Sjöström Audio DIY forum

Projects => Headphone amplifiers => Topic started by: semola on March 03, 2010, 09:19:30 AM

Title: Questions about QRV01 QRV03 QRV08
Post by: semola on March 03, 2010, 09:19:30 AM
Questions about QRV01 QRV03 QRV08.

Hallo, Per-Anders,

You have a huge variety of nice headphone amplifier for all tastes!
Among this various kind I like QRV01 QRV03 QRV08. But before to make my choice I wish to know what are the differences in sound print and performances among this amplifiers and what are the best for drive low impedance loads ( 25 Ohm)

And now many questions (sorry ..) about:

1) Have You find a equivalent ,or better, substitute for BF471/472 (don’t matter the case)?
2) Have you test the  amplifier with the new one?
3 ) What transistors is better to match?
4  ) Since the output mosfets don’t have degeneration resistors ,.it’s useful to match this devices?
5 ) Can You suggest a right way to do?
6) What do You think about IRFZ24/IRF9Z34 pair?
7) Since is possible to mount Bjt in the output stage can you tell us the difference in term of performances and       sound ?
8) The bias circuit can handle  Bjt or Mos without any changes?
9) Better Alternative for BD139/140 in the output stage?
10) What do You think about the MJE1534/1535  pair?
11) Have You tested the amplifier THD at various frequencies and loads and with different output devices?

12) What transistors is useful to match?  (T3-T5    T4-T6) ?
13)  Is possible to use the outstanding LME49710 as input IC and if yes what changes should be made for optimal match with the rest of the circuit? (compensations , R18/R19  R5 R6..…)
14) Is useful to increase the supply voltage for this IC to 12/15V using  a 12/15V zener in position DZ7/DZ8?
15) MJE 1534/1535 for output pair?
16) alternative IC for servo opamp?
17) Theoretical question: In the circuit description  You tell the output of IC1 is connected to heavy load and this modulated current is present in the supply pin then fed to the next stage. Since a heavy load in general worse a lot the performances of  an opamp, why this behaviour is not transfered in the signal modulated current present on the supply pins that I suppose is the same flowing in the load? In other words, if the current at the load is distorted more than normal because the load is low, and if this (distorted) current is the same present at the supply pins, why the performances of the entire amplifier don’t suffer for this?

18) What resistors I have to change for vary the overall gain?

Sorry again for the high number of questions and Best Regards.

Title: Re: Questions about QRV01 QRV03 QRV08
Post by: peranders on March 03, 2010, 03:34:43 PM

1 BC5xx/BC8xx works fine

2 No

3 Input transistors may be matched but not necessary.

4 No, it works fine without matching.

5 -

6 it could work but you should strive to have as low Vds as possible and also as low current as possible since the capacitances will be smaller.

7 Not much difference.

8 The bias circuit should have a mosfet as temp sensing element if you use mosfets. BS170 is fine.

9 You could try D44H11/D45H11 but otherwise BD139/140 is more than enough.

10 Can't find any datahseets

11 No


12 None but if you insist V3, V5 and V4, V6

13 Maybe but low current consumption and low supply voltage  is a virtue here.

14 No, see no. 13.

15 Don't know, no datasheets

16 Some type with low current consumption, low supply voltage and low input bas currents

17 Your theories applies to a conventional circuit. This is different. You can read all about it in the AES paper and the application note.

18 R14, decrease it for higher gain. Don't change the R15.