going to generate heat, let it be from super nitro, hot-rodding the well designed B1 and not my amateur attempts to power this low current control pcb. I know it will get a bit better with the 15v tranny, but even so, I would like to keep it as cool as possible. I am considering one of those DC-DC integrated circuits, but want to avoid anything that could genarate any extra noise if at all possible.

Brad

Brad
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Old 28th May 2011, 01:42 AM   #1082
nezbleu is online now nezbleu  Canada
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I assume you are trying to lower the voltage going into the 5V regulator because it can't handle the higher voltage. I assume the unregulated voltage must be around 30VDC. If your volume control board is pulling a steady 150mA then your parallel 47R resistors are dropping around 3.5V, and the 22R about the same. So you are putting about 26V into the 7812, and then dropping it's output to about 8V. But the point is, you are dropping about 22V all together, and the current is 150mA, so that's something over 3W that needs to be dissipated somewhere; you're just spreading it over 4 devices. I would think 12V would be an OK input to the 5V regulator, so put your 47R resistors in series and drop the input to the 7812 to about 15V. The regulator will be warm, and so will the resistors. If the heat is too much then get rid of the 21V xformer, and maybe use a much lower voltage one to power the volume board. There is no magic way to dump that voltage without turning it into heat.
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Old 29th May 2011, 12:01 PM   #1083
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cheers Nezbleu,

I may try out a DC-DC ic, with 90+ % efficiency.

does anyone have an approx figure for the output impedance of the B1?

Brad
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Old 29th May 2011, 12:30 PM   #1084
Salas is offline Salas  Greece
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260 Ohm
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Old 29th May 2011, 12:45 PM   #1085
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cheers Salas,

do I need to make any other changes to the buffer values, with the largish difference on the DC regulated readings?

Brad
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Old 29th May 2011, 04:13 PM   #1086
Salas is offline Salas  Greece
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Not really, no.
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Old 1st June 2011, 09:26 AM   #1087
Siberia is offline Siberia  Lithuania
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Default DCB1

Advice needed, again.

I've ordered LDR pot kit from Uriah. I'm looking for the best way to implement it in (before) my dcb1, as I don't want to do it twice. As I understand, I have these options:

1. LM317 regulator way, tapping voltage straight from DCB1.
2. Using spare DCB1 board as a shunt reg. only. (Do I need additional transformer in this case?)
3. +5V Salas Shunt reg. board and +/- PSU board as in Oliver's version.

My transformer is R-Core 50VA 2X15V, which if I remember correctly, actually gives near 2x18V.

Talking about the sound... After spending some time with TX2575, I love their sound so much that I've ordered a pair of TX2352. But there's still one thing, lack of expression in lower regions. It's not that it lacks just a little more punch for my taste, it's very recessed. I guess, the buffer is not there to blame and I look with suspicion towards my amp now. Dried caps? Something else?

In case of caps replacement, I would spend half of new amps budget replacing all (I have no means to detect a leaking cap, right?) of them. That being said, I accept new project suggestions for my new amp. Beware of even more noob questions coming your way! But I promise to work on my technical knowledge, independently too.

P.S. There's a thing suggesting me it could be my worn out amp caps. A little, almost inaudible from listening position hum/buzz going from one channel, when there's nothing connected except speakers to the amp. Interconnects with or without passive pre or DCB1 give two channel hum/buzz. In a couple of days I will try adding CL60, but I doubt it's a grounding issue. Or could it be? My old soviet flat doesn't have a separate safety ground wire. As I understand there's only earth connected to neutral somewhere at a breaker pannel. And the whole house could be sharing it!
That complicates virtual grounding of my Quad 707 a bit, doesn't it?

Ok, mabe I'm asking too much attention now Thanks for all the help, anyway
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Old 1st June 2011, 09:45 AM   #1088
Marra is offline Marra  United Kingdom
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Option 3 was the way I went but using a separate 12V transformer; rectifier and caps to power the +5V regulator. Very pleased with the results although I must try out the TX2575 resistors; using Shinkoh tantalums at the moment.
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Old 1st June 2011, 11:01 AM   #1089
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Quote:
Originally Posted by Siberia View Post
Advice needed, again.

I've ordered LDR pot kit from Uriah. I'm looking for the best way to implement it in (before) my dcb1, as I don't want to do it twice. As I understand, I have these options:

1. LM317 regulator way, tapping voltage straight from DCB1.
2. Using spare DCB1 board as a shunt reg. only. (Do I need additional transformer in this case?)
3. +5V Salas Shunt reg. board and +/- PSU board as in Oliver's version.

My transformer is R-Core 50VA 2X15V, which if I remember correctly, actually gives near 2x18V.

Talking about the sound... After spending some time with TX2575, I love their sound so much that I've ordered a pair of TX2352. But there's still one thing, lack of expression in lower regions. It's not that it lacks just a little more punch for my taste, it's very recessed. I guess, the buffer is not there to blame and I look with suspicion towards my amp now. Dried caps? Something else?

In case of caps replacement, I would spend half of new amps budget replacing all (I have no means to detect a leaking cap, right?) of them. That being said, I accept new project suggestions for my new amp. Beware of even more noob questions coming your way! But I promise to work on my technical knowledge, independently too.

P.S. There's a thing suggesting me it could be my worn out amp caps. A little, almost inaudible from listening position hum/buzz going from one channel, when there's nothing connected except speakers to the amp. Interconnects with or without passive pre or DCB1 give two channel hum/buzz. In a couple of days I will try adding CL60, but I doubt it's a grounding issue. Or could it be? My old soviet flat doesn't have a separate safety ground wire. As I understand there's only earth connected to neutral somewhere at a breaker pannel. And the whole house could be sharing it!
That complicates virtual grounding of my Quad 707 a bit, doesn't it?

Ok, mabe I'm asking too much attention now Thanks for all the help, anyway
I did option 2.

Yes you'd need a new transformer for any but option 1. Go with option 1 - by far the easiest. The power supply only needs to power some leds - not a big deal.

Is your Quad 707 over 25 years old? If so, it could be the caps - you can test them - you have to remove them and test if them for continuity and also capacitance value. They're probably fine though - that's not an old amp and Quad used good caps.
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Old 1st June 2011, 12:20 PM   #1090
Siberia is offline Siberia  Lithuania
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Lucas, thanks. Yes, the first way is the easiest, but I wonder will it sound much different compared to other options.

My amp must be around 14 years old. As a rule of thumb, all electrolytes in an amplifier should be replaced after 15 years, that is what I've been told by Dada Quad revision team from Belgium. Normally that kind of noise would rather be independent from a connected input.

I realise now, it could be a transformer...
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